/[pcre]/code/trunk/doc/pcre.txt
ViewVC logotype

Diff of /code/trunk/doc/pcre.txt

Parent Directory Parent Directory | Revision Log Revision Log | View Patch Patch

revision 123 by ph10, Mon Mar 12 15:19:06 2007 UTC revision 313 by ph10, Wed Jan 23 18:05:06 2008 UTC
# Line 45  INTRODUCTION Line 45  INTRODUCTION
45    
46         Details of exactly which Perl regular expression features are  and  are         Details of exactly which Perl regular expression features are  and  are
47         not supported by PCRE are given in separate documents. See the pcrepat-         not supported by PCRE are given in separate documents. See the pcrepat-
48         tern and pcrecompat pages.         tern and pcrecompat pages. There is a syntax summary in the  pcresyntax
49           page.
50    
51         Some features of PCRE can be included, excluded, or  changed  when  the         Some  features  of  PCRE can be included, excluded, or changed when the
52         library  is  built.  The pcre_config() function makes it possible for a         library is built. The pcre_config() function makes it  possible  for  a
53         client to discover which features are  available.  The  features  them-         client  to  discover  which  features are available. The features them-
54         selves  are described in the pcrebuild page. Documentation about build-         selves are described in the pcrebuild page. Documentation about  build-
55         ing PCRE for various operating systems can be found in the README  file         ing  PCRE for various operating systems can be found in the README file
56         in the source distribution.         in the source distribution.
57    
58         The  library  contains  a number of undocumented internal functions and         The library contains a number of undocumented  internal  functions  and
59         data tables that are used by more than one  of  the  exported  external         data  tables  that  are  used by more than one of the exported external
60         functions,  but  which  are  not  intended for use by external callers.         functions, but which are not intended  for  use  by  external  callers.
61         Their names all begin with "_pcre_", which hopefully will  not  provoke         Their  names  all begin with "_pcre_", which hopefully will not provoke
62         any name clashes. In some environments, it is possible to control which         any name clashes. In some environments, it is possible to control which
63         external symbols are exported when a shared library is  built,  and  in         external  symbols  are  exported when a shared library is built, and in
64         these cases the undocumented symbols are not exported.         these cases the undocumented symbols are not exported.
65    
66    
67  USER DOCUMENTATION  USER DOCUMENTATION
68    
69         The  user  documentation  for PCRE comprises a number of different sec-         The user documentation for PCRE comprises a number  of  different  sec-
70         tions. In the "man" format, each of these is a separate "man page".  In         tions.  In the "man" format, each of these is a separate "man page". In
71         the  HTML  format, each is a separate page, linked from the index page.         the HTML format, each is a separate page, linked from the  index  page.
72         In the plain text format, all the sections are concatenated,  for  ease         In  the  plain text format, all the sections are concatenated, for ease
73         of searching. The sections are as follows:         of searching. The sections are as follows:
74    
75           pcre              this document           pcre              this document
76             pcre-config       show PCRE installation configuration information
77           pcreapi           details of PCRE's native C API           pcreapi           details of PCRE's native C API
78           pcrebuild         options for building PCRE           pcrebuild         options for building PCRE
79           pcrecallout       details of the callout feature           pcrecallout       details of the callout feature
# Line 82  USER DOCUMENTATION Line 84  USER DOCUMENTATION
84           pcrepartial       details of the partial matching facility           pcrepartial       details of the partial matching facility
85           pcrepattern       syntax and semantics of supported           pcrepattern       syntax and semantics of supported
86                               regular expressions                               regular expressions
87             pcresyntax        quick syntax reference
88           pcreperform       discussion of performance issues           pcreperform       discussion of performance issues
89           pcreposix         the POSIX-compatible C API           pcreposix         the POSIX-compatible C API
90           pcreprecompile    details of saving and re-using precompiled patterns           pcreprecompile    details of saving and re-using precompiled patterns
# Line 89  USER DOCUMENTATION Line 92  USER DOCUMENTATION
92           pcrestack         discussion of stack usage           pcrestack         discussion of stack usage
93           pcretest          description of the pcretest testing command           pcretest          description of the pcretest testing command
94    
95         In addition, in the "man" and HTML formats, there is a short  page  for         In  addition,  in the "man" and HTML formats, there is a short page for
96         each C library function, listing its arguments and results.         each C library function, listing its arguments and results.
97    
98    
99  LIMITATIONS  LIMITATIONS
100    
101         There  are some size limitations in PCRE but it is hoped that they will         There are some size limitations in PCRE but it is hoped that they  will
102         never in practice be relevant.         never in practice be relevant.
