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# Line 18  INTRODUCTION Line 18  INTRODUCTION
18    
19         The  PCRE  library is a set of functions that implement regular expres-         The  PCRE  library is a set of functions that implement regular expres-
20         sion pattern matching using the same syntax and semantics as Perl, with         sion pattern matching using the same syntax and semantics as Perl, with
21         just  a  few differences. (Certain features that appeared in Python and         just  a  few  differences. Certain features that appeared in Python and
22         PCRE before they appeared in Perl are also available using  the  Python         PCRE before they appeared in Perl are also available using  the  Python
23         syntax.)         syntax.  There is also some support for certain .NET and Oniguruma syn-
24           tax items, and there is an option for  requesting  some  minor  changes
25           that give better JavaScript compatibility.
26    
27         The  current  implementation of PCRE (release 7.x) corresponds approxi-         The  current  implementation of PCRE (release 7.x) corresponds approxi-
28         mately with Perl 5.10, including support for UTF-8 encoded strings  and         mately with Perl 5.10, including support for UTF-8 encoded strings  and
# Line 45  INTRODUCTION Line 47  INTRODUCTION
47    
48         Details of exactly which Perl regular expression features are  and  are         Details of exactly which Perl regular expression features are  and  are
49         not supported by PCRE are given in separate documents. See the pcrepat-         not supported by PCRE are given in separate documents. See the pcrepat-
50         tern and pcrecompat pages.         tern and pcrecompat pages. There is a syntax summary in the  pcresyntax
51           page.
52    
53         Some features of PCRE can be included, excluded, or  changed  when  the         Some  features  of  PCRE can be included, excluded, or changed when the
54         library  is  built.  The pcre_config() function makes it possible for a         library is built. The pcre_config() function makes it  possible  for  a
55         client to discover which features are  available.  The  features  them-         client  to  discover  which  features are available. The features them-
56         selves  are described in the pcrebuild page. Documentation about build-         selves are described in the pcrebuild page. Documentation about  build-
57         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
58         in the source distribution.         in the source distribution.
59    
60         The  library  contains  a number of undocumented internal functions and         The library contains a number of undocumented  internal  functions  and
61         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
62         functions,  but  which  are  not  intended for use by external callers.         functions, but which are not intended  for  use  by  external  callers.
63         Their names all begin with "_pcre_", which hopefully will  not  provoke         Their  names  all begin with "_pcre_", which hopefully will not provoke
64         any name clashes. In some environments, it is possible to control which         any name clashes. In some environments, it is possible to control which
65         external symbols are exported when a shared library is  built,  and  in         external  symbols  are  exported when a shared library is built, and in
66         these cases the undocumented symbols are not exported.         these cases the undocumented symbols are not exported.
67    
68    
69  USER DOCUMENTATION  USER DOCUMENTATION
70    
71         The  user  documentation  for PCRE comprises a number of different sec-         The user documentation for PCRE comprises a number  of  different  sec-
72         tions. In the "man" format, each of these is a separate "man page".  In         tions.  In the "man" format, each of these is a separate "man page". In
73         the  HTML  format, each is a separate page, linked from the index page.         the HTML format, each is a separate page, linked from the  index  page.
74         In the plain text format, all the sections are concatenated,  for  ease         In  the  plain text format, all the sections are concatenated, for ease
75         of searching. The sections are as follows:         of searching. The sections are as follows:
76    
77           pcre              this document           pcre              this document
# Line 83  USER DOCUMENTATION Line 86  USER DOCUMENTATION
86           pcrepartial       details of the partial matching facility           pcrepartial       details of the partial matching facility
87           pcrepattern       syntax and semantics of supported           pcrepattern       syntax and semantics of supported
88                               regular expressions                               regular expressions
89             pcresyntax        quick syntax reference
90           pcreperform       discussion of performance issues           pcreperform       discussion of performance issues
91           pcreposix         the POSIX-compatible C API           pcreposix         the POSIX-compatible C API
92           pcreprecompile    details of saving and re-using precompiled patterns           pcreprecompile    details of saving and re-using precompiled patterns
# Line 90  USER DOCUMENTATION Line 94  USER DOCUMENTATION
94           pcrestack         discussion of stack usage           pcrestack         discussion of stack usage
95           pcretest          description of the pcretest testing command           pcretest          description of the pcretest testing command
96    
97         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
98         each C library function, listing its arguments and results.         each C library function, listing its arguments and results.
99    
100    
101  LIMITATIONS  LIMITATIONS
102    
103         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
104         never in practice be relevant.         never in practice be relevant.
105    
106         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
107         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
108         process regular expressions that are truly enormous,  you  can  compile         process  regular  expressions  that are truly enormous, you can compile
109         PCRE  with  an  internal linkage size of 3 or 4 (see the README file in         PCRE with an internal linkage size of 3 or 4 (see the  README  file  in
110         the source distribution and the pcrebuild documentation  for  details).         the  source  distribution and the pcrebuild documentation for details).
111         In  these  cases the limit is substantially larger.  However, the speed         In these cases the limit is substantially larger.  However,  the  speed
112         of execution is slower.         of execution is slower.
113    
114         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.  
115    
116         There is no limit to the number of parenthesized subpatterns, but there         There is no limit to the number of parenthesized subpatterns, but there
117         can be no more than 65535 capturing subpatterns.         can be no more than 65535 capturing subpatterns.
# Line 117  LIMITATIONS Line 119  LIMITATIONS
119         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
120         the maximum number of named subpatterns is 10000.         the maximum number of named subpatterns is 10000.
121    
122         The maximum length of a subject string is the largest  positive  number         The  maximum  length of a subject string is the largest positive number
123         that  an integer variable can hold. However, when using the traditional         that an integer variable can hold. However, when using the  traditional
124         matching function, PCRE uses recursion to handle subpatterns and indef-         matching function, PCRE uses recursion to handle subpatterns and indef-
125         inite  repetition.  This means that the available stack space may limit         inite repetition.  This means that the available stack space may  limit
126         the size of a subject string that can be processed by certain patterns.         the size of a subject string that can be processed by certain patterns.
127         For a discussion of stack issues, see the pcrestack documentation.         For a discussion of stack issues, see the pcrestack documentation.
128    
129    
130  UTF-8 AND UNICODE PROPERTY SUPPORT  UTF-8 AND UNICODE PROPERTY SUPPORT
131    
132         From  release  3.3,  PCRE  has  had  some support for character strings         From release 3.3, PCRE has  had  some  support  for  character  strings
133         encoded in the UTF-8 format. For release 4.0 this was greatly  extended         encoded  in the UTF-8 format. For release 4.0 this was greatly extended
134         to  cover  most common requirements, and in release 5.0 additional sup-         to cover most common requirements, and in release 5.0  additional  sup-
135         port for Unicode general category properties was added.         port for Unicode general category properties was added.
136    
137         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
138         support  in  the  code,  and, in addition, you must call pcre_compile()         support in the code, and, in addition,  you  must  call  pcre_compile()
139         with the PCRE_UTF8 option flag. When you do this, both the pattern  and         with  the PCRE_UTF8 option flag. When you do this, both the pattern and
140         any  subject  strings  that are matched against it are treated as UTF-8         any subject strings that are matched against it are  treated  as  UTF-8
141         strings instead of just strings of bytes.         strings instead of just strings of bytes.
142    
143         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,
144         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
145         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
146         very big.         very big.
147    
148         If PCRE is built with Unicode character property support (which implies         If PCRE is built with Unicode character property support (which implies
149         UTF-8 support), the escape sequences \p{..}, \P{..}, and  \X  are  sup-         UTF-8  support),  the  escape sequences \p{..}, \P{..}, and \X are sup-
150         ported.  The available properties that can be tested are limited to the         ported.  The available properties that can be tested are limited to the
151         general category properties such as Lu for an upper case letter  or  Nd         general  category  properties such as Lu for an upper case letter or Nd
152         for  a  decimal number, the Unicode script names such as Arabic or Han,         for a decimal number, the Unicode script names such as Arabic  or  Han,
153         and the derived properties Any and L&. A full  list  is  given  in  the         and  the  derived  properties  Any  and L&. A full list is given in the
154         pcrepattern documentation. Only the short names for properties are sup-         pcrepattern documentation. Only the short names for properties are sup-
155         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-
156         ter},  is  not  supported.   Furthermore,  in Perl, many properties may         ter}, is not supported.  Furthermore,  in  Perl,  many  properties  may
157         optionally be prefixed by "Is", for compatibility with Perl  5.6.  PCRE         optionally  be  prefixed by "Is", for compatibility with Perl 5.6. PCRE
158         does not support this.         does not support this.
159    
160         The following comments apply when PCRE is running in UTF-8 mode:     Validity of UTF-8 strings
161    
162           When you set the PCRE_UTF8 flag, the strings  passed  as  patterns  and
163           subjects are (by default) checked for validity on entry to the relevant
164           functions. From release 7.3 of PCRE, the check is according  the  rules
165           of  RFC  3629, which are themselves derived from the Unicode specifica-
166           tion. Earlier releases of PCRE followed the rules of  RFC  2279,  which
167           allows  the  full range of 31-bit values (0 to 0x7FFFFFFF). The current
168           check allows only values in the range U+0 to U+10FFFF, excluding U+D800
169           to U+DFFF.
170    
171           The  excluded  code  points are the "Low Surrogate Area" of Unicode, of
172           which the Unicode Standard says this: "The Low Surrogate Area does  not
173           contain  any  character  assignments,  consequently  no  character code
174           charts or namelists are provided for this area. Surrogates are reserved
175           for  use  with  UTF-16 and then must be used in pairs." The code points
176           that are encoded by UTF-16 pairs  are  available  as  independent  code
177           points  in  the  UTF-8  encoding.  (In other words, the whole surrogate
178           thing is a fudge for UTF-16 which unfortunately messes up UTF-8.)
179    
180           If an  invalid  UTF-8  string  is  passed  to  PCRE,  an  error  return
181           (PCRE_ERROR_BADUTF8) is given. In some situations, you may already know
182           that your strings are valid, and therefore want to skip these checks in
183           order to improve performance. If you set the PCRE_NO_UTF8_CHECK flag at
184           compile time or at run time, PCRE assumes that the pattern  or  subject
185           it  is  given  (respectively)  contains only valid UTF-8 codes. In this
186           case, it does not diagnose an invalid UTF-8 string.
187    
188           If you pass an invalid UTF-8 string  when  PCRE_NO_UTF8_CHECK  is  set,
189           what  happens  depends on why the string is invalid. If the string con-
190           forms to the "old" definition of UTF-8 (RFC 2279), it is processed as a
191           string  of  characters  in  the  range 0 to 0x7FFFFFFF. In other words,
192           apart from the initial validity test, PCRE (when in UTF-8 mode) handles
193           strings  according  to  the more liberal rules of RFC 2279. However, if
194           the string does not even conform to RFC 2279, the result is  undefined.
195           Your program may crash.
196    
197           If  you  want  to  process  strings  of  values  in the full range 0 to
198           0x7FFFFFFF, encoded in a UTF-8-like manner as per the old RFC, you  can
199           set PCRE_NO_UTF8_CHECK to bypass the more restrictive test. However, in
200           this situation, you will have to apply your own validity check.
201    
202         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.  
203    
204         2.  An  unbraced  hexadecimal  escape sequence (such as \xb3) matches a         1. An unbraced hexadecimal escape sequence (such  as  \xb3)  matches  a
205         two-byte UTF-8 character if the value is greater than 127.         two-byte UTF-8 character if the value is greater than 127.
206    
207         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
208         characters for values greater than \177.         characters for values greater than \177.
209    
210         4.  Repeat quantifiers apply to complete UTF-8 characters, not to indi-         3. Repeat quantifiers apply to complete UTF-8 characters, not to  indi-
211         vidual bytes, for example: \x{100}{3}.         vidual bytes, for example: \x{100}{3}.
212    
213         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-
214         gle byte.         gle byte.
215    
216         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
217         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
218         not available in the alternative matching function, pcre_dfa_exec().         not available in the alternative matching function, pcre_dfa_exec().
219    
220         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
221         test characters of any code value, but the characters that PCRE  recog-         test  characters of any code value, but the characters that PCRE recog-
222         nizes  as  digits,  spaces,  or  word characters remain the same set as         nizes as digits, spaces, or word characters  remain  the  same  set  as
223         before, all with values less than 256. This remains true even when PCRE         before, all with values less than 256. This remains true even when PCRE
224         includes  Unicode  property support, because to do otherwise would slow         includes Unicode property support, because to do otherwise  would  slow
225         down PCRE in many common cases. If you really want to test for a  wider         down  PCRE in many common cases. If you really want to test for a wider
226         sense  of,  say,  "digit",  you must use Unicode property tests such as         sense of, say, "digit", you must use Unicode  property  tests  such  as
227         \p{Nd}.         \p{Nd}.
228    
229         8. Similarly, characters that match the POSIX named  character  classes         7.  Similarly,  characters that match the POSIX named character classes
230         are all low-valued characters.         are all low-valued characters.
231    
232         9.  Case-insensitive  matching  applies only to characters whose values         8. However, the Perl 5.10 horizontal and vertical  whitespace  matching
233         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-
234         Even  when  Unicode  property support is available, PCRE still uses its         acters.
235         own character tables when checking the case of  low-valued  characters,  
236         so  as not to degrade performance.  The Unicode property information is         9. Case-insensitive matching applies only to  characters  whose  values
237           are  less than 128, unless PCRE is built with Unicode property support.
238           Even when Unicode property support is available, PCRE  still  uses  its
239           own  character  tables when checking the case of low-valued characters,
240           so as not to degrade performance.  The Unicode property information  is
241         used only for characters with higher values. Even when Unicode property         used only for characters with higher values. Even when Unicode property
242         support is available, PCRE supports case-insensitive matching only when         support is available, PCRE supports case-insensitive matching only when
243         there is a one-to-one mapping between a letter's  cases.  There  are  a         there  is  a  one-to-one  mapping between a letter's cases. There are a
244         small  number  of  many-to-one  mappings in Unicode; these are not sup-         small number of many-to-one mappings in Unicode;  these  are  not  sup-
245         ported by PCRE.         ported by PCRE.
246    
247    
# Line 215  AUTHOR Line 251  AUTHOR
251         University Computing Service         University Computing Service
252         Cambridge CB2 3QH, England.         Cambridge CB2 3QH, England.
253    
254         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,
255         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,
256         followed by the two digits 10, at the domain cam.ac.uk.         followed by the two digits 10, at the domain cam.ac.uk.
257    
258    
259  REVISION  REVISION
260    
261         Last updated: 18 April 2007         Last updated: 12 April 2008
262         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2008 University of Cambridge.
263  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
264    
265    
# Line 237  NAME Line 273  NAME
273  PCRE BUILD-TIME OPTIONS  PCRE BUILD-TIME OPTIONS
274    
275         This  document  describes  the  optional  features  of PCRE that can be         This  document  describes  the  optional  features  of PCRE that can be
276         selected when the library is compiled. They are all selected, or  dese-         selected when the library is compiled. It assumes use of the  configure
277         lected, by providing options to the configure script that is run before         script,  where the optional features are selected or deselected by pro-
278         the make command. The complete list of  options  for  configure  (which         viding options to configure before running the make  command.  However,
279         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
280         directory) can be obtained by running         environments using the GUI facility of  CMakeSetup  if  you  are  using
281           CMake instead of configure to build PCRE.
282    
283           The complete list of options for configure (which includes the standard
284           ones such as the  selection  of  the  installation  directory)  can  be
285           obtained by running
286    
287           ./configure --help           ./configure --help
288    
289         The following sections include  descriptions  of  options  whose  names         The  following  sections  include  descriptions  of options whose names
290         begin with --enable or --disable. These settings specify changes to the         begin with --enable or --disable. These settings specify changes to the
291         defaults for the configure command. Because of the way  that  configure         defaults  for  the configure command. Because of the way that configure
292         works,  --enable  and --disable always come in pairs, so the complemen-         works, --enable and --disable always come in pairs, so  the  complemen-
293         tary option always exists as well, but as it specifies the default,  it         tary  option always exists as well, but as it specifies the default, it
294         is not described.         is not described.
295    
296    
# Line 270  UTF-8 SUPPORT Line 311  UTF-8 SUPPORT
311    
312           --enable-utf8           --enable-utf8
313    
314         to  the  configure  command.  Of  itself, this does not make PCRE treat         to the configure command. Of itself, this  does  not  make  PCRE  treat
315         strings as UTF-8. As well as compiling PCRE with this option, you  also         strings  as UTF-8. As well as compiling PCRE with this option, you also
316         have  have to set the PCRE_UTF8 option when you call the pcre_compile()         have have to set the PCRE_UTF8 option when you call the  pcre_compile()
317         function.         function.
318    
319    
320  UNICODE CHARACTER PROPERTY SUPPORT  UNICODE CHARACTER PROPERTY SUPPORT
321    
322         UTF-8 support allows PCRE to process character values greater than  255         UTF-8  support allows PCRE to process character values greater than 255
323         in  the  strings that it handles. On its own, however, it does not pro-         in the strings that it handles. On its own, however, it does  not  pro-
324         vide any facilities for accessing the properties of such characters. If         vide any facilities for accessing the properties of such characters. If
325         you  want  to  be able to use the pattern escapes \P, \p, and \X, which         you want to be able to use the pattern escapes \P, \p,  and  \X,  which
326         refer to Unicode character properties, you must add         refer to Unicode character properties, you must add
327    
328           --enable-unicode-properties           --enable-unicode-properties
329    
330         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
331         not explicitly requested it.         not explicitly requested it.
332    
333         Including  Unicode  property  support  adds around 30K of tables to the         Including Unicode property support adds around 30K  of  tables  to  the
334         PCRE library. Only the general category properties such as  Lu  and  Nd         PCRE  library.  Only  the general category properties such as Lu and Nd
335         are supported. Details are given in the pcrepattern documentation.         are supported. Details are given in the pcrepattern documentation.
336    
337    
338  CODE VALUE OF NEWLINE  CODE VALUE OF NEWLINE
339    
340         By  default,  PCRE interprets character 10 (linefeed, LF) as indicating         By default, PCRE interprets character 10 (linefeed, LF)  as  indicating
341         the end of a line. This is the normal newline  character  on  Unix-like         the  end  of  a line. This is the normal newline character on Unix-like
342         systems. You can compile PCRE to use character 13 (carriage return, CR)         systems. You can compile PCRE to use character 13 (carriage return, CR)
343         instead, by adding         instead, by adding
344    
345           --enable-newline-is-cr           --enable-newline-is-cr
346    
347         to the  configure  command.  There  is  also  a  --enable-newline-is-lf         to  the  configure  command.  There  is  also  a --enable-newline-is-lf
348         option, which explicitly specifies linefeed as the newline character.         option, which explicitly specifies linefeed as the newline character.
349    
350         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 356  CODE VALUE OF NEWLINE
356    
357           --enable-newline-is-anycrlf           --enable-newline-is-anycrlf
358    
359         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
360         CRLF as indicating a line ending. Finally, a fifth option, specified by         CRLF as indicating a line ending. Finally, a fifth option, specified by
361    
362           --enable-newline-is-any           --enable-newline-is-any
363    
364         causes PCRE to recognize any Unicode newline sequence.         causes PCRE to recognize any Unicode newline sequence.
365    
366         Whatever line ending convention is selected when PCRE is built  can  be         Whatever  line  ending convention is selected when PCRE is built can be
367         overridden  when  the library functions are called. At build time it is         overridden when the library functions are called. At build time  it  is
368         conventional to use the standard for your operating system.         conventional to use the standard for your operating system.
369    
370    
371    WHAT \R MATCHES
372    
373           By  default,  the  sequence \R in a pattern matches any Unicode newline
374           sequence, whatever has been selected as the line  ending  sequence.  If
375           you specify
376    
377             --enable-bsr-anycrlf
378    
379           the  default  is changed so that \R matches only CR, LF, or CRLF. What-
380           ever is selected when PCRE is built can be overridden when the  library
381           functions are called.
382    
383    
384  BUILDING SHARED AND STATIC LIBRARIES  BUILDING SHARED AND STATIC LIBRARIES
385    
386         The PCRE building process uses libtool to build both shared and  static         The  PCRE building process uses libtool to build both shared and static
387         Unix  libraries by default. You can suppress one of these by adding one         Unix libraries by default. You can suppress one of these by adding  one
388         of         of
389    
390           --disable-shared           --disable-shared
# Line 342  BUILDING SHARED AND STATIC LIBRARIES Line 396  BUILDING SHARED AND STATIC LIBRARIES
396  POSIX MALLOC USAGE  POSIX MALLOC USAGE
397    
398         When PCRE is called through the POSIX interface (see the pcreposix doc-         When PCRE is called through the POSIX interface (see the pcreposix doc-
399         umentation),  additional  working  storage  is required for holding the         umentation), additional working storage is  required  for  holding  the
400         pointers to capturing substrings, because PCRE requires three  integers         pointers  to capturing substrings, because PCRE requires three integers
401         per  substring,  whereas  the POSIX interface provides only two. If the         per substring, whereas the POSIX interface provides only  two.  If  the
402         number of expected substrings is small, the wrapper function uses space         number of expected substrings is small, the wrapper function uses space
403         on the stack, because this is faster than using malloc() for each call.         on the stack, because this is faster than using malloc() for each call.
404         The default threshold above which the stack is no longer used is 10; it         The default threshold above which the stack is no longer used is 10; it
# Line 357  POSIX MALLOC USAGE Line 411  POSIX MALLOC USAGE
411    
412  HANDLING VERY LARGE PATTERNS  HANDLING VERY LARGE PATTERNS
413    
414         Within  a  compiled  pattern,  offset values are used to point from one         Within a compiled pattern, offset values are used  to  point  from  one
415         part to another (for example, from an opening parenthesis to an  alter-         part  to another (for example, from an opening parenthesis to an alter-
416         nation  metacharacter).  By default, two-byte values are used for these         nation metacharacter). By default, two-byte values are used  for  these
417         offsets, leading to a maximum size for a  compiled  pattern  of  around         offsets,  leading  to  a  maximum size for a compiled pattern of around
418         64K.  This  is sufficient to handle all but the most gigantic patterns.         64K. This is sufficient to handle all but the most  gigantic  patterns.
419         Nevertheless, some people do want to process enormous patterns,  so  it         Nevertheless,  some  people do want to process enormous patterns, so it
420         is  possible  to compile PCRE to use three-byte or four-byte offsets by         is possible to compile PCRE to use three-byte or four-byte  offsets  by
421         adding a setting such as         adding a setting such as
422    
423           --with-link-size=3           --with-link-size=3
424    
425         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
426         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
427         additional bytes when handling them.         additional bytes when handling them.
428    
429    
430  AVOIDING EXCESSIVE STACK USAGE  AVOIDING EXCESSIVE STACK USAGE
431    
432         When matching with the pcre_exec() function, PCRE implements backtrack-         When matching with the pcre_exec() function, PCRE implements backtrack-
433         ing  by  making recursive calls to an internal function called match().         ing by making recursive calls to an internal function  called  match().
