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# Line 45  INTRODUCTION Line 45  INTRODUCTION
45    
46         Details of exactly which Perl regular expression features are  and  are         Details of exactly which Perl regular expression features are  and  are
47         not supported by PCRE are given in separate documents. See the pcrepat-         not supported by PCRE are given in separate documents. See the pcrepat-
48         tern and pcrecompat pages.         tern and pcrecompat pages. There is a syntax summary in the  pcresyntax
49           page.
50    
51         Some features of PCRE can be included, excluded, or  changed  when  the         Some  features  of  PCRE can be included, excluded, or changed when the
52         library  is  built.  The pcre_config() function makes it possible for a         library is built. The pcre_config() function makes it  possible  for  a
53         client to discover which features are  available.  The  features  them-         client  to  discover  which  features are available. The features them-
54         selves  are described in the pcrebuild page. Documentation about build-         selves are described in the pcrebuild page. Documentation about  build-
55         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 file
56         in the source distribution.         in the source distribution.
57    
58         The  library  contains  a number of undocumented internal functions and         The library contains a number of undocumented  internal  functions  and
59         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
60         functions,  but  which  are  not  intended for use by external callers.         functions, but which are not intended  for  use  by  external  callers.
61         Their names all begin with "_pcre_", which hopefully will  not  provoke         Their  names  all begin with "_pcre_", which hopefully will not provoke
62         any name clashes. In some environments, it is possible to control which         any name clashes. In some environments, it is possible to control which
63         external symbols are exported when a shared library is  built,  and  in         external  symbols  are  exported when a shared library is built, and in
64         these cases the undocumented symbols are not exported.         these cases the undocumented symbols are not exported.
65    
66    
67  USER DOCUMENTATION  USER DOCUMENTATION
68    
69         The  user  documentation  for PCRE comprises a number of different sec-         The user documentation for PCRE comprises a number  of  different  sec-
70         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
71         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.
72         In the plain text format, all the sections are concatenated,  for  ease         In  the  plain text format, all the sections are concatenated, for ease
73         of searching. The sections are as follows:         of searching. The sections are as follows:
74    
75           pcre              this document           pcre              this document
# Line 83  USER DOCUMENTATION Line 84  USER DOCUMENTATION
84           pcrepartial       details of the partial matching facility           pcrepartial       details of the partial matching facility
85           pcrepattern       syntax and semantics of supported           pcrepattern       syntax and semantics of supported
86                               regular expressions                               regular expressions
87             pcresyntax        quick syntax reference
88           pcreperform       discussion of performance issues           pcreperform       discussion of performance issues
89           pcreposix         the POSIX-compatible C API           pcreposix         the POSIX-compatible C API
90           pcreprecompile    details of saving and re-using precompiled patterns           pcreprecompile    details of saving and re-using precompiled patterns
# Line 90  USER DOCUMENTATION Line 92  USER DOCUMENTATION
92           pcrestack         discussion of stack usage           pcrestack         discussion of stack usage
93           pcretest          description of the pcretest testing command           pcretest          description of the pcretest testing command
94    
95         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
96         each C library function, listing its arguments and results.         each C library function, listing its arguments and results.
97    
98    
99  LIMITATIONS  LIMITATIONS
100    
101         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
102         never in practice be relevant.         never in practice be relevant.
103    
104         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
105         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
106         process regular expressions that are truly enormous,  you  can  compile         process  regular  expressions  that are truly enormous, you can compile
107         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
108         the source distribution and the pcrebuild documentation  for  details).         the  source  distribution and the pcrebuild documentation for details).
109         In  these  cases the limit is substantially larger.  However, the speed         In these cases the limit is substantially larger.  However,  the  speed
110         of execution is slower.         of execution is slower.
111    
112         All values in repeating quantifiers must be less than 65536. The  maxi-         All values in repeating quantifiers must be less than 65536.
        mum  compiled  length  of  subpattern  with an explicit repeat count is  
        30000 bytes. The maximum number of capturing subpatterns is 65535.  
113    
114         There is no limit to the number of parenthesized subpatterns, but there         There is no limit to the number of parenthesized subpatterns, but there
115         can be no more than 65535 capturing subpatterns.         can be no more than 65535 capturing subpatterns.
# Line 117  LIMITATIONS Line 117  LIMITATIONS
117         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
118         the maximum number of named subpatterns is 10000.         the maximum number of named subpatterns is 10000.
119    
120         The maximum length of a subject string is the largest  positive  number         The  maximum  length of a subject string is the largest positive number
121         that  an integer variable can hold. However, when using the traditional         that an integer variable can hold. However, when using the  traditional
122         matching function, PCRE uses recursion to handle subpatterns and indef-         matching function, PCRE uses recursion to handle subpatterns and indef-
123         inite  repetition.  This means that the available stack space may limit         inite repetition.  This means that the available stack space may  limit
124         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.
125         For a discussion of stack issues, see the pcrestack documentation.         For a discussion of stack issues, see the pcrestack documentation.
126    
127    
128  UTF-8 AND UNICODE PROPERTY SUPPORT  UTF-8 AND UNICODE PROPERTY SUPPORT
129    
130         From  release  3.3,  PCRE  has  had  some support for character strings         From release 3.3, PCRE has  had  some  support  for  character  strings
131         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
132         to  cover  most common requirements, and in release 5.0 additional sup-         to cover most common requirements, and in release 5.0  additional  sup-
133         port for Unicode general category properties was added.         port for Unicode general category properties was added.
134    
135         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
136         support  in  the  code,  and, in addition, you must call pcre_compile()         support in the code, and, in addition,  you  must  call  pcre_compile()
137         with the PCRE_UTF8 option flag. When you do this, both the pattern  and         with  the PCRE_UTF8 option flag. When you do this, both the pattern and
138         any  subject  strings  that are matched against it are treated as UTF-8         any subject strings that are matched against it are  treated  as  UTF-8
139         strings instead of just strings of bytes.         strings instead of just strings of bytes.
140    
141         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,
142         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
143         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
144         very big.         very big.
145    
146         If PCRE is built with Unicode character property support (which implies         If PCRE is built with Unicode character property support (which implies
147         UTF-8 support), the escape sequences \p{..}, \P{..}, and  \X  are  sup-         UTF-8  support),  the  escape sequences \p{..}, \P{..}, and \X are sup-
148         ported.  The available properties that can be tested are limited to the         ported.  The available properties that can be tested are limited to the
149         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
150         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,
151         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
152         pcrepattern documentation. Only the short names for properties are sup-         pcrepattern documentation. Only the short names for properties are sup-
153         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-
154         ter},  is  not  supported.   Furthermore,  in Perl, many properties may         ter}, is not supported.  Furthermore,  in  Perl,  many  properties  may
155         optionally be prefixed by "Is", for compatibility with Perl  5.6.  PCRE         optionally  be  prefixed by "Is", for compatibility with Perl 5.6. PCRE
156         does not support this.         does not support this.
157    
158         The following comments apply when PCRE is running in UTF-8 mode:     Validity of UTF-8 strings
159    
160           When you set the PCRE_UTF8 flag, the strings  passed  as  patterns  and
161           subjects are (by default) checked for validity on entry to the relevant
162           functions. From release 7.3 of PCRE, the check is according  the  rules
163           of  RFC  3629, which are themselves derived from the Unicode specifica-
164           tion. Earlier releases of PCRE followed the rules of  RFC  2279,  which
165           allows  the  full range of 31-bit values (0 to 0x7FFFFFFF). The current
166           check allows only values in the range U+0 to U+10FFFF, excluding U+D800
167           to U+DFFF.
168    
169           The  excluded  code  points are the "Low Surrogate Area" of Unicode, of
170           which the Unicode Standard says this: "The Low Surrogate Area does  not
171           contain  any  character  assignments,  consequently  no  character code
172           charts or namelists are provided for this area. Surrogates are reserved
173           for  use  with  UTF-16 and then must be used in pairs." The code points
174           that are encoded by UTF-16 pairs  are  available  as  independent  code
175           points  in  the  UTF-8  encoding.  (In other words, the whole surrogate
176           thing is a fudge for UTF-16 which unfortunately messes up UTF-8.)
177    
178           If an  invalid  UTF-8  string  is  passed  to  PCRE,  an  error  return
179           (PCRE_ERROR_BADUTF8) is given. In some situations, you may already know
180           that your strings are valid, and therefore want to skip these checks in
181           order to improve performance. If you set the PCRE_NO_UTF8_CHECK flag at
182           compile time or at run time, PCRE assumes that the pattern  or  subject
183           it  is  given  (respectively)  contains only valid UTF-8 codes. In this
184           case, it does not diagnose an invalid UTF-8 string.
185    
186           If you pass an invalid UTF-8 string  when  PCRE_NO_UTF8_CHECK  is  set,
187           what  happens  depends on why the string is invalid. If the string con-
188           forms to the "old" definition of UTF-8 (RFC 2279), it is processed as a
189           string  of  characters  in  the  range 0 to 0x7FFFFFFF. In other words,
190           apart from the initial validity test, PCRE (when in UTF-8 mode) handles
191           strings  according  to  the more liberal rules of RFC 2279. However, if
192           the string does not even conform to RFC 2279, the result is  undefined.
193           Your program may crash.
194    
195           If  you  want  to  process  strings  of  values  in the full range 0 to
196           0x7FFFFFFF, encoded in a UTF-8-like manner as per the old RFC, you  can
197           set PCRE_NO_UTF8_CHECK to bypass the more restrictive test. However, in
198           this situation, you will have to apply your own validity check.
199    
200         1.  When you set the PCRE_UTF8 flag, the strings passed as patterns and     General comments about UTF-8 mode
        subjects are checked for validity on entry to the  relevant  functions.  
        If an invalid UTF-8 string is passed, an error return is given. In some  
        situations, you may already know  that  your  strings  are  valid,  and  
        therefore want to skip these checks in order to improve performance. If  
        you set the PCRE_NO_UTF8_CHECK flag at compile time  or  at  run  time,  
        PCRE  assumes  that  the  pattern or subject it is given (respectively)  
        contains only valid UTF-8 codes. In this case, it does not diagnose  an  
        invalid  UTF-8 string. If you pass an invalid UTF-8 string to PCRE when  
        PCRE_NO_UTF8_CHECK is set, the results are undefined. Your program  may  
        crash.  
201    
202         2.  An  unbraced  hexadecimal  escape sequence (such as \xb3) matches a         1. An unbraced hexadecimal escape sequence (such  as  \xb3)  matches  a
203         two-byte UTF-8 character if the value is greater than 127.         two-byte UTF-8 character if the value is greater than 127.
204    
205         3. 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
206         characters for values greater than \177.         characters for values greater than \177.
207    
208         4.  Repeat quantifiers apply to complete UTF-8 characters, not to indi-         3. Repeat quantifiers apply to complete UTF-8 characters, not to  indi-
209         vidual bytes, for example: \x{100}{3}.         vidual bytes, for example: \x{100}{3}.
210    
211         5. 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-
212         gle byte.         gle byte.
213    
214         6.  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
215         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
216         not available in the alternative matching function, pcre_dfa_exec().         not available in the alternative matching function, pcre_dfa_exec().
217    
218         7.  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
219         test characters of any code value, but the characters that PCRE  recog-         test  characters of any code value, but the characters that PCRE recog-
220         nizes  as  digits,  spaces,  or  word characters remain the same set as         nizes as digits, spaces, or word characters  remain  the  same  set  as
221         before, all with values less than 256. This remains true even when PCRE         before, all with values less than 256. This remains true even when PCRE
222         includes  Unicode  property support, because to do otherwise would slow         includes Unicode property support, because to do otherwise  would  slow
223         down PCRE in many common cases. If you really want to test for a  wider         down  PCRE in many common cases. If you really want to test for a wider
224         sense  of,  say,  "digit",  you must use Unicode property tests such as         sense of, say, "digit", you must use Unicode  property  tests  such  as
225         \p{Nd}.         \p{Nd}.
226    
227         8. Similarly, characters that match the POSIX named  character  classes         7.  Similarly,  characters that match the POSIX named character classes
228         are all low-valued characters.         are all low-valued characters.
229    
230         9.  Case-insensitive  matching  applies only to characters whose values         8. However, the Perl 5.10 horizontal and vertical  whitespace  matching
231         are less than 128, unless PCRE is built with Unicode property  support.         escapes (\h, \H, \v, and \V) do match all the appropriate Unicode char-
232         Even  when  Unicode  property support is available, PCRE still uses its         acters.
233         own character tables when checking the case of  low-valued  characters,  
234         so  as not to degrade performance.  The Unicode property information is         9. Case-insensitive matching applies only to  characters  whose  values
235           are  less than 128, unless PCRE is built with Unicode property support.
236           Even when Unicode property support is available, PCRE  still  uses  its
237           own  character  tables when checking the case of low-valued characters,
238           so as not to degrade performance.  The Unicode property information  is
239         used only for characters with higher values. Even when Unicode property         used only for characters with higher values. Even when Unicode property
240         support is available, PCRE supports case-insensitive matching only when         support is available, PCRE supports case-insensitive matching only when
241         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
242         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-
243         ported by PCRE.         ported by PCRE.
244    
245    
# Line 215  AUTHOR Line 249  AUTHOR
249         University Computing Service         University Computing Service
250         Cambridge CB2 3QH, England.         Cambridge CB2 3QH, England.
251    
252         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,
253         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,
254         followed by the two digits 10, at the domain cam.ac.uk.         followed by the two digits 10, at the domain cam.ac.uk.
255    
256    
257  REVISION  REVISION
258    
259         Last updated: 18 April 2007         Last updated: 09 August 2007
260         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
261  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
262    
# Line 237  NAME Line 271  NAME
271  PCRE BUILD-TIME OPTIONS  PCRE BUILD-TIME OPTIONS
272    
273         This  document  describes  the  optional  features  of PCRE that can be         This  document  describes  the  optional  features  of PCRE that can be
274         selected when the library is compiled. They are all selected, or  dese-         selected when the library is compiled. It assumes use of the  configure
275         lected, by providing options to the configure script that is run before         script,  where the optional features are selected or deselected by pro-
276         the make command. The complete list of  options  for  configure  (which         viding options to configure before running the make  command.  However,
277         includes  the  standard  ones such as the selection of the installation         the  same  options  can be selected in both Unix-like and non-Unix-like
278         directory) can be obtained by running         environments using the GUI facility of  CMakeSetup  if  you  are  using
279           CMake instead of configure to build PCRE.
280    
281           The complete list of options for configure (which includes the standard
282           ones such as the  selection  of  the  installation  directory)  can  be
283           obtained by running
284    
285           ./configure --help           ./configure --help
286    
287         The following sections include  descriptions  of  options  whose  names         The  following  sections  include  descriptions  of options whose names
288         begin with --enable or --disable. These settings specify changes to the         begin with --enable or --disable. These settings specify changes to the
289         defaults for the configure command. Because of the way  that  configure         defaults  for  the configure command. Because of the way that configure
290         works,  --enable  and --disable always come in pairs, so the complemen-         works, --enable and --disable always come in pairs, so  the  complemen-
291         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
292         is not described.         is not described.
293    
294    
# Line 270  UTF-8 SUPPORT Line 309  UTF-8 SUPPORT
309    
310           --enable-utf8           --enable-utf8
311    
312         to  the  configure  command.  Of  itself, this does not make PCRE treat         to the configure command. Of itself, this  does  not  make  PCRE  treat
313         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
314         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()
315         function.         function.
316    
317    
318  UNICODE CHARACTER PROPERTY SUPPORT  UNICODE CHARACTER PROPERTY SUPPORT
319    
320         UTF-8 support allows PCRE to process character values greater than  255         UTF-8  support allows PCRE to process character values greater than 255
321         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-
322         vide any facilities for accessing the properties of such characters. If         vide any facilities for accessing the properties of such characters. If
323         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
324         refer to Unicode character properties, you must add         refer to Unicode character properties, you must add
325    
326           --enable-unicode-properties           --enable-unicode-properties
327    
328         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
329         not explicitly requested it.         not explicitly requested it.
330    
331         Including  Unicode  property  support  adds around 30K of tables to the         Including Unicode property support adds around 30K  of  tables  to  the
332         PCRE library. Only the general category properties such as  Lu  and  Nd         PCRE  library.  Only  the general category properties such as Lu and Nd
333         are supported. Details are given in the pcrepattern documentation.         are supported. Details are given in the pcrepattern documentation.
334    
335    
336  CODE VALUE OF NEWLINE  CODE VALUE OF NEWLINE
337    
338         By  default,  PCRE interprets character 10 (linefeed, LF) as indicating         By default, PCRE interprets character 10 (linefeed, LF)  as  indicating
339         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
340         systems. You can compile PCRE to use character 13 (carriage return, CR)         systems. You can compile PCRE to use character 13 (carriage return, CR)
341         instead, by adding         instead, by adding
342    
343           --enable-newline-is-cr           --enable-newline-is-cr
344    
345         to the  configure  command.  There  is  also  a  --enable-newline-is-lf         to  the  configure  command.  There  is  also  a --enable-newline-is-lf
346         option, which explicitly specifies linefeed as the newline character.         option, which explicitly specifies linefeed as the newline character.
347    
348         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 315  CODE VALUE OF NEWLINE Line 354  CODE VALUE OF NEWLINE
354    
355           --enable-newline-is-anycrlf           --enable-newline-is-anycrlf
356    
357         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
358         CRLF as indicating a line ending. Finally, a fifth option, specified by         CRLF as indicating a line ending. Finally, a fifth option, specified by
359    
360           --enable-newline-is-any           --enable-newline-is-any
361    
362         causes PCRE to recognize any Unicode newline sequence.         causes PCRE to recognize any Unicode newline sequence.
363    
364         Whatever line ending convention is selected when PCRE is built  can  be         Whatever  line  ending convention is selected when PCRE is built can be
365         overridden  when  the library functions are called. At build time it is         overridden when the library functions are called. At build time  it  is
366         conventional to use the standard for your operating system.         conventional to use the standard for your operating system.
367    
368    
369    WHAT \R MATCHES
370    
371           By  default,  the  sequence \R in a pattern matches any Unicode newline
372           sequence, whatever has been selected as the line  ending  sequence.  If
373           you specify
374    
375             --enable-bsr-anycrlf
376    
377           the  default  is changed so that \R matches only CR, LF, or CRLF. What-
378           ever is selected when PCRE is built can be overridden when the  library
379           functions are called.
380    
381    
382  BUILDING SHARED AND STATIC LIBRARIES  BUILDING SHARED AND STATIC LIBRARIES
383    
384         The PCRE building process uses libtool to build both shared and  static         The  PCRE building process uses libtool to build both shared and static
385         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
386         of         of
387    
388           --disable-shared           --disable-shared
# Line 342  BUILDING SHARED AND STATIC LIBRARIES Line 394  BUILDING SHARED AND STATIC LIBRARIES
394  POSIX MALLOC USAGE  POSIX MALLOC USAGE
395    
396         When PCRE is called through the POSIX interface (see the pcreposix doc-         When PCRE is called through the POSIX interface (see the pcreposix doc-
397         umentation),  additional  working  storage  is required for holding the         umentation), additional working storage is  required  for  holding  the
398         pointers to capturing substrings, because PCRE requires three  integers         pointers  to capturing substrings, because PCRE requires three integers
399         per  substring,  whereas  the POSIX interface provides only two. If the         per substring, whereas the POSIX interface provides only  two.  If  the
400         number of expected substrings is small, the wrapper function uses space         number of expected substrings is small, the wrapper function uses space
401         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.
402         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 357  POSIX MALLOC USAGE Line 409  POSIX MALLOC USAGE
409    
410  HANDLING VERY LARGE PATTERNS  HANDLING VERY LARGE PATTERNS
411    
412         Within  a  compiled  pattern,  offset values are used to point from one         Within a compiled pattern, offset values are used  to  point  from  one
413         part to another (for example, from an opening parenthesis to an  alter-         part  to another (for example, from an opening parenthesis to an alter-
414         nation  metacharacter).  By default, two-byte values are used for these         nation metacharacter). By default, two-byte values are used  for  these
415         offsets, leading to a maximum size for a  compiled  pattern  of  around         offsets,  leading  to  a  maximum size for a compiled pattern of around
416         64K.  This  is sufficient to handle all but the most gigantic patterns.         64K. This is sufficient to handle all but the most  gigantic  patterns.
417         Nevertheless, some people do want to process enormous patterns,  so  it         Nevertheless,  some  people do want to process enormous patterns, so it
418         is  possible  to compile PCRE to use three-byte or four-byte offsets by         is possible to compile PCRE to use three-byte or four-byte  offsets  by
419         adding a setting such as         adding a setting such as
420    
421           --with-link-size=3           --with-link-size=3
422    
423         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
424         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
425         additional bytes when handling them.         additional bytes when handling them.
426    
427    
428  AVOIDING EXCESSIVE STACK USAGE  AVOIDING EXCESSIVE STACK USAGE
429    
430         When matching with the pcre_exec() function, PCRE implements backtrack-         When matching with the pcre_exec() function, PCRE implements backtrack-
431         ing  by  making recursive calls to an internal function called match().         ing by making recursive calls to an internal function  called  match().
432         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-
433         verely  limit  PCRE's operation. (The Unix environment does not usually         verely limit PCRE's operation. (The Unix environment does  not  usually
434         suffer from this problem, but it may sometimes be necessary to increase         suffer from this problem, but it may sometimes be necessary to increase
435         the  maximum  stack size.  There is a discussion in the pcrestack docu-         the maximum stack size.  There is a discussion in the  pcrestack  docu-
436         mentation.) An alternative approach to recursion that uses memory  from         mentation.)  An alternative approach to recursion that uses memory from
437         the  heap  to remember data, instead of using recursive function calls,         the heap to remember data, instead of using recursive  function  calls,
438         has been implemented to work round the problem of limited  stack  size.         has  been  implemented to work round the problem of limited stack size.
439         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
440    
441           --disable-stack-for-recursion           --disable-stack-for-recursion
442    
443         to  the  configure  command. With this configuration, PCRE will use the         to the configure command. With this configuration, PCRE  will  use  the
444         pcre_stack_malloc and pcre_stack_free variables to call memory  manage-         pcre_stack_malloc  and pcre_stack_free variables to call memory manage-
445         ment  functions.  Separate  functions are provided because the usage is         ment functions. By default these point to malloc() and free(), but  you
446         very predictable: the block sizes requested are always  the  same,  and         can replace the pointers so that your own functions are used.
447         the  blocks  are always freed in reverse order. A calling program might  
448         be able to implement optimized functions that perform better  than  the         Separate  functions  are  provided  rather  than  using pcre_malloc and
449         standard  malloc()  and  free()  functions.  PCRE  runs noticeably more         pcre_free because the  usage  is  very  predictable:  the  block  sizes
450         slowly when built in this way. This option affects only the pcre_exec()         requested  are  always  the  same,  and  the blocks are always freed in
451         function; it is not relevant for the the pcre_dfa_exec() function.         reverse order. A calling program might be able to  implement  optimized
452           functions  that  perform  better  than  malloc()  and free(). PCRE runs
453           noticeably more slowly when built in this way. This option affects only
454           the   pcre_exec()   function;   it   is   not   relevant  for  the  the
455           pcre_dfa_exec() function.