103    
104         The maximum length of a compiled pattern is 65539 (sic) bytes  if  PCRE         The  maximum  length of a compiled pattern is 65539 (sic) bytes if PCRE
105         is compiled with the default internal linkage size of 2. If you want to         is compiled with the default internal linkage size of 2. If you want to
106         process regular expressions that are truly enormous,  you  can  compile         process  regular  expressions  that are truly enormous, you can compile
107         PCRE  with  an  internal linkage size of 3 or 4 (see the README file in         PCRE with an internal linkage size of 3 or 4 (see the  README  file  in
108         the source distribution and the pcrebuild documentation  for  details).         the  source  distribution and the pcrebuild documentation for details).
109         In  these  cases the limit is substantially larger.  However, the speed         In these cases the limit is substantially larger.  However,  the  speed
110         of execution is slower.         of execution is slower.
111    
112         All values in repeating quantifiers must be less than 65536. The  maxi-         All values in repeating quantifiers must be less than 65536.
        mum  compiled  length  of  subpattern  with an explicit repeat count is  
        30000 bytes. The maximum number of capturing subpatterns is 65535.  
113    
114         There is no limit to the number of parenthesized subpatterns, but there         There is no limit to the number of parenthesized subpatterns, but there
115         can be no more than 65535 capturing subpatterns.         can be no more than 65535 capturing subpatterns.
# Line 116  LIMITATIONS Line 117  LIMITATIONS
117         The maximum length of name for a named subpattern is 32 characters, and         The maximum length of name for a named subpattern is 32 characters, and
118         the maximum number of named subpatterns is 10000.         the maximum number of named subpatterns is 10000.
119    
120         The maximum length of a subject string is the largest  positive  number         The  maximum  length of a subject string is the largest positive number
121         that  an integer variable can hold. However, when using the traditional         that an integer variable can hold. However, when using the  traditional
122         matching function, PCRE uses recursion to handle subpatterns and indef-         matching function, PCRE uses recursion to handle subpatterns and indef-
123         inite  repetition.  This means that the available stack space may limit         inite repetition.  This means that the available stack space may  limit
124         the size of a subject string that can be processed by certain patterns.         the size of a subject string that can be processed by certain patterns.
125         For a discussion of stack issues, see the pcrestack documentation.         For a discussion of stack issues, see the pcrestack documentation.
126    
127    
128  UTF-8 AND UNICODE PROPERTY SUPPORT  UTF-8 AND UNICODE PROPERTY SUPPORT
129    
130         From  release  3.3,  PCRE  has  had  some support for character strings         From release 3.3, PCRE has  had  some  support  for  character  strings
131         encoded in the UTF-8 format. For release 4.0 this was greatly  extended         encoded  in the UTF-8 format. For release 4.0 this was greatly extended
132         to  cover  most common requirements, and in release 5.0 additional sup-         to cover most common requirements, and in release 5.0  additional  sup-
133         port for Unicode general category properties was added.         port for Unicode general category properties was added.
134    
135         In order process UTF-8 strings, you must build PCRE  to  include  UTF-8         In  order  process  UTF-8 strings, you must build PCRE to include UTF-8
136         support  in  the  code,  and, in addition, you must call pcre_compile()         support in the code, and, in addition,  you  must  call  pcre_compile()
137         with the PCRE_UTF8 option flag. When you do this, both the pattern  and         with  the PCRE_UTF8 option flag. When you do this, both the pattern and
138         any  subject  strings  that are matched against it are treated as UTF-8         any subject strings that are matched against it are  treated  as  UTF-8
139         strings instead of just strings of bytes.         strings instead of just strings of bytes.
140    
141         If you compile PCRE with UTF-8 support, but do not use it at run  time,         If  you compile PCRE with UTF-8 support, but do not use it at run time,
142         the  library will be a bit bigger, but the additional run time overhead         the library will be a bit bigger, but the additional run time  overhead
143         is limited to testing the PCRE_UTF8 flag occasionally, so should not be         is limited to testing the PCRE_UTF8 flag occasionally, so should not be
144         very big.         very big.
145    
146         If PCRE is built with Unicode character property support (which implies         If PCRE is built with Unicode character property support (which implies
147         UTF-8 support), the escape sequences \p{..}, \P{..}, and  \X  are  sup-         UTF-8  support),  the  escape sequences \p{..}, \P{..}, and \X are sup-
148         ported.  The available properties that can be tested are limited to the         ported.  The available properties that can be tested are limited to the
149         general category properties such as Lu for an upper case letter  or  Nd         general  category  properties such as Lu for an upper case letter or Nd
150         for  a  decimal number, the Unicode script names such as Arabic or Han,         for a decimal number, the Unicode script names such as Arabic  or  Han,
151         and the derived properties Any and L&. A full  list  is  given  in  the         and  the  derived  properties  Any  and L&. A full list is given in the
152         pcrepattern documentation. Only the short names for properties are sup-         pcrepattern documentation. Only the short names for properties are sup-
153         ported. For example, \p{L} matches a letter. Its Perl synonym,  \p{Let-         ported.  For example, \p{L} matches a letter. Its Perl synonym, \p{Let-
154         ter},  is  not  supported.   Furthermore,  in Perl, many properties may         ter}, is not supported.  Furthermore,  in  Perl,  many  properties  may
155         optionally be prefixed by "Is", for compatibility with Perl  5.6.  PCRE         optionally  be  prefixed by "Is", for compatibility with Perl 5.6. PCRE
156         does not support this.         does not support this.