434         In environments where the size of the stack is limited,  this  can  se-         In  environments  where  the size of the stack is limited, this can se-
435         verely  limit  PCRE's operation. (The Unix environment does not usually         verely limit PCRE's operation. (The Unix environment does  not  usually
436         suffer from this problem, but it may sometimes be necessary to increase         suffer from this problem, but it may sometimes be necessary to increase
437         the  maximum  stack size.  There is a discussion in the pcrestack docu-         the maximum stack size.  There is a discussion in the  pcrestack  docu-
438         mentation.) An alternative approach to recursion that uses memory  from         mentation.)  An alternative approach to recursion that uses memory from
439         the  heap  to remember data, instead of using recursive function calls,         the heap to remember data, instead of using recursive  function  calls,
440         has been implemented to work round the problem of limited  stack  size.         has  been  implemented to work round the problem of limited stack size.
441         If you want to build a version of PCRE that works this way, add         If you want to build a version of PCRE that works this way, add
442    
443           --disable-stack-for-recursion           --disable-stack-for-recursion
444    
445         to  the  configure  command. With this configuration, PCRE will use the         to the configure command. With this configuration, PCRE  will  use  the
446         pcre_stack_malloc and pcre_stack_free variables to call memory  manage-         pcre_stack_malloc  and pcre_stack_free variables to call memory manage-
447         ment  functions.  Separate  functions are provided because the usage is         ment functions. By default these point to malloc() and free(), but  you
448         very predictable: the block sizes requested are always  the  same,  and         can replace the pointers so that your own functions are used.
449         the  blocks  are always freed in reverse order. A calling program might  
450         be able to implement optimized functions that perform better  than  the         Separate  functions  are  provided  rather  than  using pcre_malloc and
451         standard  malloc()  and  free()  functions.  PCRE  runs noticeably more         pcre_free because the  usage  is  very  predictable:  the  block  sizes
452         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
453         function; it is not relevant for the the pcre_dfa_exec() function.         reverse order. A calling program might be able to  implement  optimized
454           functions  that  perform  better  than  malloc()  and free(). PCRE runs
455           noticeably more slowly when built in this way. This option affects only
456           the   pcre_exec()   function;   it   is   not   relevant  for  the  the
457           pcre_dfa_exec() function.
458    
459    
460  LIMITING PCRE RESOURCE USAGE  LIMITING PCRE RESOURCE USAGE
461    
462         Internally,  PCRE has a function called match(), which it calls repeat-         Internally, PCRE has a function called match(), which it calls  repeat-
463         edly  (sometimes  recursively)  when  matching  a  pattern   with   the         edly   (sometimes   recursively)  when  matching  a  pattern  with  the
464         pcre_exec()  function.  By controlling the maximum number of times this         pcre_exec() function. By controlling the maximum number of  times  this
465         function may be called during a single matching operation, a limit  can         function  may be called during a single matching operation, a limit can
466         be  placed  on  the resources used by a single call to pcre_exec(). The         be placed on the resources used by a single call  to  pcre_exec().  The
467         limit can be changed at run time, as described in the pcreapi  documen-         limit  can be changed at run time, as described in the pcreapi documen-
468         tation.  The default is 10 million, but this can be changed by adding a         tation. The default is 10 million, but this can be changed by adding  a
469         setting such as         setting such as
470    
471           --with-match-limit=500000           --with-match-limit=500000
472    
473         to  the  configure  command.  This  setting  has  no  effect   on   the         to   the   configure  command.  This  setting  has  no  effect  on  the
474         pcre_dfa_exec() matching function.         pcre_dfa_exec() matching function.
475    
476         In  some  environments  it is desirable to limit the depth of recursive         In some environments it is desirable to limit the  depth  of  recursive
477         calls of match() more strictly than the total number of calls, in order         calls of match() more strictly than the total number of calls, in order
478         to  restrict  the maximum amount of stack (or heap, if --disable-stack-         to restrict the maximum amount of stack (or heap,  if  --disable-stack-
479         for-recursion is specified) that is used. A second limit controls this;         for-recursion is specified) that is used. A second limit controls this;
480         it  defaults  to  the  value  that is set for --with-match-limit, which         it defaults to the value that  is  set  for  --with-match-limit,  which
481         imposes no additional constraints. However, you can set a  lower  limit         imposes  no  additional constraints. However, you can set a lower limit
482         by adding, for example,         by adding, for example,
483    
484           --with-match-limit-recursion=10000           --with-match-limit-recursion=10000
485    
486         to  the  configure  command.  This  value can also be overridden at run         to the configure command. This value can  also  be  overridden  at  run
487         time.         time.
488    
489    
490  CREATING CHARACTER TABLES AT BUILD TIME  CREATING CHARACTER TABLES AT BUILD TIME
491    
492         PCRE uses fixed tables for processing characters whose code values  are         PCRE  uses fixed tables for processing characters whose code values are
493         less  than 256. By default, PCRE is built with a set of tables that are         less than 256. By default, PCRE is built with a set of tables that  are
494         distributed in the file pcre_chartables.c.dist. These  tables  are  for         distributed  in  the  file pcre_chartables.c.dist. These tables are for
495         ASCII codes only. If you add         ASCII codes only. If you add
496    
497           --enable-rebuild-chartables           --enable-rebuild-chartables
498    
499         to  the  configure  command, the distributed tables are no longer used.         to the configure command, the distributed tables are  no  longer  used.
500         Instead, a program called dftables is compiled and  run.  This  outputs         Instead,  a  program  called dftables is compiled and run. This outputs
501         the source for new set of tables, created in the default locale of your         the source for new set of tables, created in the default locale of your
502         C runtime system. (This method of replacing the tables does not work if         C runtime system. (This method of replacing the tables does not work if
503         you  are cross compiling, because dftables is run on the local host. If         you are cross compiling, because dftables is run on the local host.  If
504         you need to create alternative tables when cross  compiling,  you  will         you  need  to  create alternative tables when cross compiling, you will
505         have to do so "by hand".)         have to do so "by hand".)
506    
507    
508  USING EBCDIC CODE  USING EBCDIC CODE
509    
510         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
511         character code is ASCII (or Unicode, which is  a  superset  of  ASCII).         character  code  is  ASCII  (or Unicode, which is a superset of ASCII).
512         PCRE  can,  however,  be  compiled  to  run in an EBCDIC environment by         This is the case for most computer operating systems.  PCRE  can,  how-
513         adding         ever, be compiled to run in an EBCDIC environment by adding
514    
515           --enable-ebcdic           --enable-ebcdic
516    
517         to the configure command. This setting implies --enable-rebuild-charta-         to the configure command. This setting implies --enable-rebuild-charta-
518         bles.         bles. You should only use it if you know that  you  are  in  an  EBCDIC
519           environment (for example, an IBM mainframe operating system).
520    
521    
522    PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT
523    
524           By default, pcregrep reads all files as plain text. You can build it so
525           that it recognizes files whose names end in .gz or .bz2, and reads them
526           with libz or libbz2, respectively, by adding one or both of
527    
528             --enable-pcregrep-libz
529             --enable-pcregrep-libbz2
530    
531           to the configure command. These options naturally require that the rel-
532           evant libraries are installed on your system. Configuration  will  fail
533           if they are not.
534    
535    
536    PCRETEST OPTION FOR LIBREADLINE SUPPORT
537    
538           If you add
539    
540             --enable-pcretest-libreadline
541    
542           to  the  configure  command,  pcretest  is  linked with the libreadline
543           library, and when its input is from a terminal, it reads it  using  the
544           readline() function. This provides line-editing and history facilities.
545           Note that libreadline is GPL-licenced, so if you distribute a binary of
546           pcretest linked in this way, there may be licensing issues.
547    
548           Setting  this  option  causes  the -lreadline option to be added to the
549           pcretest build. In many operating environments with  a  sytem-installed
550           libreadline this is sufficient. However, in some environments (e.g.  if
551           an unmodified distribution version of readline is in use),  some  extra
552           configuration  may  be necessary. The INSTALL file for libreadline says
553           this:
554    
555             "Readline uses the termcap functions, but does not link with the
556             termcap or curses library itself, allowing applications which link
557             with readline the to choose an appropriate library."
558    
559           If your environment has not been set up so that an appropriate  library
560           is automatically included, you may need to add something like
561    
562             LIBS="-ncurses"
563    
564           immediately before the configure command.
565    
566    
567  SEE ALSO  SEE ALSO
# Line 474  AUTHOR Line 578  AUTHOR
578    
579  REVISION  REVISION
580    
581         Last updated: 16 April 2007         Last updated: 13 April 2008
582         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2008 University of Cambridge.
583  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
584    
585    
# Line 618  THE ALTERNATIVE MATCHING ALGORITHM Line 722  THE ALTERNATIVE MATCHING ALGORITHM
722         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
723         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.
724    
725         7.  The \C escape sequence, which (in the standard algorithm) matches a         7. The \C escape sequence, which (in the standard algorithm) matches  a
726         single  byte, even in UTF-8 mode, is not supported because the alterna-         single  byte, even in UTF-8 mode, is not supported because the alterna-
727         tive algorithm moves through the subject  string  one  character  at  a         tive algorithm moves through the subject  string  one  character  at  a
728         time, for all active paths through the tree.         time, for all active paths through the tree.
729    
730           8.  Except for (*FAIL), the backtracking control verbs such as (*PRUNE)
731           are not supported. (*FAIL) is supported, and  behaves  like  a  failing
732           negative assertion.
733    
734    
735  ADVANTAGES OF THE ALTERNATIVE ALGORITHM  ADVANTAGES OF THE ALTERNATIVE ALGORITHM
736    
# Line 669  AUTHOR Line 777  AUTHOR
777    
778  REVISION  REVISION
779    
780         Last updated: 29 May 2007         Last updated: 19 April 2008
781         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2008 University of Cambridge.
782  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
783    
784    
# Line 782  PCRE API OVERVIEW Line 890  PCRE API OVERVIEW
890         a  Perl-compatible  manner. A sample program that demonstrates the sim-         a  Perl-compatible  manner. A sample program that demonstrates the sim-
891         plest way of using them is provided in the file  called  pcredemo.c  in         plest way of using them is provided in the file  called  pcredemo.c  in
892         the  source distribution. The pcresample documentation describes how to         the  source distribution. The pcresample documentation describes how to
893         run it.         compile and run it.
894    
895         A second matching function, pcre_dfa_exec(), which is not Perl-compati-         A second matching function, pcre_dfa_exec(), which is not Perl-compati-
896         ble,  is  also provided. This uses a different algorithm for the match-         ble,  is  also provided. This uses a different algorithm for the match-
# Line 866  NEWLINES Line 974  NEWLINES
974         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
975         pattern is compiled, or when it is matched.         pattern is compiled, or when it is matched.
976    
977           At compile time, the newline convention can be specified by the options
978           argument of pcre_compile(), or it can be specified by special  text  at
979           the start of the pattern itself; this overrides any other settings. See
980           the pcrepattern page for details of the special character sequences.
981    
982         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-
983         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
984         newline  convention  affects  the  handling of the dot, circumflex, and         newline convention affects the handling of  the  dot,  circumflex,  and
985         dollar metacharacters, the handling of #-comments in /x mode, and, when         dollar metacharacters, the handling of #-comments in /x mode, and, when
986         CRLF  is a recognized line ending sequence, the match position advance-         CRLF is a recognized line ending sequence, the match position  advance-
987         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
988         not affect the interpretation of the \n or \r escape sequences.         section on pcre_exec() options below.
989    
990           The choice of newline convention does not affect the interpretation  of
991           the  \n  or  \r  escape  sequences, nor does it affect what \R matches,
992           which is controlled in a similar way, but by separate options.
993    
994    
995  MULTITHREADING  MULTITHREADING
996    
997         The  PCRE  functions  can be used in multi-threading applications, with         The PCRE functions can be used in  multi-threading  applications,  with
998         the  proviso  that  the  memory  management  functions  pointed  to  by         the  proviso  that  the  memory  management  functions  pointed  to  by
999         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
1000         callout function pointed to by pcre_callout, are shared by all threads.         callout function pointed to by pcre_callout, are shared by all threads.
1001    
1002         The  compiled form of a regular expression is not altered during match-         The compiled form of a regular expression is not altered during  match-
1003         ing, so the same compiled pattern can safely be used by several threads         ing, so the same compiled pattern can safely be used by several threads
1004         at once.         at once.
1005    
# Line 890  MULTITHREADING Line 1007  MULTITHREADING
1007  SAVING PRECOMPILED PATTERNS FOR LATER USE  SAVING PRECOMPILED PATTERNS FOR LATER USE
1008    
1009         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
1010         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
1011         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
1012         pcreprecompile documentation. However, compiling a  regular  expression         pcreprecompile  documentation.  However, compiling a regular expression
1013         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-
1014         anteed to work and may cause crashes.         anteed to work and may cause crashes.
1015    
1016    
# Line 901  CHECKING BUILD-TIME OPTIONS Line 1018  CHECKING BUILD-TIME OPTIONS
1018    
1019         int pcre_config(int what, void *where);         int pcre_config(int what, void *where);
1020    
1021         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-
1022         cover which optional features have been compiled into the PCRE library.         cover which optional features have been compiled into the PCRE library.
1023         The pcrebuild documentation has more details about these optional  fea-         The  pcrebuild documentation has more details about these optional fea-
1024         tures.         tures.
1025    
1026         The  first  argument  for pcre_config() is an integer, specifying which         The first argument for pcre_config() is an  integer,  specifying  which
1027         information is required; the second argument is a pointer to a variable         information is required; the second argument is a pointer to a variable
1028         into  which  the  information  is  placed. The following information is         into which the information is  placed.  The  following  information  is
1029         available:         available:
1030    
1031           PCRE_CONFIG_UTF8           PCRE_CONFIG_UTF8
1032    
1033         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-
1034         able; otherwise it is set to zero.         able; otherwise it is set to zero.
1035    
1036           PCRE_CONFIG_UNICODE_PROPERTIES           PCRE_CONFIG_UNICODE_PROPERTIES
1037    
1038         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
1039         character properties is available; otherwise it is set to zero.         character properties is available; otherwise it is set to zero.
1040    
1041           PCRE_CONFIG_NEWLINE           PCRE_CONFIG_NEWLINE
1042    
1043         The output is an integer whose value specifies  the  default  character         The  output  is  an integer whose value specifies the default character
1044         sequence  that is recognized as meaning "newline". The four values that         sequence that is recognized as meaning "newline". The four values  that
1045         are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,         are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,
1046         and  -1  for  ANY. The default should normally be the standard sequence         and -1 for ANY. The default should normally be  the  standard  sequence
1047         for your operating system.         for your operating system.
1048    
1049             PCRE_CONFIG_BSR
1050    
1051           The output is an integer whose value indicates what character sequences
1052           the \R escape sequence matches by default. A value of 0 means  that  \R
1053           matches  any  Unicode  line ending sequence; a value of 1 means that \R
1054           matches only CR, LF, or CRLF. The default can be overridden when a pat-
1055           tern is compiled or matched.
1056    
1057           PCRE_CONFIG_LINK_SIZE           PCRE_CONFIG_LINK_SIZE
1058    
1059         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
1060         internal linkage in compiled regular expressions. The value is 2, 3, or         internal linkage in compiled regular expressions. The value is 2, 3, or
1061         4. Larger values allow larger regular expressions to  be  compiled,  at         4.  Larger  values  allow larger regular expressions to be compiled, at
1062         the  expense  of  slower matching. The default value of 2 is sufficient         the expense of slower matching. The default value of  2  is  sufficient
1063         for all but the most massive patterns, since  it  allows  the  compiled         for  all  but  the  most massive patterns, since it allows the compiled
1064         pattern to be up to 64K in size.         pattern to be up to 64K in size.
1065    
1066           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
1067    
1068         The  output  is  an integer that contains the threshold above which the         The output is an integer that contains the threshold  above  which  the
1069         POSIX interface uses malloc() for output vectors. Further  details  are         POSIX  interface  uses malloc() for output vectors. Further details are
1070         given in the pcreposix documentation.         given in the pcreposix documentation.
1071    
1072           PCRE_CONFIG_MATCH_LIMIT           PCRE_CONFIG_MATCH_LIMIT
1073    
1074         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
1075         internal matching function calls in a  pcre_exec()  execution.  Further         internal  matching  function  calls in a pcre_exec() execution. Further
1076         details are given with pcre_exec() below.         details are given with pcre_exec() below.
1077    
1078           PCRE_CONFIG_MATCH_LIMIT_RECURSION           PCRE_CONFIG_MATCH_LIMIT_RECURSION
1079    
1080         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
1081         recursion when calling the internal matching function in a  pcre_exec()         recursion  when calling the internal matching function in a pcre_exec()
1082         execution. Further details are given with pcre_exec() below.         execution. Further details are given with pcre_exec() below.
1083    
1084           PCRE_CONFIG_STACKRECURSE           PCRE_CONFIG_STACKRECURSE
1085    
1086         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
1087         running pcre_exec() is implemented by recursive function calls that use         running pcre_exec() is implemented by recursive function calls that use
1088         the  stack  to remember their state. This is the usual way that PCRE is         the stack to remember their state. This is the usual way that  PCRE  is
1089         compiled. The output is zero if PCRE was compiled to use blocks of data         compiled. The output is zero if PCRE was compiled to use blocks of data
1090         on  the  heap  instead  of  recursive  function  calls.  In  this case,         on the  heap  instead  of  recursive  function  calls.  In  this  case,
1091         pcre_stack_malloc and  pcre_stack_free  are  called  to  manage  memory         pcre_stack_malloc  and  pcre_stack_free  are  called  to  manage memory
1092         blocks on the heap, thus avoiding the use of the stack.         blocks on the heap, thus avoiding the use of the stack.
1093    
1094    
# Line 980  COMPILING A PATTERN Line 1105  COMPILING A PATTERN
1105    
1106         Either of the functions pcre_compile() or pcre_compile2() can be called         Either of the functions pcre_compile() or pcre_compile2() can be called
1107         to compile a pattern into an internal form. The only difference between         to compile a pattern into an internal form. The only difference between
1108         the  two interfaces is that pcre_compile2() has an additional argument,         the two interfaces is that pcre_compile2() has an additional  argument,
1109         errorcodeptr, via which a numerical error code can be returned.         errorcodeptr, via which a numerical error code can be returned.
1110    
1111         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
1112         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
1113         obtained via pcre_malloc is returned. This contains the  compiled  code         obtained  via  pcre_malloc is returned. This contains the compiled code
1114         and related data. The pcre type is defined for the returned block; this         and related data. The pcre type is defined for the returned block; this
1115         is a typedef for a structure whose contents are not externally defined.         is a typedef for a structure whose contents are not externally defined.
1116         It is up to the caller to free the memory (via pcre_free) when it is no         It is up to the caller to free the memory (via pcre_free) when it is no
1117         longer required.         longer required.
1118    
1119         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
1120         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
1121         fully relocatable, because it may contain a copy of the tableptr  argu-         fully  relocatable, because it may contain a copy of the tableptr argu-
1122         ment, which is an address (see below).         ment, which is an address (see below).
1123    
1124         The options argument contains various bit settings that affect the com-         The options argument contains various bit settings that affect the com-
1125         pilation. It should be zero if no options are required.  The  available         pilation.  It  should be zero if no options are required. The available
1126         options  are  described  below. Some of them, in particular, those that         options are described below. Some of them, in  particular,  those  that
1127         are compatible with Perl, can also be set and  unset  from  within  the         are  compatible  with  Perl,  can also be set and unset from within the
1128         pattern  (see  the  detailed  description in the pcrepattern documenta-         pattern (see the detailed description  in  the  pcrepattern  documenta-
1129         tion). For these options, the contents of the options  argument  speci-         tion).  For  these options, the contents of the options argument speci-
1130         fies  their initial settings at the start of compilation and execution.         fies their initial settings at the start of compilation and  execution.
1131         The PCRE_ANCHORED and PCRE_NEWLINE_xxx options can be set at  the  time         The  PCRE_ANCHORED  and PCRE_NEWLINE_xxx options can be set at the time
1132         of matching as well as at compile time.         of matching as well as at compile time.
1133    
1134         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
1135         if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and
1136         sets the variable pointed to by errptr to point to a textual error mes-         sets the variable pointed to by errptr to point to a textual error mes-
1137         sage. This is a static string that is part of the library. You must not         sage. This is a static string that is part of the library. You must not
1138         try to free it. The offset from the start of the pattern to the charac-         try to free it. The offset from the start of the pattern to the charac-
1139         ter where the error was discovered is placed in the variable pointed to         ter where the error was discovered is placed in the variable pointed to
1140         by  erroffset,  which must not be NULL. If it is, an immediate error is         by erroffset, which must not be NULL. If it is, an immediate  error  is
1141         given.         given.
1142    
1143         If pcre_compile2() is used instead of pcre_compile(),  and  the  error-         If  pcre_compile2()  is  used instead of pcre_compile(), and the error-
1144         codeptr  argument is not NULL, a non-zero error code number is returned         codeptr argument is not NULL, a non-zero error code number is  returned
1145         via this argument in the event of an error. This is in addition to  the         via  this argument in the event of an error. This is in addition to the
1146         textual error message. Error codes and messages are listed below.         textual error message. Error codes and messages are listed below.
1147    
1148         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
1149         character tables that are  built  when  PCRE  is  compiled,  using  the         character  tables  that  are  built  when  PCRE  is compiled, using the
1150         default  C  locale.  Otherwise, tableptr must be an address that is the         default C locale. Otherwise, tableptr must be an address  that  is  the
1151         result of a call to pcre_maketables(). This value is  stored  with  the         result  of  a  call to pcre_maketables(). This value is stored with the
1152         compiled  pattern,  and used again by pcre_exec(), unless another table         compiled pattern, and used again by pcre_exec(), unless  another  table
1153         pointer is passed to it. For more discussion, see the section on locale         pointer is passed to it. For more discussion, see the section on locale
1154         support below.         support below.
1155    
1156         This  code  fragment  shows a typical straightforward call to pcre_com-         This code fragment shows a typical straightforward  call  to  pcre_com-
1157         pile():         pile():
1158    
1159           pcre *re;           pcre *re;
# Line 1041  COMPILING A PATTERN Line 1166  COMPILING A PATTERN
1166             &erroffset,       /* for error offset */             &erroffset,       /* for error offset */
1167             NULL);            /* use default character tables */             NULL);            /* use default character tables */
1168    
1169         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
1170         file:         file:
1171    
1172           PCRE_ANCHORED           PCRE_ANCHORED
1173    
1174         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
1175         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
1176         that  is being searched (the "subject string"). This effect can also be         that is being searched (the "subject string"). This effect can also  be
1177         achieved by appropriate constructs in the pattern itself, which is  the         achieved  by appropriate constructs in the pattern itself, which is the
1178         only way to do it in Perl.         only way to do it in Perl.