456    
457    
458  LIMITING PCRE RESOURCE USAGE  LIMITING PCRE RESOURCE USAGE
459    
460         Internally,  PCRE has a function called match(), which it calls repeat-         Internally, PCRE has a function called match(), which it calls  repeat-
461         edly  (sometimes  recursively)  when  matching  a  pattern   with   the         edly   (sometimes   recursively)  when  matching  a  pattern  with  the
462         pcre_exec()  function.  By controlling the maximum number of times this         pcre_exec() function. By controlling the maximum number of  times  this
463         function may be called during a single matching operation, a limit  can         function  may be called during a single matching operation, a limit can
464         be  placed  on  the resources used by a single call to pcre_exec(). The         be placed on the resources used by a single call  to  pcre_exec().  The
465         limit can be changed at run time, as described in the pcreapi  documen-         limit  can be changed at run time, as described in the pcreapi documen-
466         tation.  The default is 10 million, but this can be changed by adding a         tation. The default is 10 million, but this can be changed by adding  a
467         setting such as         setting such as
468    
469           --with-match-limit=500000           --with-match-limit=500000
470    
471         to  the  configure  command.  This  setting  has  no  effect   on   the         to   the   configure  command.  This  setting  has  no  effect  on  the
472         pcre_dfa_exec() matching function.         pcre_dfa_exec() matching function.
473    
474         In  some  environments  it is desirable to limit the depth of recursive         In some environments it is desirable to limit the  depth  of  recursive
475         calls of match() more strictly than the total number of calls, in order         calls of match() more strictly than the total number of calls, in order
476         to  restrict  the maximum amount of stack (or heap, if --disable-stack-         to restrict the maximum amount of stack (or heap,  if  --disable-stack-
477         for-recursion is specified) that is used. A second limit controls this;         for-recursion is specified) that is used. A second limit controls this;
478         it  defaults  to  the  value  that is set for --with-match-limit, which         it defaults to the value that  is  set  for  --with-match-limit,  which
479         imposes no additional constraints. However, you can set a  lower  limit         imposes  no  additional constraints. However, you can set a lower limit
480         by adding, for example,         by adding, for example,
481    
482           --with-match-limit-recursion=10000           --with-match-limit-recursion=10000
483    
484         to  the  configure  command.  This  value can also be overridden at run         to the configure command. This value can  also  be  overridden  at  run
485         time.         time.
486    
487    
488  CREATING CHARACTER TABLES AT BUILD TIME  CREATING CHARACTER TABLES AT BUILD TIME
489    
490         PCRE uses fixed tables for processing characters whose code values  are         PCRE  uses fixed tables for processing characters whose code values are
491         less  than 256. By default, PCRE is built with a set of tables that are         less than 256. By default, PCRE is built with a set of tables that  are
492         distributed in the file pcre_chartables.c.dist. These  tables  are  for         distributed  in  the  file pcre_chartables.c.dist. These tables are for
493         ASCII codes only. If you add         ASCII codes only. If you add
494    
495           --enable-rebuild-chartables           --enable-rebuild-chartables
496    
497         to  the  configure  command, the distributed tables are no longer used.         to the configure command, the distributed tables are  no  longer  used.
498         Instead, a program called dftables is compiled and  run.  This  outputs         Instead,  a  program  called dftables is compiled and run. This outputs
499         the source for new set of tables, created in the default locale of your         the source for new set of tables, created in the default locale of your
500         C runtime system. (This method of replacing the tables does not work if         C runtime system. (This method of replacing the tables does not work if
501         you  are cross compiling, because dftables is run on the local host. If         you are cross compiling, because dftables is run on the local host.  If
502         you need to create alternative tables when cross  compiling,  you  will         you  need  to  create alternative tables when cross compiling, you will
503         have to do so "by hand".)         have to do so "by hand".)
504    
505    
506  USING EBCDIC CODE  USING EBCDIC CODE
507    
508         PCRE  assumes  by  default that it will run in an environment where the         PCRE assumes by default that it will run in an  environment  where  the
509         character code is ASCII (or Unicode, which is  a  superset  of  ASCII).         character  code  is  ASCII  (or Unicode, which is a superset of ASCII).
510         PCRE  can,  however,  be  compiled  to  run in an EBCDIC environment by         This is the case for most computer operating systems.  PCRE  can,  how-
511         adding         ever, be compiled to run in an EBCDIC environment by adding
512    
513           --enable-ebcdic           --enable-ebcdic
514    
515         to the configure command. This setting implies --enable-rebuild-charta-         to the configure command. This setting implies --enable-rebuild-charta-
516         bles.         bles. You should only use it if you know that  you  are  in  an  EBCDIC
517           environment (for example, an IBM mainframe operating system).
518    
519    
520    PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT
521    
522           By default, pcregrep reads all files as plain text. You can build it so
523           that it recognizes files whose names end in .gz or .bz2, and reads them
524           with libz or libbz2, respectively, by adding one or both of
525    
526             --enable-pcregrep-libz
527             --enable-pcregrep-libbz2
528    
529           to the configure command. These options naturally require that the rel-
530           evant libraries are installed on your system. Configuration  will  fail
531           if they are not.
532    
533    
534    PCRETEST OPTION FOR LIBREADLINE SUPPORT
535    
536           If you add
537    
538             --enable-pcretest-libreadline
539    
540           to  the  configure  command,  pcretest  is  linked with the libreadline
541           library, and when its input is from a terminal, it reads it  using  the
542           readline() function. This provides line-editing and history facilities.
543           Note that libreadline is GPL-licenced, so if you distribute a binary of
544           pcretest linked in this way, there may be licensing issues.
545    
546    
547  SEE ALSO  SEE ALSO
# Line 474  AUTHOR Line 558  AUTHOR
558    
559  REVISION  REVISION
560    
561         Last updated: 16 April 2007         Last updated: 18 December 2007
562         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
563  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
564    
# Line 618  THE ALTERNATIVE MATCHING ALGORITHM Line 702  THE ALTERNATIVE MATCHING ALGORITHM
702         6.  Callouts  are  supported, but the value of the capture_top field is         6.  Callouts  are  supported, but the value of the capture_top field is
703         always 1, and the value of the capture_last field is always -1.         always 1, and the value of the capture_last field is always -1.
704    
705         7.  The \C escape sequence, which (in the standard algorithm) matches a         7. The \C escape sequence, which (in the standard algorithm) matches  a
706         single  byte, even in UTF-8 mode, is not supported because the alterna-         single  byte, even in UTF-8 mode, is not supported because the alterna-
707         tive algorithm moves through the subject  string  one  character  at  a         tive algorithm moves through the subject  string  one  character  at  a
708         time, for all active paths through the tree.         time, for all active paths through the tree.
709    
710           8.  None  of  the  backtracking control verbs such as (*PRUNE) are sup-
711           ported.
712    
713    
714  ADVANTAGES OF THE ALTERNATIVE ALGORITHM  ADVANTAGES OF THE ALTERNATIVE ALGORITHM
715    
716         Using  the alternative matching algorithm provides the following advan-         Using the alternative matching algorithm provides the following  advan-
717         tages:         tages:
718    
719         1. All possible matches (at a single point in the subject) are automat-         1. All possible matches (at a single point in the subject) are automat-
720         ically  found,  and  in particular, the longest match is found. To find         ically found, and in particular, the longest match is  found.  To  find
721         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
722         things with callouts.         things with callouts.
723    
724         2.  There is much better support for partial matching. The restrictions         2. There is much better support for partial matching. The  restrictions
725         on the content of the pattern that apply when using the standard  algo-         on  the content of the pattern that apply when using the standard algo-
726         rithm  for  partial matching do not apply to the alternative algorithm.         rithm for partial matching do not apply to the  alternative  algorithm.
727         For non-anchored patterns, the starting position of a partial match  is         For  non-anchored patterns, the starting position of a partial match is
728         available.         available.
729    
730         3.  Because  the  alternative  algorithm  scans the subject string just         3. Because the alternative algorithm  scans  the  subject  string  just
731         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
732         subject  strings  to  the matching function in several pieces, checking         subject strings to the matching function in  several  pieces,  checking
733         for partial matching each time.         for partial matching each time.
734    
735    
# Line 650  DISADVANTAGES OF THE ALTERNATIVE ALGORIT Line 737  DISADVANTAGES OF THE ALTERNATIVE ALGORIT
737    
738         The alternative algorithm suffers from a number of disadvantages:         The alternative algorithm suffers from a number of disadvantages:
739    
740         1. It is substantially slower than  the  standard  algorithm.  This  is         1.  It  is  substantially  slower  than the standard algorithm. This is
741         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
742         because it is less susceptible to optimization.         because it is less susceptible to optimization.
743    
744         2. Capturing parentheses and back references are not supported.         2. Capturing parentheses and back references are not supported.
# Line 669  AUTHOR Line 756  AUTHOR
756    
757  REVISION  REVISION
758    
759         Last updated: 29 May 2007         Last updated: 08 August 2007
760         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
761  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
762    
# Line 866  NEWLINES Line 953  NEWLINES
953         dard. When PCRE is run, the default can be overridden,  either  when  a         dard. When PCRE is run, the default can be overridden,  either  when  a
954         pattern is compiled, or when it is matched.         pattern is compiled, or when it is matched.
955    
956           At compile time, the newline convention can be specified by the options
957           argument of pcre_compile(), or it can be specified by special  text  at
958           the start of the pattern itself; this overrides any other settings. See
959           the pcrepattern page for details of the special character sequences.
960    
961         In the PCRE documentation the word "newline" is used to mean "the char-         In the PCRE documentation the word "newline" is used to mean "the char-
962         acter or pair of characters that indicate a line break". The choice  of         acter  or pair of characters that indicate a line break". The choice of
963         newline  convention  affects  the  handling of the dot, circumflex, and         newline convention affects the handling of  the  dot,  circumflex,  and
964         dollar metacharacters, the handling of #-comments in /x mode, and, when         dollar metacharacters, the handling of #-comments in /x mode, and, when
965         CRLF  is a recognized line ending sequence, the match position advance-         CRLF is a recognized line ending sequence, the match position  advance-
966         ment for a non-anchored pattern. The choice of newline convention  does         ment for a non-anchored pattern. There is more detail about this in the
967         not affect the interpretation of the \n or \r escape sequences.         section on pcre_exec() options below.
968    
969           The choice of newline convention does not affect the interpretation  of
970           the  \n  or  \r  escape  sequences, nor does it affect what \R matches,
971           which is controlled in a similar way, but by separate options.
972    
973    
974  MULTITHREADING  MULTITHREADING
975    
976         The  PCRE  functions  can be used in multi-threading applications, with         The PCRE functions can be used in  multi-threading  applications,  with
977         the  proviso  that  the  memory  management  functions  pointed  to  by         the  proviso  that  the  memory  management  functions  pointed  to  by
978         pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the         pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the
979         callout function pointed to by pcre_callout, are shared by all threads.         callout function pointed to by pcre_callout, are shared by all threads.
980    
981         The  compiled form of a regular expression is not altered during match-         The compiled form of a regular expression is not altered during  match-
982         ing, so the same compiled pattern can safely be used by several threads         ing, so the same compiled pattern can safely be used by several threads
983         at once.         at once.
984    
# Line 890  MULTITHREADING Line 986  MULTITHREADING
986  SAVING PRECOMPILED PATTERNS FOR LATER USE  SAVING PRECOMPILED PATTERNS FOR LATER USE
987    
988         The compiled form of a regular expression can be saved and re-used at a         The compiled form of a regular expression can be saved and re-used at a
989         later time, possibly by a different program, and even on a  host  other         later  time,  possibly by a different program, and even on a host other
990         than  the  one  on  which  it  was  compiled.  Details are given in the         than the one on which  it  was  compiled.  Details  are  given  in  the
991         pcreprecompile documentation. However, compiling a  regular  expression         pcreprecompile  documentation.  However, compiling a regular expression
992         with  one version of PCRE for use with a different version is not guar-         with one version of PCRE for use with a different version is not  guar-
993         anteed to work and may cause crashes.         anteed to work and may cause crashes.
994    
995    
# Line 901  CHECKING BUILD-TIME OPTIONS Line 997  CHECKING BUILD-TIME OPTIONS
997    
998         int pcre_config(int what, void *where);         int pcre_config(int what, void *where);
999    
1000         The function pcre_config() makes it possible for a PCRE client to  dis-         The  function pcre_config() makes it possible for a PCRE client to dis-
1001         cover which optional features have been compiled into the PCRE library.         cover which optional features have been compiled into the PCRE library.
1002         The pcrebuild documentation has more details about these optional  fea-         The  pcrebuild documentation has more details about these optional fea-
1003         tures.         tures.
1004    
1005         The  first  argument  for pcre_config() is an integer, specifying which         The first argument for pcre_config() is an  integer,  specifying  which
1006         information is required; the second argument is a pointer to a variable         information is required; the second argument is a pointer to a variable
1007         into  which  the  information  is  placed. The following information is         into which the information is  placed.  The  following  information  is
1008         available:         available:
1009    
1010           PCRE_CONFIG_UTF8           PCRE_CONFIG_UTF8
1011    
1012         The output is an integer that is set to one if UTF-8 support is  avail-         The  output is an integer that is set to one if UTF-8 support is avail-
1013         able; otherwise it is set to zero.         able; otherwise it is set to zero.
1014    
1015           PCRE_CONFIG_UNICODE_PROPERTIES           PCRE_CONFIG_UNICODE_PROPERTIES
1016    
1017         The  output  is  an  integer  that is set to one if support for Unicode         The output is an integer that is set to  one  if  support  for  Unicode
1018         character properties is available; otherwise it is set to zero.         character properties is available; otherwise it is set to zero.
1019    
1020           PCRE_CONFIG_NEWLINE           PCRE_CONFIG_NEWLINE
1021    
1022         The output is an integer whose value specifies  the  default  character         The  output  is  an integer whose value specifies the default character
1023         sequence  that is recognized as meaning "newline". The four values that         sequence that is recognized as meaning "newline". The four values  that
1024         are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,         are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,
1025         and  -1  for  ANY. The default should normally be the standard sequence         and -1 for ANY. The default should normally be  the  standard  sequence
1026         for your operating system.         for your operating system.
1027    
1028             PCRE_CONFIG_BSR
1029    
1030           The output is an integer whose value indicates what character sequences
1031           the \R escape sequence matches by default. A value of 0 means  that  \R
1032           matches  any  Unicode  line ending sequence; a value of 1 means that \R
1033           matches only CR, LF, or CRLF. The default can be overridden when a pat-
1034           tern is compiled or matched.
1035    
1036           PCRE_CONFIG_LINK_SIZE           PCRE_CONFIG_LINK_SIZE
1037    
1038         The output is an integer that contains the number  of  bytes  used  for         The  output  is  an  integer that contains the number of bytes used for
1039         internal linkage in compiled regular expressions. The value is 2, 3, or         internal linkage in compiled regular expressions. The value is 2, 3, or
1040         4. Larger values allow larger regular expressions to  be  compiled,  at         4.  Larger  values  allow larger regular expressions to be compiled, at
1041         the  expense  of  slower matching. The default value of 2 is sufficient         the expense of slower matching. The default value of  2  is  sufficient
1042         for all but the most massive patterns, since  it  allows  the  compiled         for  all  but  the  most massive patterns, since it allows the compiled
1043         pattern to be up to 64K in size.         pattern to be up to 64K in size.
1044    
1045           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
1046    
1047         The  output  is  an integer that contains the threshold above which the         The output is an integer that contains the threshold  above  which  the
1048         POSIX interface uses malloc() for output vectors. Further  details  are         POSIX  interface  uses malloc() for output vectors. Further details are
1049         given in the pcreposix documentation.         given in the pcreposix documentation.
1050    
1051           PCRE_CONFIG_MATCH_LIMIT           PCRE_CONFIG_MATCH_LIMIT
1052    
1053         The output is an integer that gives the default limit for the number of         The output is an integer that gives the default limit for the number of
1054         internal matching function calls in a  pcre_exec()  execution.  Further         internal  matching  function  calls in a pcre_exec() execution. Further
1055         details are given with pcre_exec() below.         details are given with pcre_exec() below.
1056    
1057           PCRE_CONFIG_MATCH_LIMIT_RECURSION           PCRE_CONFIG_MATCH_LIMIT_RECURSION
1058    
1059         The  output is an integer that gives the default limit for the depth of         The output is an integer that gives the default limit for the depth  of
1060         recursion when calling the internal matching function in a  pcre_exec()         recursion  when calling the internal matching function in a pcre_exec()
1061         execution. Further details are given with pcre_exec() below.         execution. Further details are given with pcre_exec() below.
1062    
1063           PCRE_CONFIG_STACKRECURSE           PCRE_CONFIG_STACKRECURSE
1064    
1065         The  output is an integer that is set to one if internal recursion when         The output is an integer that is set to one if internal recursion  when
1066         running pcre_exec() is implemented by recursive function calls that use         running pcre_exec() is implemented by recursive function calls that use
1067         the  stack  to remember their state. This is the usual way that PCRE is         the stack to remember their state. This is the usual way that  PCRE  is
1068         compiled. The output is zero if PCRE was compiled to use blocks of data         compiled. The output is zero if PCRE was compiled to use blocks of data
1069         on  the  heap  instead  of  recursive  function  calls.  In  this case,         on the  heap  instead  of  recursive  function  calls.  In  this  case,
1070         pcre_stack_malloc and  pcre_stack_free  are  called  to  manage  memory         pcre_stack_malloc  and  pcre_stack_free  are  called  to  manage memory
1071         blocks on the heap, thus avoiding the use of the stack.         blocks on the heap, thus avoiding the use of the stack.
1072    
1073    
# Line 980  COMPILING A PATTERN Line 1084  COMPILING A PATTERN
1084    
1085         Either of the functions pcre_compile() or pcre_compile2() can be called         Either of the functions pcre_compile() or pcre_compile2() can be called
1086         to compile a pattern into an internal form. The only difference between         to compile a pattern into an internal form. The only difference between
1087         the  two interfaces is that pcre_compile2() has an additional argument,         the two interfaces is that pcre_compile2() has an additional  argument,
1088         errorcodeptr, via which a numerical error code can be returned.         errorcodeptr, via which a numerical error code can be returned.
1089    
1090         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
1091         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
1092         obtained via pcre_malloc is returned. This contains the  compiled  code         obtained  via  pcre_malloc is returned. This contains the compiled code
1093         and related data. The pcre type is defined for the returned block; this         and related data. The pcre type is defined for the returned block; this
1094         is a typedef for a structure whose contents are not externally defined.         is a typedef for a structure whose contents are not externally defined.
1095         It is up to the caller to free the memory (via pcre_free) when it is no         It is up to the caller to free the memory (via pcre_free) when it is no
1096         longer required.         longer required.
1097    
1098         Although the compiled code of a PCRE regex is relocatable, that is,  it         Although  the compiled code of a PCRE regex is relocatable, that is, it
1099         does not depend on memory location, the complete pcre data block is not         does not depend on memory location, the complete pcre data block is not
1100         fully relocatable, because it may contain a copy of the tableptr  argu-         fully  relocatable, because it may contain a copy of the tableptr argu-
1101         ment, which is an address (see below).         ment, which is an address (see below).
1102    
1103         The options argument contains various bit settings that affect the com-         The options argument contains various bit settings that affect the com-
1104         pilation. It should be zero if no options are required.  The  available         pilation.  It  should be zero if no options are required. The available
1105         options  are  described  below. Some of them, in particular, those that         options are described below. Some of them, in  particular,  those  that
1106         are compatible with Perl, can also be set and  unset  from  within  the         are  compatible  with  Perl,  can also be set and unset from within the
1107         pattern  (see  the  detailed  description in the pcrepattern documenta-         pattern (see the detailed description  in  the  pcrepattern  documenta-
1108         tion). For these options, the contents of the options  argument  speci-         tion).  For  these options, the contents of the options argument speci-
1109         fies  their initial settings at the start of compilation and execution.         fies their initial settings at the start of compilation and  execution.
1110         The PCRE_ANCHORED and PCRE_NEWLINE_xxx options can be set at  the  time         The  PCRE_ANCHORED  and PCRE_NEWLINE_xxx options can be set at the time
1111         of matching as well as at compile time.         of matching as well as at compile time.
1112    
1113         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
1114         if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and
1115         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-
1116         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
1117         try to free it. The offset from the start of the pattern to the charac-         try to free it. The offset from the start of the pattern to the charac-
1118         ter where the error was discovered is placed in the variable pointed to         ter where the error was discovered is placed in the variable pointed to
1119         by  erroffset,  which must not be NULL. If it is, an immediate error is         by erroffset, which must not be NULL. If it is, an immediate  error  is
1120         given.         given.
1121    
1122         If pcre_compile2() is used instead of pcre_compile(),  and  the  error-         If  pcre_compile2()  is  used instead of pcre_compile(), and the error-
1123         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
1124         via this argument in the event of an error. This is in addition to  the         via  this argument in the event of an error. This is in addition to the
1125         textual error message. Error codes and messages are listed below.         textual error message. Error codes and messages are listed below.
1126    
1127         If  the  final  argument, tableptr, is NULL, PCRE uses a default set of         If the final argument, tableptr, is NULL, PCRE uses a  default  set  of
1128         character tables that are  built  when  PCRE  is  compiled,  using  the         character  tables  that  are  built  when  PCRE  is compiled, using the
1129         default  C  locale.  Otherwise, tableptr must be an address that is the         default C locale. Otherwise, tableptr must be an address  that  is  the
1130         result of a call to pcre_maketables(). This value is  stored  with  the         result  of  a  call to pcre_maketables(). This value is stored with the
1131         compiled  pattern,  and used again by pcre_exec(), unless another table         compiled pattern, and used again by pcre_exec(), unless  another  table
1132         pointer is passed to it. For more discussion, see the section on locale         pointer is passed to it. For more discussion, see the section on locale
1133         support below.         support below.
1134    
1135         This  code  fragment  shows a typical straightforward call to pcre_com-         This code fragment shows a typical straightforward  call  to  pcre_com-
1136         pile():         pile():
1137    
1138           pcre *re;           pcre *re;
# Line 1041  COMPILING A PATTERN Line 1145  COMPILING A PATTERN
1145             &erroffset,       /* for error offset */             &erroffset,       /* for error offset */
1146             NULL);            /* use default character tables */             NULL);            /* use default character tables */
1147    
1148         The following names for option bits are defined in  the  pcre.h  header         The  following  names  for option bits are defined in the pcre.h header
1149         file:         file:
1150    
1151           PCRE_ANCHORED           PCRE_ANCHORED
1152    
1153         If this bit is set, the pattern is forced to be "anchored", that is, it         If this bit is set, the pattern is forced to be "anchored", that is, it
1154         is constrained to match only at the first matching point in the  string         is  constrained to match only at the first matching point in the string
1155         that  is being searched (the "subject string"). This effect can also be         that is being searched (the "subject string"). This effect can also  be
1156         achieved by appropriate constructs in the pattern itself, which is  the         achieved  by appropriate constructs in the pattern itself, which is the
1157         only way to do it in Perl.         only way to do it in Perl.
1158    
1159           PCRE_AUTO_CALLOUT           PCRE_AUTO_CALLOUT
1160    
1161         If this bit is set, pcre_compile() automatically inserts callout items,         If this bit is set, pcre_compile() automatically inserts callout items,
1162         all with number 255, before each pattern item. For  discussion  of  the         all  with  number  255, before each pattern item. For discussion of the
1163         callout facility, see the pcrecallout documentation.         callout facility, see the pcrecallout documentation.
1164    
1165             PCRE_BSR_ANYCRLF
1166             PCRE_BSR_UNICODE
1167    
1168           These options (which are mutually exclusive) control what the \R escape
1169           sequence  matches.  The choice is either to match only CR, LF, or CRLF,
1170           or to match any Unicode newline sequence. The default is specified when
1171           PCRE is built. It can be overridden from within the pattern, or by set-
1172           ting an option when a compiled pattern is matched.