157    
158         The following comments apply when PCRE is running in UTF-8 mode:     Validity of UTF-8 strings
159    
160           When you set the PCRE_UTF8 flag, the strings  passed  as  patterns  and
161           subjects are (by default) checked for validity on entry to the relevant
162           functions. From release 7.3 of PCRE, the check is according  the  rules
163           of  RFC  3629, which are themselves derived from the Unicode specifica-
164           tion. Earlier releases of PCRE followed the rules of  RFC  2279,  which
165           allows  the  full range of 31-bit values (0 to 0x7FFFFFFF). The current
166           check allows only values in the range U+0 to U+10FFFF, excluding U+D800
167           to U+DFFF.
168    
169           The  excluded  code  points are the "Low Surrogate Area" of Unicode, of
170           which the Unicode Standard says this: "The Low Surrogate Area does  not
171           contain  any  character  assignments,  consequently  no  character code
172           charts or namelists are provided for this area. Surrogates are reserved
173           for  use  with  UTF-16 and then must be used in pairs." The code points
174           that are encoded by UTF-16 pairs  are  available  as  independent  code
175           points  in  the  UTF-8  encoding.  (In other words, the whole surrogate
176           thing is a fudge for UTF-16 which unfortunately messes up UTF-8.)
177    
178           If an  invalid  UTF-8  string  is  passed  to  PCRE,  an  error  return
179           (PCRE_ERROR_BADUTF8) is given. In some situations, you may already know
180           that your strings are valid, and therefore want to skip these checks in
181           order to improve performance. If you set the PCRE_NO_UTF8_CHECK flag at
182           compile time or at run time, PCRE assumes that the pattern  or  subject
183           it  is  given  (respectively)  contains only valid UTF-8 codes. In this
184           case, it does not diagnose an invalid UTF-8 string.
185    
186           If you pass an invalid UTF-8 string  when  PCRE_NO_UTF8_CHECK  is  set,
187           what  happens  depends on why the string is invalid. If the string con-
188           forms to the "old" definition of UTF-8 (RFC 2279), it is processed as a
189           string  of  characters  in  the  range 0 to 0x7FFFFFFF. In other words,
190           apart from the initial validity test, PCRE (when in UTF-8 mode) handles
191           strings  according  to  the more liberal rules of RFC 2279. However, if
192           the string does not even conform to RFC 2279, the result is  undefined.
193           Your program may crash.
194    
195           If  you  want  to  process  strings  of  values  in the full range 0 to
196           0x7FFFFFFF, encoded in a UTF-8-like manner as per the old RFC, you  can
197           set PCRE_NO_UTF8_CHECK to bypass the more restrictive test. However, in
198           this situation, you will have to apply your own validity check.
199    
200         1.  When you set the PCRE_UTF8 flag, the strings passed as patterns and     General comments about UTF-8 mode
        subjects are checked for validity on entry to the  relevant  functions.  
        If an invalid UTF-8 string is passed, an error return is given. In some  
        situations, you may already know  that  your  strings  are  valid,  and  
        therefore want to skip these checks in order to improve performance. If  
        you set the PCRE_NO_UTF8_CHECK flag at compile time  or  at  run  time,  
        PCRE  assumes  that  the  pattern or subject it is given (respectively)  
        contains only valid UTF-8 codes. In this case, it does not diagnose  an  
        invalid  UTF-8 string. If you pass an invalid UTF-8 string to PCRE when  
        PCRE_NO_UTF8_CHECK is set, the results are undefined. Your program  may  
        crash.  
201    
202         2.  An  unbraced  hexadecimal  escape sequence (such as \xb3) matches a         1. An unbraced hexadecimal escape sequence (such  as  \xb3)  matches  a
203         two-byte UTF-8 character if the value is greater than 127.         two-byte UTF-8 character if the value is greater than 127.
204    
205         3. Octal numbers up to \777 are recognized, and  match  two-byte  UTF-8         2.  Octal  numbers  up to \777 are recognized, and match two-byte UTF-8
206         characters for values greater than \177.         characters for values greater than \177.
207    
208         4.  Repeat quantifiers apply to complete UTF-8 characters, not to indi-         3. Repeat quantifiers apply to complete UTF-8 characters, not to  indi-
209         vidual bytes, for example: \x{100}{3}.         vidual bytes, for example: \x{100}{3}.
210    
211         5. The dot metacharacter matches one UTF-8 character instead of a  sin-         4.  The dot metacharacter matches one UTF-8 character instead of a sin-
212         gle byte.         gle byte.