1179    
1180           PCRE_AUTO_CALLOUT           PCRE_AUTO_CALLOUT
1181    
1182         If this bit is set, pcre_compile() automatically inserts callout items,         If this bit is set, pcre_compile() automatically inserts callout items,
1183         all with number 255, before each pattern item. For  discussion  of  the         all  with  number  255, before each pattern item. For discussion of the
1184         callout facility, see the pcrecallout documentation.         callout facility, see the pcrecallout documentation.
1185    
1186             PCRE_BSR_ANYCRLF
1187             PCRE_BSR_UNICODE
1188    
1189           These options (which are mutually exclusive) control what the \R escape
1190           sequence  matches.  The choice is either to match only CR, LF, or CRLF,
1191           or to match any Unicode newline sequence. The default is specified when
1192           PCRE is built. It can be overridden from within the pattern, or by set-
1193           ting an option when a compiled pattern is matched.
1194    
1195           PCRE_CASELESS           PCRE_CASELESS
1196    
1197         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
1198         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
1199         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
1200         always understands the concept of case for characters whose values  are         always  understands the concept of case for characters whose values are
1201         less  than 128, so caseless matching is always possible. For characters         less than 128, so caseless matching is always possible. For  characters
1202         with higher values, the concept of case is supported if  PCRE  is  com-         with  higher  values,  the concept of case is supported if PCRE is com-
1203         piled  with Unicode property support, but not otherwise. If you want to         piled with Unicode property support, but not otherwise. If you want  to
1204         use caseless matching for characters 128 and  above,  you  must  ensure         use  caseless  matching  for  characters 128 and above, you must ensure
1205         that  PCRE  is  compiled  with Unicode property support as well as with         that PCRE is compiled with Unicode property support  as  well  as  with
1206         UTF-8 support.         UTF-8 support.
1207    
1208           PCRE_DOLLAR_ENDONLY           PCRE_DOLLAR_ENDONLY
1209    
1210         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
1211         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
1212         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
1213         before  any  other newlines). The PCRE_DOLLAR_ENDONLY option is ignored         before any other newlines). The PCRE_DOLLAR_ENDONLY option  is  ignored
1214         if PCRE_MULTILINE is set.  There is no equivalent  to  this  option  in         if  PCRE_MULTILINE  is  set.   There is no equivalent to this option in
1215         Perl, and no way to set it within a pattern.         Perl, and no way to set it within a pattern.
1216    
1217           PCRE_DOTALL           PCRE_DOTALL
1218    
1219         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-
1220         acters, including those that indicate newline. Without it, a  dot  does         acters,  including  those that indicate newline. Without it, a dot does
1221         not  match  when  the  current position is at a newline. This option is         not match when the current position is at a  newline.  This  option  is
1222         equivalent to Perl's /s option, and it can be changed within a  pattern         equivalent  to Perl's /s option, and it can be changed within a pattern
1223         by  a (?s) option setting. A negative class such as [^a] always matches         by a (?s) option setting. A negative class such as [^a] always  matches
1224         newline characters, independent of the setting of this option.         newline characters, independent of the setting of this option.
1225    
1226           PCRE_DUPNAMES           PCRE_DUPNAMES
1227    
1228         If this bit is set, names used to identify capturing  subpatterns  need         If  this  bit is set, names used to identify capturing subpatterns need
1229         not be unique. This can be helpful for certain types of pattern when it         not be unique. This can be helpful for certain types of pattern when it
1230         is known that only one instance of the named  subpattern  can  ever  be         is  known  that  only  one instance of the named subpattern can ever be
1231         matched.  There  are  more details of named subpatterns below; see also         matched. There are more details of named subpatterns  below;  see  also
1232         the pcrepattern documentation.         the pcrepattern documentation.
1233    
1234           PCRE_EXTENDED           PCRE_EXTENDED
1235    
1236         If this bit is set, whitespace  data  characters  in  the  pattern  are         If  this  bit  is  set,  whitespace  data characters in the pattern are
1237         totally ignored except when escaped or inside a character class. White-         totally ignored except when escaped or inside a character class. White-
1238         space does not include the VT character (code 11). In addition, charac-         space does not include the VT character (code 11). In addition, charac-
1239         ters between an unescaped # outside a character class and the next new-         ters between an unescaped # outside a character class and the next new-
1240         line, inclusive, are also ignored. This  is  equivalent  to  Perl's  /x         line,  inclusive,  are  also  ignored.  This is equivalent to Perl's /x
1241         option,  and  it  can be changed within a pattern by a (?x) option set-         option, and it can be changed within a pattern by a  (?x)  option  set-
1242         ting.         ting.
1243    
1244         This option makes it possible to include  comments  inside  complicated         This  option  makes  it possible to include comments inside complicated
1245         patterns.   Note,  however,  that this applies only to data characters.         patterns.  Note, however, that this applies only  to  data  characters.
1246         Whitespace  characters  may  never  appear  within  special   character         Whitespace   characters  may  never  appear  within  special  character
1247         sequences  in  a  pattern,  for  example  within the sequence (?( which         sequences in a pattern, for  example  within  the  sequence  (?(  which
1248         introduces a conditional subpattern.         introduces a conditional subpattern.
1249    
1250           PCRE_EXTRA           PCRE_EXTRA
1251    
1252         This option was invented in order to turn on  additional  functionality         This  option  was invented in order to turn on additional functionality
1253         of  PCRE  that  is  incompatible with Perl, but it is currently of very         of PCRE that is incompatible with Perl, but it  is  currently  of  very
1254         little use. When set, any backslash in a pattern that is followed by  a         little  use. When set, any backslash in a pattern that is followed by a
1255         letter  that  has  no  special  meaning causes an error, thus reserving         letter that has no special meaning  causes  an  error,  thus  reserving
1256         these combinations for future expansion. By  default,  as  in  Perl,  a         these  combinations  for  future  expansion.  By default, as in Perl, a
1257         backslash  followed by a letter with no special meaning is treated as a         backslash followed by a letter with no special meaning is treated as  a
1258         literal. (Perl can, however, be persuaded to give a warning for  this.)         literal.  (Perl can, however, be persuaded to give a warning for this.)
1259         There  are  at  present no other features controlled by this option. It         There are at present no other features controlled by  this  option.  It
1260         can also be set by a (?X) option setting within a pattern.         can also be set by a (?X) option setting within a pattern.
1261    
1262           PCRE_FIRSTLINE           PCRE_FIRSTLINE
1263    
1264         If this option is set, an  unanchored  pattern  is  required  to  match         If  this  option  is  set,  an  unanchored pattern is required to match
1265         before  or  at  the  first  newline  in  the subject string, though the         before or at the first  newline  in  the  subject  string,  though  the
1266         matched text may continue over the newline.         matched text may continue over the newline.
1267    
1268             PCRE_JAVASCRIPT_COMPAT
1269    
1270           If this option is set, PCRE's behaviour is changed in some ways so that
1271           it is compatible with JavaScript rather than Perl. The changes  are  as
1272           follows:
1273    
1274           (1)  A  lone  closing square bracket in a pattern causes a compile-time
1275           error, because this is illegal in JavaScript (by default it is  treated
1276           as a data character). Thus, the pattern AB]CD becomes illegal when this
1277           option is set.
1278    
1279           (2) At run time, a back reference to an unset subpattern group  matches
1280           an  empty  string (by default this causes the current matching alterna-
1281           tive to fail). A pattern such as (\1)(a) succeeds when this  option  is
1282           set  (assuming  it can find an "a" in the subject), whereas it fails by
1283           default, for Perl compatibility.
1284    
1285           PCRE_MULTILINE           PCRE_MULTILINE
1286    
1287         By default, PCRE treats the subject string as consisting  of  a  single         By default, PCRE treats the subject string as consisting  of  a  single
# Line 1213  COMPILING A PATTERN Line 1364  COMPILING A PATTERN
1364           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
1365    
1366         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
1367         automatically  checked. If an invalid UTF-8 sequence of bytes is found,         automatically  checked.  There  is  a  discussion about the validity of
1368         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
1369         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
1370         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-
1371         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
1372         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
1373         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
1374         ing of subject strings.         can also be passed to pcre_exec() and pcre_dfa_exec(), to suppress  the
1375           UTF-8 validity checking of subject strings.
1376    
1377    
1378  COMPILATION ERROR CODES  COMPILATION ERROR CODES
1379    
1380         The following table lists the error  codes  than  may  be  returned  by         The  following  table  lists  the  error  codes than may be returned by
1381         pcre_compile2(),  along with the error messages that may be returned by         pcre_compile2(), along with the error messages that may be returned  by
1382         both compiling functions. As PCRE has developed, some error codes  have         both  compiling functions. As PCRE has developed, some error codes have
1383         fallen out of use. To avoid confusion, they have not been re-used.         fallen out of use. To avoid confusion, they have not been re-used.
1384    
1385            0  no error            0  no error
# Line 1242  COMPILATION ERROR CODES Line 1394  COMPILATION ERROR CODES
1394            9  nothing to repeat            9  nothing to repeat
1395           10  [this code is not in use]           10  [this code is not in use]
1396           11  internal error: unexpected repeat           11  internal error: unexpected repeat
1397           12  unrecognized character after (?           12  unrecognized character after (? or (?-
1398           13  POSIX named classes are supported only within a class           13  POSIX named classes are supported only within a class
1399           14  missing )           14  missing )
1400           15  reference to non-existent subpattern           15  reference to non-existent subpattern
# Line 1250  COMPILATION ERROR CODES Line 1402  COMPILATION ERROR CODES
1402           17  unknown option bit(s) set           17  unknown option bit(s) set
1403           18  missing ) after comment           18  missing ) after comment
1404           19  [this code is not in use]           19  [this code is not in use]
1405           20  regular expression too large           20  regular expression is too large
1406           21  failed to get memory           21  failed to get memory
1407           22  unmatched parentheses           22  unmatched parentheses
1408           23  internal error: code overflow           23  internal error: code overflow
# Line 1259  COMPILATION ERROR CODES Line 1411  COMPILATION ERROR CODES
1411           26  malformed number or name after (?(           26  malformed number or name after (?(
1412           27  conditional group contains more than two branches           27  conditional group contains more than two branches
1413           28  assertion expected after (?(           28  assertion expected after (?(
1414           29  (?R or (?digits must be followed by )           29  (?R or (?[+-]digits must be followed by )
1415           30  unknown POSIX class name           30  unknown POSIX class name
1416           31  POSIX collating elements are not supported           31  POSIX collating elements are not supported
1417           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 1279  COMPILATION ERROR CODES Line 1431  COMPILATION ERROR CODES
1431           46  malformed \P or \p sequence           46  malformed \P or \p sequence
1432           47  unknown property name after \P or \p           47  unknown property name after \P or \p
1433           48  subpattern name is too long (maximum 32 characters)           48  subpattern name is too long (maximum 32 characters)
1434           49  too many named subpatterns (maximum 10,000)           49  too many named subpatterns (maximum 10000)
1435           50  repeated subpattern is too long           50  [this code is not in use]
1436           51  octal value is greater than \377 (not in UTF-8 mode)           51  octal value is greater than \377 (not in UTF-8 mode)
1437           52  internal error: overran compiling workspace           52  internal error: overran compiling workspace
1438           53   internal  error:  previously-checked  referenced  subpattern not           53  internal  error:  previously-checked  referenced  subpattern  not
1439         found         found
1440           54  DEFINE group contains more than one branch           54  DEFINE group contains more than one branch
1441           55  repeating a DEFINE group is not allowed           55  repeating a DEFINE group is not allowed
1442           56  inconsistent NEWLINE options"           56  inconsistent NEWLINE options
1443             57  \g is not followed by a braced, angle-bracketed, or quoted
1444                   name/number or by a plain number
1445             58  a numbered reference must not be zero
1446             59  (*VERB) with an argument is not supported
1447             60  (*VERB) not recognized
1448             61  number is too big
1449             62  subpattern name expected
1450             63  digit expected after (?+
1451             64  ] is an invalid data character in JavaScript compatibility mode
1452    
1453           The  numbers  32  and 10000 in errors 48 and 49 are defaults; different
1454           values may be used if the limits were changed when PCRE was built.
1455    
1456    
1457  STUDYING A PATTERN  STUDYING A PATTERN
# Line 1476  INFORMATION ABOUT A PATTERN Line 1640  INFORMATION ABOUT A PATTERN
1640         returned. The fourth argument should point to an unsigned char *  vari-         returned. The fourth argument should point to an unsigned char *  vari-
1641         able.         able.
1642    
1643             PCRE_INFO_HASCRORLF
1644    
1645           Return  1  if  the  pattern  contains any explicit matches for CR or LF
1646           characters, otherwise 0. The fourth argument should  point  to  an  int
1647           variable.  An explicit match is either a literal CR or LF character, or
1648           \r or \n.
1649    
1650           PCRE_INFO_JCHANGED           PCRE_INFO_JCHANGED
1651    
1652         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,
1653         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)
1654         nal option setting changes the local PCRE_DUPNAMES value.         and (?-J) set and unset the local PCRE_DUPNAMES option, respectively.
1655    
1656           PCRE_INFO_LASTLITERAL           PCRE_INFO_LASTLITERAL
1657    
1658         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
1659         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
1660         recorded. The fourth argument should point to an int variable. If there         recorded. The fourth argument should point to an int variable. If there
1661         is no such byte, -1 is returned. For anchored patterns, a last  literal         is  no such byte, -1 is returned. For anchored patterns, a last literal
1662         byte  is  recorded only if it follows something of variable length. For         byte is recorded only if it follows something of variable  length.  For
1663         example, for the pattern /^a\d+z\d+/ the returned value is "z", but for         example, for the pattern /^a\d+z\d+/ the returned value is "z", but for
1664         /^a\dz\d/ the returned value is -1.         /^a\dz\d/ the returned value is -1.
1665    
# Line 1496  INFORMATION ABOUT A PATTERN Line 1667  INFORMATION ABOUT A PATTERN
1667           PCRE_INFO_NAMEENTRYSIZE           PCRE_INFO_NAMEENTRYSIZE
1668           PCRE_INFO_NAMETABLE           PCRE_INFO_NAMETABLE
1669    
1670         PCRE  supports the use of named as well as numbered capturing parenthe-         PCRE supports the use of named as well as numbered capturing  parenthe-
1671         ses. The names are just an additional way of identifying the  parenthe-         ses.  The names are just an additional way of identifying the parenthe-
1672         ses, which still acquire numbers. Several convenience functions such as         ses, which still acquire numbers. Several convenience functions such as
1673         pcre_get_named_substring() are provided for  extracting  captured  sub-         pcre_get_named_substring()  are  provided  for extracting captured sub-
1674         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
1675         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
1676         pointers in the output vector (described with pcre_exec() below). To do         pointers in the output vector (described with pcre_exec() below). To do
1677         the conversion, you need  to  use  the  name-to-number  map,  which  is         the  conversion,  you  need  to  use  the  name-to-number map, which is
1678         described by these three values.         described by these three values.
1679    
1680         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
1681         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
1682         of  each  entry;  both  of  these  return  an int value. The entry size         of each entry; both of these  return  an  int  value.  The  entry  size
1683         depends on the length of the longest name. PCRE_INFO_NAMETABLE  returns         depends  on the length of the longest name. PCRE_INFO_NAMETABLE returns
1684         a  pointer  to  the  first  entry of the table (a pointer to char). The         a pointer to the first entry of the table  (a  pointer  to  char).  The
1685         first two bytes of each entry are the number of the capturing parenthe-         first two bytes of each entry are the number of the capturing parenthe-
1686         sis,  most  significant byte first. The rest of the entry is the corre-         sis, most significant byte first. The rest of the entry is  the  corre-
1687         sponding name, zero terminated. The names are  in  alphabetical  order.         sponding  name,  zero  terminated. The names are in alphabetical order.
1688         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-
1689         theses numbers. For example, consider  the  following  pattern  (assume         theses  numbers.  For  example,  consider the following pattern (assume
1690         PCRE_EXTENDED  is  set,  so  white  space  -  including  newlines  - is         PCRE_EXTENDED is  set,  so  white  space  -  including  newlines  -  is
1691         ignored):         ignored):
1692    
1693           (?<date> (?<year>(\d\d)?\d\d) -           (?<date> (?<year>(\d\d)?\d\d) -
1694           (?<month>\d\d) - (?<day>\d\d) )           (?<month>\d\d) - (?<day>\d\d) )
1695    
1696         There are four named subpatterns, so the table has  four  entries,  and         There  are  four  named subpatterns, so the table has four entries, and
1697         each  entry  in the table is eight bytes long. The table is as follows,         each entry in the table is eight bytes long. The table is  as  follows,
1698         with non-printing bytes shows in hexadecimal, and undefined bytes shown         with non-printing bytes shows in hexadecimal, and undefined bytes shown
1699         as ??:         as ??:
1700    
# Line 1532  INFORMATION ABOUT A PATTERN Line 1703  INFORMATION ABOUT A PATTERN
1703           00 04 m  o  n  t  h  00           00 04 m  o  n  t  h  00
1704           00 02 y  e  a  r  00 ??           00 02 y  e  a  r  00 ??
1705    
1706         When  writing  code  to  extract  data from named subpatterns using the         When writing code to extract data  from  named  subpatterns  using  the
1707         name-to-number map, remember that the length of the entries  is  likely         name-to-number  map,  remember that the length of the entries is likely
1708         to be different for each compiled pattern.         to be different for each compiled pattern.
1709    
1710           PCRE_INFO_OKPARTIAL           PCRE_INFO_OKPARTIAL
1711    
1712         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.
1713         The fourth argument should point to an int  variable.  The  pcrepartial         The  fourth  argument  should point to an int variable. The pcrepartial
1714         documentation  lists  the restrictions that apply to patterns when par-         documentation lists the restrictions that apply to patterns  when  par-
1715         tial matching is used.         tial matching is used.
1716    
1717           PCRE_INFO_OPTIONS           PCRE_INFO_OPTIONS
1718    
1719         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
1720         fourth  argument  should  point to an unsigned long int variable. These         fourth argument should point to an unsigned long  int  variable.  These
1721         option bits are those specified in the call to pcre_compile(), modified         option bits are those specified in the call to pcre_compile(), modified
1722         by any top-level option settings within the pattern itself.         by any top-level option settings at the start of the pattern itself. In
1723           other  words,  they are the options that will be in force when matching
1724           starts. For example, if the pattern /(?im)abc(?-i)d/ is  compiled  with
1725           the  PCRE_EXTENDED option, the result is PCRE_CASELESS, PCRE_MULTILINE,
1726           and PCRE_EXTENDED.
1727    
1728         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
1729         alternatives begin with one of the following:         alternatives begin with one of the following:
1730    
1731           ^     unless PCRE_MULTILINE is set           ^     unless PCRE_MULTILINE is set
# Line 1564  INFORMATION ABOUT A PATTERN Line 1739  INFORMATION ABOUT A PATTERN
1739    
1740           PCRE_INFO_SIZE           PCRE_INFO_SIZE
1741    
1742         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
1743         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
1744         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
1745         size_t variable.         size_t variable.
# Line 1572  INFORMATION ABOUT A PATTERN Line 1747  INFORMATION ABOUT A PATTERN
1747           PCRE_INFO_STUDYSIZE           PCRE_INFO_STUDYSIZE
1748    
1749         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
1750         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
1751         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
1752         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
1753         variable.         variable.
1754    
1755    
# Line 1582  OBSOLETE INFO FUNCTION Line 1757  OBSOLETE INFO FUNCTION
1757    
1758         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
1759    
1760         The pcre_info() function is now obsolete because its interface  is  too         The  pcre_info()  function is now obsolete because its interface is too
1761         restrictive  to return all the available data about a compiled pattern.         restrictive to return all the available data about a compiled  pattern.
1762         New  programs  should  use  pcre_fullinfo()  instead.  The   yield   of         New   programs   should  use  pcre_fullinfo()  instead.  The  yield  of
1763         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-
1764         lowing negative numbers:         lowing negative numbers:
1765    
1766           PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_NULL       the argument code was NULL
1767           PCRE_ERROR_BADMAGIC   the "magic number" was not found           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1768    
1769         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
1770         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
1771         PCRE_INFO_OPTIONS above).         PCRE_INFO_OPTIONS above).
1772    
1773         If the pattern is not anchored and the  firstcharptr  argument  is  not         If  the  pattern  is  not anchored and the firstcharptr argument is not
1774         NULL,  it is used to pass back information about the first character of         NULL, it is used to pass back information about the first character  of
1775         any matched string (see PCRE_INFO_FIRSTBYTE above).         any matched string (see PCRE_INFO_FIRSTBYTE above).
1776    
1777    
# Line 1604  REFERENCE COUNTS Line 1779  REFERENCE COUNTS
1779    
1780         int pcre_refcount(pcre *code, int adjust);         int pcre_refcount(pcre *code, int adjust);
1781    
1782         The pcre_refcount() function is used to maintain a reference  count  in         The  pcre_refcount()  function is used to maintain a reference count in
1783         the data block that contains a compiled pattern. It is provided for the         the data block that contains a compiled pattern. It is provided for the
1784         benefit of applications that  operate  in  an  object-oriented  manner,         benefit  of  applications  that  operate  in an object-oriented manner,
1785         where different parts of the application may be using the same compiled         where different parts of the application may be using the same compiled
1786         pattern, but you want to free the block when they are all done.         pattern, but you want to free the block when they are all done.
1787    
1788         When a pattern is compiled, the reference count field is initialized to         When a pattern is compiled, the reference count field is initialized to
1789         zero.   It is changed only by calling this function, whose action is to         zero.  It is changed only by calling this function, whose action is  to
1790         add the adjust value (which may be positive or  negative)  to  it.  The         add  the  adjust  value  (which may be positive or negative) to it. The
1791         yield of the function is the new value. However, the value of the count         yield of the function is the new value. However, the value of the count
1792         is constrained to lie between 0 and 65535, inclusive. If the new  value         is  constrained to lie between 0 and 65535, inclusive. If the new value
1793         is outside these limits, it is forced to the appropriate limit value.         is outside these limits, it is forced to the appropriate limit value.
1794    
1795         Except  when it is zero, the reference count is not correctly preserved         Except when it is zero, the reference count is not correctly  preserved
1796         if a pattern is compiled on one host and then  transferred  to  a  host         if  a  pattern  is  compiled on one host and then transferred to a host
1797         whose byte-order is different. (This seems a highly unlikely scenario.)         whose byte-order is different. (This seems a highly unlikely scenario.)
1798    
1799    
# Line 1628  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1803  MATCHING A PATTERN: THE TRADITIONAL FUNC
1803              const char *subject, int length, int startoffset,              const char *subject, int length, int startoffset,
1804              int options, int *ovector, int ovecsize);              int options, int *ovector, int ovecsize);
1805    
1806         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
1807         compiled  pattern, which is passed in the code argument. If the pattern         compiled pattern, which is passed in the code argument. If the  pattern
1808         has been studied, the result of the study should be passed in the extra         has been studied, the result of the study should be passed in the extra
1809         argument.  This  function is the main matching facility of the library,         argument. This function is the main matching facility of  the  library,
1810         and it operates in a Perl-like manner. For specialist use there is also         and it operates in a Perl-like manner. For specialist use there is also
1811         an  alternative matching function, which is described below in the sec-         an alternative matching function, which is described below in the  sec-
1812         tion about the pcre_dfa_exec() function.         tion about the pcre_dfa_exec() function.