1173    
1174           PCRE_CASELESS           PCRE_CASELESS
1175    
1176         If  this  bit is set, letters in the pattern match both upper and lower         If this bit is set, letters in the pattern match both upper  and  lower
1177         case letters. It is equivalent to Perl's  /i  option,  and  it  can  be         case  letters.  It  is  equivalent  to  Perl's /i option, and it can be
1178         changed  within a pattern by a (?i) option setting. In UTF-8 mode, PCRE         changed within a pattern by a (?i) option setting. In UTF-8 mode,  PCRE
1179         always understands the concept of case for characters whose values  are         always  understands the concept of case for characters whose values are
1180         less  than 128, so caseless matching is always possible. For characters         less than 128, so caseless matching is always possible. For  characters
1181         with higher values, the concept of case is supported if  PCRE  is  com-         with  higher  values,  the concept of case is supported if PCRE is com-
1182         piled  with Unicode property support, but not otherwise. If you want to         piled with Unicode property support, but not otherwise. If you want  to
1183         use caseless matching for characters 128 and  above,  you  must  ensure         use  caseless  matching  for  characters 128 and above, you must ensure
1184         that  PCRE  is  compiled  with Unicode property support as well as with         that PCRE is compiled with Unicode property support  as  well  as  with
1185         UTF-8 support.         UTF-8 support.
1186    
1187           PCRE_DOLLAR_ENDONLY           PCRE_DOLLAR_ENDONLY
1188    
1189         If this bit is set, a dollar metacharacter in the pattern matches  only         If  this bit is set, a dollar metacharacter in the pattern matches only
1190         at  the  end  of the subject string. Without this option, a dollar also         at the end of the subject string. Without this option,  a  dollar  also
1191         matches immediately before a newline at the end of the string (but  not         matches  immediately before a newline at the end of the string (but not
1192         before  any  other newlines). The PCRE_DOLLAR_ENDONLY option is ignored         before any other newlines). The PCRE_DOLLAR_ENDONLY option  is  ignored
1193         if PCRE_MULTILINE is set.  There is no equivalent  to  this  option  in         if  PCRE_MULTILINE  is  set.   There is no equivalent to this option in
1194         Perl, and no way to set it within a pattern.         Perl, and no way to set it within a pattern.
1195    
1196           PCRE_DOTALL           PCRE_DOTALL
1197    
1198         If this bit is set, a dot metacharater in the pattern matches all char-         If this bit is set, a dot metacharater in the pattern matches all char-
1199         acters, including those that indicate newline. Without it, a  dot  does         acters,  including  those that indicate newline. Without it, a dot does
1200         not  match  when  the  current position is at a newline. This option is         not match when the current position is at a  newline.  This  option  is
1201         equivalent to Perl's /s option, and it can be changed within a  pattern         equivalent  to Perl's /s option, and it can be changed within a pattern
1202         by  a (?s) option setting. A negative class such as [^a] always matches         by a (?s) option setting. A negative class such as [^a] always  matches
1203         newline characters, independent of the setting of this option.         newline characters, independent of the setting of this option.
1204    
1205           PCRE_DUPNAMES           PCRE_DUPNAMES
1206    
1207         If this bit is set, names used to identify capturing  subpatterns  need         If  this  bit is set, names used to identify capturing subpatterns need
1208         not be unique. This can be helpful for certain types of pattern when it         not be unique. This can be helpful for certain types of pattern when it
1209         is known that only one instance of the named  subpattern  can  ever  be         is  known  that  only  one instance of the named subpattern can ever be
1210         matched.  There  are  more details of named subpatterns below; see also         matched. There are more details of named subpatterns  below;  see  also
1211         the pcrepattern documentation.         the pcrepattern documentation.
1212    
1213           PCRE_EXTENDED           PCRE_EXTENDED
1214    
1215         If this bit is set, whitespace  data  characters  in  the  pattern  are         If  this  bit  is  set,  whitespace  data characters in the pattern are
1216         totally ignored except when escaped or inside a character class. White-         totally ignored except when escaped or inside a character class. White-
1217         space does not include the VT character (code 11). In addition, charac-         space does not include the VT character (code 11). In addition, charac-
1218         ters between an unescaped # outside a character class and the next new-         ters between an unescaped # outside a character class and the next new-
1219         line, inclusive, are also ignored. This  is  equivalent  to  Perl's  /x         line,  inclusive,  are  also  ignored.  This is equivalent to Perl's /x
1220         option,  and  it  can be changed within a pattern by a (?x) option set-         option, and it can be changed within a pattern by a  (?x)  option  set-
1221         ting.         ting.
1222    
1223         This option makes it possible to include  comments  inside  complicated         This  option  makes  it possible to include comments inside complicated
1224         patterns.   Note,  however,  that this applies only to data characters.         patterns.  Note, however, that this applies only  to  data  characters.
1225         Whitespace  characters  may  never  appear  within  special   character         Whitespace   characters  may  never  appear  within  special  character
1226         sequences  in  a  pattern,  for  example  within the sequence (?( which         sequences in a pattern, for  example  within  the  sequence  (?(  which
1227         introduces a conditional subpattern.         introduces a conditional subpattern.
1228    
1229           PCRE_EXTRA           PCRE_EXTRA
1230    
1231         This option was invented in order to turn on  additional  functionality         This  option  was invented in order to turn on additional functionality
1232         of  PCRE  that  is  incompatible with Perl, but it is currently of very         of PCRE that is incompatible with Perl, but it  is  currently  of  very
1233         little use. When set, any backslash in a pattern that is followed by  a         little  use. When set, any backslash in a pattern that is followed by a
1234         letter  that  has  no  special  meaning causes an error, thus reserving         letter that has no special meaning  causes  an  error,  thus  reserving
1235         these combinations for future expansion. By  default,  as  in  Perl,  a         these  combinations  for  future  expansion.  By default, as in Perl, a
1236         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
1237         literal. (Perl can, however, be persuaded to give a warning for  this.)         literal.  (Perl can, however, be persuaded to give a warning for this.)
1238         There  are  at  present no other features controlled by this option. It         There are at present no other features controlled by  this  option.  It
1239         can also be set by a (?X) option setting within a pattern.         can also be set by a (?X) option setting within a pattern.
1240    
1241           PCRE_FIRSTLINE           PCRE_FIRSTLINE
1242    
1243         If this option is set, an  unanchored  pattern  is  required  to  match         If  this  option  is  set,  an  unanchored pattern is required to match
1244         before  or  at  the  first  newline  in  the subject string, though the         before or at the first  newline  in  the  subject  string,  though  the
1245         matched text may continue over the newline.         matched text may continue over the newline.
1246    
1247           PCRE_MULTILINE           PCRE_MULTILINE
1248    
1249         By default, PCRE treats the subject string as consisting  of  a  single         By  default,  PCRE  treats the subject string as consisting of a single
1250         line  of characters (even if it actually contains newlines). The "start         line of characters (even if it actually contains newlines). The  "start
1251         of line" metacharacter (^) matches only at the  start  of  the  string,         of  line"  metacharacter  (^)  matches only at the start of the string,
1252         while  the  "end  of line" metacharacter ($) matches only at the end of         while the "end of line" metacharacter ($) matches only at  the  end  of
1253         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY
1254         is set). This is the same as Perl.         is set). This is the same as Perl.
1255    
1256         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"
1257         constructs match immediately following or immediately  before  internal         constructs  match  immediately following or immediately before internal
1258         newlines  in  the  subject string, respectively, as well as at the very         newlines in the subject string, respectively, as well as  at  the  very
1259         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
1260         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-
1261         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,
1262         setting PCRE_MULTILINE has no effect.         setting PCRE_MULTILINE has no effect.
1263    
1264           PCRE_NEWLINE_CR           PCRE_NEWLINE_CR
# Line 1154  COMPILING A PATTERN Line 1267  COMPILING A PATTERN
1267           PCRE_NEWLINE_ANYCRLF           PCRE_NEWLINE_ANYCRLF
1268           PCRE_NEWLINE_ANY           PCRE_NEWLINE_ANY
1269    
1270         These  options  override the default newline definition that was chosen         These options override the default newline definition that  was  chosen
1271         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
1272         newline  is  indicated  by a single character (CR or LF, respectively).         newline is indicated by a single character (CR  or  LF,  respectively).
1273         Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by  the         Setting  PCRE_NEWLINE_CRLF specifies that a newline is indicated by the
1274         two-character  CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF specifies         two-character CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF  specifies
1275         that any of the three preceding sequences should be recognized. Setting         that any of the three preceding sequences should be recognized. Setting
1276         PCRE_NEWLINE_ANY  specifies that any Unicode newline sequence should be         PCRE_NEWLINE_ANY specifies that any Unicode newline sequence should  be
1277         recognized. The Unicode newline sequences are the three just mentioned,         recognized. The Unicode newline sequences are the three just mentioned,
1278         plus  the  single  characters  VT (vertical tab, U+000B), FF (formfeed,         plus the single characters VT (vertical  tab,  U+000B),  FF  (formfeed,
1279         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
1280         (paragraph  separator,  U+2029).  The  last  two are recognized only in         (paragraph separator, U+2029). The last  two  are  recognized  only  in
1281         UTF-8 mode.         UTF-8 mode.
1282    
1283         The newline setting in the  options  word  uses  three  bits  that  are         The  newline  setting  in  the  options  word  uses three bits that are
1284         treated as a number, giving eight possibilities. Currently only six are         treated as a number, giving eight possibilities. Currently only six are
1285         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
1286         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-
1287         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
1288         PCRE_NEWLINE_CRLF,  but other combinations may yield unused numbers and         PCRE_NEWLINE_CRLF, but other combinations may yield unused numbers  and
1289         cause an error.         cause an error.
1290    
1291         The only time that a line break is specially recognized when  compiling         The  only time that a line break is specially recognized when compiling
1292         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
1293         character class is encountered. This indicates  a  comment  that  lasts         character  class  is  encountered.  This indicates a comment that lasts
1294         until  after the next line break sequence. In other circumstances, line         until after the next line break sequence. In other circumstances,  line
1295         break  sequences  are  treated  as  literal  data,   except   that   in         break   sequences   are   treated  as  literal  data,  except  that  in
1296         PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters         PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters
1297         and are therefore ignored.         and are therefore ignored.
1298    
1299         The newline option that is set at compile time becomes the default that         The newline option that is set at compile time becomes the default that
1300         is  used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.         is used for pcre_exec() and pcre_dfa_exec(), but it can be  overridden.
1301    
1302           PCRE_NO_AUTO_CAPTURE           PCRE_NO_AUTO_CAPTURE
1303    
1304         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-
1305         theses  in the pattern. Any opening parenthesis that is not followed by         theses in the pattern. Any opening parenthesis that is not followed  by
1306         ? behaves as if it were followed by ?: but named parentheses can  still         ?  behaves as if it were followed by ?: but named parentheses can still
1307         be  used  for  capturing  (and  they acquire numbers in the usual way).         be used for capturing (and they acquire  numbers  in  the  usual  way).
1308         There is no equivalent of this option in Perl.         There is no equivalent of this option in Perl.
1309    
1310           PCRE_UNGREEDY           PCRE_UNGREEDY
1311    
1312         This option inverts the "greediness" of the quantifiers  so  that  they         This  option  inverts  the "greediness" of the quantifiers so that they
1313         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
1314         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
1315         within the pattern.         within the pattern.
1316    
1317           PCRE_UTF8           PCRE_UTF8
1318    
1319         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
1320         strings of UTF-8 characters instead of single-byte  character  strings.         strings  of  UTF-8 characters instead of single-byte character strings.
1321         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-
1322         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
1323         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
1324         UTF-8 support in the main pcre page.         UTF-8 support in the main pcre page.
1325    
1326           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
1327    
1328         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
1329         automatically  checked. If an invalid UTF-8 sequence of bytes is found,         automatically checked. There is a  discussion  about  the  validity  of
1330         pcre_compile() returns an error. If you already know that your  pattern         UTF-8  strings  in  the main pcre page. If an invalid UTF-8 sequence of
1331         is  valid, and you want to skip this check for performance reasons, you         bytes is found, pcre_compile() returns an error. If  you  already  know
1332         can set the PCRE_NO_UTF8_CHECK option. When it is set,  the  effect  of         that your pattern is valid, and you want to skip this check for perfor-
1333         passing an invalid UTF-8 string as a pattern is undefined. It may cause         mance reasons, you can set the PCRE_NO_UTF8_CHECK option.  When  it  is
1334         your program to crash.  Note that this option can  also  be  passed  to         set,  the  effect  of  passing  an invalid UTF-8 string as a pattern is
1335         pcre_exec()  and pcre_dfa_exec(), to suppress the UTF-8 validity check-         undefined. It may cause your program to crash. Note  that  this  option
1336         ing of subject strings.         can  also be passed to pcre_exec() and pcre_dfa_exec(), to suppress the
1337           UTF-8 validity checking of subject strings.
1338    
1339    
1340  COMPILATION ERROR CODES  COMPILATION ERROR CODES
# Line 1259  COMPILATION ERROR CODES Line 1373  COMPILATION ERROR CODES
1373           26  malformed number or name after (?(           26  malformed number or name after (?(
1374           27  conditional group contains more than two branches           27  conditional group contains more than two branches
1375           28  assertion expected after (?(           28  assertion expected after (?(
1376           29  (?R or (?digits must be followed by )           29  (?R or (?[+-]digits must be followed by )
1377           30  unknown POSIX class name           30  unknown POSIX class name
1378           31  POSIX collating elements are not supported           31  POSIX collating elements are not supported
1379           32  this version of PCRE is not compiled with PCRE_UTF8 support           32  this version of PCRE is not compiled with PCRE_UTF8 support
# Line 1280  COMPILATION ERROR CODES Line 1394  COMPILATION ERROR CODES
1394           47  unknown property name after \P or \p           47  unknown property name after \P or \p
1395           48  subpattern name is too long (maximum 32 characters)           48  subpattern name is too long (maximum 32 characters)
1396           49  too many named subpatterns (maximum 10,000)           49  too many named subpatterns (maximum 10,000)
1397           50  repeated subpattern is too long           50  [this code is not in use]
1398           51  octal value is greater than \377 (not in UTF-8 mode)           51  octal value is greater than \377 (not in UTF-8 mode)
1399           52  internal error: overran compiling workspace           52  internal error: overran compiling workspace
1400           53   internal  error:  previously-checked  referenced  subpattern not           53   internal  error:  previously-checked  referenced  subpattern not
1401         found         found
1402           54  DEFINE group contains more than one branch           54  DEFINE group contains more than one branch
1403           55  repeating a DEFINE group is not allowed           55  repeating a DEFINE group is not allowed
1404           56  inconsistent NEWLINE options"           56  inconsistent NEWLINE options
1405             57  \g is not followed by a braced name or an optionally braced
1406                   non-zero number
1407             58  (?+ or (?- or (?(+ or (?(- must be followed by a non-zero number
1408    
1409    
1410  STUDYING A PATTERN  STUDYING A PATTERN
# Line 1476  INFORMATION ABOUT A PATTERN Line 1593  INFORMATION ABOUT A PATTERN
1593         returned. The fourth argument should point to an unsigned char *  vari-         returned. The fourth argument should point to an unsigned char *  vari-
1594         able.         able.
1595    
1596             PCRE_INFO_HASCRORLF
1597    
1598           Return  1  if  the  pattern  contains any explicit matches for CR or LF
1599           characters, otherwise 0. The fourth argument should  point  to  an  int
1600           variable.  An explicit match is either a literal CR or LF character, or
1601           \r or \n.
1602    
1603           PCRE_INFO_JCHANGED           PCRE_INFO_JCHANGED
1604    
1605         Return  1  if the (?J) option setting is used in the pattern, otherwise         Return 1 if the (?J) or (?-J) option setting is used  in  the  pattern,
1606         0. The fourth argument should point to an int variable. The (?J) inter-         otherwise  0. The fourth argument should point to an int variable. (?J)
1607         nal option setting changes the local PCRE_DUPNAMES value.         and (?-J) set and unset the local PCRE_DUPNAMES option, respectively.
1608    
1609           PCRE_INFO_LASTLITERAL           PCRE_INFO_LASTLITERAL
1610    
1611         Return  the  value of the rightmost literal byte that must exist in any         Return the value of the rightmost literal byte that must exist  in  any
1612         matched string, other than at its  start,  if  such  a  byte  has  been         matched  string,  other  than  at  its  start,  if such a byte has been
1613         recorded. The fourth argument should point to an int variable. If there         recorded. The fourth argument should point to an int variable. If there
1614         is no such byte, -1 is returned. For anchored patterns, a last  literal         is  no such byte, -1 is returned. For anchored patterns, a last literal
1615         byte  is  recorded only if it follows something of variable length. For         byte is recorded only if it follows something of variable  length.  For
1616         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
1617         /^a\dz\d/ the returned value is -1.         /^a\dz\d/ the returned value is -1.
1618    
# Line 1496  INFORMATION ABOUT A PATTERN Line 1620  INFORMATION ABOUT A PATTERN
1620           PCRE_INFO_NAMEENTRYSIZE           PCRE_INFO_NAMEENTRYSIZE
1621           PCRE_INFO_NAMETABLE           PCRE_INFO_NAMETABLE
1622    
1623         PCRE  supports the use of named as well as numbered capturing parenthe-         PCRE supports the use of named as well as numbered capturing  parenthe-
1624         ses. The names are just an additional way of identifying the  parenthe-         ses.  The names are just an additional way of identifying the parenthe-
1625         ses, which still acquire numbers. Several convenience functions such as         ses, which still acquire numbers. Several convenience functions such as
1626         pcre_get_named_substring() are provided for  extracting  captured  sub-         pcre_get_named_substring()  are  provided  for extracting captured sub-
1627         strings  by  name. It is also possible to extract the data directly, by         strings by name. It is also possible to extract the data  directly,  by
1628         first converting the name to a number in order to  access  the  correct         first  converting  the  name to a number in order to access the correct
1629         pointers in the output vector (described with pcre_exec() below). To do         pointers in the output vector (described with pcre_exec() below). To do
1630         the conversion, you need  to  use  the  name-to-number  map,  which  is         the  conversion,  you  need  to  use  the  name-to-number map, which is
1631         described by these three values.         described by these three values.
1632    
1633         The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT         The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT
1634         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
1635         of  each  entry;  both  of  these  return  an int value. The entry size         of each entry; both of these  return  an  int  value.  The  entry  size
1636         depends on the length of the longest name. PCRE_INFO_NAMETABLE  returns         depends  on the length of the longest name. PCRE_INFO_NAMETABLE returns
1637         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
1638         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-
1639         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-
1640         sponding name, zero terminated. The names are  in  alphabetical  order.         sponding  name,  zero  terminated. The names are in alphabetical order.
1641         When PCRE_DUPNAMES is set, duplicate names are in order of their paren-         When PCRE_DUPNAMES is set, duplicate names are in order of their paren-
1642         theses numbers. For example, consider  the  following  pattern  (assume         theses  numbers.  For  example,  consider the following pattern (assume
1643         PCRE_EXTENDED  is  set,  so  white  space  -  including  newlines  - is         PCRE_EXTENDED is  set,  so  white  space  -  including  newlines  -  is
1644         ignored):         ignored):
1645    
1646           (?<date> (?<year>(\d\d)?\d\d) -           (?<date> (?<year>(\d\d)?\d\d) -
1647           (?<month>\d\d) - (?<day>\d\d) )           (?<month>\d\d) - (?<day>\d\d) )
1648    
1649         There are four named subpatterns, so the table has  four  entries,  and         There  are  four  named subpatterns, so the table has four entries, and
1650         each  entry  in the table is eight bytes long. The table is as follows,         each entry in the table is eight bytes long. The table is  as  follows,
1651         with non-printing bytes shows in hexadecimal, and undefined bytes shown         with non-printing bytes shows in hexadecimal, and undefined bytes shown
1652         as ??:         as ??:
1653    
# Line 1532  INFORMATION ABOUT A PATTERN Line 1656  INFORMATION ABOUT A PATTERN
1656           00 04 m  o  n  t  h  00           00 04 m  o  n  t  h  00
1657           00 02 y  e  a  r  00 ??           00 02 y  e  a  r  00 ??
1658    
1659         When  writing  code  to  extract  data from named subpatterns using the         When writing code to extract data  from  named  subpatterns  using  the
1660         name-to-number map, remember that the length of the entries  is  likely         name-to-number  map,  remember that the length of the entries is likely
1661         to be different for each compiled pattern.         to be different for each compiled pattern.
1662    
1663           PCRE_INFO_OKPARTIAL           PCRE_INFO_OKPARTIAL
1664    
1665         Return  1 if the pattern can be used for partial matching, otherwise 0.         Return 1 if the pattern can be used for partial matching, otherwise  0.
1666         The fourth argument should point to an int  variable.  The  pcrepartial         The  fourth  argument  should point to an int variable. The pcrepartial
1667         documentation  lists  the restrictions that apply to patterns when par-         documentation lists the restrictions that apply to patterns  when  par-
1668         tial matching is used.         tial matching is used.
1669    
1670           PCRE_INFO_OPTIONS           PCRE_INFO_OPTIONS
1671    
1672         Return a copy of the options with which the pattern was  compiled.  The         Return  a  copy of the options with which the pattern was compiled. The
1673         fourth  argument  should  point to an unsigned long int variable. These         fourth argument should point to an unsigned long  int  variable.  These
1674         option bits are those specified in the call to pcre_compile(), modified         option bits are those specified in the call to pcre_compile(), modified
1675         by any top-level option settings within the pattern itself.         by any top-level option settings at the start of the pattern itself. In
1676           other  words,  they are the options that will be in force when matching
1677           starts. For example, if the pattern /(?im)abc(?-i)d/ is  compiled  with
1678           the  PCRE_EXTENDED option, the result is PCRE_CASELESS, PCRE_MULTILINE,
1679           and PCRE_EXTENDED.
1680    
1681         A  pattern  is  automatically  anchored by PCRE if all of its top-level         A pattern is automatically anchored by PCRE if  all  of  its  top-level
1682         alternatives begin with one of the following:         alternatives begin with one of the following:
1683    
1684           ^     unless PCRE_MULTILINE is set           ^     unless PCRE_MULTILINE is set
# Line 1564  INFORMATION ABOUT A PATTERN Line 1692  INFORMATION ABOUT A PATTERN
1692    
1693           PCRE_INFO_SIZE           PCRE_INFO_SIZE
1694    
1695         Return  the  size  of the compiled pattern, that is, the value that was         Return the size of the compiled pattern, that is, the  value  that  was
1696         passed as the argument to pcre_malloc() when PCRE was getting memory in         passed as the argument to pcre_malloc() when PCRE was getting memory in
1697         which to place the compiled data. The fourth argument should point to a         which to place the compiled data. The fourth argument should point to a
1698         size_t variable.         size_t variable.
# Line 1572  INFORMATION ABOUT A PATTERN Line 1700  INFORMATION ABOUT A PATTERN
1700           PCRE_INFO_STUDYSIZE           PCRE_INFO_STUDYSIZE
1701    
1702         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
1703         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
1704         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
1705         created  by  pcre_study(). The fourth argument should point to a size_t         created by pcre_study(). The fourth argument should point to  a  size_t
1706         variable.         variable.