213    
214         6.  The  escape sequence \C can be used to match a single byte in UTF-8         5. The escape sequence \C can be used to match a single byte  in  UTF-8
215         mode, but its use can lead to some strange effects.  This  facility  is         mode,  but  its  use can lead to some strange effects. This facility is
216         not available in the alternative matching function, pcre_dfa_exec().         not available in the alternative matching function, pcre_dfa_exec().
217    
218         7.  The  character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly         6. The character escapes \b, \B, \d, \D, \s, \S, \w, and  \W  correctly
219         test characters of any code value, but the characters that PCRE  recog-         test  characters of any code value, but the characters that PCRE recog-
220         nizes  as  digits,  spaces,  or  word characters remain the same set as         nizes as digits, spaces, or word characters  remain  the  same  set  as
221         before, all with values less than 256. This remains true even when PCRE         before, all with values less than 256. This remains true even when PCRE
222         includes  Unicode  property support, because to do otherwise would slow         includes Unicode property support, because to do otherwise  would  slow
223         down PCRE in many common cases. If you really want to test for a  wider         down  PCRE in many common cases. If you really want to test for a wider
224         sense  of,  say,  "digit",  you must use Unicode property tests such as         sense of, say, "digit", you must use Unicode  property  tests  such  as
225         \p{Nd}.         \p{Nd}.
226    
227         8. Similarly, characters that match the POSIX named  character  classes         7.  Similarly,  characters that match the POSIX named character classes
228         are all low-valued characters.         are all low-valued characters.
229    
230         9.  Case-insensitive  matching  applies only to characters whose values         8. However, the Perl 5.10 horizontal and vertical  whitespace  matching
231         are less than 128, unless PCRE is built with Unicode property  support.         escapes (\h, \H, \v, and \V) do match all the appropriate Unicode char-
232         Even  when  Unicode  property support is available, PCRE still uses its         acters.
233         own character tables when checking the case of  low-valued  characters,  
234         so  as not to degrade performance.  The Unicode property information is         9. Case-insensitive matching applies only to  characters  whose  values
235           are  less than 128, unless PCRE is built with Unicode property support.
236           Even when Unicode property support is available, PCRE  still  uses  its
237           own  character  tables when checking the case of low-valued characters,
238           so as not to degrade performance.  The Unicode property information  is
239         used only for characters with higher values. Even when Unicode property         used only for characters with higher values. Even when Unicode property
240         support is available, PCRE supports case-insensitive matching only when         support is available, PCRE supports case-insensitive matching only when
241         there is a one-to-one mapping between a letter's  cases.  There  are  a         there  is  a  one-to-one  mapping between a letter's cases. There are a
242         small  number  of  many-to-one  mappings in Unicode; these are not sup-         small number of many-to-one mappings in Unicode;  these  are  not  sup-
243         ported by PCRE.         ported by PCRE.
244    
245    
# Line 214  AUTHOR Line 249  AUTHOR
249         University Computing Service         University Computing Service
250         Cambridge CB2 3QH, England.         Cambridge CB2 3QH, England.
251    
252         Putting an actual email address here seems to have been a spam  magnet,         Putting  an actual email address here seems to have been a spam magnet,
253         so I've taken it away. If you want to email me, use my initial and sur-         so I've taken it away. If you want to email me, use  my  two  initials,
254         name, separated by a dot, at the domain ucs.cam.ac.uk.         followed by the two digits 10, at the domain cam.ac.uk.
255    
256    
257  REVISION  REVISION
258    
259         Last updated: 06 March 2007         Last updated: 09 August 2007
260         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
261  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
262    
# Line 236  NAME Line 271  NAME
271  PCRE BUILD-TIME OPTIONS  PCRE BUILD-TIME OPTIONS
272    
273         This  document  describes  the  optional  features  of PCRE that can be         This  document  describes  the  optional  features  of PCRE that can be
274         selected when the library is compiled. They are all selected, or  dese-         selected when the library is compiled. It assumes use of the  configure
275         lected, by providing options to the configure script that is run before         script,  where the optional features are selected or deselected by pro-
276         the make command. The complete list of  options  for  configure  (which         viding options to configure before running the make  command.  However,
277         includes  the  standard  ones such as the selection of the installation         the  same  options  can be selected in both Unix-like and non-Unix-like
278         directory) can be obtained by running         environments using the GUI facility of  CMakeSetup  if  you  are  using
279           CMake instead of configure to build PCRE.
280    
281           The complete list of options for configure (which includes the standard
282           ones such as the  selection  of  the  installation  directory)  can  be
283           obtained by running
284    
285           ./configure --help           ./configure --help
286    
287         The following sections describe certain options whose names begin  with         The  following  sections  include  descriptions  of options whose names
288         --enable  or  --disable. These settings specify changes to the defaults         begin with --enable or --disable. These settings specify changes to the
289         for the configure command. Because of the  way  that  configure  works,         defaults  for  the configure command. Because of the way that configure
290         --enable  and  --disable  always  come  in  pairs, so the complementary         works, --enable and --disable always come in pairs, so  the  complemen-
291         option always exists as well, but as it specifies the  default,  it  is         tary  option always exists as well, but as it specifies the default, it
292         not described.         is not described.