1813    
1814         In most applications, the pattern will have been compiled (and  option-         In  most applications, the pattern will have been compiled (and option-
1815         ally  studied)  in the same process that calls pcre_exec(). However, it         ally studied) in the same process that calls pcre_exec().  However,  it
1816         is possible to save compiled patterns and study data, and then use them         is possible to save compiled patterns and study data, and then use them
1817         later  in  different processes, possibly even on different hosts. For a         later in different processes, possibly even on different hosts.  For  a
1818         discussion about this, see the pcreprecompile documentation.         discussion about this, see the pcreprecompile documentation.
1819    
1820         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 1833  MATCHING A PATTERN: THE TRADITIONAL FUNC
1833    
1834     Extra data for pcre_exec()     Extra data for pcre_exec()
1835    
1836         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
1837         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
1838         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-
1839         tional  information  in it. The pcre_extra block contains the following         tional information in it. The pcre_extra block contains  the  following
1840         fields (not necessarily in this order):         fields (not necessarily in this order):
1841    
1842           unsigned long int flags;           unsigned long int flags;
# Line 1671  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1846  MATCHING A PATTERN: THE TRADITIONAL FUNC
1846           void *callout_data;           void *callout_data;
1847           const unsigned char *tables;           const unsigned char *tables;
1848    
1849         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
1850         are set. The flag bits are:         are set. The flag bits are:
1851    
1852           PCRE_EXTRA_STUDY_DATA           PCRE_EXTRA_STUDY_DATA
# Line 1680  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1855  MATCHING A PATTERN: THE TRADITIONAL FUNC
1855           PCRE_EXTRA_CALLOUT_DATA           PCRE_EXTRA_CALLOUT_DATA
1856           PCRE_EXTRA_TABLES           PCRE_EXTRA_TABLES
1857    
1858         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
1859         the pcre_extra block that is returned by  pcre_study(),  together  with         the  pcre_extra  block  that is returned by pcre_study(), together with
1860         the appropriate flag bit. You should not set this yourself, but you may         the appropriate flag bit. You should not set this yourself, but you may
1861         add to the block by setting the other fields  and  their  corresponding         add  to  the  block by setting the other fields and their corresponding
1862         flag bits.         flag bits.
1863    
1864         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
1865         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
1866         match,  but  which  have  a very large number of possibilities in their         match, but which have a very large number  of  possibilities  in  their
1867         search trees. The classic  example  is  the  use  of  nested  unlimited         search  trees.  The  classic  example  is  the  use of nested unlimited
1868         repeats.         repeats.
1869    
1870         Internally,  PCRE uses a function called match() which it calls repeat-         Internally, PCRE uses a function called match() which it calls  repeat-
1871         edly (sometimes recursively). The limit set by match_limit  is  imposed         edly  (sometimes  recursively). The limit set by match_limit is imposed
1872         on  the  number  of times this function is called during a match, which         on the number of times this function is called during  a  match,  which
1873         has the effect of limiting the amount of  backtracking  that  can  take         has  the  effect  of  limiting the amount of backtracking that can take
1874         place. For patterns that are not anchored, the count restarts from zero         place. For patterns that are not anchored, the count restarts from zero
1875         for each position in the subject string.         for each position in the subject string.
1876    
1877         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
1878         default  default  is 10 million, which handles all but the most extreme         default default is 10 million, which handles all but the  most  extreme
1879         cases. You can override the default  by  suppling  pcre_exec()  with  a         cases.  You  can  override  the  default by suppling pcre_exec() with a
1880         pcre_extra     block    in    which    match_limit    is    set,    and         pcre_extra    block    in    which    match_limit    is    set,     and
1881         PCRE_EXTRA_MATCH_LIMIT is set in the  flags  field.  If  the  limit  is         PCRE_EXTRA_MATCH_LIMIT  is  set  in  the  flags  field. If the limit is
1882         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1883    
1884         The  match_limit_recursion field is similar to match_limit, but instead         The match_limit_recursion field is similar to match_limit, but  instead
1885         of limiting the total number of times that match() is called, it limits         of limiting the total number of times that match() is called, it limits
1886         the  depth  of  recursion. The recursion depth is a smaller number than         the depth of recursion. The recursion depth is a  smaller  number  than
1887         the total number of calls, because not all calls to match() are  recur-         the  total number of calls, because not all calls to match() are recur-
1888         sive.  This limit is of use only if it is set smaller than match_limit.         sive.  This limit is of use only if it is set smaller than match_limit.
1889    
1890         Limiting the recursion depth limits the amount of  stack  that  can  be         Limiting  the  recursion  depth  limits the amount of stack that can be
1891         used, or, when PCRE has been compiled to use memory on the heap instead         used, or, when PCRE has been compiled to use memory on the heap instead
1892         of the stack, the amount of heap memory that can be used.         of the stack, the amount of heap memory that can be used.
1893    
1894         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
1895         built;  the  default  default  is  the  same  value  as the default for         built; the default default  is  the  same  value  as  the  default  for
1896         match_limit. You can override the default by suppling pcre_exec()  with         match_limit.  You can override the default by suppling pcre_exec() with
1897         a   pcre_extra   block  in  which  match_limit_recursion  is  set,  and         a  pcre_extra  block  in  which  match_limit_recursion  is   set,   and
1898         PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in  the  flags  field.  If  the         PCRE_EXTRA_MATCH_LIMIT_RECURSION  is  set  in  the  flags field. If the
1899         limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.         limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1900    
1901         The  pcre_callout  field is used in conjunction with the "callout" fea-         The pcre_callout field is used in conjunction with the  "callout"  fea-
1902         ture, which is described in the pcrecallout documentation.         ture, which is described in the pcrecallout documentation.
1903    
1904         The tables field  is  used  to  pass  a  character  tables  pointer  to         The  tables  field  is  used  to  pass  a  character  tables pointer to
1905         pcre_exec();  this overrides the value that is stored with the compiled         pcre_exec(); this overrides the value that is stored with the  compiled
1906         pattern. A non-NULL value is stored with the compiled pattern  only  if         pattern.  A  non-NULL value is stored with the compiled pattern only if
1907         custom  tables  were  supplied to pcre_compile() via its tableptr argu-         custom tables were supplied to pcre_compile() via  its  tableptr  argu-
1908         ment.  If NULL is passed to pcre_exec() using this mechanism, it forces         ment.  If NULL is passed to pcre_exec() using this mechanism, it forces
1909         PCRE's  internal  tables  to be used. This facility is helpful when re-         PCRE's internal tables to be used. This facility is  helpful  when  re-
1910         using patterns that have been saved after compiling  with  an  external         using  patterns  that  have been saved after compiling with an external
1911         set  of  tables,  because  the  external tables might be at a different         set of tables, because the external tables  might  be  at  a  different
1912         address when pcre_exec() is called. See the  pcreprecompile  documenta-         address  when  pcre_exec() is called. See the pcreprecompile documenta-
1913         tion for a discussion of saving compiled patterns for later use.         tion for a discussion of saving compiled patterns for later use.
1914    
1915     Option bits for pcre_exec()     Option bits for pcre_exec()
1916    
1917         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.
1918         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,
1919         PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and         PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and
1920         PCRE_PARTIAL.         PCRE_PARTIAL.
1921    
1922           PCRE_ANCHORED           PCRE_ANCHORED
1923    
1924         The PCRE_ANCHORED option limits pcre_exec() to matching  at  the  first         The  PCRE_ANCHORED  option  limits pcre_exec() to matching at the first
1925         matching  position.  If  a  pattern was compiled with PCRE_ANCHORED, or         matching position. If a pattern was  compiled  with  PCRE_ANCHORED,  or
1926         turned out to be anchored by virtue of its contents, it cannot be  made         turned  out to be anchored by virtue of its contents, it cannot be made
1927         unachored at matching time.         unachored at matching time.
1928    
1929             PCRE_BSR_ANYCRLF
1930             PCRE_BSR_UNICODE
1931    
1932           These options (which are mutually exclusive) control what the \R escape
1933           sequence  matches.  The choice is either to match only CR, LF, or CRLF,
1934           or to match any Unicode newline sequence. These  options  override  the
1935           choice that was made or defaulted when the pattern was compiled.
1936    
1937           PCRE_NEWLINE_CR           PCRE_NEWLINE_CR
1938           PCRE_NEWLINE_LF           PCRE_NEWLINE_LF
1939           PCRE_NEWLINE_CRLF           PCRE_NEWLINE_CRLF
# Line 1762  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1945  MATCHING A PATTERN: THE TRADITIONAL FUNC
1945         tion  of  pcre_compile()  above.  During  matching,  the newline choice         tion  of  pcre_compile()  above.  During  matching,  the newline choice
1946         affects the behaviour of the dot, circumflex,  and  dollar  metacharac-         affects the behaviour of the dot, circumflex,  and  dollar  metacharac-
1947         ters.  It may also alter the way the match position is advanced after a         ters.  It may also alter the way the match position is advanced after a
1948         match  failure  for  an  unanchored  pattern.  When  PCRE_NEWLINE_CRLF,         match failure for an unanchored pattern.
1949         PCRE_NEWLINE_ANYCRLF,  or  PCRE_NEWLINE_ANY is set, and a match attempt  
1950         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
1951         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-
1952         after the CRLF.         rent position is at a  CRLF  sequence,  and  the  pattern  contains  no
1953           explicit  matches  for  CR  or  LF  characters,  the  match position is
1954           advanced by two characters instead of one, in other words, to after the
1955           CRLF.
1956    
1957           The above rule is a compromise that makes the most common cases work as
1958           expected. For example, if the  pattern  is  .+A  (and  the  PCRE_DOTALL
1959           option is not set), it does not match the string "\r\nA" because, after
1960           failing at the start, it skips both the CR and the LF before  retrying.
1961           However,  the  pattern  [\r\n]A does match that string, because it con-
1962           tains an explicit CR or LF reference, and so advances only by one char-
1963           acter after the first failure.
1964    
1965           An explicit match for CR of LF is either a literal appearance of one of
1966           those characters, or one of the \r or  \n  escape  sequences.  Implicit
1967           matches  such  as [^X] do not count, nor does \s (which includes CR and
1968           LF in the characters that it matches).
1969    
1970           Notwithstanding the above, anomalous effects may still occur when  CRLF
1971           is a valid newline sequence and explicit \r or \n escapes appear in the
1972           pattern.
1973    
1974           PCRE_NOTBOL           PCRE_NOTBOL
1975    
# Line 1813  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2016  MATCHING A PATTERN: THE TRADITIONAL FUNC
2016         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
2017         UTF-8  string is automatically checked when pcre_exec() is subsequently         UTF-8  string is automatically checked when pcre_exec() is subsequently
2018         called.  The value of startoffset is also checked  to  ensure  that  it         called.  The value of startoffset is also checked  to  ensure  that  it
2019         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
2020         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
2021         startoffset  contains  an  invalid  value, PCRE_ERROR_BADUTF8_OFFSET is         main  pcre  page.  If  an  invalid  UTF-8  sequence  of bytes is found,
2022         returned.         pcre_exec() returns the error PCRE_ERROR_BADUTF8. If  startoffset  con-
2023           tains an invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.
2024         If you already know that your subject is valid, and you  want  to  skip  
2025         these    checks    for   performance   reasons,   you   can   set   the         If  you  already  know that your subject is valid, and you want to skip
2026         PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might  want  to         these   checks   for   performance   reasons,   you   can    set    the
2027         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
2028         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
2029         string.  However,  you  should  be  sure  that the value of startoffset         making  repeated  calls  to  find  all  the matches in a single subject
2030         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
2031         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
2032         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
2033           value  of startoffset that does not point to the start of a UTF-8 char-
2034         acter, is undefined. Your program may crash.         acter, is undefined. Your program may crash.
2035    
2036           PCRE_PARTIAL           PCRE_PARTIAL
2037    
2038         This  option  turns  on  the  partial  matching feature. If the subject         This option turns on the  partial  matching  feature.  If  the  subject
2039         string fails to match the pattern, but at some point during the  match-         string  fails to match the pattern, but at some point during the match-
2040         ing  process  the  end of the subject was reached (that is, the subject         ing process the end of the subject was reached (that  is,  the  subject
2041         partially matches the pattern and the failure to  match  occurred  only         partially  matches  the  pattern and the failure to match occurred only
2042         because  there were not enough subject characters), pcre_exec() returns         because there were not enough subject characters), pcre_exec()  returns
2043         PCRE_ERROR_PARTIAL instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL  is         PCRE_ERROR_PARTIAL  instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is
2044         used,  there  are restrictions on what may appear in the pattern. These         used, there are restrictions on what may appear in the  pattern.  These
2045         are discussed in the pcrepartial documentation.         are discussed in the pcrepartial documentation.
2046    
2047     The string to be matched by pcre_exec()     The string to be matched by pcre_exec()
2048    
2049         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
2050         length  in  length, and a starting byte offset in startoffset. In UTF-8         length (in bytes) in length, and a starting byte offset in startoffset.
2051         mode, the byte offset must point to the start  of  a  UTF-8  character.         In UTF-8 mode, the byte offset must point to the start of a UTF-8 char-
2052         Unlike  the  pattern string, the subject may contain binary zero bytes.         acter. Unlike the pattern string, the subject may contain  binary  zero
2053         When the starting offset is zero, the search for a match starts at  the         bytes.  When the starting offset is zero, the search for a match starts
2054         beginning of the subject, and this is by far the most common case.         at the beginning of the subject, and this is by  far  the  most  common
2055           case.
2056    
2057         A  non-zero  starting offset is useful when searching for another match         A  non-zero  starting offset is useful when searching for another match
2058         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-
# Line 1883  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2088  MATCHING A PATTERN: THE TRADITIONAL FUNC
2088         string. PCRE supports several other kinds of  parenthesized  subpattern         string. PCRE supports several other kinds of  parenthesized  subpattern
2089         that do not cause substrings to be captured.         that do not cause substrings to be captured.
2090    
2091         Captured  substrings are returned to the caller via a vector of integer         Captured substrings are returned to the caller via a vector of integers
2092         offsets whose address is passed in ovector. The number of  elements  in         whose address is passed in ovector. The number of elements in the  vec-
2093         the  vector is passed in ovecsize, which must be a non-negative number.         tor  is  passed in ovecsize, which must be a non-negative number. Note:
2094         Note: this argument is NOT the size of ovector in bytes.         this argument is NOT the size of ovector in bytes.
2095    
2096         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-
2097         strings,  each  substring using a pair of integers. The remaining third         strings,  each  substring using a pair of integers. The remaining third
2098         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-
2099         turing  subpatterns, and is not available for passing back information.         turing  subpatterns, and is not available for passing back information.
2100         The length passed in ovecsize should always be a multiple of three.  If         The number passed in ovecsize should always be a multiple of three.  If
2101         it is not, it is rounded down.         it is not, it is rounded down.
2102    
2103         When  a  match  is successful, information about captured substrings is         When  a  match  is successful, information about captured substrings is
2104         returned in pairs of integers, starting at the  beginning  of  ovector,         returned in pairs of integers, starting at the  beginning  of  ovector,
2105         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
2106         element of a pair is set to the offset of the first character in a sub-         element of each pair is set to the byte offset of the  first  character
2107         string,  and  the  second  is  set to the offset of the first character         in  a  substring, and the second is set to the byte offset of the first
2108         after the end of a substring. The  first  pair,  ovector[0]  and  ovec-         character after the end of a substring. Note: these values  are  always
2109         tor[1],  identify  the  portion  of  the  subject string matched by the         byte offsets, even in UTF-8 mode. They are not character counts.
2110         entire pattern. The next pair is used for the first  capturing  subpat-  
2111         tern, and so on. The value returned by pcre_exec() is one more than the         The  first  pair  of  integers, ovector[0] and ovector[1], identify the
2112         highest numbered pair that has been set. For example, if two substrings         portion of the subject string matched by the entire pattern.  The  next
2113         have  been captured, the returned value is 3. If there are no capturing         pair  is  used for the first capturing subpattern, and so on. The value
2114         subpatterns, the return value from a successful match is 1,  indicating         returned by pcre_exec() is one more than the highest numbered pair that
2115         that just the first pair of offsets has been set.         has  been  set.  For example, if two substrings have been captured, the
2116           returned value is 3. If there are no capturing subpatterns, the  return
2117           value from a successful match is 1, indicating that just the first pair
2118           of offsets has been set.
2119    
2120         If a capturing subpattern is matched repeatedly, it is the last portion         If a capturing subpattern is matched repeatedly, it is the last portion
2121         of the string that it matched that is returned.         of the string that it matched that is returned.
2122    
2123         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,
2124         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
2125         function returns a value of zero. In particular, if the substring  off-         function  returns  a value of zero. If the substring offsets are not of
2126         sets are not of interest, pcre_exec() may be called with ovector passed         interest, pcre_exec() may be called with ovector  passed  as  NULL  and
2127         as NULL and ovecsize as zero. However, if  the  pattern  contains  back         ovecsize  as zero. However, if the pattern contains back references and
2128         references  and  the  ovector is not big enough to remember the related         the ovector is not big enough to remember the related substrings,  PCRE
2129         substrings, PCRE has to get additional memory for use during  matching.         has  to  get additional memory for use during matching. Thus it is usu-
2130         Thus it is usually advisable to supply an ovector.         ally advisable to supply an ovector.
2131    
2132         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
2133         subpatterns there are in a compiled  pattern.  The  smallest  size  for         subpatterns  there  are  in  a  compiled pattern. The smallest size for
2134         ovector  that  will allow for n captured substrings, in addition to the         ovector that will allow for n captured substrings, in addition  to  the
2135         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.
2136    
2137         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
2138         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,
2139         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
2140         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
2141         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-
2142         sponding to unused subpatterns are set to -1.         sponding to unused subpatterns are set to -1.
2143    
2144         Offset  values  that correspond to unused subpatterns at the end of the         Offset values that correspond to unused subpatterns at the end  of  the
2145         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
2146         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
2147         matched. The return from the function is 2, because  the  highest  used         matched.  The  return  from the function is 2, because the highest used
2148         capturing subpattern number is 1. However, you can refer to the offsets         capturing subpattern number is 1. However, you can refer to the offsets
2149         for the second and third capturing subpatterns if  you  wish  (assuming         for  the  second  and third capturing subpatterns if you wish (assuming
2150         the vector is large enough, of course).         the vector is large enough, of course).
2151    
2152         Some  convenience  functions  are  provided for extracting the captured         Some convenience functions are provided  for  extracting  the  captured
2153         substrings as separate strings. These are described below.         substrings as separate strings. These are described below.
2154    
2155     Error return values from pcre_exec()     Error return values from pcre_exec()
2156    
2157         If pcre_exec() fails, it returns a negative number. The  following  are         If  pcre_exec()  fails, it returns a negative number. The following are
2158         defined in the header file:         defined in the header file:
2159    
2160           PCRE_ERROR_NOMATCH        (-1)           PCRE_ERROR_NOMATCH        (-1)
# Line 1955  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2163  MATCHING A PATTERN: THE TRADITIONAL FUNC
2163    
2164           PCRE_ERROR_NULL           (-2)           PCRE_ERROR_NULL           (-2)
2165    
2166         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
2167         ovecsize was not zero.         ovecsize was not zero.
2168    
2169           PCRE_ERROR_BADOPTION      (-3)           PCRE_ERROR_BADOPTION      (-3)
# Line 1964  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2172  MATCHING A PATTERN: THE TRADITIONAL FUNC
2172    
2173           PCRE_ERROR_BADMAGIC       (-4)           PCRE_ERROR_BADMAGIC       (-4)
2174    
2175         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,
2176         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
2177         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
2178         an  environment  with the other endianness. This is the error that PCRE         an environment with the other endianness. This is the error  that  PCRE
2179         gives when the magic number is not present.         gives when the magic number is not present.
2180    
2181           PCRE_ERROR_UNKNOWN_OPCODE (-5)           PCRE_ERROR_UNKNOWN_OPCODE (-5)
2182    
2183         While running the pattern match, an unknown item was encountered in the         While running the pattern match, an unknown item was encountered in the
2184         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
2185         overwriting of the compiled pattern.         overwriting of the compiled pattern.
2186    
2187           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2188    
2189         If a pattern contains back references, but the ovector that  is  passed         If  a  pattern contains back references, but the ovector that is passed
2190         to pcre_exec() is not big enough to remember the referenced substrings,         to pcre_exec() is not big enough to remember the referenced substrings,
2191         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
2192         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
2193         memory is automatically freed at the end of matching.         memory is automatically freed at the end of matching.
2194    
2195           PCRE_ERROR_NOSUBSTRING    (-7)           PCRE_ERROR_NOSUBSTRING    (-7)
2196    
2197         This error is used by the pcre_copy_substring(),  pcre_get_substring(),         This  error is used by the pcre_copy_substring(), pcre_get_substring(),
2198         and  pcre_get_substring_list()  functions  (see  below).  It  is  never         and  pcre_get_substring_list()  functions  (see  below).  It  is  never
2199         returned by pcre_exec().         returned by pcre_exec().
2200    
2201           PCRE_ERROR_MATCHLIMIT     (-8)           PCRE_ERROR_MATCHLIMIT     (-8)
2202    
2203         The backtracking limit, as specified by  the  match_limit  field  in  a         The  backtracking  limit,  as  specified  by the match_limit field in a
2204         pcre_extra  structure  (or  defaulted) was reached. See the description         pcre_extra structure (or defaulted) was reached.  See  the  description
2205         above.         above.
2206    
2207           PCRE_ERROR_CALLOUT        (-9)           PCRE_ERROR_CALLOUT        (-9)
2208    
2209         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
2210         use  by  callout functions that want to yield a distinctive error code.         use by callout functions that want to yield a distinctive  error  code.
2211         See the pcrecallout documentation for details.         See the pcrecallout documentation for details.
2212    
2213           PCRE_ERROR_BADUTF8        (-10)           PCRE_ERROR_BADUTF8        (-10)
2214    
2215         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
2216         subject.         subject.
2217    
2218           PCRE_ERROR_BADUTF8_OFFSET (-11)           PCRE_ERROR_BADUTF8_OFFSET (-11)
2219    
2220         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
2221         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-
2222         ter.         ter.
2223    
2224           PCRE_ERROR_PARTIAL        (-12)           PCRE_ERROR_PARTIAL        (-12)
2225    
2226         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
2227         pcrepartial documentation for details of partial matching.         pcrepartial documentation for details of partial matching.
2228    
2229           PCRE_ERROR_BADPARTIAL     (-13)           PCRE_ERROR_BADPARTIAL     (-13)
2230    
2231         The PCRE_PARTIAL option was used with  a  compiled  pattern  containing         The  PCRE_PARTIAL  option  was  used with a compiled pattern containing
2232         items  that are not supported for partial matching. See the pcrepartial         items that are not supported for partial matching. See the  pcrepartial
2233         documentation for details of partial matching.         documentation for details of partial matching.