1707    
1708    
# Line 1582  OBSOLETE INFO FUNCTION Line 1710  OBSOLETE INFO FUNCTION
1710    
1711         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
1712    
1713         The pcre_info() function is now obsolete because its interface  is  too         The  pcre_info()  function is now obsolete because its interface is too
1714         restrictive  to return all the available data about a compiled pattern.         restrictive to return all the available data about a compiled  pattern.
1715         New  programs  should  use  pcre_fullinfo()  instead.  The   yield   of         New   programs   should  use  pcre_fullinfo()  instead.  The  yield  of
1716         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-
1717         lowing negative numbers:         lowing negative numbers:
1718    
1719           PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_NULL       the argument code was NULL
1720           PCRE_ERROR_BADMAGIC   the "magic number" was not found           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1721    
1722         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
1723         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
1724         PCRE_INFO_OPTIONS above).         PCRE_INFO_OPTIONS above).
1725    
1726         If the pattern is not anchored and the  firstcharptr  argument  is  not         If  the  pattern  is  not anchored and the firstcharptr argument is not
1727         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
1728         any matched string (see PCRE_INFO_FIRSTBYTE above).         any matched string (see PCRE_INFO_FIRSTBYTE above).
1729    
1730    
# Line 1604  REFERENCE COUNTS Line 1732  REFERENCE COUNTS
1732    
1733         int pcre_refcount(pcre *code, int adjust);         int pcre_refcount(pcre *code, int adjust);
1734    
1735         The pcre_refcount() function is used to maintain a reference  count  in         The  pcre_refcount()  function is used to maintain a reference count in
1736         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
1737         benefit of applications that  operate  in  an  object-oriented  manner,         benefit  of  applications  that  operate  in an object-oriented manner,
1738         where different parts of the application may be using the same compiled         where different parts of the application may be using the same compiled
1739         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.
1740    
1741         When a pattern is compiled, the reference count field is initialized to         When a pattern is compiled, the reference count field is initialized to
1742         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
1743         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
1744         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
1745         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
1746         is outside these limits, it is forced to the appropriate limit value.         is outside these limits, it is forced to the appropriate limit value.
1747    
1748         Except  when it is zero, the reference count is not correctly preserved         Except when it is zero, the reference count is not correctly  preserved
1749         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
1750         whose byte-order is different. (This seems a highly unlikely scenario.)         whose byte-order is different. (This seems a highly unlikely scenario.)
1751    
1752    
# Line 1628  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1756  MATCHING A PATTERN: THE TRADITIONAL FUNC
1756              const char *subject, int length, int startoffset,              const char *subject, int length, int startoffset,
1757              int options, int *ovector, int ovecsize);              int options, int *ovector, int ovecsize);
1758    
1759         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
1760         compiled  pattern, which is passed in the code argument. If the pattern         compiled pattern, which is passed in the code argument. If the  pattern
1761         has been studied, the result of the study should be passed in the extra         has been studied, the result of the study should be passed in the extra
1762         argument.  This  function is the main matching facility of the library,         argument. This function is the main matching facility of  the  library,
1763         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
1764         an  alternative matching function, which is described below in the sec-         an alternative matching function, which is described below in the  sec-
1765         tion about the pcre_dfa_exec() function.         tion about the pcre_dfa_exec() function.
1766    
1767         In most applications, the pattern will have been compiled (and  option-         In  most applications, the pattern will have been compiled (and option-
1768         ally  studied)  in the same process that calls pcre_exec(). However, it         ally studied) in the same process that calls pcre_exec().  However,  it
1769         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
1770         later  in  different processes, possibly even on different hosts. For a         later in different processes, possibly even on different hosts.  For  a
1771         discussion about this, see the pcreprecompile documentation.         discussion about this, see the pcreprecompile documentation.
1772    
1773         Here is an example of a simple call to pcre_exec():         Here is an example of a simple call to pcre_exec():
# Line 1658  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1786  MATCHING A PATTERN: THE TRADITIONAL FUNC
1786    
1787     Extra data for pcre_exec()     Extra data for pcre_exec()
1788    
1789         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
1790         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
1791         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-
1792         tional  information  in it. The pcre_extra block contains the following         tional information in it. The pcre_extra block contains  the  following
1793         fields (not necessarily in this order):         fields (not necessarily in this order):
1794    
1795           unsigned long int flags;           unsigned long int flags;
# Line 1671  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1799  MATCHING A PATTERN: THE TRADITIONAL FUNC
1799           void *callout_data;           void *callout_data;
1800           const unsigned char *tables;           const unsigned char *tables;
1801    
1802         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
1803         are set. The flag bits are:         are set. The flag bits are:
1804    
1805           PCRE_EXTRA_STUDY_DATA           PCRE_EXTRA_STUDY_DATA
# Line 1680  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1808  MATCHING A PATTERN: THE TRADITIONAL FUNC
1808           PCRE_EXTRA_CALLOUT_DATA           PCRE_EXTRA_CALLOUT_DATA
1809           PCRE_EXTRA_TABLES           PCRE_EXTRA_TABLES
1810    
1811         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
1812         the pcre_extra block that is returned by  pcre_study(),  together  with         the  pcre_extra  block  that is returned by pcre_study(), together with
1813         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
1814         add to the block by setting the other fields  and  their  corresponding         add  to  the  block by setting the other fields and their corresponding
1815         flag bits.         flag bits.
1816    
1817         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
1818         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
1819         match,  but  which  have  a very large number of possibilities in their         match, but which have a very large number  of  possibilities  in  their
1820         search trees. The classic  example  is  the  use  of  nested  unlimited         search  trees.  The  classic  example  is  the  use of nested unlimited
1821         repeats.         repeats.
1822    
1823         Internally,  PCRE uses a function called match() which it calls repeat-         Internally, PCRE uses a function called match() which it calls  repeat-
1824         edly (sometimes recursively). The limit set by match_limit  is  imposed         edly  (sometimes  recursively). The limit set by match_limit is imposed
1825         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
1826         has the effect of limiting the amount of  backtracking  that  can  take         has  the  effect  of  limiting the amount of backtracking that can take
1827         place. For patterns that are not anchored, the count restarts from zero         place. For patterns that are not anchored, the count restarts from zero
1828         for each position in the subject string.         for each position in the subject string.
1829    
1830         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
1831         default  default  is 10 million, which handles all but the most extreme         default default is 10 million, which handles all but the  most  extreme
1832         cases. You can override the default  by  suppling  pcre_exec()  with  a         cases.  You  can  override  the  default by suppling pcre_exec() with a
1833         pcre_extra     block    in    which    match_limit    is    set,    and         pcre_extra    block    in    which    match_limit    is    set,     and
1834         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
1835         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1836    
1837         The  match_limit_recursion field is similar to match_limit, but instead         The match_limit_recursion field is similar to match_limit, but  instead
1838         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
1839         the  depth  of  recursion. The recursion depth is a smaller number than         the depth of recursion. The recursion depth is a  smaller  number  than
1840         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-
1841         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.
1842    
1843         Limiting the recursion depth limits the amount of  stack  that  can  be         Limiting  the  recursion  depth  limits the amount of stack that can be
1844         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
1845         of the stack, the amount of heap memory that can be used.         of the stack, the amount of heap memory that can be used.
1846    
1847         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
1848         built;  the  default  default  is  the  same  value  as the default for         built; the default default  is  the  same  value  as  the  default  for
1849         match_limit. You can override the default by suppling pcre_exec()  with         match_limit.  You can override the default by suppling pcre_exec() with
1850         a   pcre_extra   block  in  which  match_limit_recursion  is  set,  and         a  pcre_extra  block  in  which  match_limit_recursion  is   set,   and
1851         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
1852         limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.         limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1853    
1854         The  pcre_callout  field is used in conjunction with the "callout" fea-         The pcre_callout field is used in conjunction with the  "callout"  fea-
1855         ture, which is described in the pcrecallout documentation.         ture, which is described in the pcrecallout documentation.
1856    
1857         The tables field  is  used  to  pass  a  character  tables  pointer  to         The  tables  field  is  used  to  pass  a  character  tables pointer to
1858         pcre_exec();  this overrides the value that is stored with the compiled         pcre_exec(); this overrides the value that is stored with the  compiled
1859         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
1860         custom  tables  were  supplied to pcre_compile() via its tableptr argu-         custom tables were supplied to pcre_compile() via  its  tableptr  argu-
1861         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
1862         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-
1863         using patterns that have been saved after compiling  with  an  external         using  patterns  that  have been saved after compiling with an external
1864         set  of  tables,  because  the  external tables might be at a different         set of tables, because the external tables  might  be  at  a  different
1865         address when pcre_exec() is called. See the  pcreprecompile  documenta-         address  when  pcre_exec() is called. See the pcreprecompile documenta-
1866         tion for a discussion of saving compiled patterns for later use.         tion for a discussion of saving compiled patterns for later use.
1867    
1868     Option bits for pcre_exec()     Option bits for pcre_exec()
1869    
1870         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.
1871         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,
1872         PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and         PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and
1873         PCRE_PARTIAL.         PCRE_PARTIAL.
1874    
1875           PCRE_ANCHORED           PCRE_ANCHORED
1876    
1877         The PCRE_ANCHORED option limits pcre_exec() to matching  at  the  first         The  PCRE_ANCHORED  option  limits pcre_exec() to matching at the first
1878         matching  position.  If  a  pattern was compiled with PCRE_ANCHORED, or         matching position. If a pattern was  compiled  with  PCRE_ANCHORED,  or
1879         turned out to be anchored by virtue of its contents, it cannot be  made         turned  out to be anchored by virtue of its contents, it cannot be made
1880         unachored at matching time.         unachored at matching time.
1881    
1882             PCRE_BSR_ANYCRLF
1883             PCRE_BSR_UNICODE
1884    
1885           These options (which are mutually exclusive) control what the \R escape
1886           sequence  matches.  The choice is either to match only CR, LF, or CRLF,
1887           or to match any Unicode newline sequence. These  options  override  the
1888           choice that was made or defaulted when the pattern was compiled.
1889    
1890           PCRE_NEWLINE_CR           PCRE_NEWLINE_CR
1891           PCRE_NEWLINE_LF           PCRE_NEWLINE_LF
1892           PCRE_NEWLINE_CRLF           PCRE_NEWLINE_CRLF
# Line 1762  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1898  MATCHING A PATTERN: THE TRADITIONAL FUNC
1898         tion  of  pcre_compile()  above.  During  matching,  the newline choice         tion  of  pcre_compile()  above.  During  matching,  the newline choice
1899         affects the behaviour of the dot, circumflex,  and  dollar  metacharac-         affects the behaviour of the dot, circumflex,  and  dollar  metacharac-
1900         ters.  It may also alter the way the match position is advanced after a         ters.  It may also alter the way the match position is advanced after a
1901         match  failure  for  an  unanchored  pattern.  When  PCRE_NEWLINE_CRLF,         match failure for an unanchored pattern.
1902         PCRE_NEWLINE_ANYCRLF,  or  PCRE_NEWLINE_ANY is set, and a match attempt  
1903         fails when the current position is at a CRLF sequence, the match  posi-         When PCRE_NEWLINE_CRLF, PCRE_NEWLINE_ANYCRLF,  or  PCRE_NEWLINE_ANY  is
1904         tion  is  advanced by two characters instead of one, in other words, to         set,  and a match attempt for an unanchored pattern fails when the cur-
1905         after the CRLF.         rent position is at a  CRLF  sequence,  and  the  pattern  contains  no
1906           explicit  matches  for  CR  or  LF  characters,  the  match position is
1907           advanced by two characters instead of one, in other words, to after the
1908           CRLF.
1909    
1910           The above rule is a compromise that makes the most common cases work as
1911           expected. For example, if the  pattern  is  .+A  (and  the  PCRE_DOTALL
1912           option is not set), it does not match the string "\r\nA" because, after
1913           failing at the start, it skips both the CR and the LF before  retrying.
1914           However,  the  pattern  [\r\n]A does match that string, because it con-
1915           tains an explicit CR or LF reference, and so advances only by one char-
1916           acter after the first failure.
1917    
1918           An explicit match for CR of LF is either a literal appearance of one of
1919           those characters, or one of the \r or  \n  escape  sequences.  Implicit
1920           matches  such  as [^X] do not count, nor does \s (which includes CR and
1921           LF in the characters that it matches).
1922    
1923           Notwithstanding the above, anomalous effects may still occur when  CRLF
1924           is a valid newline sequence and explicit \r or \n escapes appear in the
1925           pattern.
1926    
1927           PCRE_NOTBOL           PCRE_NOTBOL
1928    
# Line 1813  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1969  MATCHING A PATTERN: THE TRADITIONAL FUNC
1969         When PCRE_UTF8 is set at compile time, the validity of the subject as a         When PCRE_UTF8 is set at compile time, the validity of the subject as a
1970         UTF-8  string is automatically checked when pcre_exec() is subsequently         UTF-8  string is automatically checked when pcre_exec() is subsequently
1971         called.  The value of startoffset is also checked  to  ensure  that  it         called.  The value of startoffset is also checked  to  ensure  that  it
1972         points  to the start of a UTF-8 character. If an invalid UTF-8 sequence         points  to  the start of a UTF-8 character. There is a discussion about
1973         of bytes is found, pcre_exec() returns the error PCRE_ERROR_BADUTF8. If         the validity of UTF-8 strings in the section on UTF-8  support  in  the
1974         startoffset  contains  an  invalid  value, PCRE_ERROR_BADUTF8_OFFSET is         main  pcre  page.  If  an  invalid  UTF-8  sequence  of bytes is found,
1975         returned.         pcre_exec() returns the error PCRE_ERROR_BADUTF8. If  startoffset  con-
1976           tains an invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.
1977         If you already know that your subject is valid, and you  want  to  skip  
1978         these    checks    for   performance   reasons,   you   can   set   the         If  you  already  know that your subject is valid, and you want to skip
1979         PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might  want  to         these   checks   for   performance   reasons,   you   can    set    the
1980         do  this  for the second and subsequent calls to pcre_exec() if you are         PCRE_NO_UTF8_CHECK  option  when calling pcre_exec(). You might want to
1981         making repeated calls to find all  the  matches  in  a  single  subject         do this for the second and subsequent calls to pcre_exec() if  you  are
1982         string.  However,  you  should  be  sure  that the value of startoffset         making  repeated  calls  to  find  all  the matches in a single subject
1983         points to the start of a UTF-8 character.  When  PCRE_NO_UTF8_CHECK  is         string. However, you should be  sure  that  the  value  of  startoffset
1984         set,  the  effect of passing an invalid UTF-8 string as a subject, or a         points  to  the  start of a UTF-8 character. When PCRE_NO_UTF8_CHECK is
1985         value of startoffset that does not point to the start of a UTF-8  char-         set, the effect of passing an invalid UTF-8 string as a subject,  or  a
1986           value  of startoffset that does not point to the start of a UTF-8 char-
1987         acter, is undefined. Your program may crash.         acter, is undefined. Your program may crash.
1988    
1989           PCRE_PARTIAL           PCRE_PARTIAL
1990    
1991         This  option  turns  on  the  partial  matching feature. If the subject         This option turns on the  partial  matching  feature.  If  the  subject
1992         string fails to match the pattern, but at some point during the  match-         string  fails to match the pattern, but at some point during the match-
1993         ing  process  the  end of the subject was reached (that is, the subject         ing process the end of the subject was reached (that  is,  the  subject
1994         partially matches the pattern and the failure to  match  occurred  only         partially  matches  the  pattern and the failure to match occurred only
1995         because  there were not enough subject characters), pcre_exec() returns         because there were not enough subject characters), pcre_exec()  returns
1996         PCRE_ERROR_PARTIAL instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL  is         PCRE_ERROR_PARTIAL  instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is
1997         used,  there  are restrictions on what may appear in the pattern. These         used, there are restrictions on what may appear in the  pattern.  These
1998         are discussed in the pcrepartial documentation.         are discussed in the pcrepartial documentation.
1999    
2000     The string to be matched by pcre_exec()     The string to be matched by pcre_exec()
2001    
2002         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
2003         length  in  length, and a starting byte offset in startoffset. In UTF-8         length in length, and a starting byte offset in startoffset.  In  UTF-8
2004         mode, the byte offset must point to the start  of  a  UTF-8  character.         mode,  the  byte  offset  must point to the start of a UTF-8 character.
2005         Unlike  the  pattern string, the subject may contain binary zero bytes.         Unlike the pattern string, the subject may contain binary  zero  bytes.
2006         When the starting offset is zero, the search for a match starts at  the         When  the starting offset is zero, the search for a match starts at the
2007         beginning of the subject, and this is by far the most common case.         beginning of the subject, and this is by far the most common case.
2008    
2009         A  non-zero  starting offset is useful when searching for another match         A non-zero starting offset is useful when searching for  another  match
2010         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-
2011         cess.   Setting  startoffset differs from just passing over a shortened         cess.  Setting startoffset differs from just passing over  a  shortened
2012         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
2013         with any kind of lookbehind. For example, consider the pattern         with any kind of lookbehind. For example, consider the pattern
2014    
2015           \Biss\B           \Biss\B
2016    
2017         which  finds  occurrences  of "iss" in the middle of words. (\B matches         which finds occurrences of "iss" in the middle of  words.  (\B  matches
2018         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.)
2019         When  applied  to the string "Mississipi" the first call to pcre_exec()         When applied to the string "Mississipi" the first call  to  pcre_exec()
2020         finds the first occurrence. If pcre_exec() is called  again  with  just         finds  the  first  occurrence. If pcre_exec() is called again with just
2021         the  remainder  of  the  subject,  namely  "issipi", it does not match,         the remainder of the subject,  namely  "issipi",  it  does  not  match,
2022         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
2023         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
2024         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-
2025         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
2026         discover that it is preceded by a letter.         discover that it is preceded by a letter.
2027    
2028         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,
2029         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
2030         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
2031         subject.         subject.
2032    
2033     How pcre_exec() returns captured substrings     How pcre_exec() returns captured substrings
2034    
2035         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
2036         addition, further substrings from the subject  may  be  picked  out  by         addition,  further  substrings  from  the  subject may be picked out by
2037         parts  of  the  pattern.  Following the usage in Jeffrey Friedl's book,         parts of the pattern. Following the usage  in  Jeffrey  Friedl's  book,
2038         this is called "capturing" in what follows, and the  phrase  "capturing         this  is  called "capturing" in what follows, and the phrase "capturing
2039         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-
2040         string. PCRE supports several other kinds of  parenthesized  subpattern         string.  PCRE  supports several other kinds of parenthesized subpattern
2041         that do not cause substrings to be captured.         that do not cause substrings to be captured.
2042    
2043         Captured  substrings are returned to the caller via a vector of integer         Captured substrings are returned to the caller via a vector of  integer
2044         offsets whose address is passed in ovector. The number of  elements  in         offsets  whose  address is passed in ovector. The number of elements in
2045         the  vector is passed in ovecsize, which must be a non-negative number.         the vector is passed in ovecsize, which must be a non-negative  number.
2046         Note: this argument is NOT the size of ovector in bytes.         Note: this argument is NOT the size of ovector in bytes.
2047    
2048         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-
2049         strings,  each  substring using a pair of integers. The remaining third         strings, each substring using a pair of integers. The  remaining  third
2050         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-
2051         turing  subpatterns, and is not available for passing back information.         turing subpatterns, and is not available for passing back  information.
2052         The length passed in ovecsize should always be a multiple of three.  If         The  length passed in ovecsize should always be a multiple of three. If
2053         it is not, it is rounded down.         it is not, it is rounded down.
2054    
2055         When  a  match  is successful, information about captured substrings is         When a match is successful, information about  captured  substrings  is
2056         returned in pairs of integers, starting at the  beginning  of  ovector,         returned  in  pairs  of integers, starting at the beginning of ovector,
2057         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
2058         element of a pair is set to the offset of the first character in a sub-         element of a pair is set to the offset of the first character in a sub-
2059         string,  and  the  second  is  set to the offset of the first character         string, and the second is set to the  offset  of  the  first  character
2060         after the end of a substring. The  first  pair,  ovector[0]  and  ovec-         after  the  end  of  a  substring. The first pair, ovector[0] and ovec-
2061         tor[1],  identify  the  portion  of  the  subject string matched by the         tor[1], identify the portion of  the  subject  string  matched  by  the
2062         entire pattern. The next pair is used for the first  capturing  subpat-         entire  pattern.  The next pair is used for the first capturing subpat-
2063         tern, and so on. The value returned by pcre_exec() is one more than the         tern, and so on. The value returned by pcre_exec() is one more than the
2064         highest numbered pair that has been set. For example, if two substrings         highest numbered pair that has been set. For example, if two substrings
2065         have  been captured, the returned value is 3. If there are no capturing         have been captured, the returned value is 3. If there are no  capturing
2066         subpatterns, the return value from a successful match is 1,  indicating         subpatterns,  the return value from a successful match is 1, indicating
2067         that just the first pair of offsets has been set.         that just the first pair of offsets has been set.
2068    
2069         If a capturing subpattern is matched repeatedly, it is the last portion         If a capturing subpattern is matched repeatedly, it is the last portion
2070         of the string that it matched that is returned.         of the string that it matched that is returned.
2071    
2072         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,
2073         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
2074         function returns a value of zero. In particular, if the substring  off-         function  returns a value of zero. In particular, if the substring off-
2075         sets are not of interest, pcre_exec() may be called with ovector passed         sets are not of interest, pcre_exec() may be called with ovector passed
2076         as NULL and ovecsize as zero. However, if  the  pattern  contains  back         as  NULL  and  ovecsize  as zero. However, if the pattern contains back
2077         references  and  the  ovector is not big enough to remember the related         references and the ovector is not big enough to  remember  the  related
2078         substrings, PCRE has to get additional memory for use during  matching.         substrings,  PCRE has to get additional memory for use during matching.
2079         Thus it is usually advisable to supply an ovector.         Thus it is usually advisable to supply an ovector.
2080    
2081         The  pcre_info()  function  can  be used to find out how many capturing         The pcre_info() function can be used to find  out  how  many  capturing
2082         subpatterns there are in a compiled  pattern.  The  smallest  size  for         subpatterns  there  are  in  a  compiled pattern. The smallest size for
2083         ovector  that  will allow for n captured substrings, in addition to the         ovector that will allow for n captured substrings, in addition  to  the
2084         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.
2085    
2086         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
2087         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,
2088         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
2089         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
2090         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-
2091         sponding to unused subpatterns are set to -1.         sponding to unused subpatterns are set to -1.
2092    
2093         Offset  values  that correspond to unused subpatterns at the end of the         Offset values that correspond to unused subpatterns at the end  of  the
2094         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
2095         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
2096         matched. The return from the function is 2, because  the  highest  used         matched.  The  return  from the function is 2, because the highest used
2097         capturing subpattern number is 1. However, you can refer to the offsets         capturing subpattern number is 1. However, you can refer to the offsets
2098         for the second and third capturing subpatterns if  you  wish  (assuming         for  the  second  and third capturing subpatterns if you wish (assuming
2099         the vector is large enough, of course).         the vector is large enough, of course).
2100    
2101         Some  convenience  functions  are  provided for extracting the captured         Some convenience functions are provided  for  extracting  the  captured
2102         substrings as separate strings. These are described below.         substrings as separate strings. These are described below.
2103    
2104     Error return values from pcre_exec()     Error return values from pcre_exec()
2105    
2106         If pcre_exec() fails, it returns a negative number. The  following  are         If  pcre_exec()  fails, it returns a negative number. The following are
2107         defined in the header file:         defined in the header file:
2108    
2109           PCRE_ERROR_NOMATCH        (-1)           PCRE_ERROR_NOMATCH        (-1)
# Line 1955  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2112  MATCHING A PATTERN: THE TRADITIONAL FUNC
2112    
2113           PCRE_ERROR_NULL           (-2)           PCRE_ERROR_NULL           (-2)
2114    
2115         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
2116         ovecsize was not zero.         ovecsize was not zero.