293    
294    
295  C++ SUPPORT  C++ SUPPORT
# Line 269  UTF-8 SUPPORT Line 309  UTF-8 SUPPORT
309    
310           --enable-utf8           --enable-utf8
311    
312         to  the  configure  command.  Of  itself, this does not make PCRE treat         to the configure command. Of itself, this  does  not  make  PCRE  treat
313         strings as UTF-8. As well as compiling PCRE with this option, you  also         strings  as UTF-8. As well as compiling PCRE with this option, you also
314         have  have to set the PCRE_UTF8 option when you call the pcre_compile()         have have to set the PCRE_UTF8 option when you call the  pcre_compile()
315         function.         function.
316    
317    
318  UNICODE CHARACTER PROPERTY SUPPORT  UNICODE CHARACTER PROPERTY SUPPORT
319    
320         UTF-8 support allows PCRE to process character values greater than  255         UTF-8  support allows PCRE to process character values greater than 255
321         in  the  strings that it handles. On its own, however, it does not pro-         in the strings that it handles. On its own, however, it does  not  pro-
322         vide any facilities for accessing the properties of such characters. If         vide any facilities for accessing the properties of such characters. If
323         you  want  to  be able to use the pattern escapes \P, \p, and \X, which         you want to be able to use the pattern escapes \P, \p,  and  \X,  which
324         refer to Unicode character properties, you must add         refer to Unicode character properties, you must add
325    
326           --enable-unicode-properties           --enable-unicode-properties
327    
328         to the configure command. This implies UTF-8 support, even if you  have         to  the configure command. This implies UTF-8 support, even if you have
329         not explicitly requested it.         not explicitly requested it.
330    
331         Including  Unicode  property  support  adds around 90K of tables to the         Including Unicode property support adds around 30K  of  tables  to  the
332         PCRE library, approximately doubling its size. Only the  general  cate-         PCRE  library.  Only  the general category properties such as Lu and Nd
333         gory  properties  such as Lu and Nd are supported. Details are given in         are supported. Details are given in the pcrepattern documentation.
        the pcrepattern documentation.  
334    
335    
336  CODE VALUE OF NEWLINE  CODE VALUE OF NEWLINE
# Line 313  CODE VALUE OF NEWLINE Line 352  CODE VALUE OF NEWLINE
352    
353         to the configure command. There is a fourth option, specified by         to the configure command. There is a fourth option, specified by
354    
355             --enable-newline-is-anycrlf
356    
357           which  causes  PCRE  to recognize any of the three sequences CR, LF, or
358           CRLF as indicating a line ending. Finally, a fifth option, specified by
359    
360           --enable-newline-is-any           --enable-newline-is-any
361    
362         which causes PCRE to recognize any Unicode newline sequence.         causes PCRE to recognize any Unicode newline sequence.
363    
364         Whatever  line  ending convention is selected when PCRE is built can be         Whatever  line  ending convention is selected when PCRE is built can be
365         overridden when the library functions are called. At build time  it  is         overridden when the library functions are called. At build time  it  is
366         conventional to use the standard for your operating system.         conventional to use the standard for your operating system.
367    
368    
369    WHAT \R MATCHES
370    
371           By  default,  the  sequence \R in a pattern matches any Unicode newline
372           sequence, whatever has been selected as the line  ending  sequence.  If
373           you specify
374    
375             --enable-bsr-anycrlf
376    
377           the  default  is changed so that \R matches only CR, LF, or CRLF. What-
378           ever is selected when PCRE is built can be overridden when the  library
379           functions are called.
380    
381    
382  BUILDING SHARED AND STATIC LIBRARIES  BUILDING SHARED AND STATIC LIBRARIES
383    
384         The  PCRE building process uses libtool to build both shared and static         The  PCRE building process uses libtool to build both shared and static
# Line 367  HANDLING VERY LARGE PATTERNS Line 424  HANDLING VERY LARGE PATTERNS
424         longer offsets slows down the operation of PCRE because it has to  load         longer offsets slows down the operation of PCRE because it has to  load
425         additional bytes when handling them.         additional bytes when handling them.
426    
        If  you  build  PCRE with an increased link size, test 2 (and test 5 if  
        you are using UTF-8) will fail. Part of the output of these tests is  a  
        representation  of the compiled pattern, and this changes with the link  
        size.  