2234    
2235           PCRE_ERROR_INTERNAL       (-14)           PCRE_ERROR_INTERNAL       (-14)
2236    
2237         An unexpected internal error has occurred. This error could  be  caused         An  unexpected  internal error has occurred. This error could be caused
2238         by a bug in PCRE or by overwriting of the compiled pattern.         by a bug in PCRE or by overwriting of the compiled pattern.
2239    
2240           PCRE_ERROR_BADCOUNT       (-15)           PCRE_ERROR_BADCOUNT       (-15)
2241    
2242         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.
2243    
2244           PCRE_ERROR_RECURSIONLIMIT (-21)           PCRE_ERROR_RECURSIONLIMIT (-21)
2245    
2246         The internal recursion limit, as specified by the match_limit_recursion         The internal recursion limit, as specified by the match_limit_recursion
2247         field  in  a  pcre_extra  structure (or defaulted) was reached. See the         field in a pcre_extra structure (or defaulted)  was  reached.  See  the
2248         description above.         description above.
2249    
          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.  
   
2250           PCRE_ERROR_BADNEWLINE     (-23)           PCRE_ERROR_BADNEWLINE     (-23)
2251    
2252         An invalid combination of PCRE_NEWLINE_xxx options was given.         An invalid combination of PCRE_NEWLINE_xxx options was given.
2253    
2254         Error numbers -16 to -20 are not used by pcre_exec().         Error numbers -16 to -20 and -22 are not used by pcre_exec().
2255    
2256    
2257  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
# Line 2067  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2267  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2267         int pcre_get_substring_list(const char *subject,         int pcre_get_substring_list(const char *subject,
2268              int *ovector, int stringcount, const char ***listptr);              int *ovector, int stringcount, const char ***listptr);
2269    
2270         Captured substrings can be  accessed  directly  by  using  the  offsets         Captured  substrings  can  be  accessed  directly  by using the offsets
2271         returned  by  pcre_exec()  in  ovector.  For convenience, the functions         returned by pcre_exec() in  ovector.  For  convenience,  the  functions
2272         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-
2273         string_list()  are  provided for extracting captured substrings as new,         string_list() are provided for extracting captured substrings  as  new,
2274         separate, zero-terminated strings. These functions identify  substrings         separate,  zero-terminated strings. These functions identify substrings
2275         by  number.  The  next section describes functions for extracting named         by number. The next section describes functions  for  extracting  named
2276         substrings.         substrings.
2277    
2278         A substring that contains a binary zero is correctly extracted and  has         A  substring that contains a binary zero is correctly extracted and has
2279         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
2280         string.  However, you can process such a string  by  referring  to  the         string.   However,  you  can  process such a string by referring to the
2281         length  that  is  returned  by  pcre_copy_substring() and pcre_get_sub-         length that is  returned  by  pcre_copy_substring()  and  pcre_get_sub-
2282         string().  Unfortunately, the interface to pcre_get_substring_list() is         string().  Unfortunately, the interface to pcre_get_substring_list() is
2283         not  adequate for handling strings containing binary zeros, because the         not adequate for handling strings containing binary zeros, because  the
2284         end of the final string is not independently indicated.         end of the final string is not independently indicated.
2285    
2286         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-
2287         tions:  subject  is  the subject string that has just been successfully         tions: subject is the subject string that has  just  been  successfully
2288         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
2289         passed to pcre_exec(), and stringcount is the number of substrings that         passed to pcre_exec(), and stringcount is the number of substrings that
2290         were captured by the match, including the substring  that  matched  the         were  captured  by  the match, including the substring that matched the
2291         entire regular expression. This is the value returned by pcre_exec() if         entire regular expression. This is the value returned by pcre_exec() if
2292         it is greater than zero. If pcre_exec() returned zero, indicating  that         it  is greater than zero. If pcre_exec() returned zero, indicating that
2293         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
2294         be the number of elements in the vector divided by three.         be the number of elements in the vector divided by three.
2295    
2296         The functions pcre_copy_substring() and pcre_get_substring() extract  a         The  functions pcre_copy_substring() and pcre_get_substring() extract a
2297         single  substring,  whose  number  is given as stringnumber. A value of         single substring, whose number is given as  stringnumber.  A  value  of
2298         zero extracts the substring that matched the  entire  pattern,  whereas         zero  extracts  the  substring that matched the entire pattern, whereas
2299         higher  values  extract  the  captured  substrings.  For pcre_copy_sub-         higher values  extract  the  captured  substrings.  For  pcre_copy_sub-
2300         string(), the string is placed in buffer,  whose  length  is  given  by         string(),  the  string  is  placed  in buffer, whose length is given by
2301         buffersize,  while  for  pcre_get_substring()  a new block of memory is         buffersize, while for pcre_get_substring() a new  block  of  memory  is
2302         obtained via pcre_malloc, and its address is  returned  via  stringptr.         obtained  via  pcre_malloc,  and its address is returned via stringptr.
2303         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
2304         the terminating zero, or one of these error codes:         the terminating zero, or one of these error codes:
2305    
2306           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2307    
2308         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
2309         get memory failed for pcre_get_substring().         get memory failed for pcre_get_substring().
2310    
2311           PCRE_ERROR_NOSUBSTRING    (-7)           PCRE_ERROR_NOSUBSTRING    (-7)
2312    
2313         There is no substring whose number is stringnumber.         There is no substring whose number is stringnumber.
2314    
2315         The  pcre_get_substring_list()  function  extracts  all  available sub-         The pcre_get_substring_list()  function  extracts  all  available  sub-
2316         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
2317         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
2318         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
2319         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
2320         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
2321         error code         error code
2322    
2323           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2324    
2325         if the attempt to get the memory block failed.         if the attempt to get the memory block failed.
2326    
2327         When  any of these functions encounter a substring that is unset, which         When any of these functions encounter a substring that is unset,  which
2328         can happen when capturing subpattern number n+1 matches  some  part  of         can  happen  when  capturing subpattern number n+1 matches some part of
2329         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
2330         empty string. This can be distinguished from a genuine zero-length sub-         empty string. This can be distinguished from a genuine zero-length sub-
2331         string  by inspecting the appropriate offset in ovector, which is nega-         string by inspecting the appropriate offset in ovector, which is  nega-
2332         tive for unset substrings.         tive for unset substrings.
2333    
2334         The two convenience functions pcre_free_substring() and  pcre_free_sub-         The  two convenience functions pcre_free_substring() and pcre_free_sub-
2335         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
2336         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-
2337         tively.  They  do  nothing  more  than  call the function pointed to by         tively. They do nothing more than  call  the  function  pointed  to  by
2338         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.
2339         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-
2340         cial  interface  to  another  programming  language  that  cannot   use         cial   interface  to  another  programming  language  that  cannot  use
2341         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-
2342         vided.         vided.
2343    
2344    
# Line 2157  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2357  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2357              int stringcount, const char *stringname,              int stringcount, const char *stringname,
2358              const char **stringptr);              const char **stringptr);
2359    
2360         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-
2361         ber.  For example, for this pattern         ber.  For example, for this pattern
2362    
2363           (a+)b(?<xxx>\d+)...           (a+)b(?<xxx>\d+)...
# Line 2166  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2366  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2366         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
2367         name by calling pcre_get_stringnumber(). The first argument is the com-         name by calling pcre_get_stringnumber(). The first argument is the com-
2368         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
2369         the  subpattern  number,  or PCRE_ERROR_NOSUBSTRING (-7) if there is no         the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if  there  is  no
2370         subpattern of that name.         subpattern of that name.
2371    
2372         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
2373         the functions described in the previous section. For convenience, there         the functions described in the previous section. For convenience, there
2374         are also two functions that do the whole job.         are also two functions that do the whole job.
2375    
2376         Most   of   the   arguments    of    pcre_copy_named_substring()    and         Most    of    the    arguments   of   pcre_copy_named_substring()   and
2377         pcre_get_named_substring()  are  the  same  as  those for the similarly         pcre_get_named_substring() are the same  as  those  for  the  similarly
2378         named functions that extract by number. As these are described  in  the         named  functions  that extract by number. As these are described in the
2379         previous  section,  they  are not re-described here. There are just two         previous section, they are not re-described here. There  are  just  two
2380         differences:         differences:
2381    
2382         First, instead of a substring number, a substring name is  given.  Sec-         First,  instead  of a substring number, a substring name is given. Sec-
2383         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
2384         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
2385         name-to-number translation table.         name-to-number translation table.
2386    
2387         These  functions call pcre_get_stringnumber(), and if it succeeds, they         These functions call pcre_get_stringnumber(), and if it succeeds,  they
2388         then call pcre_copy_substring() or pcre_get_substring(),  as  appropri-         then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-
2389         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
2390         behaviour may not be what you want (see the next section).         behaviour may not be what you want (see the next section).
2391    
2392    
# Line 2195  DUPLICATE SUBPATTERN NAMES Line 2395  DUPLICATE SUBPATTERN NAMES
2395         int pcre_get_stringtable_entries(const pcre *code,         int pcre_get_stringtable_entries(const pcre *code,
2396              const char *name, char **first, char **last);              const char *name, char **first, char **last);
2397    
2398         When a pattern is compiled with the  PCRE_DUPNAMES  option,  names  for         When  a  pattern  is  compiled with the PCRE_DUPNAMES option, names for
2399         subpatterns  are  not  required  to  be unique. Normally, patterns with         subpatterns are not required to  be  unique.  Normally,  patterns  with
2400         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
2401         subpatterns  participates. An example is shown in the pcrepattern docu-         subpatterns participates. An example is shown in the pcrepattern  docu-
2402         mentation. When duplicates are present, pcre_copy_named_substring() and         mentation.
        pcre_get_named_substring()  return the first substring corresponding to  
        the given name that is set.  If  none  are  set,  an  empty  string  is  
        returned.  The pcre_get_stringnumber() function returns one of the num-  
        bers that are associated with the name, but it is not defined which  it  
        is.  
2403    
2404         If  you want to get full details of all captured substrings for a given         When    duplicates   are   present,   pcre_copy_named_substring()   and
2405         name, you must use  the  pcre_get_stringtable_entries()  function.  The         pcre_get_named_substring() return the first substring corresponding  to
2406           the  given  name  that  is set. If none are set, PCRE_ERROR_NOSUBSTRING
2407           (-7) is returned; no  data  is  returned.  The  pcre_get_stringnumber()
2408           function  returns one of the numbers that are associated with the name,
2409           but it is not defined which it is.
2410    
2411           If you want to get full details of all captured substrings for a  given
2412           name,  you  must  use  the pcre_get_stringtable_entries() function. The
2413         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
2414         third and fourth are pointers to variables which  are  updated  by  the         third  and  fourth  are  pointers to variables which are updated by the
2415         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
2416         the name-to-number table  for  the  given  name.  The  function  itself         the  name-to-number  table  for  the  given  name.  The function itself
2417         returns  the  length  of  each entry, or PCRE_ERROR_NOSUBSTRING (-7) if         returns the length of each entry,  or  PCRE_ERROR_NOSUBSTRING  (-7)  if
2418         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-
2419         tion  entitled  Information  about  a  pattern.  Given all the relevant         tion entitled Information about a  pattern.   Given  all  the  relevant
2420         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
2421         the captured data, if any.         the captured data, if any.
2422    
2423    
2424  FINDING ALL POSSIBLE MATCHES  FINDING ALL POSSIBLE MATCHES
2425    
2426         The  traditional  matching  function  uses a similar algorithm to Perl,         The traditional matching function uses a  similar  algorithm  to  Perl,
2427         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
2428         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
2429         possible match, consider using the alternative matching  function  (see         possible  match,  consider using the alternative matching function (see
2430         below)  instead.  If you cannot use the alternative function, but still         below) instead. If you cannot use the alternative function,  but  still
2431         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
2432         of the callout facility, which is described in the pcrecallout documen-         of the callout facility, which is described in the pcrecallout documen-
2433         tation.         tation.
2434    
2435         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-
2436         tern.   When your callout function is called, extract and save the cur-         tern.  When your callout function is called, extract and save the  cur-
2437         rent matched substring. Then return  1,  which  forces  pcre_exec()  to         rent  matched  substring.  Then  return  1, which forces pcre_exec() to
2438         backtrack  and  try other alternatives. Ultimately, when it runs out of         backtrack and try other alternatives. Ultimately, when it runs  out  of
2439         matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.         matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
2440    
2441    
# Line 2244  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2446  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2446              int options, int *ovector, int ovecsize,              int options, int *ovector, int ovecsize,
2447              int *workspace, int wscount);              int *workspace, int wscount);
2448    
2449         The function pcre_dfa_exec()  is  called  to  match  a  subject  string         The  function  pcre_dfa_exec()  is  called  to  match  a subject string
2450         against  a  compiled pattern, using a matching algorithm that scans the         against a compiled pattern, using a matching algorithm that  scans  the
2451         subject string just once, and does not backtrack.  This  has  different         subject  string  just  once, and does not backtrack. This has different
2452         characteristics  to  the  normal  algorithm, and is not compatible with         characteristics to the normal algorithm, and  is  not  compatible  with
2453         Perl. Some of the features of PCRE patterns are not  supported.  Never-         Perl.  Some  of the features of PCRE patterns are not supported. Never-
2454         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
2455         a discussion of the two matching algorithms, see the pcrematching docu-         a discussion of the two matching algorithms, see the pcrematching docu-
2456         mentation.         mentation.
2457    
2458         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
2459         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-
2460         ent  way,  and  this is described below. The other common arguments are         ent way, and this is described below. The other  common  arguments  are
2461         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
2462         repeated here.         repeated here.
2463    
2464         The  two  additional  arguments provide workspace for the function. The         The two additional arguments provide workspace for  the  function.  The
2465         workspace vector should contain at least 20 elements. It  is  used  for         workspace  vector  should  contain at least 20 elements. It is used for
2466         keeping  track  of  multiple  paths  through  the  pattern  tree.  More         keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2467         workspace will be needed for patterns and subjects where  there  are  a         workspace  will  be  needed for patterns and subjects where there are a
2468         lot of potential matches.         lot of potential matches.
2469    
2470         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 2486  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2486    
2487     Option bits for pcre_dfa_exec()     Option bits for pcre_dfa_exec()
2488    
2489         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
2490         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-
2491         LINE_xxx,  PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK,         LINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,  PCRE_NO_UTF8_CHECK,
2492         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
2493         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
2494         not repeated here.         not repeated here.
2495    
2496           PCRE_PARTIAL           PCRE_PARTIAL
2497    
2498         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
2499         details   are   slightly   different.  When  PCRE_PARTIAL  is  set  for         details  are  slightly  different.  When  PCRE_PARTIAL   is   set   for
2500         pcre_dfa_exec(), the return code PCRE_ERROR_NOMATCH is  converted  into         pcre_dfa_exec(),  the  return code PCRE_ERROR_NOMATCH is converted into
2501         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
2502         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-
2503         sibility.  The portion of the string that provided the partial match is         sibility. The portion of the string that provided the partial match  is
2504         set as the first matching string.         set as the first matching string.
2505    
2506           PCRE_DFA_SHORTEST           PCRE_DFA_SHORTEST
2507    
2508         Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to         Setting  the  PCRE_DFA_SHORTEST option causes the matching algorithm to
2509         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-
2510         tive algorithm works, this is necessarily the shortest  possible  match         tive  algorithm  works, this is necessarily the shortest possible match
2511         at the first possible matching point in the subject string.         at the first possible matching point in the subject string.
2512    
2513           PCRE_DFA_RESTART           PCRE_DFA_RESTART
2514    
2515         When  pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option, and         When pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option,  and
2516         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-
2517         tional  subject  characters,  and have it continue with the same match.         tional subject characters, and have it continue with  the  same  match.
2518         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
2519         workspace  and wscount options must reference the same vector as before         workspace and wscount options must reference the same vector as  before
2520         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
2521         match.  There  is  more  discussion of this facility in the pcrepartial         match. There is more discussion of this  facility  in  the  pcrepartial
2522         documentation.         documentation.
2523    
2524     Successful returns from pcre_dfa_exec()     Successful returns from pcre_dfa_exec()
2525    
2526         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-
2527         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
2528         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
2529         matches  are all initial substrings of the longer matches. For example,         matches are all initial substrings of the longer matches. For  example,
2530         if the pattern         if the pattern
2531    
2532           <.*>           <.*>
# Line 2339  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2541  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2541           <something> <something else>           <something> <something else>
2542           <something> <something else> <something further>           <something> <something else> <something further>
2543    
2544         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,
2545         which  is  the  number of matched substrings. The substrings themselves         which is the number of matched substrings.  The  substrings  themselves
2546         are returned in ovector. Each string uses two elements;  the  first  is         are  returned  in  ovector. Each string uses two elements; the first is
2547         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
2548         fact, all the strings have the same start  offset.  (Space  could  have         fact,  all  the  strings  have the same start offset. (Space could have
2549         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
2550         compatibility with the way pcre_exec() returns data,  even  though  the         compatibility  with  the  way pcre_exec() returns data, even though the
2551         meaning of the strings is different.)         meaning of the strings is different.)
2552    
2553         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-
2554         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
2555         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
2556         filled with the longest matches.         filled with the longest matches.
2557    
2558     Error returns from pcre_dfa_exec()     Error returns from pcre_dfa_exec()
2559    
2560         The pcre_dfa_exec() function returns a negative number when  it  fails.         The  pcre_dfa_exec()  function returns a negative number when it fails.
2561         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
2562         described above.  There are in addition the following errors  that  are         described  above.   There are in addition the following errors that are
2563         specific to pcre_dfa_exec():         specific to pcre_dfa_exec():
2564    
2565           PCRE_ERROR_DFA_UITEM      (-16)           PCRE_ERROR_DFA_UITEM      (-16)
2566    
2567         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-
2568         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
2569         reference.         reference.
2570    
2571           PCRE_ERROR_DFA_UCOND      (-17)           PCRE_ERROR_DFA_UCOND      (-17)
2572    
2573         This  return  is  given  if pcre_dfa_exec() encounters a condition item         This return is given if pcre_dfa_exec()  encounters  a  condition  item
2574         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
2575         in a specific group. These are not supported.         in a specific group. These are not supported.
2576    
2577           PCRE_ERROR_DFA_UMLIMIT    (-18)           PCRE_ERROR_DFA_UMLIMIT    (-18)
2578    
2579         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
2580         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
2581         (it is meaningless).         (it is meaningless).
2582    
2583           PCRE_ERROR_DFA_WSSIZE     (-19)           PCRE_ERROR_DFA_WSSIZE     (-19)
2584    
2585         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
2586         workspace vector.         workspace vector.
2587    
2588           PCRE_ERROR_DFA_RECURSE    (-20)           PCRE_ERROR_DFA_RECURSE    (-20)
2589    
2590         When a recursive subpattern is processed, the matching  function  calls         When  a  recursive subpattern is processed, the matching function calls
2591         itself  recursively,  using  private vectors for ovector and workspace.         itself recursively, using private vectors for  ovector  and  workspace.
2592         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
2593         should be extremely rare, as a vector of size 1000 is used.         should be extremely rare, as a vector of size 1000 is used.
2594    
2595    
2596  SEE ALSO  SEE ALSO
2597    
2598         pcrebuild(3),  pcrecallout(3), pcrecpp(3)(3), pcrematching(3), pcrepar-         pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3),  pcrepar-
2599         tial(3), pcreposix(3), pcreprecompile(3), pcresample(3),  pcrestack(3).         tial(3),  pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
2600    
2601    
2602  AUTHOR  AUTHOR
# Line 2406  AUTHOR Line 2608  AUTHOR
2608    
2609  REVISION  REVISION
2610    
2611         Last updated: 04 June 2007         Last updated: 24 August 2008
2612         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2008 University of Cambridge.
2613  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2614    
2615    
# Line 2593  DIFFERENCES BETWEEN PCRE AND PERL Line 2795  DIFFERENCES BETWEEN PCRE AND PERL
2795    
2796         This  document describes the differences in the ways that PCRE and Perl         This  document describes the differences in the ways that PCRE and Perl
2797         handle regular expressions. The differences described here  are  mainly         handle regular expressions. The differences described here  are  mainly
2798         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
2799         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.
2800    
2801         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
2802         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 2861  DIFFERENCES BETWEEN PCRE AND PERL
2861         matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2         matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2
2862         unset, but in PCRE it is set to "b".         unset, but in PCRE it is set to "b".
2863    
2864         11. PCRE provides some extensions to the Perl regular expression facil-         11.  PCRE  does  support  Perl  5.10's  backtracking  verbs  (*ACCEPT),
2865           (*FAIL),  (*F),  (*COMMIT), (*PRUNE), (*SKIP), and (*THEN), but only in
2866           the forms without an  argument.  PCRE  does  not  support  (*MARK).  If
2867           (*ACCEPT)  is within capturing parentheses, PCRE does not set that cap-
2868           ture group; this is different to Perl.
2869    
2870           12. PCRE provides some extensions to the Perl regular expression facil-
2871         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
2872         versions, some of which (such as named parentheses) have been  in  PCRE         versions, some of which (such as named parentheses) have been  in  PCRE
2873         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 2880  DIFFERENCES BETWEEN PCRE AND PERL
2880         meta-character matches only at the very end of the string.         meta-character matches only at the very end of the string.
2881    
2882         (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-
2883         cial  meaning  is  faulted.  Otherwise,  like  Perl,  the  backslash is         cial meaning is faulted. Otherwise, like Perl, the backslash is quietly
2884         ignored. (Perl can be made to issue a warning.)         ignored.  (Perl can be made to issue a warning.)
2885    
2886         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-
2887         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 2893  DIFFERENCES BETWEEN PCRE AND PERL
2893         (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-
2894         TURE options for pcre_exec() have no Perl equivalents.         TURE options for pcre_exec() have no Perl equivalents.
2895    
2896         (g) The callout facility is PCRE-specific.         (g) The \R escape sequence can be restricted to match only CR,  LF,  or
2897           CRLF by the PCRE_BSR_ANYCRLF option.
2898    
2899         (h) The partial matching facility is PCRE-specific.         (h) The callout facility is PCRE-specific.
2900    
2901         (i) Patterns compiled by PCRE can be saved and re-used at a later time,         (i) The partial matching facility is PCRE-specific.
2902    
2903           (j) Patterns compiled by PCRE can be saved and re-used at a later time,
2904         even on different hosts that have the other endianness.         even on different hosts that have the other endianness.
2905    
2906         (j)  The  alternative  matching function (pcre_dfa_exec()) matches in a         (k) The alternative matching function (pcre_dfa_exec())  matches  in  a
2907         different way and is not Perl-compatible.         different way and is not Perl-compatible.
2908    
2909           (l)  PCRE  recognizes some special sequences such as (*CR) at the start
2910           of a pattern that set overall options that cannot be changed within the
2911           pattern.