2117    
2118           PCRE_ERROR_BADOPTION      (-3)           PCRE_ERROR_BADOPTION      (-3)
# Line 1964  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2121  MATCHING A PATTERN: THE TRADITIONAL FUNC
2121    
2122           PCRE_ERROR_BADMAGIC       (-4)           PCRE_ERROR_BADMAGIC       (-4)
2123    
2124         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,
2125         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
2126         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
2127         an  environment  with the other endianness. This is the error that PCRE         an environment with the other endianness. This is the error  that  PCRE
2128         gives when the magic number is not present.         gives when the magic number is not present.
2129    
2130           PCRE_ERROR_UNKNOWN_OPCODE (-5)           PCRE_ERROR_UNKNOWN_OPCODE (-5)
2131    
2132         While running the pattern match, an unknown item was encountered in the         While running the pattern match, an unknown item was encountered in the
2133         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
2134         overwriting of the compiled pattern.         overwriting of the compiled pattern.
2135    
2136           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2137    
2138         If a pattern contains back references, but the ovector that  is  passed         If  a  pattern contains back references, but the ovector that is passed
2139         to pcre_exec() is not big enough to remember the referenced substrings,         to pcre_exec() is not big enough to remember the referenced substrings,
2140         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
2141         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
2142         memory is automatically freed at the end of matching.         memory is automatically freed at the end of matching.
2143    
2144           PCRE_ERROR_NOSUBSTRING    (-7)           PCRE_ERROR_NOSUBSTRING    (-7)
2145    
2146         This error is used by the pcre_copy_substring(),  pcre_get_substring(),         This  error is used by the pcre_copy_substring(), pcre_get_substring(),
2147         and  pcre_get_substring_list()  functions  (see  below).  It  is  never         and  pcre_get_substring_list()  functions  (see  below).  It  is  never
2148         returned by pcre_exec().         returned by pcre_exec().
2149    
2150           PCRE_ERROR_MATCHLIMIT     (-8)           PCRE_ERROR_MATCHLIMIT     (-8)
2151    
2152         The backtracking limit, as specified by  the  match_limit  field  in  a         The  backtracking  limit,  as  specified  by the match_limit field in a
2153         pcre_extra  structure  (or  defaulted) was reached. See the description         pcre_extra structure (or defaulted) was reached.  See  the  description
2154         above.         above.
2155    
2156           PCRE_ERROR_CALLOUT        (-9)           PCRE_ERROR_CALLOUT        (-9)
2157    
2158         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
2159         use  by  callout functions that want to yield a distinctive error code.         use by callout functions that want to yield a distinctive  error  code.
2160         See the pcrecallout documentation for details.         See the pcrecallout documentation for details.
2161    
2162           PCRE_ERROR_BADUTF8        (-10)           PCRE_ERROR_BADUTF8        (-10)
2163    
2164         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
2165         subject.         subject.
2166    
2167           PCRE_ERROR_BADUTF8_OFFSET (-11)           PCRE_ERROR_BADUTF8_OFFSET (-11)
2168    
2169         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
2170         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-
2171         ter.         ter.
2172    
2173           PCRE_ERROR_PARTIAL        (-12)           PCRE_ERROR_PARTIAL        (-12)
2174    
2175         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
2176         pcrepartial documentation for details of partial matching.         pcrepartial documentation for details of partial matching.
2177    
2178           PCRE_ERROR_BADPARTIAL     (-13)           PCRE_ERROR_BADPARTIAL     (-13)
2179    
2180         The PCRE_PARTIAL option was used with  a  compiled  pattern  containing         The  PCRE_PARTIAL  option  was  used with a compiled pattern containing
2181         items  that are not supported for partial matching. See the pcrepartial         items that are not supported for partial matching. See the  pcrepartial
2182         documentation for details of partial matching.         documentation for details of partial matching.
2183    
2184           PCRE_ERROR_INTERNAL       (-14)           PCRE_ERROR_INTERNAL       (-14)
2185    
2186         An unexpected internal error has occurred. This error could  be  caused         An  unexpected  internal error has occurred. This error could be caused
2187         by a bug in PCRE or by overwriting of the compiled pattern.         by a bug in PCRE or by overwriting of the compiled pattern.
2188    
2189           PCRE_ERROR_BADCOUNT       (-15)           PCRE_ERROR_BADCOUNT       (-15)
2190    
2191         This  error is given if the value of the ovecsize argument is negative.         This error is given if the value of the ovecsize argument is  negative.
2192    
2193           PCRE_ERROR_RECURSIONLIMIT (-21)           PCRE_ERROR_RECURSIONLIMIT (-21)
2194    
2195         The internal recursion limit, as specified by the match_limit_recursion         The internal recursion limit, as specified by the match_limit_recursion
2196         field  in  a  pcre_extra  structure (or defaulted) was reached. See the         field in a pcre_extra structure (or defaulted)  was  reached.  See  the
2197         description above.         description above.
2198    
          PCRE_ERROR_NULLWSLIMIT    (-22)  
   
        When a group that can match an empty  substring  is  repeated  with  an  
        unbounded  upper  limit, the subject position at the start of the group  
        must be remembered, so that a test for an empty string can be made when  
        the  end  of the group is reached. Some workspace is required for this;  
        if it runs out, this error is given.  
   
2199           PCRE_ERROR_BADNEWLINE     (-23)           PCRE_ERROR_BADNEWLINE     (-23)
2200    
2201         An invalid combination of PCRE_NEWLINE_xxx options was given.         An invalid combination of PCRE_NEWLINE_xxx options was given.
2202    
2203         Error numbers -16 to -20 are not used by pcre_exec().         Error numbers -16 to -20 and -22 are not used by pcre_exec().
2204    
2205    
2206  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
# Line 2067  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2216  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2216         int pcre_get_substring_list(const char *subject,         int pcre_get_substring_list(const char *subject,
2217              int *ovector, int stringcount, const char ***listptr);              int *ovector, int stringcount, const char ***listptr);
2218    
2219         Captured substrings can be  accessed  directly  by  using  the  offsets         Captured  substrings  can  be  accessed  directly  by using the offsets
2220         returned  by  pcre_exec()  in  ovector.  For convenience, the functions         returned by pcre_exec() in  ovector.  For  convenience,  the  functions
2221         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-
2222         string_list()  are  provided for extracting captured substrings as new,         string_list() are provided for extracting captured substrings  as  new,
2223         separate, zero-terminated strings. These functions identify  substrings         separate,  zero-terminated strings. These functions identify substrings
2224         by  number.  The  next section describes functions for extracting named         by number. The next section describes functions  for  extracting  named
2225         substrings.         substrings.
2226    
2227         A substring that contains a binary zero is correctly extracted and  has         A  substring that contains a binary zero is correctly extracted and has
2228         a  further zero added on the end, but the result is not, of course, a C         a further zero added on the end, but the result is not, of course, a  C
2229         string.  However, you can process such a string  by  referring  to  the         string.   However,  you  can  process such a string by referring to the
2230         length  that  is  returned  by  pcre_copy_substring() and pcre_get_sub-         length that is  returned  by  pcre_copy_substring()  and  pcre_get_sub-
2231         string().  Unfortunately, the interface to pcre_get_substring_list() is         string().  Unfortunately, the interface to pcre_get_substring_list() is
2232         not  adequate for handling strings containing binary zeros, because the         not adequate for handling strings containing binary zeros, because  the
2233         end of the final string is not independently indicated.         end of the final string is not independently indicated.
2234    
2235         The first three arguments are the same for all  three  of  these  func-         The  first  three  arguments  are the same for all three of these func-
2236         tions:  subject  is  the subject string that has just been successfully         tions: subject is the subject string that has  just  been  successfully
2237         matched, ovector is a pointer to the vector of integer offsets that was         matched, ovector is a pointer to the vector of integer offsets that was
2238         passed to pcre_exec(), and stringcount is the number of substrings that         passed to pcre_exec(), and stringcount is the number of substrings that
2239         were captured by the match, including the substring  that  matched  the         were  captured  by  the match, including the substring that matched the
2240         entire regular expression. This is the value returned by pcre_exec() if         entire regular expression. This is the value returned by pcre_exec() if
2241         it is greater than zero. If pcre_exec() returned zero, indicating  that         it  is greater than zero. If pcre_exec() returned zero, indicating that
2242         it  ran out of space in ovector, the value passed as stringcount should         it ran out of space in ovector, the value passed as stringcount  should
2243         be the number of elements in the vector divided by three.         be the number of elements in the vector divided by three.
2244    
2245         The functions pcre_copy_substring() and pcre_get_substring() extract  a         The  functions pcre_copy_substring() and pcre_get_substring() extract a
2246         single  substring,  whose  number  is given as stringnumber. A value of         single substring, whose number is given as  stringnumber.  A  value  of
2247         zero extracts the substring that matched the  entire  pattern,  whereas         zero  extracts  the  substring that matched the entire pattern, whereas
2248         higher  values  extract  the  captured  substrings.  For pcre_copy_sub-         higher values  extract  the  captured  substrings.  For  pcre_copy_sub-
2249         string(), the string is placed in buffer,  whose  length  is  given  by         string(),  the  string  is  placed  in buffer, whose length is given by
2250         buffersize,  while  for  pcre_get_substring()  a new block of memory is         buffersize, while for pcre_get_substring() a new  block  of  memory  is
2251         obtained via pcre_malloc, and its address is  returned  via  stringptr.         obtained  via  pcre_malloc,  and its address is returned via stringptr.
2252         The  yield  of  the function is the length of the string, not including         The yield of the function is the length of the  string,  not  including
2253         the terminating zero, or one of these error codes:         the terminating zero, or one of these error codes:
2254    
2255           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2256    
2257         The buffer was too small for pcre_copy_substring(), or the  attempt  to         The  buffer  was too small for pcre_copy_substring(), or the attempt to
2258         get memory failed for pcre_get_substring().         get memory failed for pcre_get_substring().
2259    
2260           PCRE_ERROR_NOSUBSTRING    (-7)           PCRE_ERROR_NOSUBSTRING    (-7)
2261    
2262         There is no substring whose number is stringnumber.         There is no substring whose number is stringnumber.
2263    
2264         The  pcre_get_substring_list()  function  extracts  all  available sub-         The pcre_get_substring_list()  function  extracts  all  available  sub-
2265         strings and builds a list of pointers to them. All this is  done  in  a         strings  and  builds  a list of pointers to them. All this is done in a
2266         single block of memory that is obtained via pcre_malloc. The address of         single block of memory that is obtained via pcre_malloc. The address of
2267         the memory block is returned via listptr, which is also  the  start  of         the  memory  block  is returned via listptr, which is also the start of
2268         the  list  of  string pointers. The end of the list is marked by a NULL         the list of string pointers. The end of the list is marked  by  a  NULL
2269         pointer. The yield of the function is zero if all  went  well,  or  the         pointer.  The  yield  of  the function is zero if all went well, or the
2270         error code         error code
2271    
2272           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2273    
2274         if the attempt to get the memory block failed.         if the attempt to get the memory block failed.
2275    
2276         When  any of these functions encounter a substring that is unset, which         When any of these functions encounter a substring that is unset,  which
2277         can happen when capturing subpattern number n+1 matches  some  part  of         can  happen  when  capturing subpattern number n+1 matches some part of
2278         the  subject, but subpattern n has not been used at all, they return an         the subject, but subpattern n has not been used at all, they return  an
2279         empty string. This can be distinguished from a genuine zero-length sub-         empty string. This can be distinguished from a genuine zero-length sub-
2280         string  by inspecting the appropriate offset in ovector, which is nega-         string by inspecting the appropriate offset in ovector, which is  nega-
2281         tive for unset substrings.         tive for unset substrings.
2282    
2283         The two convenience functions pcre_free_substring() and  pcre_free_sub-         The  two convenience functions pcre_free_substring() and pcre_free_sub-
2284         string_list()  can  be  used  to free the memory returned by a previous         string_list() can be used to free the memory  returned  by  a  previous
2285         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-
2286         tively.  They  do  nothing  more  than  call the function pointed to by         tively. They do nothing more than  call  the  function  pointed  to  by
2287         pcre_free, which of course could be called directly from a  C  program.         pcre_free,  which  of course could be called directly from a C program.
2288         However,  PCRE is used in some situations where it is linked via a spe-         However, PCRE is used in some situations where it is linked via a  spe-
2289         cial  interface  to  another  programming  language  that  cannot   use         cial   interface  to  another  programming  language  that  cannot  use
2290         pcre_free  directly;  it is for these cases that the functions are pro-         pcre_free directly; it is for these cases that the functions  are  pro-
2291         vided.         vided.
2292    
2293    
# Line 2157  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2306  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2306              int stringcount, const char *stringname,              int stringcount, const char *stringname,
2307              const char **stringptr);              const char **stringptr);
2308    
2309         To extract a substring by name, you first have to find associated  num-         To  extract a substring by name, you first have to find associated num-
2310         ber.  For example, for this pattern         ber.  For example, for this pattern
2311    
2312           (a+)b(?<xxx>\d+)...           (a+)b(?<xxx>\d+)...
# Line 2166  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2315  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2315         be unique (PCRE_DUPNAMES was not set), you can find the number from the         be unique (PCRE_DUPNAMES was not set), you can find the number from the
2316         name by calling pcre_get_stringnumber(). The first argument is the com-         name by calling pcre_get_stringnumber(). The first argument is the com-
2317         piled pattern, and the second is the name. The yield of the function is         piled pattern, and the second is the name. The yield of the function is
2318         the  subpattern  number,  or PCRE_ERROR_NOSUBSTRING (-7) if there is no         the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if  there  is  no
2319         subpattern of that name.         subpattern of that name.
2320    
2321         Given the number, you can extract the substring directly, or use one of         Given the number, you can extract the substring directly, or use one of
2322         the functions described in the previous section. For convenience, there         the functions described in the previous section. For convenience, there
2323         are also two functions that do the whole job.         are also two functions that do the whole job.
2324    
2325         Most   of   the   arguments    of    pcre_copy_named_substring()    and         Most    of    the    arguments   of   pcre_copy_named_substring()   and
2326         pcre_get_named_substring()  are  the  same  as  those for the similarly         pcre_get_named_substring() are the same  as  those  for  the  similarly
2327         named functions that extract by number. As these are described  in  the         named  functions  that extract by number. As these are described in the
2328         previous  section,  they  are not re-described here. There are just two         previous section, they are not re-described here. There  are  just  two
2329         differences:         differences:
2330    
2331         First, instead of a substring number, a substring name is  given.  Sec-         First,  instead  of a substring number, a substring name is given. Sec-
2332         ond, there is an extra argument, given at the start, which is a pointer         ond, there is an extra argument, given at the start, which is a pointer
2333         to the compiled pattern. This is needed in order to gain access to  the         to  the compiled pattern. This is needed in order to gain access to the
2334         name-to-number translation table.         name-to-number translation table.
2335    
2336         These  functions call pcre_get_stringnumber(), and if it succeeds, they         These functions call pcre_get_stringnumber(), and if it succeeds,  they
2337         then call pcre_copy_substring() or pcre_get_substring(),  as  appropri-         then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-
2338         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
2339         behaviour may not be what you want (see the next section).         behaviour may not be what you want (see the next section).
2340    
2341    
# Line 2195  DUPLICATE SUBPATTERN NAMES Line 2344  DUPLICATE SUBPATTERN NAMES
2344         int pcre_get_stringtable_entries(const pcre *code,         int pcre_get_stringtable_entries(const pcre *code,
2345              const char *name, char **first, char **last);              const char *name, char **first, char **last);
2346    
2347         When a pattern is compiled with the  PCRE_DUPNAMES  option,  names  for         When  a  pattern  is  compiled with the PCRE_DUPNAMES option, names for
2348         subpatterns  are  not  required  to  be unique. Normally, patterns with         subpatterns are not required to  be  unique.  Normally,  patterns  with
2349         duplicate names are such that in any one match, only one of  the  named         duplicate  names  are such that in any one match, only one of the named
2350         subpatterns  participates. An example is shown in the pcrepattern docu-         subpatterns participates. An example is shown in the pcrepattern  docu-
2351         mentation. When duplicates are present, pcre_copy_named_substring() and         mentation.
2352         pcre_get_named_substring()  return the first substring corresponding to  
2353         the given name that is set.  If  none  are  set,  an  empty  string  is         When    duplicates   are   present,   pcre_copy_named_substring()   and
2354         returned.  The pcre_get_stringnumber() function returns one of the num-         pcre_get_named_substring() return the first substring corresponding  to
2355         bers that are associated with the name, but it is not defined which  it         the  given  name  that  is set. If none are set, PCRE_ERROR_NOSUBSTRING
2356         is.         (-7) is returned; no  data  is  returned.  The  pcre_get_stringnumber()
2357           function  returns one of the numbers that are associated with the name,
2358           but it is not defined which it is.
2359    
2360         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
2361         name, you must use  the  pcre_get_stringtable_entries()  function.  The         name,  you  must  use  the pcre_get_stringtable_entries() function. The
2362         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
2363         third and fourth are pointers to variables which  are  updated  by  the         third  and  fourth  are  pointers to variables which are updated by the
2364         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
2365         the name-to-number table  for  the  given  name.  The  function  itself         the  name-to-number  table  for  the  given  name.  The function itself
2366         returns  the  length  of  each entry, or PCRE_ERROR_NOSUBSTRING (-7) if         returns the length of each entry,  or  PCRE_ERROR_NOSUBSTRING  (-7)  if
2367         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-
2368         tion  entitled  Information  about  a  pattern.  Given all the relevant         tion entitled Information about a  pattern.   Given  all  the  relevant
2369         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
2370         the captured data, if any.         the captured data, if any.
2371    
2372    
2373  FINDING ALL POSSIBLE MATCHES  FINDING ALL POSSIBLE MATCHES
2374    
2375         The  traditional  matching  function  uses a similar algorithm to Perl,         The traditional matching function uses a  similar  algorithm  to  Perl,
2376         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
2377         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
2378         possible match, consider using the alternative matching  function  (see         possible  match,  consider using the alternative matching function (see
2379         below)  instead.  If you cannot use the alternative function, but still         below) instead. If you cannot use the alternative function,  but  still
2380         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
2381         of the callout facility, which is described in the pcrecallout documen-         of the callout facility, which is described in the pcrecallout documen-
2382         tation.         tation.
2383    
2384         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-
2385         tern.   When your callout function is called, extract and save the cur-         tern.  When your callout function is called, extract and save the  cur-
2386         rent matched substring. Then return  1,  which  forces  pcre_exec()  to         rent  matched  substring.  Then  return  1, which forces pcre_exec() to
2387         backtrack  and  try other alternatives. Ultimately, when it runs out of         backtrack and try other alternatives. Ultimately, when it runs  out  of
2388         matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.         matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
2389    
2390    
# Line 2244  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2395  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2395              int options, int *ovector, int ovecsize,              int options, int *ovector, int ovecsize,
2396              int *workspace, int wscount);              int *workspace, int wscount);
2397    
2398         The function pcre_dfa_exec()  is  called  to  match  a  subject  string         The  function  pcre_dfa_exec()  is  called  to  match  a subject string
2399         against  a  compiled pattern, using a matching algorithm that scans the         against a compiled pattern, using a matching algorithm that  scans  the
2400         subject string just once, and does not backtrack.  This  has  different         subject  string  just  once, and does not backtrack. This has different
2401         characteristics  to  the  normal  algorithm, and is not compatible with         characteristics to the normal algorithm, and  is  not  compatible  with
2402         Perl. Some of the features of PCRE patterns are not  supported.  Never-         Perl.  Some  of the features of PCRE patterns are not supported. Never-
2403         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
2404         a discussion of the two matching algorithms, see the pcrematching docu-         a discussion of the two matching algorithms, see the pcrematching docu-
2405         mentation.         mentation.
2406    
2407         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
2408         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-
2409         ent  way,  and  this is described below. The other common arguments are         ent way, and this is described below. The other  common  arguments  are
2410         used in the same way as for pcre_exec(), so their  description  is  not         used  in  the  same way as for pcre_exec(), so their description is not
2411         repeated here.         repeated here.
2412    
2413         The  two  additional  arguments provide workspace for the function. The         The two additional arguments provide workspace for  the  function.  The
2414         workspace vector should contain at least 20 elements. It  is  used  for         workspace  vector  should  contain at least 20 elements. It is used for
2415         keeping  track  of  multiple  paths  through  the  pattern  tree.  More         keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2416         workspace will be needed for patterns and subjects where  there  are  a         workspace  will  be  needed for patterns and subjects where there are a
2417         lot of potential matches.         lot of potential matches.
2418    
2419         Here is an example of a simple call to pcre_dfa_exec():         Here is an example of a simple call to pcre_dfa_exec():
# Line 2284  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2435  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2435    
2436     Option bits for pcre_dfa_exec()     Option bits for pcre_dfa_exec()
2437    
2438         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
2439         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-
2440         LINE_xxx,  PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK,         LINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,  PCRE_NO_UTF8_CHECK,
2441         PCRE_PARTIAL, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last         PCRE_PARTIAL, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last
2442         three of these are the same as for pcre_exec(), so their description is         three of these are the same as for pcre_exec(), so their description is
2443         not repeated here.         not repeated here.
2444    
2445           PCRE_PARTIAL           PCRE_PARTIAL
2446    
2447         This has the same general effect as it does for  pcre_exec(),  but  the         This  has  the  same general effect as it does for pcre_exec(), but the
2448         details   are   slightly   different.  When  PCRE_PARTIAL  is  set  for         details  are  slightly  different.  When  PCRE_PARTIAL   is   set   for
2449         pcre_dfa_exec(), the return code PCRE_ERROR_NOMATCH is  converted  into         pcre_dfa_exec(),  the  return code PCRE_ERROR_NOMATCH is converted into
2450         PCRE_ERROR_PARTIAL  if  the  end  of the subject is reached, there have         PCRE_ERROR_PARTIAL if the end of the subject  is  reached,  there  have
2451         been no complete matches, but there is still at least one matching pos-         been no complete matches, but there is still at least one matching pos-
2452         sibility.  The portion of the string that provided the partial match is         sibility. The portion of the string that provided the partial match  is
2453         set as the first matching string.         set as the first matching string.
2454    
2455           PCRE_DFA_SHORTEST           PCRE_DFA_SHORTEST
2456    
2457         Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to         Setting  the  PCRE_DFA_SHORTEST option causes the matching algorithm to
2458         stop as soon as it has found one match. Because of the way the alterna-         stop as soon as it has found one match. Because of the way the alterna-
2459         tive algorithm works, this is necessarily the shortest  possible  match         tive  algorithm  works, this is necessarily the shortest possible match
2460         at the first possible matching point in the subject string.         at the first possible matching point in the subject string.
2461    
2462           PCRE_DFA_RESTART           PCRE_DFA_RESTART
2463    
2464         When  pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option, and         When pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option,  and
2465         returns a partial match, it is possible to call it  again,  with  addi-         returns  a  partial  match, it is possible to call it again, with addi-
2466         tional  subject  characters,  and have it continue with the same match.         tional subject characters, and have it continue with  the  same  match.