   
427    
428  AVOIDING EXCESSIVE STACK USAGE  AVOIDING EXCESSIVE STACK USAGE
429    
430         When matching with the pcre_exec() function, PCRE implements backtrack-         When matching with the pcre_exec() function, PCRE implements backtrack-
431         ing  by  making recursive calls to an internal function called match().         ing by making recursive calls to an internal function  called  match().
432         In environments where the size of the stack is limited,  this  can  se-         In  environments  where  the size of the stack is limited, this can se-
433         verely  limit  PCRE's operation. (The Unix environment does not usually         verely limit PCRE's operation. (The Unix environment does  not  usually
434         suffer from this problem, but it may sometimes be necessary to increase         suffer from this problem, but it may sometimes be necessary to increase
435         the  maximum  stack size.  There is a discussion in the pcrestack docu-         the maximum stack size.  There is a discussion in the  pcrestack  docu-
436         mentation.) An alternative approach to recursion that uses memory  from         mentation.)  An alternative approach to recursion that uses memory from
437         the  heap  to remember data, instead of using recursive function calls,         the heap to remember data, instead of using recursive  function  calls,
438         has been implemented to work round the problem of limited  stack  size.         has  been  implemented to work round the problem of limited stack size.
439         If you want to build a version of PCRE that works this way, add         If you want to build a version of PCRE that works this way, add
440    
441           --disable-stack-for-recursion           --disable-stack-for-recursion
442    
443         to  the  configure  command. With this configuration, PCRE will use the         to the configure command. With this configuration, PCRE  will  use  the
444         pcre_stack_malloc and pcre_stack_free variables to call memory  manage-         pcre_stack_malloc  and pcre_stack_free variables to call memory manage-
445         ment  functions.  Separate  functions are provided because the usage is         ment functions. By default these point to malloc() and free(), but  you
446         very predictable: the block sizes requested are always  the  same,  and         can replace the pointers so that your own functions are used.
447         the  blocks  are always freed in reverse order. A calling program might  
448         be able to implement optimized functions that perform better  than  the         Separate  functions  are  provided  rather  than  using pcre_malloc and
449         standard  malloc()  and  free()  functions.  PCRE  runs noticeably more         pcre_free because the  usage  is  very  predictable:  the  block  sizes
450         slowly when built in this way. This option affects only the pcre_exec()         requested  are  always  the  same,  and  the blocks are always freed in
451         function; it is not relevant for the the pcre_dfa_exec() function.         reverse order. A calling program might be able to  implement  optimized
452           functions  that  perform  better  than  malloc()  and free(). PCRE runs
453           noticeably more slowly when built in this way. This option affects only
454           the   pcre_exec()   function;   it   is   not   relevant  for  the  the
455           pcre_dfa_exec() function.
456    
457    
458  LIMITING PCRE RESOURCE USAGE  LIMITING PCRE RESOURCE USAGE
459    
460         Internally,  PCRE has a function called match(), which it calls repeat-         Internally, PCRE has a function called match(), which it calls  repeat-
461         edly  (sometimes  recursively)  when  matching  a  pattern   with   the         edly   (sometimes   recursively)  when  matching  a  pattern  with  the
462         pcre_exec()  function.  By controlling the maximum number of times this         pcre_exec() function. By controlling the maximum number of  times  this
463         function may be called during a single matching operation, a limit  can         function  may be called during a single matching operation, a limit can
464         be  placed  on  the resources used by a single call to pcre_exec(). The         be placed on the resources used by a single call  to  pcre_exec().  The
465         limit can be changed at run time, as described in the pcreapi  documen-         limit  can be changed at run time, as described in the pcreapi documen-
466         tation.  The default is 10 million, but this can be changed by adding a         tation. The default is 10 million, but this can be changed by adding  a
467         setting such as         setting such as
468    
469           --with-match-limit=500000           --with-match-limit=500000
470    
471         to  the  configure  command.  This  setting  has  no  effect   on   the         to   the   configure  command.  This  setting  has  no  effect  on  the
472         pcre_dfa_exec() matching function.         pcre_dfa_exec() matching function.
473    
474         In  some  environments  it is desirable to limit the depth of recursive         In some environments it is desirable to limit the  depth  of  recursive
475         calls of match() more strictly than the total number of calls, in order         calls of match() more strictly than the total number of calls, in order
476         to  restrict  the maximum amount of stack (or heap, if --disable-stack-         to restrict the maximum amount of stack (or heap,  if  --disable-stack-
477         for-recursion is specified) that is used. A second limit controls this;         for-recursion is specified) that is used. A second limit controls this;
478         it  defaults  to  the  value  that is set for --with-match-limit, which         it defaults to the value that  is  set  for  --with-match-limit,  which
479         imposes no additional constraints. However, you can set a  lower  limit         imposes  no  additional constraints. However, you can set a lower limit
480         by adding, for example,         by adding, for example,
481    
482           --with-match-limit-recursion=10000           --with-match-limit-recursion=10000
483    
484         to  the  configure  command.  This  value can also be overridden at run         to the configure command. This value can  also  be  overridden  at  run
485         time.         time.