2912    
2913    
2914  AUTHOR  AUTHOR
2915    
# Line 2705  AUTHOR Line 2920  AUTHOR
2920    
2921  REVISION  REVISION
2922    
2923         Last updated: 06 March 2007         Last updated: 11 September 2007
2924         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
2925  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2926    
# Line 2719  NAME Line 2934  NAME
2934    
2935  PCRE REGULAR EXPRESSION DETAILS  PCRE REGULAR EXPRESSION DETAILS
2936    
2937         The  syntax  and semantics of the regular expressions supported by PCRE         The  syntax and semantics of the regular expressions that are supported
2938         are described below. Regular expressions are also described in the Perl         by PCRE are described in detail below. There is a quick-reference  syn-
2939         documentation  and  in  a  number  of books, some of which have copious         tax summary in the pcresyntax page. PCRE tries to match Perl syntax and
2940         examples.  Jeffrey Friedl's "Mastering Regular Expressions",  published         semantics as closely as it can. PCRE  also  supports  some  alternative
2941         by  O'Reilly, covers regular expressions in great detail. This descrip-         regular  expression  syntax (which does not conflict with the Perl syn-
2942         tion of PCRE's regular expressions is intended as reference material.         tax) in order to provide some compatibility with regular expressions in
2943           Python, .NET, and Oniguruma.
2944    
2945           Perl's  regular expressions are described in its own documentation, and
2946           regular expressions in general are covered in a number of  books,  some
2947           of  which  have  copious  examples. Jeffrey Friedl's "Mastering Regular
2948           Expressions", published by  O'Reilly,  covers  regular  expressions  in
2949           great  detail.  This  description  of  PCRE's  regular  expressions  is
2950           intended as reference material.
2951    
2952         The original operation of PCRE was on strings of  one-byte  characters.         The original operation of PCRE was on strings of  one-byte  characters.
2953         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 2967  PCRE REGULAR EXPRESSION DETAILS
2967         discussed in the pcrematching page.         discussed in the pcrematching page.
2968    
2969    
2970    NEWLINE CONVENTIONS
2971    
2972           PCRE  supports five different conventions for indicating line breaks in
2973           strings: a single CR (carriage return) character, a  single  LF  (line-
2974           feed) character, the two-character sequence CRLF, any of the three pre-
2975           ceding, or any Unicode newline sequence. The pcreapi page  has  further
2976           discussion  about newlines, and shows how to set the newline convention
2977           in the options arguments for the compiling and matching functions.
2978    
2979           It is also possible to specify a newline convention by starting a  pat-
2980           tern string with one of the following five sequences:
2981    
2982             (*CR)        carriage return
2983             (*LF)        linefeed
2984             (*CRLF)      carriage return, followed by linefeed
2985             (*ANYCRLF)   any of the three above
2986             (*ANY)       all Unicode newline sequences
2987    
2988           These override the default and the options given to pcre_compile(). For
2989           example, on a Unix system where LF is the default newline sequence, the
2990           pattern
2991    
2992             (*CR)a.b
2993    
2994           changes the convention to CR. That pattern matches "a\nb" because LF is
2995           no longer a newline. Note that these special settings,  which  are  not
2996           Perl-compatible,  are  recognized  only at the very start of a pattern,
2997           and that they must be in upper case.  If  more  than  one  of  them  is
2998           present, the last one is used.
2999    
3000           The  newline  convention  does  not  affect what the \R escape sequence
3001           matches. By default, this is any Unicode  newline  sequence,  for  Perl
3002           compatibility.  However, this can be changed; see the description of \R
3003           in the section entitled "Newline sequences" below. A change of \R  set-
3004           ting can be combined with a change of newline convention.
3005    
3006    
3007  CHARACTERS AND METACHARACTERS  CHARACTERS AND METACHARACTERS
3008    
3009         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 3111  BACKSLASH
3111           \cx       "control-x", where x is any character           \cx       "control-x", where x is any character
3112           \e        escape (hex 1B)           \e        escape (hex 1B)
3113           \f        formfeed (hex 0C)           \f        formfeed (hex 0C)
3114           \n        newline (hex 0A)           \n        linefeed (hex 0A)
3115           \r        carriage return (hex 0D)           \r        carriage return (hex 0D)
3116           \t        tab (hex 09)           \t        tab (hex 09)
3117           \ddd      character with octal code ddd, or backreference           \ddd      character with octal code ddd, or backreference
# Line 2866  BACKSLASH Line 3126  BACKSLASH
3126         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
3127         in upper or lower case). Any number of hexadecimal  digits  may  appear         in upper or lower case). Any number of hexadecimal  digits  may  appear
3128         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
3129         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,
3130         the  maximum  hexadecimal  value is 7FFFFFFF). If characters other than         the  maximum value in hexadecimal is 7FFFFFFF. Note that this is bigger
3131         hexadecimal digits appear between \x{ and }, or if there is  no  termi-         than the largest Unicode code point, which is 10FFFF.
3132         nating  }, this form of escape is not recognized.  Instead, the initial  
3133         \x will be interpreted as a basic hexadecimal escape, with no following         If characters other than hexadecimal digits appear between \x{  and  },
3134         digits, giving a character whose value is zero.         or if there is no terminating }, this form of escape is not recognized.
3135           Instead, the initial \x will be  interpreted  as  a  basic  hexadecimal
3136           escape,  with  no  following  digits, giving a character whose value is
3137           zero.
3138    
3139         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
3140         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-
3141         dled. For example, \xdc is exactly the same as \x{dc}.         dled. For example, \xdc is exactly the same as \x{dc}.
3142    
3143         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
3144         than two digits, just  those  that  are  present  are  used.  Thus  the         than  two  digits,  just  those  that  are  present  are used. Thus the
3145         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
3146         (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
3147         if the pattern character that follows is itself an octal digit.         if the pattern character that follows is itself an octal digit.
3148    
3149         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-
3150         cated.  Outside a character class, PCRE reads it and any following dig-         cated.  Outside a character class, PCRE reads it and any following dig-
3151         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
3152         have been at least that many previous capturing left parentheses in the         have been at least that many previous capturing left parentheses in the
3153         expression,  the  entire  sequence  is  taken  as  a  back reference. A         expression, the entire  sequence  is  taken  as  a  back  reference.  A
3154         description of how this works is given later, following the  discussion         description  of how this works is given later, following the discussion
3155         of parenthesized subpatterns.         of parenthesized subpatterns.
3156    
3157         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
3158         and there have not been that many capturing subpatterns, PCRE  re-reads         and  there have not been that many capturing subpatterns, PCRE re-reads
3159         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-
3160         erate a data character. Any subsequent digits stand for themselves.  In         erate  a data character. Any subsequent digits stand for themselves. In
3161         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
3162         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
3163         example:         example:
3164    
3165           \040   is another way of writing a space           \040   is another way of writing a space
# Line 2914  BACKSLASH Line 3177  BACKSLASH
3177           \81    is either a back reference, or a binary zero           \81    is either a back reference, or a binary zero
3178                     followed by the two characters "8" and "1"                     followed by the two characters "8" and "1"
3179    
3180         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
3181         leading zero, because no more than three octal digits are ever read.         leading zero, because no more than three octal digits are ever read.
3182    
3183         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
3184         inside  and  outside character classes. In addition, inside a character         inside and outside character classes. In addition, inside  a  character
3185         class, the sequence \b is interpreted as the backspace  character  (hex         class,  the  sequence \b is interpreted as the backspace character (hex
3186         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"
3187         and "X", respectively. Outside a character class, these sequences  have         and  "X", respectively. Outside a character class, these sequences have
3188         different meanings (see below).         different meanings (see below).
3189    
3190     Absolute and relative back references     Absolute and relative back references
3191    
3192         The  sequence  \g followed by a positive or negative number, optionally         The sequence \g followed by an unsigned or a negative  number,  option-
3193         enclosed in braces, is an absolute or relative back reference. A  named         ally  enclosed  in braces, is an absolute or relative back reference. A
3194         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-
3195         later, following the discussion of parenthesized subpatterns.         cussed later, following the discussion of parenthesized subpatterns.
3196    
3197       Absolute and relative subroutine calls
3198    
3199           For  compatibility with Oniguruma, the non-Perl syntax \g followed by a
3200           name or a number enclosed either in angle brackets or single quotes, is
3201           an  alternative  syntax for referencing a subpattern as a "subroutine".
3202           Details are discussed later.   Note  that  \g{...}  (Perl  syntax)  and
3203           \g<...>  (Oniguruma  syntax)  are  not synonymous. The former is a back
3204           reference; the latter is a subroutine call.
3205    
3206     Generic character types     Generic character types
3207    
# Line 2938  BACKSLASH Line 3210  BACKSLASH
3210    
3211           \d     any decimal digit           \d     any decimal digit
3212           \D     any character that is not a decimal digit           \D     any character that is not a decimal digit
3213             \h     any horizontal whitespace character
3214             \H     any character that is not a horizontal whitespace character
3215           \s     any whitespace character           \s     any whitespace character
3216           \S     any character that is not a whitespace character           \S     any character that is not a whitespace character
3217             \v     any vertical whitespace character
3218             \V     any character that is not a vertical whitespace character
3219           \w     any "word" character           \w     any "word" character
3220           \W     any "non-word" character           \W     any "non-word" character
3221    
# Line 2954  BACKSLASH Line 3230  BACKSLASH
3230    
3231         For compatibility with Perl, \s does not match the VT  character  (code         For compatibility with Perl, \s does not match the VT  character  (code
3232         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
3233         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
3234         "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-
3235         ter. In PCRE, it never does.)         ter. In PCRE, it never does.
3236    
3237           In UTF-8 mode, characters with values greater than 128 never match  \d,
3238           \s, or \w, and always match \D, \S, and \W. This is true even when Uni-
3239           code character property support is available.  These  sequences  retain
3240           their original meanings from before UTF-8 support was available, mainly
3241           for efficiency reasons.
3242    
3243           The sequences \h, \H, \v, and \V are Perl 5.10 features. In contrast to
3244           the  other  sequences, these do match certain high-valued codepoints in
3245           UTF-8 mode.  The horizontal space characters are:
3246    
3247             U+0009     Horizontal tab
3248             U+0020     Space
3249             U+00A0     Non-break space
3250             U+1680     Ogham space mark
3251             U+180E     Mongolian vowel separator
3252             U+2000     En quad
3253             U+2001     Em quad
3254             U+2002     En space
3255             U+2003     Em space
3256             U+2004     Three-per-em space
3257             U+2005     Four-per-em space
3258             U+2006     Six-per-em space
3259             U+2007     Figure space
3260             U+2008     Punctuation space
3261             U+2009     Thin space
3262             U+200A     Hair space
3263             U+202F     Narrow no-break space
3264             U+205F     Medium mathematical space
3265             U+3000     Ideographic space
3266    
3267           The vertical space characters are:
3268    
3269             U+000A     Linefeed
3270             U+000B     Vertical tab
3271             U+000C     Formfeed
3272             U+000D     Carriage return
3273             U+0085     Next line
3274             U+2028     Line separator
3275             U+2029     Paragraph separator
3276    
3277         A "word" character is an underscore or any character less than 256 that         A "word" character is an underscore or any character less than 256 that
3278         is  a  letter  or  digit.  The definition of letters and digits is con-         is  a  letter  or  digit.  The definition of letters and digits is con-
# Line 2964  BACKSLASH Line 3280  BACKSLASH
3280         specific  matching is taking place (see "Locale support" in the pcreapi         specific  matching is taking place (see "Locale support" in the pcreapi
3281         page). For example, in a French locale such  as  "fr_FR"  in  Unix-like         page). For example, in a French locale such  as  "fr_FR"  in  Unix-like
3282         systems,  or "french" in Windows, some character codes greater than 128         systems,  or "french" in Windows, some character codes greater than 128
3283         are used for accented letters, and these are matched by \w.         are used for accented letters, and these are matched by \w. The use  of
3284           locales with Unicode is discouraged.
        In UTF-8 mode, characters with values greater than 128 never match  \d,  
        \s, or \w, and always match \D, \S, and \W. This is true even when Uni-  
        code character property support is available. The use of  locales  with  
        Unicode is discouraged.  
3285    
3286     Newline sequences     Newline sequences
3287    
3288         Outside  a  character class, the escape sequence \R matches any Unicode         Outside  a  character class, by default, the escape sequence \R matches
3289         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
3290         equivalent to the following:         mode \R is equivalent to the following:
3291    
3292           (?>\r\n|\n|\x0b|\f|\r|\x85)           (?>\r\n|\n|\x0b|\f|\r|\x85)
3293    
# Line 2991  BACKSLASH Line 3303  BACKSLASH
3303         rator, U+2029).  Unicode character property support is not  needed  for         rator, U+2029).  Unicode character property support is not  needed  for
3304         these characters to be recognized.         these characters to be recognized.
3305    
3306           It is possible to restrict \R to match only CR, LF, or CRLF (instead of
3307           the complete set  of  Unicode  line  endings)  by  setting  the  option
3308           PCRE_BSR_ANYCRLF either at compile time or when the pattern is matched.
3309           (BSR is an abbrevation for "backslash R".) This can be made the default
3310           when  PCRE  is  built;  if this is the case, the other behaviour can be
3311           requested via the PCRE_BSR_UNICODE option.   It  is  also  possible  to
3312           specify  these  settings  by  starting a pattern string with one of the
3313           following sequences:
3314    
3315             (*BSR_ANYCRLF)   CR, LF, or CRLF only
3316             (*BSR_UNICODE)   any Unicode newline sequence
3317    
3318           These override the default and the options given to pcre_compile(), but
3319           they can be overridden by options given to pcre_exec(). Note that these
3320           special settings, which are not Perl-compatible, are recognized only at
3321           the  very  start  of a pattern, and that they must be in upper case. If
3322           more than one of them is present, the last one is  used.  They  can  be
3323           combined  with  a  change of newline convention, for example, a pattern
3324           can start with:
3325    
3326             (*ANY)(*BSR_ANYCRLF)
3327    
3328         Inside a character class, \R matches the letter "R".         Inside a character class, \R matches the letter "R".
3329    
3330     Unicode character properties     Unicode character properties
3331    
3332         When PCRE is built with Unicode character property support, three addi-         When PCRE is built with Unicode character property support, three addi-
3333         tional escape sequences to match  character  properties  are  available         tional  escape sequences that match characters with specific properties
3334         when UTF-8 mode is selected. They are:         are available.  When not in UTF-8 mode, these sequences are  of  course
3335           limited  to  testing characters whose codepoints are less than 256, but
3336           they do work in this mode.  The extra escape sequences are:
3337    
3338           \p{xx}   a character with the xx property           \p{xx}   a character with the xx property
3339           \P{xx}   a character without the xx property           \P{xx}   a character without the xx property
3340           \X       an extended Unicode sequence           \X       an extended Unicode sequence
3341    
3342         The  property  names represented by xx above are limited to the Unicode         The property names represented by xx above are limited to  the  Unicode
3343         script names, the general category properties, and "Any", which matches         script names, the general category properties, and "Any", which matches
3344         any character (including newline). Other properties such as "InMusical-         any character (including newline). Other properties such as "InMusical-
3345         Symbols" are not currently supported by PCRE. Note  that  \P{Any}  does         Symbols"  are  not  currently supported by PCRE. Note that \P{Any} does
3346         not match any characters, so always causes a match failure.         not match any characters, so always causes a match failure.
3347    
3348         Sets of Unicode characters are defined as belonging to certain scripts.         Sets of Unicode characters are defined as belonging to certain scripts.
3349         A character from one of these sets can be matched using a script  name.         A  character from one of these sets can be matched using a script name.
3350         For example:         For example:
3351    
3352           \p{Greek}           \p{Greek}
3353           \P{Han}           \P{Han}
3354    
3355         Those  that are not part of an identified script are lumped together as         Those that are not part of an identified script are lumped together  as
3356         "Common". The current list of scripts is:         "Common". The current list of scripts is:
3357    
3358         Arabic,  Armenian,  Balinese,  Bengali,  Bopomofo,  Braille,  Buginese,         Arabic,  Armenian,  Balinese,  Bengali,  Bopomofo,  Braille,  Buginese,
3359         Buhid,   Canadian_Aboriginal,   Cherokee,  Common,  Coptic,  Cuneiform,         Buhid,  Canadian_Aboriginal,  Cherokee,  Common,   Coptic,   Cuneiform,
3360         Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,         Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,
3361         Gothic,  Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hira-         Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew,  Hira-
3362         gana, Inherited, Kannada,  Katakana,  Kharoshthi,  Khmer,  Lao,  Latin,         gana,  Inherited,  Kannada,  Katakana,  Kharoshthi,  Khmer, Lao, Latin,
3363         Limbu,  Linear_B,  Malayalam,  Mongolian,  Myanmar,  New_Tai_Lue,  Nko,         Limbu,  Linear_B,  Malayalam,  Mongolian,  Myanmar,  New_Tai_Lue,  Nko,
3364         Ogham, Old_Italic, Old_Persian, Oriya, Osmanya,  Phags_Pa,  Phoenician,         Ogham,  Old_Italic,  Old_Persian, Oriya, Osmanya, Phags_Pa, Phoenician,
3365         Runic,  Shavian,  Sinhala,  Syloti_Nagri,  Syriac,  Tagalog,  Tagbanwa,         Runic,  Shavian,  Sinhala,  Syloti_Nagri,  Syriac,  Tagalog,  Tagbanwa,
3366         Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.         Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.
3367    
3368         Each character has exactly one general category property, specified  by         Each  character has exactly one general category property, specified by
3369         a two-letter abbreviation. For compatibility with Perl, negation can be         a two-letter abbreviation. For compatibility with Perl, negation can be
3370         specified by including a circumflex between the opening brace  and  the         specified  by  including a circumflex between the opening brace and the
3371         property name. For example, \p{^Lu} is the same as \P{Lu}.         property name. For example, \p{^Lu} is the same as \P{Lu}.
3372    
3373         If only one letter is specified with \p or \P, it includes all the gen-         If only one letter is specified with \p or \P, it includes all the gen-
3374         eral category properties that start with that letter. In this case,  in         eral  category properties that start with that letter. In this case, in
3375         the  absence of negation, the curly brackets in the escape sequence are         the absence of negation, the curly brackets in the escape sequence  are
3376         optional; these two examples have the same effect:         optional; these two examples have the same effect:
3377    
3378           \p{L}           \p{L}
# Line 3088  BACKSLASH Line 3424  BACKSLASH
3424           Zp    Paragraph separator           Zp    Paragraph separator
3425           Zs    Space separator           Zs    Space separator
3426    
3427         The special property L& is also supported: it matches a character  that         The  special property L& is also supported: it matches a character that
3428         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
3429         classified as a modifier or "other".         classified as a modifier or "other".
3430    
3431         The long synonyms for these properties  that  Perl  supports  (such  as         The  Cs  (Surrogate)  property  applies only to characters in the range
3432         \p{Letter})  are  not  supported by PCRE, nor is it permitted to prefix         U+D800 to U+DFFF. Such characters are not valid in UTF-8  strings  (see
3433           RFC 3629) and so cannot be tested by PCRE, unless UTF-8 validity check-
3434           ing has been turned off (see the discussion  of  PCRE_NO_UTF8_CHECK  in
3435           the pcreapi page).
3436    
3437           The  long  synonyms  for  these  properties that Perl supports (such as
3438           \p{Letter}) are not supported by PCRE, nor is it  permitted  to  prefix
3439         any of these properties with "Is".         any of these properties with "Is".
3440    
3441         No character that is in the Unicode table has the Cn (unassigned) prop-         No character that is in the Unicode table has the Cn (unassigned) prop-
3442         erty.  Instead, this property is assumed for any code point that is not         erty.  Instead, this property is assumed for any code point that is not
3443         in the Unicode table.         in the Unicode table.
3444    
3445         Specifying caseless matching does not affect  these  escape  sequences.         Specifying  caseless  matching  does not affect these escape sequences.
3446         For example, \p{Lu} always matches only upper case letters.         For example, \p{Lu} always matches only upper case letters.
3447    
3448         The  \X  escape  matches  any number of Unicode characters that form an         The \X escape matches any number of Unicode  characters  that  form  an
3449         extended Unicode sequence. \X is equivalent to         extended Unicode sequence. \X is equivalent to
3450    
3451           (?>\PM\pM*)           (?>\PM\pM*)
3452    
3453         That is, it matches a character without the "mark"  property,  followed         That  is,  it matches a character without the "mark" property, followed
3454         by  zero  or  more  characters with the "mark" property, and treats the         by zero or more characters with the "mark"  property,  and  treats  the
3455         sequence as an atomic group (see below).  Characters  with  the  "mark"         sequence  as  an  atomic group (see below).  Characters with the "mark"
3456         property are typically accents that affect the preceding character.         property are typically accents that  affect  the  preceding  character.
3457           None  of  them  have  codepoints less than 256, so in non-UTF-8 mode \X
3458           matches any one character.
3459    
3460         Matching  characters  by Unicode property is not fast, because PCRE has         Matching characters by Unicode property is not fast, because  PCRE  has
3461         to search a structure that contains  data  for  over  fifteen  thousand         to  search  a  structure  that  contains data for over fifteen thousand
3462         characters. That is why the traditional escape sequences such as \d and         characters. That is why the traditional escape sequences such as \d and
3463         \w do not use Unicode properties in PCRE.         \w do not use Unicode properties in PCRE.
3464    
3465     Resetting the match start     Resetting the match start
3466    
3467         The escape sequence \K, which is a Perl 5.10 feature, causes any previ-         The escape sequence \K, which is a Perl 5.10 feature, causes any previ-
3468         ously  matched  characters  not  to  be  included  in the final matched         ously matched characters not  to  be  included  in  the  final  matched
3469         sequence. For example, the pattern:         sequence. For example, the pattern:
3470    
3471           foo\Kbar           foo\Kbar
3472    
3473         matches "foobar", but reports that it has matched "bar".  This  feature         matches  "foobar",  but reports that it has matched "bar". This feature
3474         is  similar  to  a lookbehind assertion (described below).  However, in         is similar to a lookbehind assertion (described  below).   However,  in
3475         this case, the part of the subject before the real match does not  have         this  case, the part of the subject before the real match does not have
3476         to  be of fixed length, as lookbehind assertions do. The use of \K does         to be of fixed length, as lookbehind assertions do. The use of \K  does
3477         not interfere with the setting of captured  substrings.   For  example,         not  interfere  with  the setting of captured substrings.  For example,
3478         when the pattern         when the pattern
3479    
3480           (foo)\Kbar           (foo)\Kbar
# Line 3139  BACKSLASH Line 3483  BACKSLASH
3483    
3484     Simple assertions     Simple assertions
3485    
3486         The  final use of backslash is for certain simple assertions. An asser-         The final use of backslash is for certain simple assertions. An  asser-
3487         tion specifies a condition that has to be met at a particular point  in         tion  specifies a condition that has to be met at a particular point in
3488         a  match, without consuming any characters from the subject string. The         a match, without consuming any characters from the subject string.  The
3489         use of subpatterns for more complicated assertions is described  below.         use  of subpatterns for more complicated assertions is described below.