2467         The PCRE_DFA_RESTART option requests this action; when it is  set,  the         The  PCRE_DFA_RESTART  option requests this action; when it is set, the
2468         workspace  and wscount options must reference the same vector as before         workspace and wscount options must reference the same vector as  before
2469         because data about the match so far is left in  them  after  a  partial         because  data  about  the  match so far is left in them after a partial
2470         match.  There  is  more  discussion of this facility in the pcrepartial         match. There is more discussion of this  facility  in  the  pcrepartial
2471         documentation.         documentation.
2472    
2473     Successful returns from pcre_dfa_exec()     Successful returns from pcre_dfa_exec()
2474    
2475         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-
2476         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
2477         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
2478         matches  are all initial substrings of the longer matches. For example,         matches are all initial substrings of the longer matches. For  example,
2479         if the pattern         if the pattern
2480    
2481           <.*>           <.*>
# Line 2339  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2490  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2490           <something> <something else>           <something> <something else>
2491           <something> <something else> <something further>           <something> <something else> <something further>
2492    
2493         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,
2494         which  is  the  number of matched substrings. The substrings themselves         which is the number of matched substrings.  The  substrings  themselves
2495         are returned in ovector. Each string uses two elements;  the  first  is         are  returned  in  ovector. Each string uses two elements; the first is
2496         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
2497         fact, all the strings have the same start  offset.  (Space  could  have         fact,  all  the  strings  have the same start offset. (Space could have
2498         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
2499         compatibility with the way pcre_exec() returns data,  even  though  the         compatibility  with  the  way pcre_exec() returns data, even though the
2500         meaning of the strings is different.)         meaning of the strings is different.)
2501    
2502         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-
2503         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
2504         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
2505         filled with the longest matches.         filled with the longest matches.
2506    
2507     Error returns from pcre_dfa_exec()     Error returns from pcre_dfa_exec()
2508    
2509         The pcre_dfa_exec() function returns a negative number when  it  fails.         The  pcre_dfa_exec()  function returns a negative number when it fails.
2510         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
2511         described above.  There are in addition the following errors  that  are         described  above.   There are in addition the following errors that are
2512         specific to pcre_dfa_exec():         specific to pcre_dfa_exec():
2513    
2514           PCRE_ERROR_DFA_UITEM      (-16)           PCRE_ERROR_DFA_UITEM      (-16)
2515    
2516         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-
2517         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
2518         reference.         reference.
2519    
2520           PCRE_ERROR_DFA_UCOND      (-17)           PCRE_ERROR_DFA_UCOND      (-17)
2521    
2522         This  return  is  given  if pcre_dfa_exec() encounters a condition item         This return is given if pcre_dfa_exec()  encounters  a  condition  item
2523         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
2524         in a specific group. These are not supported.         in a specific group. These are not supported.
2525    
2526           PCRE_ERROR_DFA_UMLIMIT    (-18)           PCRE_ERROR_DFA_UMLIMIT    (-18)
2527    
2528         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
2529         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
2530         (it is meaningless).         (it is meaningless).
2531    
2532           PCRE_ERROR_DFA_WSSIZE     (-19)           PCRE_ERROR_DFA_WSSIZE     (-19)
2533    
2534         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
2535         workspace vector.         workspace vector.
2536    
2537           PCRE_ERROR_DFA_RECURSE    (-20)           PCRE_ERROR_DFA_RECURSE    (-20)
2538    
2539         When a recursive subpattern is processed, the matching  function  calls         When  a  recursive subpattern is processed, the matching function calls
2540         itself  recursively,  using  private vectors for ovector and workspace.         itself recursively, using private vectors for  ovector  and  workspace.
2541         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
2542         should be extremely rare, as a vector of size 1000 is used.         should be extremely rare, as a vector of size 1000 is used.
2543    
2544    
2545  SEE ALSO  SEE ALSO
2546    
2547         pcrebuild(3),  pcrecallout(3), pcrecpp(3)(3), pcrematching(3), pcrepar-         pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3),  pcrepar-
2548         tial(3), pcreposix(3), pcreprecompile(3), pcresample(3),  pcrestack(3).         tial(3),  pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
2549    
2550    
2551  AUTHOR  AUTHOR
# Line 2406  AUTHOR Line 2557  AUTHOR
2557    
2558  REVISION  REVISION
2559    
2560         Last updated: 04 June 2007         Last updated: 27 November 2007
2561         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
2562  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2563    
# Line 2593  DIFFERENCES BETWEEN PCRE AND PERL Line 2744  DIFFERENCES BETWEEN PCRE AND PERL
2744    
2745         This  document describes the differences in the ways that PCRE and Perl         This  document describes the differences in the ways that PCRE and Perl
2746         handle regular expressions. The differences described here  are  mainly         handle regular expressions. The differences described here  are  mainly
2747         with  respect  to  Perl 5.8, though PCRE version 7.0 contains some fea-         with  respect  to  Perl 5.8, though PCRE versions 7.0 and later contain
2748         tures that are expected to be in the forthcoming Perl 5.10.         some features that are expected to be in the forthcoming Perl 5.10.
2749    
2750         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
2751         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
# Line 2659  DIFFERENCES BETWEEN PCRE AND PERL Line 2810  DIFFERENCES BETWEEN PCRE AND PERL
2810         matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2         matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2
2811         unset, but in PCRE it is set to "b".         unset, but in PCRE it is set to "b".
2812    
2813         11. PCRE provides some extensions to the Perl regular expression facil-         11.  PCRE  does  support  Perl  5.10's  backtracking  verbs  (*ACCEPT),
2814           (*FAIL),  (*F),  (*COMMIT), (*PRUNE), (*SKIP), and (*THEN), but only in
2815           the forms without an  argument.  PCRE  does  not  support  (*MARK).  If
2816           (*ACCEPT)  is within capturing parentheses, PCRE does not set that cap-
2817           ture group; this is different to Perl.
2818    
2819           12. PCRE provides some extensions to the Perl regular expression facil-
2820         ities.   Perl  5.10  will  include new features that are not in earlier         ities.   Perl  5.10  will  include new features that are not in earlier
2821         versions, some of which (such as named parentheses) have been  in  PCRE         versions, some of which (such as named parentheses) have been  in  PCRE
2822         for some time. This list is with respect to Perl 5.10:         for some time. This list is with respect to Perl 5.10:
# Line 2672  DIFFERENCES BETWEEN PCRE AND PERL Line 2829  DIFFERENCES BETWEEN PCRE AND PERL
2829         meta-character matches only at the very end of the string.         meta-character matches only at the very end of the string.
2830    
2831         (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-
2832         cial  meaning  is  faulted.  Otherwise,  like  Perl,  the  backslash is         cial meaning is faulted. Otherwise, like Perl, the backslash is quietly
2833         ignored. (Perl can be made to issue a warning.)         ignored.  (Perl can be made to issue a warning.)
2834    
2835         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-
2836         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-
# Line 2685  DIFFERENCES BETWEEN PCRE AND PERL Line 2842  DIFFERENCES BETWEEN PCRE AND PERL
2842         (f)  The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAP-         (f)  The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAP-
2843         TURE options for pcre_exec() have no Perl equivalents.         TURE options for pcre_exec() have no Perl equivalents.
2844    
2845         (g) The callout facility is PCRE-specific.         (g) The \R escape sequence can be restricted to match only CR,  LF,  or
2846           CRLF by the PCRE_BSR_ANYCRLF option.
2847    
2848           (h) The callout facility is PCRE-specific.
2849    
2850         (h) The partial matching facility is PCRE-specific.         (i) The partial matching facility is PCRE-specific.
2851    
2852         (i) Patterns compiled by PCRE can be saved and re-used at a later time,         (j) Patterns compiled by PCRE can be saved and re-used at a later time,
2853         even on different hosts that have the other endianness.         even on different hosts that have the other endianness.
2854    
2855         (j)  The  alternative  matching function (pcre_dfa_exec()) matches in a         (k) The alternative matching function (pcre_dfa_exec())  matches  in  a
2856         different way and is not Perl-compatible.         different way and is not Perl-compatible.
2857    
2858           (l)  PCRE  recognizes some special sequences such as (*CR) at the start
2859           of a pattern that set overall options that cannot be changed within the
2860           pattern.
2861    
2862    
2863  AUTHOR  AUTHOR
2864    
# Line 2705  AUTHOR Line 2869  AUTHOR
2869    
2870  REVISION  REVISION
2871    
2872         Last updated: 06 March 2007         Last updated: 11 September 2007
2873         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
2874  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2875    
# Line 2719  NAME Line 2883  NAME
2883    
2884  PCRE REGULAR EXPRESSION DETAILS  PCRE REGULAR EXPRESSION DETAILS
2885    
2886         The  syntax  and semantics of the regular expressions supported by PCRE         The  syntax and semantics of the regular expressions that are supported
2887         are described below. Regular expressions are also described in the Perl         by PCRE are described in detail below. There is a quick-reference  syn-
2888         documentation  and  in  a  number  of books, some of which have copious         tax  summary  in  the  pcresyntax  page. Perl's regular expressions are
2889         examples.  Jeffrey Friedl's "Mastering Regular Expressions",  published         described in its own documentation, and regular expressions in  general
2890         by  O'Reilly, covers regular expressions in great detail. This descrip-         are  covered in a number of books, some of which have copious examples.
2891         tion of PCRE's regular expressions is intended as reference material.         Jeffrey  Friedl's  "Mastering  Regular   Expressions",   published   by
2892           O'Reilly,  covers regular expressions in great detail. This description
2893           of PCRE's regular expressions is intended as reference material.
2894    
2895         The original operation of PCRE was on strings of  one-byte  characters.         The original operation of PCRE was on strings of  one-byte  characters.
2896         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
# Line 2744  PCRE REGULAR EXPRESSION DETAILS Line 2910  PCRE REGULAR EXPRESSION DETAILS
2910         discussed in the pcrematching page.         discussed in the pcrematching page.
2911    
2912    
2913    NEWLINE CONVENTIONS
2914    
2915           PCRE  supports five different conventions for indicating line breaks in
2916           strings: a single CR (carriage return) character, a  single  LF  (line-
2917           feed) character, the two-character sequence CRLF, any of the three pre-
2918           ceding, or any Unicode newline sequence. The pcreapi page  has  further
2919           discussion  about newlines, and shows how to set the newline convention
2920           in the options arguments for the compiling and matching functions.
2921    
2922           It is also possible to specify a newline convention by starting a  pat-
2923           tern string with one of the following five sequences:
2924    
2925             (*CR)        carriage return
2926             (*LF)        linefeed
2927             (*CRLF)      carriage return, followed by linefeed
2928             (*ANYCRLF)   any of the three above
2929             (*ANY)       all Unicode newline sequences
2930    
2931           These override the default and the options given to pcre_compile(). For
2932           example, on a Unix system where LF is the default newline sequence, the
2933           pattern
2934    
2935             (*CR)a.b
2936    
2937           changes the convention to CR. That pattern matches "a\nb" because LF is
2938           no longer a newline. Note that these special settings,  which  are  not
2939           Perl-compatible,  are  recognized  only at the very start of a pattern,
2940           and that they must be in upper case.  If  more  than  one  of  them  is
2941           present, the last one is used.
2942    
2943           The  newline  convention  does  not  affect what the \R escape sequence
2944           matches. By default, this is any Unicode  newline  sequence,  for  Perl
2945           compatibility.  However, this can be changed; see the description of \R
2946           in the section entitled "Newline sequences" below. A change of \R  set-
2947           ting can be combined with a change of newline convention.
2948    
2949    
2950  CHARACTERS AND METACHARACTERS  CHARACTERS AND METACHARACTERS
2951    
2952         A  regular  expression  is  a pattern that is matched against a subject         A  regular  expression  is  a pattern that is matched against a subject
# Line 2851  BACKSLASH Line 3054  BACKSLASH
3054           \cx       "control-x", where x is any character           \cx       "control-x", where x is any character
3055           \e        escape (hex 1B)           \e        escape (hex 1B)
3056           \f        formfeed (hex 0C)           \f        formfeed (hex 0C)
3057           \n        newline (hex 0A)           \n        linefeed (hex 0A)
3058           \r        carriage return (hex 0D)           \r        carriage return (hex 0D)
3059           \t        tab (hex 09)           \t        tab (hex 09)
3060           \ddd      character with octal code ddd, or backreference           \ddd      character with octal code ddd, or backreference
# Line 2866  BACKSLASH Line 3069  BACKSLASH
3069         After  \x, from zero to two hexadecimal digits are read (letters can be         After  \x, from zero to two hexadecimal digits are read (letters can be
3070         in upper or lower case). Any number of hexadecimal  digits  may  appear         in upper or lower case). Any number of hexadecimal  digits  may  appear
3071         between  \x{  and  },  but the value of the character code must be less         between  \x{  and  },  but the value of the character code must be less
3072         than 256 in non-UTF-8 mode, and less than 2**31 in UTF-8 mode (that is,         than 256 in non-UTF-8 mode, and less than 2**31 in UTF-8 mode. That is,
3073         the  maximum  hexadecimal  value is 7FFFFFFF). If characters other than         the  maximum value in hexadecimal is 7FFFFFFF. Note that this is bigger
3074         hexadecimal digits appear between \x{ and }, or if there is  no  termi-         than the largest Unicode code point, which is 10FFFF.
3075         nating  }, this form of escape is not recognized.  Instead, the initial  
3076         \x will be interpreted as a basic hexadecimal escape, with no following         If characters other than hexadecimal digits appear between \x{  and  },
3077         digits, giving a character whose value is zero.         or if there is no terminating }, this form of escape is not recognized.
3078           Instead, the initial \x will be  interpreted  as  a  basic  hexadecimal
3079           escape,  with  no  following  digits, giving a character whose value is
3080           zero.
3081    
3082         Characters whose value is less than 256 can be defined by either of the         Characters whose value is less than 256 can be defined by either of the
3083         two syntaxes for \x. There is no difference in the way  they  are  han-         two  syntaxes  for  \x. There is no difference in the way they are han-
3084         dled. For example, \xdc is exactly the same as \x{dc}.         dled. For example, \xdc is exactly the same as \x{dc}.
3085    
3086         After  \0  up  to two further octal digits are read. If there are fewer         After \0 up to two further octal digits are read. If  there  are  fewer
3087         than two digits, just  those  that  are  present  are  used.  Thus  the         than  two  digits,  just  those  that  are  present  are used. Thus the
3088         sequence \0\x\07 specifies two binary zeros followed by a BEL character         sequence \0\x\07 specifies two binary zeros followed by a BEL character
3089         (code value 7). Make sure you supply two digits after the initial  zero         (code  value 7). Make sure you supply two digits after the initial zero
3090         if the pattern character that follows is itself an octal digit.         if the pattern character that follows is itself an octal digit.
3091    
3092         The handling of a backslash followed by a digit other than 0 is compli-         The handling of a backslash followed by a digit other than 0 is compli-
3093         cated.  Outside a character class, PCRE reads it and any following dig-         cated.  Outside a character class, PCRE reads it and any following dig-
3094         its  as  a  decimal  number. If the number is less than 10, or if there         its as a decimal number. If the number is less than  10,  or  if  there
3095         have been at least that many previous capturing left parentheses in the         have been at least that many previous capturing left parentheses in the
3096         expression,  the  entire  sequence  is  taken  as  a  back reference. A         expression, the entire  sequence  is  taken  as  a  back  reference.  A
3097         description of how this works is given later, following the  discussion         description  of how this works is given later, following the discussion
3098         of parenthesized subpatterns.         of parenthesized subpatterns.
3099    
3100         Inside  a  character  class, or if the decimal number is greater than 9         Inside a character class, or if the decimal number is  greater  than  9
3101         and there have not been that many capturing subpatterns, PCRE  re-reads         and  there have not been that many capturing subpatterns, PCRE re-reads
3102         up to three octal digits following the backslash, and uses them to gen-         up to three octal digits following the backslash, and uses them to gen-
3103         erate a data character. Any subsequent digits stand for themselves.  In         erate  a data character. Any subsequent digits stand for themselves. In
3104         non-UTF-8  mode,  the  value  of a character specified in octal must be         non-UTF-8 mode, the value of a character specified  in  octal  must  be
3105         less than \400. In UTF-8 mode, values up to  \777  are  permitted.  For         less  than  \400.  In  UTF-8 mode, values up to \777 are permitted. For
3106         example:         example:
3107    
3108           \040   is another way of writing a space           \040   is another way of writing a space
# Line 2914  BACKSLASH Line 3120  BACKSLASH
3120           \81    is either a back reference, or a binary zero           \81    is either a back reference, or a binary zero
3121                     followed by the two characters "8" and "1"                     followed by the two characters "8" and "1"
3122    
3123         Note  that  octal  values of 100 or greater must not be introduced by a         Note that octal values of 100 or greater must not be  introduced  by  a
3124         leading zero, because no more than three octal digits are ever read.         leading zero, because no more than three octal digits are ever read.
3125    
3126         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
3127         inside  and  outside character classes. In addition, inside a character         inside and outside character classes. In addition, inside  a  character
3128         class, the sequence \b is interpreted as the backspace  character  (hex         class,  the  sequence \b is interpreted as the backspace character (hex
3129         08),  and the sequences \R and \X are interpreted as the characters "R"         08), and the sequences \R and \X are interpreted as the characters  "R"
3130         and "X", respectively. Outside a character class, these sequences  have         and  "X", respectively. Outside a character class, these sequences have
3131         different meanings (see below).         different meanings (see below).
3132    
3133     Absolute and relative back references     Absolute and relative back references
3134    
3135         The  sequence  \g followed by a positive or negative number, optionally         The sequence \g followed by an unsigned or a negative  number,  option-
3136         enclosed in braces, is an absolute or relative back reference. A  named         ally  enclosed  in braces, is an absolute or relative back reference. A
3137         back  reference can be coded as \g{name}. Back references are discussed         named back reference can be coded as \g{name}. Back references are dis-
3138         later, following the discussion of parenthesized subpatterns.         cussed later, following the discussion of parenthesized subpatterns.
3139    
3140     Generic character types     Generic character types
3141    
# Line 2938  BACKSLASH Line 3144  BACKSLASH
3144    
3145           \d     any decimal digit           \d     any decimal digit
3146           \D     any character that is not a decimal digit           \D     any character that is not a decimal digit
3147             \h     any horizontal whitespace character
3148             \H     any character that is not a horizontal whitespace character
3149           \s     any whitespace character           \s     any whitespace character
3150           \S     any character that is not a whitespace character           \S     any character that is not a whitespace character
3151             \v     any vertical whitespace character
3152             \V     any character that is not a vertical whitespace character
3153           \w     any "word" character           \w     any "word" character
3154           \W     any "non-word" character           \W     any "non-word" character
3155    
3156         Each pair of escape sequences partitions the complete set of characters         Each pair of escape sequences partitions the complete set of characters
3157         into two disjoint sets. Any given character matches one, and only  one,         into  two disjoint sets. Any given character matches one, and only one,
3158         of each pair.         of each pair.
3159    
3160         These character type sequences can appear both inside and outside char-         These character type sequences can appear both inside and outside char-
3161         acter classes. They each match one character of the  appropriate  type.         acter  classes.  They each match one character of the appropriate type.
3162         If  the current matching point is at the end of the subject string, all         If the current matching point is at the end of the subject string,  all
3163         of them fail, since there is no character to match.         of them fail, since there is no character to match.
3164    
3165         For compatibility with Perl, \s does not match the VT  character  (code         For  compatibility  with Perl, \s does not match the VT character (code
3166         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
3167         characters are HT (9), LF (10), FF (12), CR (13), and space  (32).  (If         characters  are  HT  (9), LF (10), FF (12), CR (13), and space (32). If
3168         "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-
3169         ter. In PCRE, it never does.)         ter. In PCRE, it never does.
   
        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.  
3170    
3171         In UTF-8 mode, characters with values greater than 128 never match  \d,         In  UTF-8 mode, characters with values greater than 128 never match \d,
3172         \s, or \w, and always match \D, \S, and \W. This is true even when Uni-         \s, or \w, and always match \D, \S, and \W. This is true even when Uni-
3173         code character property support is available. The use of  locales  with         code  character  property  support is available. These sequences retain
3174         Unicode is discouraged.         their original meanings from before UTF-8 support was available, mainly
3175           for efficiency reasons.
3176    
3177           The sequences \h, \H, \v, and \V are Perl 5.10 features. In contrast to
3178           the other sequences, these do match certain high-valued  codepoints  in
3179           UTF-8 mode.  The horizontal space characters are:
3180    
3181             U+0009     Horizontal tab
3182             U+0020     Space
3183             U+00A0     Non-break space
3184             U+1680     Ogham space mark
3185             U+180E     Mongolian vowel separator
3186             U+2000     En quad
3187             U+2001     Em quad
3188             U+2002     En space
3189             U+2003     Em space
3190             U+2004     Three-per-em space
3191             U+2005     Four-per-em space
3192             U+2006     Six-per-em space
3193             U+2007     Figure space
3194             U+2008     Punctuation space
3195             U+2009     Thin space
3196             U+200A     Hair space
3197             U+202F     Narrow no-break space
3198             U+205F     Medium mathematical space
3199             U+3000     Ideographic space
3200    
3201           The vertical space characters are:
3202    
3203             U+000A     Linefeed
3204             U+000B     Vertical tab
3205             U+000C     Formfeed
3206             U+000D     Carriage return
3207             U+0085     Next line
3208             U+2028     Line separator
3209             U+2029     Paragraph separator
3210    
3211           A "word" character is an underscore or any character less than 256 that
3212           is a letter or digit. The definition of  letters  and  digits  is  con-
3213           trolled  by PCRE's low-valued character tables, and may vary if locale-
3214           specific matching is taking place (see "Locale support" in the  pcreapi
3215           page).  For  example,  in  a French locale such as "fr_FR" in Unix-like
3216           systems, or "french" in Windows, some character codes greater than  128
3217           are  used for accented letters, and these are matched by \w. The use of
3218           locales with Unicode is discouraged.
3219    
3220     Newline sequences     Newline sequences
3221    
3222         Outside  a  character class, the escape sequence \R matches any Unicode         Outside a character class, by default, the escape sequence  \R  matches
3223         newline sequence. This is an extension to Perl. In non-UTF-8 mode \R is         any Unicode newline sequence. This is a Perl 5.10 feature. In non-UTF-8
3224         equivalent to the following:         mode \R is equivalent to the following:
3225    
3226           (?>\r\n|\n|\x0b|\f|\r|\x85)           (?>\r\n|\n|\x0b|\f|\r|\x85)
3227    
3228         This  is  an  example  of an "atomic group", details of which are given         This is an example of an "atomic group", details  of  which  are  given
3229         below.  This particular group matches either the two-character sequence         below.  This particular group matches either the two-character sequence
3230         CR  followed  by  LF,  or  one  of  the single characters LF (linefeed,         CR followed by LF, or  one  of  the  single  characters  LF  (linefeed,
3231         U+000A), VT (vertical tab, U+000B), FF (formfeed, U+000C), CR (carriage         U+000A), VT (vertical tab, U+000B), FF (formfeed, U+000C), CR (carriage
3232         return, U+000D), or NEL (next line, U+0085). The two-character sequence         return, U+000D), or NEL (next line, U+0085). The two-character sequence
3233         is treated as a single unit that cannot be split.         is treated as a single unit that cannot be split.
3234    
3235         In UTF-8 mode, two additional characters whose codepoints  are  greater         In  UTF-8  mode, two additional characters whose codepoints are greater
3236         than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa-         than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa-
3237         rator, U+2029).  Unicode character property support is not  needed  for         rator,  U+2029).   Unicode character property support is not needed for
3238         these characters to be recognized.         these characters to be recognized.