486    
487    
488    CREATING CHARACTER TABLES AT BUILD TIME
489    
490           PCRE  uses fixed tables for processing characters whose code values are
491           less than 256. By default, PCRE is built with a set of tables that  are
492           distributed  in  the  file pcre_chartables.c.dist. These tables are for
493           ASCII codes only. If you add
494    
495             --enable-rebuild-chartables
496    
497           to the configure command, the distributed tables are  no  longer  used.
498           Instead,  a  program  called dftables is compiled and run. This outputs
499           the source for new set of tables, created in the default locale of your
500           C runtime system. (This method of replacing the tables does not work if
501           you are cross compiling, because dftables is run on the local host.  If
502           you  need  to  create alternative tables when cross compiling, you will
503           have to do so "by hand".)
504    
505    
506  USING EBCDIC CODE  USING EBCDIC CODE
507    
508         PCRE assumes by default that it will run in an  environment  where  the         PCRE assumes by default that it will run in an  environment  where  the
509         character  code  is  ASCII  (or Unicode, which is a superset of ASCII).         character  code  is  ASCII  (or Unicode, which is a superset of ASCII).
510         PCRE can, however, be compiled to  run  in  an  EBCDIC  environment  by         This is the case for most computer operating systems.  PCRE  can,  how-
511         adding         ever, be compiled to run in an EBCDIC environment by adding
512    
513           --enable-ebcdic           --enable-ebcdic
514    
515         to the configure command.         to the configure command. This setting implies --enable-rebuild-charta-
516           bles. You should only use it if you know that  you  are  in  an  EBCDIC
517           environment (for example, an IBM mainframe operating system).
518    
519    
520    PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT
521    
522           By default, pcregrep reads all files as plain text. You can build it so
523           that it recognizes files whose names end in .gz or .bz2, and reads them
524           with libz or libbz2, respectively, by adding one or both of
525    
526             --enable-pcregrep-libz
527             --enable-pcregrep-libbz2
528    
529           to the configure command. These options naturally require that the rel-
530           evant libraries are installed on your system. Configuration  will  fail
531           if they are not.
532    
533    
534    PCRETEST OPTION FOR LIBREADLINE SUPPORT
535    
536           If you add
537    
538             --enable-pcretest-libreadline
539    
540           to  the  configure  command,  pcretest  is  linked with the libreadline
541           library, and when its input is from a terminal, it reads it  using  the
542           readline() function. This provides line-editing and history facilities.
543           Note that libreadline is GPL-licenced, so if you distribute a binary of
544           pcretest linked in this way, there may be licensing issues.
545    
546    
547  SEE ALSO  SEE ALSO
# Line 455  AUTHOR Line 558  AUTHOR
558    
559  REVISION  REVISION
560    
561         Last updated: 06 March 2007         Last updated: 18 December 2007
562         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
563  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
564    
# Line 508  REGULAR EXPRESSIONS AS TREES Line 611  REGULAR EXPRESSIONS AS TREES
611    
612  THE STANDARD MATCHING ALGORITHM  THE STANDARD MATCHING ALGORITHM
613    
614         In the terminology of Jeffrey Friedl's book Mastering  Regular  Expres-         In the terminology of Jeffrey Friedl's book "Mastering Regular  Expres-
615         sions,  the  standard  algorithm  is  an "NFA algorithm". It conducts a         sions",  the  standard  algorithm  is an "NFA algorithm". It conducts a
616         depth-first search of the pattern tree. That is, it  proceeds  along  a         depth-first search of the pattern tree. That is, it  proceeds  along  a
617         single path through the tree, checking that the subject matches what is         single path through the tree, checking that the subject matches what is
618         required. When there is a mismatch, the algorithm  tries  any  alterna-         required. When there is a mismatch, the algorithm  tries  any  alterna-
# Line 591  THE ALTERNATIVE MATCHING ALGORITHM Line 694  THE ALTERNATIVE MATCHING ALGORITHM
694         ence  as  the  condition or test for a specific group recursion are not         ence  as  the  condition or test for a specific group recursion are not
695         supported.         supported.
696    
697         5. Callouts are supported, but the value of the  capture_top  field  is         5. Because many paths through the tree may be  active,  the  \K  escape
698           sequence, which resets the start of the match when encountered (but may
699           be on some paths and not on others), is not  supported.  It  causes  an
700           error if encountered.
701    
702           6.  Callouts  are  supported, but the value of the capture_top field is
703         always 1, and the value of the capture_last field is always -1.         always 1, and the value of the capture_last field is always -1.
704    
705         6.  The \C escape sequence, which (in the standard algorithm) matches a         7. The \C escape sequence, which (in the standard algorithm) matches  a
706         single byte, even in UTF-8 mode, is not supported because the  alterna-         single  byte, even in UTF-8 mode, is not supported because the alterna-
707         tive  algorithm  moves  through  the  subject string one character at a         tive algorithm moves through the subject  string  one  character  at  a
708         time, for all active paths through the tree.         time, for all active paths through the tree.