3490         The backslashed assertions are:         The backslashed assertions are:
3491    
3492           \b     matches at a word boundary           \b     matches at a word boundary
# Line 3153  BACKSLASH Line 3497  BACKSLASH
3497           \z     matches only at the end of the subject           \z     matches only at the end of the subject
3498           \G     matches at the first matching position in the subject           \G     matches at the first matching position in the subject
3499    
3500         These  assertions may not appear in character classes (but note that \b         These assertions may not appear in character classes (but note that  \b
3501         has a different meaning, namely the backspace character, inside a char-         has a different meaning, namely the backspace character, inside a char-
3502         acter class).         acter class).
3503    
3504         A  word  boundary is a position in the subject string where the current         A word boundary is a position in the subject string where  the  current
3505         character and the previous character do not both match \w or  \W  (i.e.         character  and  the previous character do not both match \w or \W (i.e.
3506         one  matches  \w  and the other matches \W), or the start or end of the         one matches \w and the other matches \W), or the start or  end  of  the
3507         string if the first or last character matches \w, respectively.         string if the first or last character matches \w, respectively.
3508    
3509         The \A, \Z, and \z assertions differ from  the  traditional  circumflex         The  \A,  \Z,  and \z assertions differ from the traditional circumflex
3510         and dollar (described in the next section) in that they only ever match         and dollar (described in the next section) in that they only ever match
3511         at the very start and end of the subject string, whatever  options  are         at  the  very start and end of the subject string, whatever options are
3512         set.  Thus,  they are independent of multiline mode. These three asser-         set. Thus, they are independent of multiline mode. These  three  asser-
3513         tions are not affected by the PCRE_NOTBOL or PCRE_NOTEOL options, which         tions are not affected by the PCRE_NOTBOL or PCRE_NOTEOL options, which
3514         affect  only the behaviour of the circumflex and dollar metacharacters.         affect only the behaviour of the circumflex and dollar  metacharacters.
3515         However, if the startoffset argument of pcre_exec() is non-zero,  indi-         However,  if the startoffset argument of pcre_exec() is non-zero, indi-
3516         cating that matching is to start at a point other than the beginning of         cating that matching is to start at a point other than the beginning of
3517         the subject, \A can never match. The difference between \Z  and  \z  is         the  subject,  \A  can never match. The difference between \Z and \z is
3518         that \Z matches before a newline at the end of the string as well as at         that \Z matches before a newline at the end of the string as well as at
3519         the very end, whereas \z matches only at the end.         the very end, whereas \z matches only at the end.
3520    
3521         The \G assertion is true only when the current matching position is  at         The  \G assertion is true only when the current matching position is at
3522         the  start point of the match, as specified by the startoffset argument         the start point of the match, as specified by the startoffset  argument
3523         of pcre_exec(). It differs from \A when the  value  of  startoffset  is         of  pcre_exec().  It  differs  from \A when the value of startoffset is
3524         non-zero.  By calling pcre_exec() multiple times with appropriate argu-         non-zero. By calling pcre_exec() multiple times with appropriate  argu-
3525         ments, you can mimic Perl's /g option, and it is in this kind of imple-         ments, you can mimic Perl's /g option, and it is in this kind of imple-
3526         mentation where \G can be useful.         mentation where \G can be useful.
3527    
3528         Note,  however,  that  PCRE's interpretation of \G, as the start of the         Note, however, that PCRE's interpretation of \G, as the  start  of  the
3529         current match, is subtly different from Perl's, which defines it as the         current match, is subtly different from Perl's, which defines it as the
3530         end  of  the  previous  match. In Perl, these can be different when the         end of the previous match. In Perl, these can  be  different  when  the
3531         previously matched string was empty. Because PCRE does just  one  match         previously  matched  string was empty. Because PCRE does just one match
3532         at a time, it cannot reproduce this behaviour.         at a time, it cannot reproduce this behaviour.
3533    
3534         If  all  the alternatives of a pattern begin with \G, the expression is         If all the alternatives of a pattern begin with \G, the  expression  is
3535         anchored to the starting match position, and the "anchored" flag is set         anchored to the starting match position, and the "anchored" flag is set
3536         in the compiled regular expression.         in the compiled regular expression.
3537    
# Line 3195  BACKSLASH Line 3539  BACKSLASH
3539  CIRCUMFLEX AND DOLLAR  CIRCUMFLEX AND DOLLAR
3540    
3541         Outside a character class, in the default matching mode, the circumflex         Outside a character class, in the default matching mode, the circumflex
3542         character is an assertion that is true only  if  the  current  matching         character  is  an  assertion  that is true only if the current matching
3543         point  is  at the start of the subject string. If the startoffset argu-         point is at the start of the subject string. If the  startoffset  argu-
3544         ment of pcre_exec() is non-zero, circumflex  can  never  match  if  the         ment  of  pcre_exec()  is  non-zero,  circumflex can never match if the
3545         PCRE_MULTILINE  option  is  unset. Inside a character class, circumflex         PCRE_MULTILINE option is unset. Inside a  character  class,  circumflex
3546         has an entirely different meaning (see below).         has an entirely different meaning (see below).
3547    
3548         Circumflex need not be the first character of the pattern if  a  number         Circumflex  need  not be the first character of the pattern if a number
3549         of  alternatives are involved, but it should be the first thing in each         of alternatives are involved, but it should be the first thing in  each
3550         alternative in which it appears if the pattern is ever  to  match  that         alternative  in  which  it appears if the pattern is ever to match that
3551         branch.  If all possible alternatives start with a circumflex, that is,         branch. If all possible alternatives start with a circumflex, that  is,
3552         if the pattern is constrained to match only at the start  of  the  sub-         if  the  pattern  is constrained to match only at the start of the sub-
3553         ject,  it  is  said  to be an "anchored" pattern. (There are also other         ject, it is said to be an "anchored" pattern.  (There  are  also  other
3554         constructs that can cause a pattern to be anchored.)         constructs that can cause a pattern to be anchored.)
3555    
3556         A dollar character is an assertion that is true  only  if  the  current         A  dollar  character  is  an assertion that is true only if the current
3557         matching  point  is  at  the  end of the subject string, or immediately         matching point is at the end of  the  subject  string,  or  immediately
3558         before a newline at the end of the string (by default). Dollar need not         before a newline at the end of the string (by default). Dollar need not
3559         be  the  last  character of the pattern if a number of alternatives are         be the last character of the pattern if a number  of  alternatives  are
3560         involved, but it should be the last item in  any  branch  in  which  it         involved,  but  it  should  be  the last item in any branch in which it
3561         appears. Dollar has no special meaning in a character class.         appears. Dollar has no special meaning in a character class.
3562    
3563         The  meaning  of  dollar  can be changed so that it matches only at the         The meaning of dollar can be changed so that it  matches  only  at  the
3564         very end of the string, by setting the  PCRE_DOLLAR_ENDONLY  option  at         very  end  of  the string, by setting the PCRE_DOLLAR_ENDONLY option at
3565         compile time. This does not affect the \Z assertion.         compile time. This does not affect the \Z assertion.
3566    
3567         The meanings of the circumflex and dollar characters are changed if the         The meanings of the circumflex and dollar characters are changed if the
3568         PCRE_MULTILINE option is set. When  this  is  the  case,  a  circumflex         PCRE_MULTILINE  option  is  set.  When  this  is the case, a circumflex
3569         matches  immediately after internal newlines as well as at the start of         matches immediately after internal newlines as well as at the start  of
3570         the subject string. It does not match after a  newline  that  ends  the         the  subject  string.  It  does not match after a newline that ends the
3571         string.  A dollar matches before any newlines in the string, as well as         string. A dollar matches before any newlines in the string, as well  as
3572         at the very end, when PCRE_MULTILINE is set. When newline is  specified         at  the very end, when PCRE_MULTILINE is set. When newline is specified
3573         as  the  two-character  sequence CRLF, isolated CR and LF characters do         as the two-character sequence CRLF, isolated CR and  LF  characters  do
3574         not indicate newlines.         not indicate newlines.
3575    
3576         For example, the pattern /^abc$/ matches the subject string  "def\nabc"         For  example, the pattern /^abc$/ matches the subject string "def\nabc"
3577         (where  \n  represents a newline) in multiline mode, but not otherwise.         (where \n represents a newline) in multiline mode, but  not  otherwise.
3578         Consequently, patterns that are anchored in single  line  mode  because         Consequently,  patterns  that  are anchored in single line mode because
3579         all  branches  start  with  ^ are not anchored in multiline mode, and a         all branches start with ^ are not anchored in  multiline  mode,  and  a
3580         match for circumflex is  possible  when  the  startoffset  argument  of         match  for  circumflex  is  possible  when  the startoffset argument of
3581         pcre_exec()  is  non-zero. The PCRE_DOLLAR_ENDONLY option is ignored if         pcre_exec() is non-zero. The PCRE_DOLLAR_ENDONLY option is  ignored  if
3582         PCRE_MULTILINE is set.         PCRE_MULTILINE is set.
3583    
3584         Note that the sequences \A, \Z, and \z can be used to match  the  start         Note  that  the sequences \A, \Z, and \z can be used to match the start
3585         and  end of the subject in both modes, and if all branches of a pattern         and end of the subject in both modes, and if all branches of a  pattern
3586         start with \A it is always anchored, whether or not  PCRE_MULTILINE  is         start  with  \A it is always anchored, whether or not PCRE_MULTILINE is
3587         set.         set.
3588    
3589    
3590  FULL STOP (PERIOD, DOT)  FULL STOP (PERIOD, DOT)
3591    
3592         Outside a character class, a dot in the pattern matches any one charac-         Outside a character class, a dot in the pattern matches any one charac-
3593         ter in the subject string except (by default) a character  that  signi-         ter  in  the subject string except (by default) a character that signi-
3594         fies  the  end  of  a line. In UTF-8 mode, the matched character may be         fies the end of a line. In UTF-8 mode, the  matched  character  may  be
3595         more than one byte long.         more than one byte long.
3596    
3597         When a line ending is defined as a single character, dot never  matches         When  a line ending is defined as a single character, dot never matches
3598         that  character; when the two-character sequence CRLF is used, dot does         that character; when the two-character sequence CRLF is used, dot  does
3599         not match CR if it is immediately followed  by  LF,  but  otherwise  it         not  match  CR  if  it  is immediately followed by LF, but otherwise it
3600         matches  all characters (including isolated CRs and LFs). When any Uni-         matches all characters (including isolated CRs and LFs). When any  Uni-
3601         code line endings are being recognized, dot does not match CR or LF  or         code  line endings are being recognized, dot does not match CR or LF or
3602         any of the other line ending characters.         any of the other line ending characters.
3603    
3604         The  behaviour  of  dot  with regard to newlines can be changed. If the         The behaviour of dot with regard to newlines can  be  changed.  If  the
3605         PCRE_DOTALL option is set, a dot matches  any  one  character,  without         PCRE_DOTALL  option  is  set,  a dot matches any one character, without
3606         exception. If the two-character sequence CRLF is present in the subject         exception. If the two-character sequence CRLF is present in the subject
3607         string, it takes two dots to match it.         string, it takes two dots to match it.
3608    
3609         The handling of dot is entirely independent of the handling of  circum-         The  handling of dot is entirely independent of the handling of circum-
3610         flex  and  dollar,  the  only relationship being that they both involve         flex and dollar, the only relationship being  that  they  both  involve
3611         newlines. Dot has no special meaning in a character class.         newlines. Dot has no special meaning in a character class.
3612    
3613    
3614  MATCHING A SINGLE BYTE  MATCHING A SINGLE BYTE
3615    
3616         Outside a character class, the escape sequence \C matches any one byte,         Outside a character class, the escape sequence \C matches any one byte,
3617         both  in  and  out  of  UTF-8 mode. Unlike a dot, it always matches any         both in and out of UTF-8 mode. Unlike a  dot,  it  always  matches  any
3618         line-ending characters. The feature is provided in  Perl  in  order  to         line-ending  characters.  The  feature  is provided in Perl in order to
3619         match  individual bytes in UTF-8 mode. Because it breaks up UTF-8 char-         match individual bytes in UTF-8 mode. Because it breaks up UTF-8  char-
3620         acters into individual bytes, what remains in the string may be a  mal-         acters  into individual bytes, what remains in the string may be a mal-
3621         formed  UTF-8  string.  For this reason, the \C escape sequence is best         formed UTF-8 string. For this reason, the \C escape  sequence  is  best
3622         avoided.         avoided.
3623    
3624         PCRE does not allow \C to appear in  lookbehind  assertions  (described         PCRE  does  not  allow \C to appear in lookbehind assertions (described
3625         below),  because  in UTF-8 mode this would make it impossible to calcu-         below), because in UTF-8 mode this would make it impossible  to  calcu-
3626         late the length of the lookbehind.         late the length of the lookbehind.
3627    
3628    
# Line 3287  SQUARE BRACKETS AND CHARACTER CLASSES Line 3631  SQUARE BRACKETS AND CHARACTER CLASSES
3631         An opening square bracket introduces a character class, terminated by a         An opening square bracket introduces a character class, terminated by a
3632         closing square bracket. A closing square bracket on its own is not spe-         closing square bracket. A closing square bracket on its own is not spe-
3633         cial. If a closing square bracket is required as a member of the class,         cial. If a closing square bracket is required as a member of the class,
3634         it  should  be  the first data character in the class (after an initial         it should be the first data character in the class  (after  an  initial
3635         circumflex, if present) or escaped with a backslash.         circumflex, if present) or escaped with a backslash.
3636    
3637         A character class matches a single character in the subject.  In  UTF-8         A  character  class matches a single character in the subject. In UTF-8
3638         mode,  the character may occupy more than one byte. A matched character         mode, the character may occupy more than one byte. A matched  character
3639         must be in the set of characters defined by the class, unless the first         must be in the set of characters defined by the class, unless the first
3640         character  in  the  class definition is a circumflex, in which case the         character in the class definition is a circumflex, in  which  case  the
3641         subject character must not be in the set defined by  the  class.  If  a         subject  character  must  not  be in the set defined by the class. If a
3642         circumflex  is actually required as a member of the class, ensure it is         circumflex is actually required as a member of the class, ensure it  is
3643         not the first character, or escape it with a backslash.         not the first character, or escape it with a backslash.
3644    
3645         For example, the character class [aeiou] matches any lower case  vowel,         For  example, the character class [aeiou] matches any lower case vowel,
3646         while  [^aeiou]  matches  any character that is not a lower case vowel.         while [^aeiou] matches any character that is not a  lower  case  vowel.
3647         Note that a circumflex is just a convenient notation for specifying the         Note that a circumflex is just a convenient notation for specifying the
3648         characters  that  are in the class by enumerating those that are not. A         characters that are in the class by enumerating those that are  not.  A
3649         class that starts with a circumflex is not an assertion: it still  con-         class  that starts with a circumflex is not an assertion: it still con-
3650         sumes  a  character  from the subject string, and therefore it fails if         sumes a character from the subject string, and therefore  it  fails  if
3651         the current pointer is at the end of the string.         the current pointer is at the end of the string.
3652    
3653         In UTF-8 mode, characters with values greater than 255 can be  included         In  UTF-8 mode, characters with values greater than 255 can be included
3654         in  a  class as a literal string of bytes, or by using the \x{ escaping         in a class as a literal string of bytes, or by using the  \x{  escaping
3655         mechanism.         mechanism.
3656    
3657         When caseless matching is set, any letters in a  class  represent  both         When  caseless  matching  is set, any letters in a class represent both
3658         their  upper  case  and lower case versions, so for example, a caseless         their upper case and lower case versions, so for  example,  a  caseless
3659         [aeiou] matches "A" as well as "a", and a caseless  [^aeiou]  does  not         [aeiou]  matches  "A"  as well as "a", and a caseless [^aeiou] does not
3660         match  "A", whereas a caseful version would. In UTF-8 mode, PCRE always         match "A", whereas a caseful version would. In UTF-8 mode, PCRE  always
3661         understands the concept of case for characters whose  values  are  less         understands  the  concept  of case for characters whose values are less
3662         than  128, so caseless matching is always possible. For characters with         than 128, so caseless matching is always possible. For characters  with
3663         higher values, the concept of case is supported  if  PCRE  is  compiled         higher  values,  the  concept  of case is supported if PCRE is compiled
3664         with  Unicode  property support, but not otherwise.  If you want to use         with Unicode property support, but not otherwise.  If you want  to  use
3665         caseless matching for characters 128 and above, you  must  ensure  that         caseless  matching  for  characters 128 and above, you must ensure that
3666         PCRE  is  compiled  with Unicode property support as well as with UTF-8         PCRE is compiled with Unicode property support as well  as  with  UTF-8
3667         support.         support.
3668    
3669         Characters that might indicate line breaks are  never  treated  in  any         Characters  that  might  indicate  line breaks are never treated in any
3670         special  way  when  matching  character  classes,  whatever line-ending         special way  when  matching  character  classes,  whatever  line-ending
3671         sequence is in  use,  and  whatever  setting  of  the  PCRE_DOTALL  and         sequence  is  in  use,  and  whatever  setting  of  the PCRE_DOTALL and
3672         PCRE_MULTILINE options is used. A class such as [^a] always matches one         PCRE_MULTILINE options is used. A class such as [^a] always matches one
3673         of these characters.         of these characters.
3674    
3675         The minus (hyphen) character can be used to specify a range of  charac-         The  minus (hyphen) character can be used to specify a range of charac-
3676         ters  in  a  character  class.  For  example,  [d-m] matches any letter         ters in a character  class.  For  example,  [d-m]  matches  any  letter
3677         between d and m, inclusive. If a  minus  character  is  required  in  a         between  d  and  m,  inclusive.  If  a minus character is required in a
3678         class,  it  must  be  escaped  with a backslash or appear in a position         class, it must be escaped with a backslash  or  appear  in  a  position
3679         where it cannot be interpreted as indicating a range, typically as  the         where  it cannot be interpreted as indicating a range, typically as the
3680         first or last character in the class.         first or last character in the class.
3681    
3682         It is not possible to have the literal character "]" as the end charac-         It is not possible to have the literal character "]" as the end charac-
3683         ter of a range. A pattern such as [W-]46] is interpreted as a class  of         ter  of a range. A pattern such as [W-]46] is interpreted as a class of
3684         two  characters ("W" and "-") followed by a literal string "46]", so it         two characters ("W" and "-") followed by a literal string "46]", so  it
3685         would match "W46]" or "-46]". However, if the "]"  is  escaped  with  a         would  match  "W46]"  or  "-46]". However, if the "]" is escaped with a
3686         backslash  it is interpreted as the end of range, so [W-\]46] is inter-         backslash it is interpreted as the end of range, so [W-\]46] is  inter-
3687         preted as a class containing a range followed by two other  characters.         preted  as a class containing a range followed by two other characters.
3688         The  octal or hexadecimal representation of "]" can also be used to end         The octal or hexadecimal representation of "]" can also be used to  end
3689         a range.         a range.
3690    
3691         Ranges operate in the collating sequence of character values. They  can         Ranges  operate in the collating sequence of character values. They can
3692         also   be  used  for  characters  specified  numerically,  for  example         also  be  used  for  characters  specified  numerically,  for   example
3693         [\000-\037]. In UTF-8 mode, ranges can include characters whose  values         [\000-\037].  In UTF-8 mode, ranges can include characters whose values
3694         are greater than 255, for example [\x{100}-\x{2ff}].         are greater than 255, for example [\x{100}-\x{2ff}].
3695    
3696         If a range that includes letters is used when caseless matching is set,         If a range that includes letters is used when caseless matching is set,
3697         it matches the letters in either case. For example, [W-c] is equivalent         it matches the letters in either case. For example, [W-c] is equivalent
3698         to  [][\\^_`wxyzabc],  matched  caselessly,  and  in non-UTF-8 mode, if         to [][\\^_`wxyzabc], matched caselessly,  and  in  non-UTF-8  mode,  if
3699         character tables for a French locale are in  use,  [\xc8-\xcb]  matches         character  tables  for  a French locale are in use, [\xc8-\xcb] matches
3700         accented  E  characters in both cases. In UTF-8 mode, PCRE supports the         accented E characters in both cases. In UTF-8 mode, PCRE  supports  the
3701         concept of case for characters with values greater than 128  only  when         concept  of  case for characters with values greater than 128 only when
3702         it is compiled with Unicode property support.         it is compiled with Unicode property support.
3703    
3704         The  character types \d, \D, \p, \P, \s, \S, \w, and \W may also appear         The character types \d, \D, \p, \P, \s, \S, \w, and \W may also  appear
3705         in a character class, and add the characters that  they  match  to  the         in  a  character  class,  and add the characters that they match to the
3706         class. For example, [\dABCDEF] matches any hexadecimal digit. A circum-         class. For example, [\dABCDEF] matches any hexadecimal digit. A circum-
3707         flex can conveniently be used with the upper case  character  types  to         flex  can  conveniently  be used with the upper case character types to
3708         specify  a  more  restricted  set of characters than the matching lower         specify a more restricted set of characters  than  the  matching  lower
3709         case type. For example, the class [^\W_] matches any letter  or  digit,         case  type.  For example, the class [^\W_] matches any letter or digit,
3710         but not underscore.         but not underscore.
3711    
3712         The  only  metacharacters  that are recognized in character classes are         The only metacharacters that are recognized in  character  classes  are
3713         backslash, hyphen (only where it can be  interpreted  as  specifying  a         backslash,  hyphen  (only  where  it can be interpreted as specifying a
3714         range),  circumflex  (only  at the start), opening square bracket (only         range), circumflex (only at the start), opening  square  bracket  (only
3715         when it can be interpreted as introducing a POSIX class name - see  the         when  it can be interpreted as introducing a POSIX class name - see the
3716         next  section),  and  the  terminating closing square bracket. However,         next section), and the terminating  closing  square  bracket.  However,
3717         escaping other non-alphanumeric characters does no harm.         escaping other non-alphanumeric characters does no harm.
3718    
3719    
3720  POSIX CHARACTER CLASSES  POSIX CHARACTER CLASSES
3721    
3722         Perl supports the POSIX notation for character classes. This uses names         Perl supports the POSIX notation for character classes. This uses names
3723         enclosed  by  [: and :] within the enclosing square brackets. PCRE also         enclosed by [: and :] within the enclosing square brackets.  PCRE  also
3724         supports this notation. For example,         supports this notation. For example,
3725    
3726           [01[:alpha:]%]           [01[:alpha:]%]
# Line 3399  POSIX CHARACTER CLASSES Line 3743  POSIX CHARACTER CLASSES
3743           word     "word" characters (same as \w)           word     "word" characters (same as \w)
3744           xdigit   hexadecimal digits           xdigit   hexadecimal digits
3745    
3746         The  "space" characters are HT (9), LF (10), VT (11), FF (12), CR (13),         The "space" characters are HT (9), LF (10), VT (11), FF (12), CR  (13),
3747         and space (32). Notice that this list includes the VT  character  (code         and  space  (32). Notice that this list includes the VT character (code
3748         11). This makes "space" different to \s, which does not include VT (for         11). This makes "space" different to \s, which does not include VT (for
3749         Perl compatibility).         Perl compatibility).
3750    
3751         The name "word" is a Perl extension, and "blank"  is  a  GNU  extension         The  name  "word"  is  a Perl extension, and "blank" is a GNU extension
3752         from  Perl  5.8. Another Perl extension is negation, which is indicated         from Perl 5.8. Another Perl extension is negation, which  is  indicated
3753         by a ^ character after the colon. For example,         by a ^ character after the colon. For example,
3754    
3755           [12[:^digit:]]           [12[:^digit:]]
3756    
3757         matches "1", "2", or any non-digit. PCRE (and Perl) also recognize  the         matches  "1", "2", or any non-digit. PCRE (and Perl) also recognize the
3758         POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but         POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but
3759         these are not supported, and an error is given if they are encountered.         these are not supported, and an error is given if they are encountered.