3239    
3240           It is possible to restrict \R to match only CR, LF, or CRLF (instead of
3241           the  complete  set  of  Unicode  line  endings)  by  setting the option
3242           PCRE_BSR_ANYCRLF either at compile time or when the pattern is matched.
3243           (BSR is an abbrevation for "backslash R".) This can be made the default
3244           when PCRE is built; if this is the case, the  other  behaviour  can  be
3245           requested  via  the  PCRE_BSR_UNICODE  option.   It is also possible to
3246           specify these settings by starting a pattern string  with  one  of  the
3247           following sequences:
3248    
3249             (*BSR_ANYCRLF)   CR, LF, or CRLF only
3250             (*BSR_UNICODE)   any Unicode newline sequence
3251    
3252           These override the default and the options given to pcre_compile(), but
3253           they can be overridden by options given to pcre_exec(). Note that these
3254           special settings, which are not Perl-compatible, are recognized only at
3255           the very start of a pattern, and that they must be in  upper  case.  If
3256           more  than  one  of  them is present, the last one is used. They can be
3257           combined with a change of newline convention, for  example,  a  pattern
3258           can start with:
3259    
3260             (*ANY)(*BSR_ANYCRLF)
3261    
3262         Inside a character class, \R matches the letter "R".         Inside a character class, \R matches the letter "R".
3263    
3264     Unicode character properties     Unicode character properties
3265    
3266         When PCRE is built with Unicode character property support, three addi-         When PCRE is built with Unicode character property support, three addi-
3267         tional escape sequences to match  character  properties  are  available         tional escape sequences that match characters with specific  properties
3268         when UTF-8 mode is selected. They are:         are  available.   When not in UTF-8 mode, these sequences are of course
3269           limited to testing characters whose codepoints are less than  256,  but
3270           they do work in this mode.  The extra escape sequences are:
3271    
3272           \p{xx}   a character with the xx property           \p{xx}   a character with the xx property
3273           \P{xx}   a character without the xx property           \P{xx}   a character without the xx property
# Line 3092  BACKSLASH Line 3362  BACKSLASH
3362         has  the  Lu,  Ll, or Lt property, in other words, a letter that is not         has  the  Lu,  Ll, or Lt property, in other words, a letter that is not
3363         classified as a modifier or "other".         classified as a modifier or "other".
3364    
3365           The Cs (Surrogate) property applies only to  characters  in  the  range
3366           U+D800  to  U+DFFF. Such characters are not valid in UTF-8 strings (see
3367           RFC 3629) and so cannot be tested by PCRE, unless UTF-8 validity check-
3368           ing  has  been  turned off (see the discussion of PCRE_NO_UTF8_CHECK in
3369           the pcreapi page).
3370    
3371         The long synonyms for these properties  that  Perl  supports  (such  as         The long synonyms for these properties  that  Perl  supports  (such  as
3372         \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
3373         any of these properties with "Is".         any of these properties with "Is".
# Line 3111  BACKSLASH Line 3387  BACKSLASH
3387         That is, it matches a character without the "mark"  property,  followed         That is, it matches a character without the "mark"  property,  followed
3388         by  zero  or  more  characters with the "mark" property, and treats the         by  zero  or  more  characters with the "mark" property, and treats the
3389         sequence as an atomic group (see below).  Characters  with  the  "mark"         sequence as an atomic group (see below).  Characters  with  the  "mark"
3390         property are typically accents that affect the preceding character.         property  are  typically  accents  that affect the preceding character.
3391           None of them have codepoints less than 256, so  in  non-UTF-8  mode  \X
3392           matches any one character.
3393    
3394         Matching  characters  by Unicode property is not fast, because PCRE has         Matching  characters  by Unicode property is not fast, because PCRE has
3395         to search a structure that contains  data  for  over  fifteen  thousand         to search a structure that contains  data  for  over  fifteen  thousand
# Line 3436  VERTICAL BAR Line 3714  VERTICAL BAR
3714  INTERNAL OPTION SETTING  INTERNAL OPTION SETTING
3715    
3716         The  settings  of  the  PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and         The  settings  of  the  PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and
3717         PCRE_EXTENDED options can be changed  from  within  the  pattern  by  a         PCRE_EXTENDED options (which are Perl-compatible) can be  changed  from
3718         sequence  of  Perl  option  letters  enclosed between "(?" and ")". The         within  the  pattern  by  a  sequence  of  Perl option letters enclosed
3719         option letters are         between "(?" and ")".  The option letters are
3720    
3721           i  for PCRE_CASELESS           i  for PCRE_CASELESS
3722           m  for PCRE_MULTILINE           m  for PCRE_MULTILINE
# Line 3452  INTERNAL OPTION SETTING Line 3730  INTERNAL OPTION SETTING
3730         is also permitted. If a  letter  appears  both  before  and  after  the         is also permitted. If a  letter  appears  both  before  and  after  the
3731         hyphen, the option is unset.         hyphen, the option is unset.
3732    
3733           The  PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and PCRE_EXTRA
3734           can be changed in the same way as the Perl-compatible options by  using
3735           the characters J, U and X respectively.
3736    
3737         When  an option change occurs at top level (that is, not inside subpat-         When  an option change occurs at top level (that is, not inside subpat-
3738         tern parentheses), the change applies to the remainder of  the  pattern         tern parentheses), the change applies to the remainder of  the  pattern
3739         that follows.  If the change is placed right at the start of a pattern,         that follows.  If the change is placed right at the start of a pattern,
# Line 3477  INTERNAL OPTION SETTING Line 3759  INTERNAL OPTION SETTING
3759         the  effects  of option settings happen at compile time. There would be         the  effects  of option settings happen at compile time. There would be
3760         some very weird behaviour otherwise.         some very weird behaviour otherwise.
3761    
3762         The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and  PCRE_EXTRA         Note: There are other PCRE-specific options that  can  be  set  by  the
3763         can  be changed in the same way as the Perl-compatible options by using         application  when  the  compile  or match functions are called. In some
3764         the characters J, U and X respectively.         cases the pattern can contain special  leading  sequences  to  override
3765           what  the  application  has set or what has been defaulted. Details are
3766           given in the section entitled "Newline sequences" above.
3767    
3768    
3769  SUBPATTERNS  SUBPATTERNS
# Line 3537  SUBPATTERNS Line 3821  SUBPATTERNS
3821         "Saturday".         "Saturday".
3822    
3823    
3824    DUPLICATE SUBPATTERN NUMBERS
3825    
3826           Perl 5.10 introduced a feature whereby each alternative in a subpattern
3827           uses the same numbers for its capturing parentheses. Such a  subpattern
3828           starts  with (?| and is itself a non-capturing subpattern. For example,
3829           consider this pattern:
3830    
3831             (?|(Sat)ur|(Sun))day
3832    
3833           Because the two alternatives are inside a (?| group, both sets of  cap-
3834           turing  parentheses  are  numbered one. Thus, when the pattern matches,
3835           you can look at captured substring number  one,  whichever  alternative
3836           matched.  This  construct  is useful when you want to capture part, but
3837           not all, of one of a number of alternatives. Inside a (?| group, paren-
3838           theses  are  numbered as usual, but the number is reset at the start of
3839           each branch. The numbers of any capturing buffers that follow the  sub-
3840           pattern  start after the highest number used in any branch. The follow-
3841           ing example is taken from the Perl documentation.  The  numbers  under-
3842           neath show in which buffer the captured content will be stored.
3843    
3844             # before  ---------------branch-reset----------- after
3845             / ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x
3846             # 1            2         2  3        2     3     4
3847    
3848           A  backreference  or  a  recursive call to a numbered subpattern always
3849           refers to the first one in the pattern with the given number.
3850    
3851           An alternative approach to using this "branch reset" feature is to  use
3852           duplicate named subpatterns, as described in the next section.
3853    
3854    
3855  NAMED SUBPATTERNS  NAMED SUBPATTERNS
3856    
3857         Identifying  capturing  parentheses  by number is simple, but it can be         Identifying  capturing  parentheses  by number is simple, but it can be
# Line 3576  NAMED SUBPATTERNS Line 3891  NAMED SUBPATTERNS
3891           (?<DN>Sat)(?:urday)?           (?<DN>Sat)(?:urday)?
3892    
3893         There  are  five capturing substrings, but only one is ever set after a         There  are  five capturing substrings, but only one is ever set after a
3894         match.  The convenience  function  for  extracting  the  data  by  name         match.  (An alternative way of solving this problem is to use a "branch
3895         returns  the  substring  for  the first (and in this example, the only)         reset" subpattern, as described in the previous section.)
3896         subpattern of that name that matched.  This  saves  searching  to  find  
3897         which  numbered  subpattern  it  was. If you make a reference to a non-         The  convenience  function  for extracting the data by name returns the
3898         unique named subpattern from elsewhere in the  pattern,  the  one  that         substring for the first (and in this example, the only)  subpattern  of
3899         corresponds  to  the  lowest number is used. For further details of the         that  name  that  matched.  This saves searching to find which numbered
3900         interfaces for handling named subpatterns, see the  pcreapi  documenta-         subpattern it was. If you make a reference to a non-unique  named  sub-
3901         tion.         pattern  from elsewhere in the pattern, the one that corresponds to the
3902           lowest number is used. For further details of the interfaces  for  han-
3903           dling named subpatterns, see the pcreapi documentation.
3904    
3905    
3906  REPETITION  REPETITION
# Line 3788  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE Line 4105  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
4105    
4106           \d++foo           \d++foo
4107    
4108         Possessive  quantifiers  are  always  greedy;  the   setting   of   the         Note that a possessive quantifier can be used with an entire group, for
4109           example:
4110    
4111             (abc|xyz){2,3}+
4112    
4113           Possessive   quantifiers   are   always  greedy;  the  setting  of  the
4114         PCRE_UNGREEDY option is ignored. They are a convenient notation for the         PCRE_UNGREEDY option is ignored. They are a convenient notation for the
4115         simpler forms of atomic group. However, there is no difference  in  the         simpler  forms  of atomic group. However, there is no difference in the
4116         meaning  of  a  possessive  quantifier and the equivalent atomic group,         meaning of a possessive quantifier and  the  equivalent  atomic  group,
4117         though there may be a performance  difference;  possessive  quantifiers         though  there  may  be a performance difference; possessive quantifiers
4118         should be slightly faster.         should be slightly faster.
4119    
4120         The  possessive  quantifier syntax is an extension to the Perl 5.8 syn-         The possessive quantifier syntax is an extension to the Perl  5.8  syn-
4121         tax.  Jeffrey Friedl originated the idea (and the name)  in  the  first         tax.   Jeffrey  Friedl  originated the idea (and the name) in the first
4122         edition of his book. Mike McCloskey liked it, so implemented it when he         edition of his book. Mike McCloskey liked it, so implemented it when he
4123         built Sun's Java package, and PCRE copied it from there. It  ultimately         built  Sun's Java package, and PCRE copied it from there. It ultimately
4124         found its way into Perl at release 5.10.         found its way into Perl at release 5.10.
4125    
4126         PCRE has an optimization that automatically "possessifies" certain sim-         PCRE has an optimization that automatically "possessifies" certain sim-
4127         ple pattern constructs. For example, the sequence  A+B  is  treated  as         ple  pattern  constructs.  For  example, the sequence A+B is treated as
4128         A++B  because  there is no point in backtracking into a sequence of A's         A++B because there is no point in backtracking into a sequence  of  A's
4129         when B must follow.         when B must follow.
4130    
4131         When a pattern contains an unlimited repeat inside  a  subpattern  that         When  a  pattern  contains an unlimited repeat inside a subpattern that
4132         can  itself  be  repeated  an  unlimited number of times, the use of an         can itself be repeated an unlimited number of  times,  the  use  of  an
4133         atomic group is the only way to avoid some  failing  matches  taking  a         atomic  group  is  the  only way to avoid some failing matches taking a
4134         very long time indeed. The pattern         very long time indeed. The pattern
4135    
4136           (\D+|<\d+>)*[!?]           (\D+|<\d+>)*[!?]
4137    
4138         matches  an  unlimited number of substrings that either consist of non-         matches an unlimited number of substrings that either consist  of  non-
4139         digits, or digits enclosed in <>, followed by either ! or  ?.  When  it         digits,  or  digits  enclosed in <>, followed by either ! or ?. When it
4140         matches, it runs quickly. However, if it is applied to         matches, it runs quickly. However, if it is applied to
4141    
4142           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
4143    
4144         it  takes  a  long  time  before reporting failure. This is because the         it takes a long time before reporting  failure.  This  is  because  the
4145         string can be divided between the internal \D+ repeat and the  external         string  can be divided between the internal \D+ repeat and the external
4146         *  repeat  in  a  large  number of ways, and all have to be tried. (The         * repeat in a large number of ways, and all  have  to  be  tried.  (The
4147         example uses [!?] rather than a single character at  the  end,  because         example  uses  [!?]  rather than a single character at the end, because
4148         both  PCRE  and  Perl have an optimization that allows for fast failure         both PCRE and Perl have an optimization that allows  for  fast  failure
4149         when a single character is used. They remember the last single  charac-         when  a single character is used. They remember the last single charac-
4150         ter  that  is required for a match, and fail early if it is not present         ter that is required for a match, and fail early if it is  not  present
4151         in the string.) If the pattern is changed so that  it  uses  an  atomic         in  the  string.)  If  the pattern is changed so that it uses an atomic
4152         group, like this:         group, like this:
4153    
4154           ((?>\D+)|<\d+>)*[!?]           ((?>\D+)|<\d+>)*[!?]
4155    
4156         sequences  of non-digits cannot be broken, and failure happens quickly.         sequences of non-digits cannot be broken, and failure happens  quickly.
4157    
4158    
4159  BACK REFERENCES  BACK REFERENCES
4160    
4161         Outside a character class, a backslash followed by a digit greater than         Outside a character class, a backslash followed by a digit greater than
4162         0 (and possibly further digits) is a back reference to a capturing sub-         0 (and possibly further digits) is a back reference to a capturing sub-
4163         pattern earlier (that is, to its left) in the pattern,  provided  there         pattern  earlier  (that is, to its left) in the pattern, provided there
4164         have been that many previous capturing left parentheses.         have been that many previous capturing left parentheses.
4165    
4166         However, if the decimal number following the backslash is less than 10,         However, if the decimal number following the backslash is less than 10,
4167         it is always taken as a back reference, and causes  an  error  only  if         it  is  always  taken  as a back reference, and causes an error only if
4168         there  are  not that many capturing left parentheses in the entire pat-         there are not that many capturing left parentheses in the  entire  pat-
4169         tern. In other words, the parentheses that are referenced need  not  be         tern.  In  other words, the parentheses that are referenced need not be
4170         to  the left of the reference for numbers less than 10. A "forward back         to the left of the reference for numbers less than 10. A "forward  back
4171         reference" of this type can make sense when a  repetition  is  involved         reference"  of  this  type can make sense when a repetition is involved
4172         and  the  subpattern to the right has participated in an earlier itera-         and the subpattern to the right has participated in an  earlier  itera-
4173         tion.         tion.
4174    
4175         It is not possible to have a numerical "forward back  reference"  to  a         It  is  not  possible to have a numerical "forward back reference" to a
4176         subpattern  whose  number  is  10  or  more using this syntax because a         subpattern whose number is 10 or  more  using  this  syntax  because  a
4177         sequence such as \50 is interpreted as a character  defined  in  octal.         sequence  such  as  \50 is interpreted as a character defined in octal.
4178         See the subsection entitled "Non-printing characters" above for further         See the subsection entitled "Non-printing characters" above for further
4179         details of the handling of digits following a backslash.  There  is  no         details  of  the  handling of digits following a backslash. There is no
4180         such  problem  when named parentheses are used. A back reference to any         such problem when named parentheses are used. A back reference  to  any
4181         subpattern is possible using named parentheses (see below).         subpattern is possible using named parentheses (see below).
4182    
4183         Another way of avoiding the ambiguity inherent in  the  use  of  digits         Another  way  of  avoiding  the ambiguity inherent in the use of digits
4184         following a backslash is to use the \g escape sequence, which is a fea-         following a backslash is to use the \g escape sequence, which is a fea-
4185         ture introduced in Perl 5.10. This escape must be followed by  a  posi-         ture  introduced  in  Perl  5.10.  This  escape  must be followed by an
4186         tive  or  a negative number, optionally enclosed in braces. These exam-         unsigned number or a negative number, optionally  enclosed  in  braces.
4187         ples are all identical:         These examples are all identical:
4188    
4189           (ring), \1           (ring), \1
4190           (ring), \g1           (ring), \g1
4191           (ring), \g{1}           (ring), \g{1}
4192    
4193         A positive number specifies an absolute reference without the ambiguity         An  unsigned number specifies an absolute reference without the ambigu-
4194         that  is  present  in  the older syntax. It is also useful when literal         ity that is present in the older syntax. It is also useful when literal
4195         digits follow the reference. A negative number is a relative reference.         digits follow the reference. A negative number is a relative reference.
4196         Consider this example:         Consider this example:
4197    
4198           (abc(def)ghi)\g{-1}           (abc(def)ghi)\g{-1}
4199    
4200         The sequence \g{-1} is a reference to the most recently started captur-         The sequence \g{-1} is a reference to the most recently started captur-
4201         ing subpattern before \g, that is, is it equivalent to  \2.  Similarly,         ing  subpattern  before \g, that is, is it equivalent to \2. Similarly,
4202         \g{-2} would be equivalent to \1. The use of relative references can be         \g{-2} would be equivalent to \1. The use of relative references can be
4203         helpful in long patterns, and also in  patterns  that  are  created  by         helpful  in  long  patterns,  and  also in patterns that are created by
4204         joining together fragments that contain references within themselves.         joining together fragments that contain references within themselves.
4205    
4206         A  back  reference matches whatever actually matched the capturing sub-         A back reference matches whatever actually matched the  capturing  sub-
4207         pattern in the current subject string, rather  than  anything  matching         pattern  in  the  current subject string, rather than anything matching
4208         the subpattern itself (see "Subpatterns as subroutines" below for a way         the subpattern itself (see "Subpatterns as subroutines" below for a way
4209         of doing that). So the pattern         of doing that). So the pattern
4210    
4211           (sens|respons)e and \1ibility           (sens|respons)e and \1ibility
4212    
4213         matches "sense and sensibility" and "response and responsibility",  but         matches  "sense and sensibility" and "response and responsibility", but
4214         not  "sense and responsibility". If caseful matching is in force at the         not "sense and responsibility". If caseful matching is in force at  the
4215         time of the back reference, the case of letters is relevant. For  exam-         time  of the back reference, the case of letters is relevant. For exam-
4216         ple,         ple,
4217    
4218           ((?i)rah)\s+\1           ((?i)rah)\s+\1
4219    
4220         matches  "rah  rah"  and  "RAH RAH", but not "RAH rah", even though the         matches "rah rah" and "RAH RAH", but not "RAH  rah",  even  though  the
4221         original capturing subpattern is matched caselessly.         original capturing subpattern is matched caselessly.
4222    
4223         There are several different ways of writing back  references  to  named         There  are  several  different ways of writing back references to named
4224         subpatterns.  The  .NET syntax \k{name} and the Perl syntax \k<name> or         subpatterns. The .NET syntax \k{name} and the Perl syntax  \k<name>  or
4225         \k'name' are supported, as is the Python syntax (?P=name). Perl  5.10's         \k'name'  are supported, as is the Python syntax (?P=name). Perl 5.10's
4226         unified back reference syntax, in which \g can be used for both numeric         unified back reference syntax, in which \g can be used for both numeric
4227         and named references, is also supported. We  could  rewrite  the  above         and  named  references,  is  also supported. We could rewrite the above
4228         example in any of the following ways:         example in any of the following ways:
4229    
4230           (?<p1>(?i)rah)\s+\k<p1>           (?<p1>(?i)rah)\s+\k<p1>
# Line 3910  BACK REFERENCES Line 4232  BACK REFERENCES
4232           (?P<p1>(?i)rah)\s+(?P=p1)           (?P<p1>(?i)rah)\s+(?P=p1)
4233           (?<p1>(?i)rah)\s+\g{p1}           (?<p1>(?i)rah)\s+\g{p1}
4234    
4235         A  subpattern  that  is  referenced  by  name may appear in the pattern         A subpattern that is referenced by  name  may  appear  in  the  pattern
4236         before or after the reference.         before or after the reference.
4237    
4238         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
4239         subpattern  has  not actually been used in a particular match, any back         subpattern has not actually been used in a particular match,  any  back
4240         references to it always fail. For example, the pattern         references to it always fail. For example, the pattern
4241    
4242           (a|(bc))\2           (a|(bc))\2
4243    
4244         always fails if it starts to match "a" rather than "bc". Because  there         always  fails if it starts to match "a" rather than "bc". Because there
4245         may  be  many  capturing parentheses in a pattern, all digits following         may be many capturing parentheses in a pattern,  all  digits  following
4246         the backslash are taken as part of a potential back  reference  number.         the  backslash  are taken as part of a potential back reference number.
4247         If the pattern continues with a digit character, some delimiter must be         If the pattern continues with a digit character, some delimiter must be
4248         used to terminate the back reference. If the  PCRE_EXTENDED  option  is         used  to  terminate  the back reference. If the PCRE_EXTENDED option is
4249         set,  this  can  be  whitespace.  Otherwise an empty comment (see "Com-         set, this can be whitespace.  Otherwise an  empty  comment  (see  "Com-
4250         ments" below) can be used.         ments" below) can be used.
4251    
4252         A back reference that occurs inside the parentheses to which it  refers         A  back reference that occurs inside the parentheses to which it refers
4253         fails  when  the subpattern is first used, so, for example, (a\1) never         fails when the subpattern is first used, so, for example,  (a\1)  never
4254         matches.  However, such references can be useful inside  repeated  sub-         matches.   However,  such references can be useful inside repeated sub-
4255         patterns. For example, the pattern         patterns. For example, the pattern
4256    
4257           (a|b\1)+           (a|b\1)+
4258    
4259         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-
4260         ation of the subpattern,  the  back  reference  matches  the  character         ation  of  the  subpattern,  the  back  reference matches the character
4261         string  corresponding  to  the previous iteration. In order for this to         string corresponding to the previous iteration. In order  for  this  to
4262         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
4263         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
4264         the example above, or by a quantifier with a minimum of zero.         the example above, or by a quantifier with a minimum of zero.
4265    
4266    
4267  ASSERTIONS  ASSERTIONS
4268    
4269         An assertion is a test on the characters  following  or  preceding  the         An  assertion  is  a  test on the characters following or preceding the
4270         current  matching  point that does not actually consume any characters.         current matching point that does not actually consume  any  characters.
4271         The simple assertions coded as \b, \B, \A, \G, \Z,  \z,  ^  and  $  are         The  simple  assertions  coded  as  \b, \B, \A, \G, \Z, \z, ^ and $ are
4272         described above.         described above.
4273    
4274         More  complicated  assertions  are  coded as subpatterns. There are two         More complicated assertions are coded as  subpatterns.  There  are  two
4275         kinds: those that look ahead of the current  position  in  the  subject         kinds:  those  that  look  ahead of the current position in the subject
4276         string,  and  those  that  look  behind  it. An assertion subpattern is         string, and those that look  behind  it.  An  assertion  subpattern  is
4277         matched in the normal way, except that it does not  cause  the  current         matched  in  the  normal way, except that it does not cause the current
4278         matching position to be changed.         matching position to be changed.