3760    
# Line 3420  POSIX CHARACTER CLASSES Line 3764  POSIX CHARACTER CLASSES
3764    
3765  VERTICAL BAR  VERTICAL BAR
3766    
3767         Vertical bar characters are used to separate alternative patterns.  For         Vertical  bar characters are used to separate alternative patterns. For
3768         example, the pattern         example, the pattern
3769    
3770           gilbert|sullivan           gilbert|sullivan
3771    
3772         matches  either "gilbert" or "sullivan". Any number of alternatives may         matches either "gilbert" or "sullivan". Any number of alternatives  may
3773         appear, and an empty  alternative  is  permitted  (matching  the  empty         appear,  and  an  empty  alternative  is  permitted (matching the empty
3774         string). The matching process tries each alternative in turn, from left         string). The matching process tries each alternative in turn, from left
3775         to right, and the first one that succeeds is used. If the  alternatives         to  right, and the first one that succeeds is used. If the alternatives
3776         are  within a subpattern (defined below), "succeeds" means matching the         are within a subpattern (defined below), "succeeds" means matching  the
3777         rest of the main pattern as well as the alternative in the  subpattern.         rest  of the main pattern as well as the alternative in the subpattern.
3778    
3779    
3780  INTERNAL OPTION SETTING  INTERNAL OPTION SETTING
3781    
3782         The  settings  of  the  PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and         The settings of the  PCRE_CASELESS,  PCRE_MULTILINE,  PCRE_DOTALL,  and
3783         PCRE_EXTENDED options can be changed  from  within  the  pattern  by  a         PCRE_EXTENDED  options  (which are Perl-compatible) can be changed from
3784         sequence  of  Perl  option  letters  enclosed between "(?" and ")". The         within the pattern by  a  sequence  of  Perl  option  letters  enclosed
3785         option letters are         between "(?" and ")".  The option letters are
3786    
3787           i  for PCRE_CASELESS           i  for PCRE_CASELESS
3788           m  for PCRE_MULTILINE           m  for PCRE_MULTILINE
# Line 3447  INTERNAL OPTION SETTING Line 3791  INTERNAL OPTION SETTING
3791    
3792         For example, (?im) sets caseless, multiline matching. It is also possi-         For example, (?im) sets caseless, multiline matching. It is also possi-
3793         ble to unset these options by preceding the letter with a hyphen, and a         ble to unset these options by preceding the letter with a hyphen, and a
3794         combined setting and unsetting such as (?im-sx), which sets  PCRE_CASE-         combined  setting and unsetting such as (?im-sx), which sets PCRE_CASE-
3795         LESS  and PCRE_MULTILINE while unsetting PCRE_DOTALL and PCRE_EXTENDED,         LESS and PCRE_MULTILINE while unsetting PCRE_DOTALL and  PCRE_EXTENDED,
3796         is also permitted. If a  letter  appears  both  before  and  after  the         is  also  permitted.  If  a  letter  appears  both before and after the
3797         hyphen, the option is unset.         hyphen, the option is unset.
3798    
3799         When  an option change occurs at top level (that is, not inside subpat-         The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and  PCRE_EXTRA
3800         tern parentheses), the change applies to the remainder of  the  pattern         can  be changed in the same way as the Perl-compatible options by using
3801           the characters J, U and X respectively.
3802    
3803           When an option change occurs at top level (that is, not inside  subpat-
3804           tern  parentheses),  the change applies to the remainder of the pattern
3805         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,
3806         PCRE extracts it into the global options (and it will therefore show up         PCRE extracts it into the global options (and it will therefore show up
3807         in data extracted by the pcre_fullinfo() function).         in data extracted by the pcre_fullinfo() function).
3808    
3809         An  option  change  within a subpattern (see below for a description of         An option change within a subpattern (see below for  a  description  of
3810         subpatterns) affects only that part of the current pattern that follows         subpatterns) affects only that part of the current pattern that follows
3811         it, so         it, so
3812    
3813           (a(?i)b)c           (a(?i)b)c
3814    
3815         matches abc and aBc and no other strings (assuming PCRE_CASELESS is not         matches abc and aBc and no other strings (assuming PCRE_CASELESS is not
3816         used).  By this means, options can be made to have  different  settings         used).   By  this means, options can be made to have different settings
3817         in  different parts of the pattern. Any changes made in one alternative         in different parts of the pattern. Any changes made in one  alternative
3818         do carry on into subsequent branches within the  same  subpattern.  For         do  carry  on  into subsequent branches within the same subpattern. For
3819         example,         example,
3820    
3821           (a(?i)b|c)           (a(?i)b|c)
3822    
3823         matches  "ab",  "aB",  "c",  and "C", even though when matching "C" the         matches "ab", "aB", "c", and "C", even though  when  matching  "C"  the
3824         first branch is abandoned before the option setting.  This  is  because         first  branch  is  abandoned before the option setting. This is because
3825         the  effects  of option settings happen at compile time. There would be         the effects of option settings happen at compile time. There  would  be
3826         some very weird behaviour otherwise.         some very weird behaviour otherwise.
3827    
3828         The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and  PCRE_EXTRA         Note:  There  are  other  PCRE-specific  options that can be set by the
3829         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
3830         the characters J, U and X respectively.         cases  the  pattern  can  contain special leading sequences to override
3831           what the application has set or what has been  defaulted.  Details  are
3832           given in the section entitled "Newline sequences" above.
3833    
3834    
3835  SUBPATTERNS  SUBPATTERNS
# Line 3491  SUBPATTERNS Line 3841  SUBPATTERNS
3841    
3842           cat(aract|erpillar|)           cat(aract|erpillar|)
3843    
3844         matches  one  of the words "cat", "cataract", or "caterpillar". Without         matches one of the words "cat", "cataract", or  "caterpillar".  Without
3845         the parentheses, it would match  "cataract",  "erpillar"  or  an  empty         the  parentheses,  it  would  match  "cataract", "erpillar" or an empty
3846         string.         string.
3847    
3848         2.  It  sets  up  the  subpattern as a capturing subpattern. This means         2. It sets up the subpattern as  a  capturing  subpattern.  This  means
3849         that, when the whole pattern  matches,  that  portion  of  the  subject         that,  when  the  whole  pattern  matches,  that portion of the subject
3850         string that matched the subpattern is passed back to the caller via the         string that matched the subpattern is passed back to the caller via the
3851         ovector argument of pcre_exec(). Opening parentheses are  counted  from         ovector  argument  of pcre_exec(). Opening parentheses are counted from
3852         left  to  right  (starting  from 1) to obtain numbers for the capturing         left to right (starting from 1) to obtain  numbers  for  the  capturing
3853         subpatterns.         subpatterns.
3854    
3855         For example, if the string "the red king" is matched against  the  pat-         For  example,  if the string "the red king" is matched against the pat-
3856         tern         tern
3857    
3858           the ((red|white) (king|queen))           the ((red|white) (king|queen))
# Line 3510  SUBPATTERNS Line 3860  SUBPATTERNS
3860         the captured substrings are "red king", "red", and "king", and are num-         the captured substrings are "red king", "red", and "king", and are num-
3861         bered 1, 2, and 3, respectively.         bered 1, 2, and 3, respectively.
3862    
3863         The fact that plain parentheses fulfil  two  functions  is  not  always         The  fact  that  plain  parentheses  fulfil two functions is not always
3864         helpful.   There are often times when a grouping subpattern is required         helpful.  There are often times when a grouping subpattern is  required
3865         without a capturing requirement. If an opening parenthesis is  followed         without  a capturing requirement. If an opening parenthesis is followed
3866         by  a question mark and a colon, the subpattern does not do any captur-         by a question mark and a colon, the subpattern does not do any  captur-
3867         ing, and is not counted when computing the  number  of  any  subsequent         ing,  and  is  not  counted when computing the number of any subsequent
3868         capturing  subpatterns. For example, if the string "the white queen" is         capturing subpatterns. For example, if the string "the white queen"  is
3869         matched against the pattern         matched against the pattern
3870    
3871           the ((?:red|white) (king|queen))           the ((?:red|white) (king|queen))
# Line 3523  SUBPATTERNS Line 3873  SUBPATTERNS
3873         the captured substrings are "white queen" and "queen", and are numbered         the captured substrings are "white queen" and "queen", and are numbered
3874         1 and 2. The maximum number of capturing subpatterns is 65535.         1 and 2. The maximum number of capturing subpatterns is 65535.
3875    
3876         As  a  convenient shorthand, if any option settings are required at the         As a convenient shorthand, if any option settings are required  at  the
3877         start of a non-capturing subpattern,  the  option  letters  may  appear         start  of  a  non-capturing  subpattern,  the option letters may appear
3878         between the "?" and the ":". Thus the two patterns         between the "?" and the ":". Thus the two patterns
3879    
3880           (?i:saturday|sunday)           (?i:saturday|sunday)
3881           (?:(?i)saturday|sunday)           (?:(?i)saturday|sunday)
3882    
3883         match exactly the same set of strings. Because alternative branches are         match exactly the same set of strings. Because alternative branches are
3884         tried from left to right, and options are not reset until  the  end  of         tried  from  left  to right, and options are not reset until the end of
3885         the  subpattern is reached, an option setting in one branch does affect         the subpattern is reached, an option setting in one branch does  affect
3886         subsequent branches, so the above patterns match "SUNDAY"  as  well  as         subsequent  branches,  so  the above patterns match "SUNDAY" as well as
3887         "Saturday".         "Saturday".
3888    
3889    
3890    DUPLICATE SUBPATTERN NUMBERS
3891    
3892           Perl 5.10 introduced a feature whereby each alternative in a subpattern
3893           uses  the same numbers for its capturing parentheses. Such a subpattern
3894           starts with (?| and is itself a non-capturing subpattern. For  example,
3895           consider this pattern:
3896    
3897             (?|(Sat)ur|(Sun))day
3898    
3899           Because  the two alternatives are inside a (?| group, both sets of cap-
3900           turing parentheses are numbered one. Thus, when  the  pattern  matches,
3901           you  can  look  at captured substring number one, whichever alternative
3902           matched. This construct is useful when you want to  capture  part,  but
3903           not all, of one of a number of alternatives. Inside a (?| group, paren-
3904           theses are numbered as usual, but the number is reset at the  start  of
3905           each  branch. The numbers of any capturing buffers that follow the sub-
3906           pattern start after the highest number used in any branch. The  follow-
3907           ing  example  is taken from the Perl documentation.  The numbers under-
3908           neath show in which buffer the captured content will be stored.
3909    
3910             # before  ---------------branch-reset----------- after
3911             / ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x
3912             # 1            2         2  3        2     3     4
3913    
3914           A backreference or a recursive call to  a  numbered  subpattern  always
3915           refers to the first one in the pattern with the given number.
3916    
3917           An  alternative approach to using this "branch reset" feature is to use
3918           duplicate named subpatterns, as described in the next section.
3919    
3920    
3921  NAMED SUBPATTERNS  NAMED SUBPATTERNS
3922    
3923         Identifying  capturing  parentheses  by number is simple, but it can be         Identifying capturing parentheses by number is simple, but  it  can  be
3924         very hard to keep track of the numbers in complicated  regular  expres-         very  hard  to keep track of the numbers in complicated regular expres-
3925         sions.  Furthermore,  if  an  expression  is  modified, the numbers may         sions. Furthermore, if an  expression  is  modified,  the  numbers  may
3926         change. To help with this difficulty, PCRE supports the naming of  sub-         change.  To help with this difficulty, PCRE supports the naming of sub-
3927         patterns. This feature was not added to Perl until release 5.10. Python         patterns. This feature was not added to Perl until release 5.10. Python
3928         had the feature earlier, and PCRE introduced it at release  4.0,  using         had  the  feature earlier, and PCRE introduced it at release 4.0, using
3929         the  Python syntax. PCRE now supports both the Perl and the Python syn-         the Python syntax. PCRE now supports both the Perl and the Python  syn-
3930         tax.         tax.
3931    
3932         In PCRE, a subpattern can be named in one of three  ways:  (?<name>...)         In  PCRE,  a subpattern can be named in one of three ways: (?<name>...)
3933         or  (?'name'...)  as in Perl, or (?P<name>...) as in Python. References         or (?'name'...) as in Perl, or (?P<name>...) as in  Python.  References
3934         to capturing parentheses from other parts of the pattern, such as back-         to capturing parentheses from other parts of the pattern, such as back-
3935         references,  recursion,  and conditions, can be made by name as well as         references, recursion, and conditions, can be made by name as  well  as
3936         by number.         by number.
3937    
3938         Names consist of up to  32  alphanumeric  characters  and  underscores.         Names  consist  of  up  to  32 alphanumeric characters and underscores.
3939         Named  capturing  parentheses  are  still  allocated numbers as well as         Named capturing parentheses are still  allocated  numbers  as  well  as
3940         names, exactly as if the names were not present. The PCRE API  provides         names,  exactly as if the names were not present. The PCRE API provides
3941         function calls for extracting the name-to-number translation table from         function calls for extracting the name-to-number translation table from
3942         a compiled pattern. There is also a convenience function for extracting         a compiled pattern. There is also a convenience function for extracting
3943         a captured substring by name.         a captured substring by name.
3944    
3945         By  default, a name must be unique within a pattern, but it is possible         By default, a name must be unique within a pattern, but it is  possible
3946         to relax this constraint by setting the PCRE_DUPNAMES option at compile         to relax this constraint by setting the PCRE_DUPNAMES option at compile
3947         time.  This  can  be useful for patterns where only one instance of the         time. This can be useful for patterns where only one  instance  of  the
3948         named parentheses can match. Suppose you want to match the  name  of  a         named  parentheses  can  match. Suppose you want to match the name of a
3949         weekday,  either as a 3-letter abbreviation or as the full name, and in         weekday, either as a 3-letter abbreviation or as the full name, and  in
3950         both cases you want to extract the abbreviation. This pattern (ignoring         both cases you want to extract the abbreviation. This pattern (ignoring
3951         the line breaks) does the job:         the line breaks) does the job:
3952    
# Line 3575  NAMED SUBPATTERNS Line 3956  NAMED SUBPATTERNS
3956           (?<DN>Thu)(?:rsday)?|           (?<DN>Thu)(?:rsday)?|
3957           (?<DN>Sat)(?:urday)?           (?<DN>Sat)(?:urday)?
3958    
3959         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
3960         match.  The convenience  function  for  extracting  the  data  by  name         match.  (An alternative way of solving this problem is to use a "branch
3961         returns  the  substring  for  the first (and in this example, the only)         reset" subpattern, as described in the previous section.)
3962         subpattern of that name that matched.  This  saves  searching  to  find  
3963         which  numbered  subpattern  it  was. If you make a reference to a non-         The convenience function for extracting the data by  name  returns  the
3964         unique named subpattern from elsewhere in the  pattern,  the  one  that         substring  for  the first (and in this example, the only) subpattern of
3965         corresponds  to  the  lowest number is used. For further details of the         that name that matched. This saves searching  to  find  which  numbered
3966         interfaces for handling named subpatterns, see the  pcreapi  documenta-         subpattern  it  was. If you make a reference to a non-unique named sub-
3967         tion.         pattern from elsewhere in the pattern, the one that corresponds to  the
3968           lowest  number  is used. For further details of the interfaces for han-
3969           dling named subpatterns, see the pcreapi documentation.
3970    
3971    
3972  REPETITION  REPETITION
3973    
3974         Repetition  is  specified  by  quantifiers, which can follow any of the         Repetition is specified by quantifiers, which can  follow  any  of  the
3975         following items:         following items:
3976    
3977           a literal data character           a literal data character
# Line 3601  REPETITION Line 3984  REPETITION
3984           a back reference (see next section)           a back reference (see next section)
3985           a parenthesized subpattern (unless it is an assertion)           a parenthesized subpattern (unless it is an assertion)
3986    
3987         The general repetition quantifier specifies a minimum and maximum  num-         The  general repetition quantifier specifies a minimum and maximum num-
3988         ber  of  permitted matches, by giving the two numbers in curly brackets         ber of permitted matches, by giving the two numbers in  curly  brackets
3989         (braces), separated by a comma. The numbers must be  less  than  65536,         (braces),  separated  by  a comma. The numbers must be less than 65536,
3990         and the first must be less than or equal to the second. For example:         and the first must be less than or equal to the second. For example:
3991    
3992           z{2,4}           z{2,4}
3993    
3994         matches  "zz",  "zzz",  or  "zzzz". A closing brace on its own is not a         matches "zz", "zzz", or "zzzz". A closing brace on its  own  is  not  a
3995         special character. If the second number is omitted, but  the  comma  is         special  character.  If  the second number is omitted, but the comma is
3996         present,  there  is  no upper limit; if the second number and the comma         present, there is no upper limit; if the second number  and  the  comma
3997         are both omitted, the quantifier specifies an exact number of  required         are  both omitted, the quantifier specifies an exact number of required
3998         matches. Thus         matches. Thus
3999    
4000           [aeiou]{3,}           [aeiou]{3,}
# Line 3620  REPETITION Line 4003  REPETITION
4003    
4004           \d{8}           \d{8}
4005    
4006         matches  exactly  8  digits. An opening curly bracket that appears in a         matches exactly 8 digits. An opening curly bracket that  appears  in  a
4007         position where a quantifier is not allowed, or one that does not  match         position  where a quantifier is not allowed, or one that does not match
4008         the  syntax of a quantifier, is taken as a literal character. For exam-         the syntax of a quantifier, is taken as a literal character. For  exam-
4009         ple, {,6} is not a quantifier, but a literal string of four characters.         ple, {,6} is not a quantifier, but a literal string of four characters.
4010    
4011         In  UTF-8  mode,  quantifiers  apply to UTF-8 characters rather than to         In UTF-8 mode, quantifiers apply to UTF-8  characters  rather  than  to
4012         individual bytes. Thus, for example, \x{100}{2} matches two UTF-8 char-         individual bytes. Thus, for example, \x{100}{2} matches two UTF-8 char-
4013         acters, each of which is represented by a two-byte sequence. Similarly,         acters, each of which is represented by a two-byte sequence. Similarly,
4014         when Unicode property support is available, \X{3} matches three Unicode         when Unicode property support is available, \X{3} matches three Unicode
4015         extended  sequences,  each of which may be several bytes long (and they         extended sequences, each of which may be several bytes long  (and  they
4016         may be of different lengths).         may be of different lengths).
4017    
4018         The quantifier {0} is permitted, causing the expression to behave as if         The quantifier {0} is permitted, causing the expression to behave as if
4019         the previous item and the quantifier were not present.         the previous item and the quantifier were not present. This may be use-
4020           ful  for  subpatterns that are referenced as subroutines from elsewhere
4021           in the pattern. Items other than subpatterns that have a {0} quantifier
4022           are omitted from the compiled pattern.
4023    
4024         For  convenience, the three most common quantifiers have single-charac-         For  convenience, the three most common quantifiers have single-charac-
4025         ter abbreviations:         ter abbreviations:
# Line 3788  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE Line 4174  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
4174    
4175           \d++foo           \d++foo
4176    
4177         Possessive  quantifiers  are  always  greedy;  the   setting   of   the         Note that a possessive quantifier can be used with an entire group, for
4178           example:
4179    
4180             (abc|xyz){2,3}+
4181    
4182           Possessive   quantifiers   are   always  greedy;  the  setting  of  the
4183         PCRE_UNGREEDY option is ignored. They are a convenient notation for the         PCRE_UNGREEDY option is ignored. They are a convenient notation for the
4184         simpler forms of atomic group. However, there is no difference  in  the         simpler  forms  of atomic group. However, there is no difference in the
4185         meaning  of  a  possessive  quantifier and the equivalent atomic group,         meaning of a possessive quantifier and  the  equivalent  atomic  group,
4186         though there may be a performance  difference;  possessive  quantifiers         though  there  may  be a performance difference; possessive quantifiers
4187         should be slightly faster.         should be slightly faster.
4188    
4189         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-
4190         tax.  Jeffrey Friedl originated the idea (and the name)  in  the  first         tax.   Jeffrey  Friedl  originated the idea (and the name) in the first
4191         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
4192         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
4193         found its way into Perl at release 5.10.         found its way into Perl at release 5.10.
4194    
4195         PCRE has an optimization that automatically "possessifies" certain sim-         PCRE has an optimization that automatically "possessifies" certain sim-
4196         ple pattern constructs. For example, the sequence  A+B  is  treated  as         ple  pattern  constructs.  For  example, the sequence A+B is treated as
4197         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
4198         when B must follow.         when B must follow.
4199    
4200         When a pattern contains an unlimited repeat inside  a  subpattern  that         When  a  pattern  contains an unlimited repeat inside a subpattern that
4201         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
4202         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
4203         very long time indeed. The pattern         very long time indeed. The pattern
4204    
4205           (\D+|<\d+>)*[!?]           (\D+|<\d+>)*[!?]
4206    
4207         matches  an  unlimited number of substrings that either consist of non-         matches an unlimited number of substrings that either consist  of  non-
4208         digits, or digits enclosed in <>, followed by either ! or  ?.  When  it         digits,  or  digits  enclosed in <>, followed by either ! or ?. When it
4209         matches, it runs quickly. However, if it is applied to         matches, it runs quickly. However, if it is applied to
4210    
4211           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
4212    
4213         it  takes  a  long  time  before reporting failure. This is because the         it takes a long time before reporting  failure.  This  is  because  the
4214         string can be divided between the internal \D+ repeat and the  external         string  can be divided between the internal \D+ repeat and the external
4215         *  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
4216         example uses [!?] rather than a single character at  the  end,  because         example  uses  [!?]  rather than a single character at the end, because
4217         both  PCRE  and  Perl have an optimization that allows for fast failure         both PCRE and Perl have an optimization that allows  for  fast  failure
4218         when a single character is used. They remember the last single  charac-         when  a single character is used. They remember the last single charac-
4219         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
4220         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
4221         group, like this:         group, like this:
4222    
4223           ((?>\D+)|<\d+>)*[!?]           ((?>\D+)|<\d+>)*[!?]
4224    
4225         sequences  of non-digits cannot be broken, and failure happens quickly.         sequences of non-digits cannot be broken, and failure happens  quickly.
4226    
4227    
4228  BACK REFERENCES  BACK REFERENCES
4229    
4230         Outside a character class, a backslash followed by a digit greater than         Outside a character class, a backslash followed by a digit greater than
4231         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-
4232         pattern earlier (that is, to its left) in the pattern,  provided  there         pattern  earlier  (that is, to its left) in the pattern, provided there