4279    
4280         Assertion  subpatterns  are  not  capturing subpatterns, and may not be         Assertion subpatterns are not capturing subpatterns,  and  may  not  be
4281         repeated, because it makes no sense to assert the  same  thing  several         repeated,  because  it  makes no sense to assert the same thing several
4282         times.  If  any kind of assertion contains capturing subpatterns within         times. If any kind of assertion contains capturing  subpatterns  within
4283         it, these are counted for the purposes of numbering the capturing  sub-         it,  these are counted for the purposes of numbering the capturing sub-
4284         patterns in the whole pattern.  However, substring capturing is carried         patterns in the whole pattern.  However, substring capturing is carried
4285         out only for positive assertions, because it does not  make  sense  for         out  only  for  positive assertions, because it does not make sense for
4286         negative assertions.         negative assertions.
4287    
4288     Lookahead assertions     Lookahead assertions
# Line 3970  ASSERTIONS Line 4292  ASSERTIONS
4292    
4293           \w+(?=;)           \w+(?=;)
4294    
4295         matches a word followed by a semicolon, but does not include the  semi-         matches  a word followed by a semicolon, but does not include the semi-
4296         colon in the match, and         colon in the match, and
4297    
4298           foo(?!bar)           foo(?!bar)
4299    
4300         matches  any  occurrence  of  "foo" that is not followed by "bar". Note         matches any occurrence of "foo" that is not  followed  by  "bar".  Note
4301         that the apparently similar pattern         that the apparently similar pattern
4302    
4303           (?!foo)bar           (?!foo)bar
4304    
4305         does not find an occurrence of "bar"  that  is  preceded  by  something         does  not  find  an  occurrence  of "bar" that is preceded by something
4306         other  than "foo"; it finds any occurrence of "bar" whatsoever, because         other than "foo"; it finds any occurrence of "bar" whatsoever,  because
4307         the assertion (?!foo) is always true when the next three characters are         the assertion (?!foo) is always true when the next three characters are
4308         "bar". A lookbehind assertion is needed to achieve the other effect.         "bar". A lookbehind assertion is needed to achieve the other effect.
4309    
4310         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
4311         most convenient way to do it is  with  (?!)  because  an  empty  string         most  convenient  way  to  do  it  is with (?!) because an empty string
4312         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
4313         string must always fail.         string must always fail.
4314    
4315     Lookbehind assertions     Lookbehind assertions
4316    
4317         Lookbehind assertions start with (?<= for positive assertions and  (?<!         Lookbehind  assertions start with (?<= for positive assertions and (?<!
4318         for negative assertions. For example,         for negative assertions. For example,
4319    
4320           (?<!foo)bar           (?<!foo)bar
4321    
4322         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
4323         contents of a lookbehind assertion are restricted  such  that  all  the         contents  of  a  lookbehind  assertion are restricted such that all the
4324         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-
4325         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
4326         fixed length. Thus         fixed length. Thus
4327    
4328           (?<=bullock|donkey)           (?<=bullock|donkey)
# Line 4009  ASSERTIONS Line 4331  ASSERTIONS
4331    
4332           (?<!dogs?|cats?)           (?<!dogs?|cats?)
4333    
4334         causes  an  error at compile time. Branches that match different length         causes an error at compile time. Branches that match  different  length
4335         strings are permitted only at the top level of a lookbehind  assertion.         strings  are permitted only at the top level of a lookbehind assertion.
4336         This  is  an  extension  compared  with  Perl (at least for 5.8), which         This is an extension compared with  Perl  (at  least  for  5.8),  which
4337         requires all branches to match the same length of string. An  assertion         requires  all branches to match the same length of string. An assertion
4338         such as         such as
4339    
4340           (?<=ab(c|de))           (?<=ab(c|de))
4341    
4342         is  not  permitted,  because  its single top-level branch can match two         is not permitted, because its single top-level  branch  can  match  two
4343         different lengths, but it is acceptable if rewritten to  use  two  top-         different  lengths,  but  it is acceptable if rewritten to use two top-
4344         level branches:         level branches:
4345    
4346           (?<=abc|abde)           (?<=abc|abde)
4347    
4348         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
4349         instead of a lookbehind assertion; this is not restricted to  a  fixed-         instead  of  a lookbehind assertion; this is not restricted to a fixed-
4350         length.         length.
4351    
4352         The  implementation  of lookbehind assertions is, for each alternative,         The implementation of lookbehind assertions is, for  each  alternative,
4353         to temporarily move the current position back by the fixed  length  and         to  temporarily  move the current position back by the fixed length and
4354         then try to match. If there are insufficient characters before the cur-         then try to match. If there are insufficient characters before the cur-
4355         rent position, the assertion fails.         rent position, the assertion fails.
4356    
4357         PCRE does not allow the \C escape (which matches a single byte in UTF-8         PCRE does not allow the \C escape (which matches a single byte in UTF-8
4358         mode)  to appear in lookbehind assertions, because it makes it impossi-         mode) to appear in lookbehind assertions, because it makes it  impossi-
4359         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,
4360         which can match different numbers of bytes, are also not permitted.         which can match different numbers of bytes, are also not permitted.
4361    
4362         Possessive  quantifiers  can  be  used  in  conjunction with lookbehind         Possessive quantifiers can  be  used  in  conjunction  with  lookbehind
4363         assertions to specify efficient matching at  the  end  of  the  subject         assertions  to  specify  efficient  matching  at the end of the subject
4364         string. Consider a simple pattern such as         string. Consider a simple pattern such as
4365    
4366           abcd$           abcd$
4367    
4368         when  applied  to  a  long string that does not match. Because matching         when applied to a long string that does  not  match.  Because  matching
4369         proceeds from left to right, PCRE will look for each "a" in the subject         proceeds from left to right, PCRE will look for each "a" in the subject
4370         and  then  see  if what follows matches the rest of the pattern. If the         and then see if what follows matches the rest of the  pattern.  If  the
4371         pattern is specified as         pattern is specified as
4372    
4373           ^.*abcd$           ^.*abcd$
4374    
4375         the initial .* matches the entire string at first, but when this  fails         the  initial .* matches the entire string at first, but when this fails
4376         (because there is no following "a"), it backtracks to match all but the         (because there is no following "a"), it backtracks to match all but the
4377         last character, then all but the last two characters, and so  on.  Once         last  character,  then all but the last two characters, and so on. Once
4378         again  the search for "a" covers the entire string, from right to left,         again the search for "a" covers the entire string, from right to  left,
4379         so we are no better off. However, if the pattern is written as         so we are no better off. However, if the pattern is written as
4380    
4381           ^.*+(?<=abcd)           ^.*+(?<=abcd)
4382    
4383         there can be no backtracking for the .*+ item; it can  match  only  the         there  can  be  no backtracking for the .*+ item; it can match only the
4384         entire  string.  The subsequent lookbehind assertion does a single test         entire string. The subsequent lookbehind assertion does a  single  test
4385         on the last four characters. If it fails, the match fails  immediately.         on  the last four characters. If it fails, the match fails immediately.
4386         For  long  strings, this approach makes a significant difference to the         For long strings, this approach makes a significant difference  to  the
4387         processing time.         processing time.
4388    
4389     Using multiple assertions     Using multiple assertions
# Line 4070  ASSERTIONS Line 4392  ASSERTIONS
4392    
4393           (?<=\d{3})(?<!999)foo           (?<=\d{3})(?<!999)foo
4394    
4395         matches "foo" preceded by three digits that are not "999". Notice  that         matches  "foo" preceded by three digits that are not "999". Notice that
4396         each  of  the  assertions is applied independently at the same point in         each of the assertions is applied independently at the  same  point  in
4397         the subject string. First there is a  check  that  the  previous  three         the  subject  string.  First  there  is a check that the previous three
4398         characters  are  all  digits,  and  then there is a check that the same         characters are all digits, and then there is  a  check  that  the  same
4399         three characters are not "999".  This pattern does not match "foo" pre-         three characters are not "999".  This pattern does not match "foo" pre-
4400         ceded  by  six  characters,  the first of which are digits and the last         ceded by six characters, the first of which are  digits  and  the  last
4401         three of which are not "999". For example, it  doesn't  match  "123abc-         three  of  which  are not "999". For example, it doesn't match "123abc-
4402         foo". A pattern to do that is         foo". A pattern to do that is
4403    
4404           (?<=\d{3}...)(?<!999)foo           (?<=\d{3}...)(?<!999)foo
4405    
4406         This  time  the  first assertion looks at the preceding six characters,         This time the first assertion looks at the  preceding  six  characters,
4407         checking that the first three are digits, and then the second assertion         checking that the first three are digits, and then the second assertion
4408         checks that the preceding three characters are not "999".         checks that the preceding three characters are not "999".
4409    
# Line 4089  ASSERTIONS Line 4411  ASSERTIONS
4411    
4412           (?<=(?<!foo)bar)baz           (?<=(?<!foo)bar)baz
4413    
4414         matches  an occurrence of "baz" that is preceded by "bar" which in turn         matches an occurrence of "baz" that is preceded by "bar" which in  turn
4415         is not preceded by "foo", while         is not preceded by "foo", while
4416    
4417           (?<=\d{3}(?!999)...)foo           (?<=\d{3}(?!999)...)foo
4418    
4419         is another pattern that matches "foo" preceded by three digits and  any         is  another pattern that matches "foo" preceded by three digits and any
4420         three characters that are not "999".         three characters that are not "999".
4421    
4422    
4423  CONDITIONAL SUBPATTERNS  CONDITIONAL SUBPATTERNS
4424    
4425         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-
4426         ditionally or to choose between two alternative subpatterns,  depending         ditionally  or to choose between two alternative subpatterns, depending
4427         on  the result of an assertion, or whether a previous capturing subpat-         on the result of an assertion, or whether a previous capturing  subpat-
4428         tern matched or not. The two possible forms of  conditional  subpattern         tern  matched  or not. The two possible forms of conditional subpattern
4429         are         are
4430    
4431           (?(condition)yes-pattern)           (?(condition)yes-pattern)
4432           (?(condition)yes-pattern|no-pattern)           (?(condition)yes-pattern|no-pattern)
4433    
4434         If  the  condition is satisfied, the yes-pattern is used; otherwise the         If the condition is satisfied, the yes-pattern is used;  otherwise  the
4435         no-pattern (if present) is used. If there are more  than  two  alterna-         no-pattern  (if  present)  is used. If there are more than two alterna-
4436         tives in the subpattern, a compile-time error occurs.         tives in the subpattern, a compile-time error occurs.
4437    
4438         There  are  four  kinds of condition: references to subpatterns, refer-         There are four kinds of condition: references  to  subpatterns,  refer-
4439         ences to recursion, a pseudo-condition called DEFINE, and assertions.         ences to recursion, a pseudo-condition called DEFINE, and assertions.
4440    
4441     Checking for a used subpattern by number     Checking for a used subpattern by number
4442    
4443         If the text between the parentheses consists of a sequence  of  digits,         If  the  text between the parentheses consists of a sequence of digits,
4444         the  condition  is  true if the capturing subpattern of that number has         the condition is true if the capturing subpattern of  that  number  has
4445         previously matched. An alternative notation is to  precede  the  digits         previously  matched.  An  alternative notation is to precede the digits
4446         with a plus or minus sign. In this case, the subpattern number is rela-         with a plus or minus sign. In this case, the subpattern number is rela-
4447         tive rather than absolute.  The most recently opened parentheses can be         tive rather than absolute.  The most recently opened parentheses can be
4448         referenced  by  (?(-1),  the  next most recent by (?(-2), and so on. In         referenced by (?(-1), the next most recent by (?(-2),  and  so  on.  In
4449         looping constructs it can also make sense to refer to subsequent groups         looping constructs it can also make sense to refer to subsequent groups
4450         with constructs such as (?(+2).         with constructs such as (?(+2).
4451    
4452         Consider  the  following  pattern, which contains non-significant white         Consider the following pattern, which  contains  non-significant  white
4453         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
4454         divide it into three parts for ease of discussion:         divide it into three parts for ease of discussion:
4455    
4456           ( \( )?    [^()]+    (?(1) \) )           ( \( )?    [^()]+    (?(1) \) )
4457    
4458         The  first  part  matches  an optional opening parenthesis, and if that         The first part matches an optional opening  parenthesis,  and  if  that
4459         character is present, sets it as the first captured substring. The sec-         character is present, sets it as the first captured substring. The sec-
4460         ond  part  matches one or more characters that are not parentheses. The         ond part matches one or more characters that are not  parentheses.  The
4461         third part is a conditional subpattern that tests whether the first set         third part is a conditional subpattern that tests whether the first set
4462         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
4463         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-
4464         tern  is  executed  and  a  closing parenthesis is required. Otherwise,         tern is executed and a  closing  parenthesis  is  required.  Otherwise,
4465         since no-pattern is not present, the  subpattern  matches  nothing.  In         since  no-pattern  is  not  present, the subpattern matches nothing. In
4466         other  words,  this  pattern  matches  a  sequence  of non-parentheses,         other words,  this  pattern  matches  a  sequence  of  non-parentheses,
4467         optionally enclosed in parentheses.         optionally enclosed in parentheses.
4468    
4469         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
4470         relative reference:         relative reference:
4471    
4472           ...other stuff... ( \( )?    [^()]+    (?(-1) \) ) ...           ...other stuff... ( \( )?    [^()]+    (?(-1) \) ) ...
4473    
4474         This  makes  the  fragment independent of the parentheses in the larger         This makes the fragment independent of the parentheses  in  the  larger
4475         pattern.         pattern.
4476    
4477     Checking for a used subpattern by name     Checking for a used subpattern by name
4478    
4479         Perl uses the syntax (?(<name>)...) or (?('name')...)  to  test  for  a         Perl  uses  the  syntax  (?(<name>)...) or (?('name')...) to test for a
4480         used  subpattern  by  name.  For compatibility with earlier versions of         used subpattern by name. For compatibility  with  earlier  versions  of
4481         PCRE, which had this facility before Perl, the syntax  (?(name)...)  is         PCRE,  which  had this facility before Perl, the syntax (?(name)...) is
4482         also  recognized. However, there is a possible ambiguity with this syn-         also recognized. However, there is a possible ambiguity with this  syn-
4483         tax, because subpattern names may  consist  entirely  of  digits.  PCRE         tax,  because  subpattern  names  may  consist entirely of digits. PCRE
4484         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
4485         consists entirely of digits, PCRE looks for a subpattern of  that  num-         consists  entirely  of digits, PCRE looks for a subpattern of that num-
4486         ber,  which must be greater than zero. Using subpattern names that con-         ber, which must be greater than zero. Using subpattern names that  con-
4487         sist entirely of digits is not recommended.         sist entirely of digits is not recommended.
4488    
4489         Rewriting the above example to use a named subpattern gives this:         Rewriting the above example to use a named subpattern gives this:
# Line 4172  CONDITIONAL SUBPATTERNS Line 4494  CONDITIONAL SUBPATTERNS
4494     Checking for pattern recursion     Checking for pattern recursion
4495    
4496         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
4497         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
4498         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-
4499         sand follow the letter R, for example:         sand follow the letter R, for example:
4500    
4501           (?(R3)...) or (?(R&name)...)           (?(R3)...) or (?(R&name)...)
4502    
4503         the  condition is true if the most recent recursion is into the subpat-         the condition is true if the most recent recursion is into the  subpat-
4504         tern whose number or name is given. This condition does not  check  the         tern  whose  number or name is given. This condition does not check the
4505         entire recursion stack.         entire recursion stack.
4506    
4507         At  "top  level", all these recursion test conditions are false. Recur-         At "top level", all these recursion test conditions are  false.  Recur-
4508         sive patterns are described below.         sive patterns are described below.
4509    
4510     Defining subpatterns for use by reference only     Defining subpatterns for use by reference only
4511    
4512         If the condition is the string (DEFINE), and  there  is  no  subpattern         If  the  condition  is  the string (DEFINE), and there is no subpattern
4513         with  the  name  DEFINE,  the  condition is always false. In this case,         with the name DEFINE, the condition is  always  false.  In  this  case,
4514         there may be only one alternative  in  the  subpattern.  It  is  always         there  may  be  only  one  alternative  in the subpattern. It is always
4515         skipped  if  control  reaches  this  point  in the pattern; the idea of         skipped if control reaches this point  in  the  pattern;  the  idea  of
4516         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-
4517         erenced  from elsewhere. (The use of "subroutines" is described below.)         erenced from elsewhere. (The use of "subroutines" is described  below.)
4518         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
4519         this (ignore whitespace and line breaks):         this (ignore whitespace and line breaks):
4520    
4521           (?(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) )
4522           \b (?&byte) (\.(?&byte)){3} \b           \b (?&byte) (\.(?&byte)){3} \b
4523    
4524         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
4525         group named "byte" is defined. This matches an individual component  of         group  named "byte" is defined. This matches an individual component of
4526         an  IPv4  address  (a number less than 256). When matching takes place,         an IPv4 address (a number less than 256). When  matching  takes  place,
4527         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
4528         condition.         condition.
4529    
4530         The rest of the pattern uses references to the named group to match the         The rest of the pattern uses references to the named group to match the
4531         four dot-separated components of an IPv4 address, insisting on  a  word         four  dot-separated  components of an IPv4 address, insisting on a word
4532         boundary at each end.         boundary at each end.
4533    
4534     Assertion conditions     Assertion conditions
4535    
4536         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
4537         assertion.  This may be a positive or negative lookahead or  lookbehind         assertion.   This may be a positive or negative lookahead or lookbehind
4538         assertion.  Consider  this  pattern,  again  containing non-significant         assertion. Consider  this  pattern,  again  containing  non-significant
4539         white space, and with the two alternatives on the second line:         white space, and with the two alternatives on the second line:
4540    
4541           (?(?=[^a-z]*[a-z])           (?(?=[^a-z]*[a-z])
4542           \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} )
4543    
4544         The condition  is  a  positive  lookahead  assertion  that  matches  an         The  condition  is  a  positive  lookahead  assertion  that  matches an
4545         optional  sequence of non-letters followed by a letter. In other words,         optional sequence of non-letters followed by a letter. In other  words,
4546         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
4547         letter  is found, the subject is matched against the first alternative;         letter is found, the subject is matched against the first  alternative;
4548         otherwise it is  matched  against  the  second.  This  pattern  matches         otherwise  it  is  matched  against  the  second.  This pattern matches
4549         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
4550         letters and dd are digits.         letters and dd are digits.
4551    
4552    
4553  COMMENTS  COMMENTS
4554    
4555         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
4556         next  closing  parenthesis.  Nested  parentheses are not permitted. The         next closing parenthesis. Nested parentheses  are  not  permitted.  The
4557         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
4558         at all.         at all.
4559    
4560         If  the PCRE_EXTENDED option is set, an unescaped # character outside a         If the PCRE_EXTENDED option is set, an unescaped # character outside  a
4561         character class introduces a  comment  that  continues  to  immediately         character  class  introduces  a  comment  that continues to immediately
4562         after the next newline in the pattern.         after the next newline in the pattern.
4563    
4564    
4565  RECURSIVE PATTERNS  RECURSIVE PATTERNS
4566    
4567         Consider  the problem of matching a string in parentheses, allowing for         Consider the problem of matching a string in parentheses, allowing  for
4568         unlimited nested parentheses. Without the use of  recursion,  the  best         unlimited  nested  parentheses.  Without the use of recursion, the best
4569         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
4570         depth of nesting. It is not possible to  handle  an  arbitrary  nesting         depth  of  nesting.  It  is not possible to handle an arbitrary nesting
4571         depth.         depth.
4572    
4573         For some time, Perl has provided a facility that allows regular expres-         For some time, Perl has provided a facility that allows regular expres-
4574         sions to recurse (amongst other things). It does this by  interpolating         sions  to recurse (amongst other things). It does this by interpolating
4575         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
4576         expression itself. A Perl pattern using code interpolation to solve the         expression itself. A Perl pattern using code interpolation to solve the
4577         parentheses problem can be created like this:         parentheses problem can be created like this:
4578    
# Line 4260  RECURSIVE PATTERNS Line 4582  RECURSIVE PATTERNS
4582         refers recursively to the pattern in which it appears.         refers recursively to the pattern in which it appears.
4583    
4584         Obviously, PCRE cannot support the interpolation of Perl code. Instead,         Obviously, PCRE cannot support the interpolation of Perl code. Instead,
4585         it  supports  special  syntax  for recursion of the entire pattern, and         it supports special syntax for recursion of  the  entire  pattern,  and
4586         also for individual subpattern recursion.  After  its  introduction  in         also  for  individual  subpattern  recursion. After its introduction in
4587         PCRE  and  Python,  this  kind of recursion was introduced into Perl at         PCRE and Python, this kind of recursion was  introduced  into  Perl  at
4588         release 5.10.         release 5.10.
4589    
4590         A special item that consists of (? followed by a  number  greater  than         A  special  item  that consists of (? followed by a number greater than
4591         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
4592         the given number, provided that it occurs inside that  subpattern.  (If         the  given  number, provided that it occurs inside that subpattern. (If
4593         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-
4594         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
4595         regular expression.         regular expression.
4596    
4597         In  PCRE (like Python, but unlike Perl), a recursive subpattern call is         In PCRE (like Python, but unlike Perl), a recursive subpattern call  is
4598         always treated as an atomic group. That is, once it has matched some of         always treated as an atomic group. That is, once it has matched some of
4599         the subject string, it is never re-entered, even if it contains untried         the subject string, it is never re-entered, even if it contains untried
4600         alternatives and there is a subsequent matching failure.         alternatives and there is a subsequent matching failure.
4601    
4602         This PCRE pattern solves the nested  parentheses  problem  (assume  the         This  PCRE  pattern  solves  the nested parentheses problem (assume the
4603         PCRE_EXTENDED option is set so that white space is ignored):         PCRE_EXTENDED option is set so that white space is ignored):
4604    
4605           \( ( (?>[^()]+) | (?R) )* \)           \( ( (?>[^()]+) | (?R) )* \)
4606    
4607         First  it matches an opening parenthesis. Then it matches any number of         First it matches an opening parenthesis. Then it matches any number  of
4608         substrings which can either be a  sequence  of  non-parentheses,  or  a         substrings  which  can  either  be  a sequence of non-parentheses, or a
4609         recursive  match  of the pattern itself (that is, a correctly parenthe-         recursive match of the pattern itself (that is, a  correctly  parenthe-
4610         sized substring).  Finally there is a closing parenthesis.         sized substring).  Finally there is a closing parenthesis.
4611    
4612         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
4613         the entire pattern, so instead you could use this:         the entire pattern, so instead you could use this:
4614    
4615           ( \( ( (?>[^()]+) | (?1) )* \) )           ( \( ( (?>[^()]+) | (?1) )* \) )
4616    
4617         We  have  put the pattern into parentheses, and caused the recursion to         We have put the pattern into parentheses, and caused the  recursion  to
4618         refer to them instead of the whole pattern.         refer to them instead of the whole pattern.
4619    
4620         In a larger pattern,  keeping  track  of  parenthesis  numbers  can  be         In  a  larger  pattern,  keeping  track  of  parenthesis numbers can be
4621         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
4622         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
4623         (?-2) to refer to the second most recently opened parentheses preceding         (?-2) to refer to the second most recently opened parentheses preceding
4624         the recursion. In other  words,  a  negative  number  counts  capturing         the  recursion.  In  other  words,  a  negative number counts capturing
4625         parentheses leftwards from the point at which it is encountered.         parentheses leftwards from the point at which it is encountered.
4626    
4627         It  is  also  possible  to refer to subsequently opened parentheses, by         It is also possible to refer to  subsequently  opened  parentheses,  by
4628         writing references such as (?+2). However, these  cannot  be  recursive         writing  references  such  as (?+2). How