709    
710           8.  None  of  the  backtracking control verbs such as (*PRUNE) are sup-
711           ported.
712    
713    
714  ADVANTAGES OF THE ALTERNATIVE ALGORITHM  ADVANTAGES OF THE ALTERNATIVE ALGORITHM
715    
# Line 645  AUTHOR Line 756  AUTHOR
756    
757  REVISION  REVISION
758    
759         Last updated: 06 March 2007         Last updated: 08 August 2007
760         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
761  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
762    
# Line 758  PCRE API OVERVIEW Line 869  PCRE API OVERVIEW
869         a  Perl-compatible  manner. A sample program that demonstrates the sim-         a  Perl-compatible  manner. A sample program that demonstrates the sim-
870         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
871         the  source distribution. The pcresample documentation describes how to         the  source distribution. The pcresample documentation describes how to
872         run it.         compile and run it.
873    
874         A second matching function, pcre_dfa_exec(), which is not Perl-compati-         A second matching function, pcre_dfa_exec(), which is not Perl-compati-
875         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 828  PCRE API OVERVIEW Line 939  PCRE API OVERVIEW
939    
940  NEWLINES  NEWLINES
941    
942         PCRE  supports four different conventions for indicating line breaks in         PCRE  supports five different conventions for indicating line breaks in
943         strings: a single CR (carriage return) character, a  single  LF  (line-         strings: a single CR (carriage return) character, a  single  LF  (line-
944         feed)  character,  the two-character sequence CRLF, or any Unicode new-         feed) character, the two-character sequence CRLF, any of the three pre-
945         line sequence.  The Unicode newline sequences are the three  just  men-         ceding, or any Unicode newline sequence. The Unicode newline  sequences
946         tioned, plus the single characters VT (vertical tab, U+000B), FF (form-         are  the  three just mentioned, plus the single characters VT (vertical
947         feed, U+000C), NEL (next line, U+0085), LS  (line  separator,  U+2028),         tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS  (line
948         and PS (paragraph separator, U+2029).         separator, U+2028), and PS (paragraph separator, U+2029).
949    
950         Each  of  the first three conventions is used by at least one operating         Each  of  the first three conventions is used by at least one operating
951         system as its standard newline sequence. When PCRE is built, a  default         system as its standard newline sequence. When PCRE is built, a  default
# Line 842  NEWLINES Line 953  NEWLINES
953         dard. When PCRE is run, the default can be overridden,  either  when  a         dard. When PCRE is run, the default can be overridden,  either  when  a
954         pattern is compiled, or when it is matched.         pattern is compiled, or when it is matched.
955    
956           At compile time, the newline convention can be specified by the options
957           argument of pcre_compile(), or it can be specified by special  text  at
958           the start of the pattern itself; this overrides any other settings. See
959           the pcrepattern page for details of the special character sequences.
960    
961         In the PCRE documentation the word "newline" is used to mean "the char-         In the PCRE documentation the word "newline" is used to mean "the char-
962         acter or pair of characters that indicate a line break". The choice  of         acter  or pair of characters that indicate a line break". The choice of
963         newline  convention  affects  the  handling of the dot, circumflex, and         newline convention affects the handling of  the  dot,  circumflex,  and
964         dollar metacharacters, the handling of #-comments in /x mode, and, when         dollar metacharacters, the handling of #-comments in /x mode, and, when
965         CRLF  is a recognized line ending sequence, the match position advance-         CRLF is a recognized line ending sequence, the match position  advance-
966         ment for a non-anchored pattern. The choice of newline convention  does         ment for a non-anchored pattern. There is more detail about this in the
967         not affect the interpretation of the \n or \r escape sequences.         section on pcre_exec() options below.
968    
969           The choice of newline convention does not affect the interpretation  of
970           the  \n  or  \r  escape  sequences, nor does it affect what \R matches,
971           which is controlled in a similar way, but by separate options.
972    
973    
974  MULTITHREADING  MULTITHREADING
975    
976         The  PCRE  functions  can be used in multi-threading applications, with         The PCRE functions can be used in  multi-threading  applications,  with
977         the  proviso  that  the  memory  management  functions  pointed  to  by         the  proviso  that  the  memory  management  functions  pointed  to  by
978         pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the         pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the
979         callout function pointed to by pcre_callout, are shared by all threads.         callout function pointed to by pcre_callout, are shared by all threads.
980    
981         The  compiled form of a regular expression is not altered during match-         The compiled form of a regular expression is not altered during  match-
982         ing, so the same compiled pattern can safely be used by several threads         ing, so the same compiled pattern can safely be used by several threads
983         at once.         at once.
984    
# Line 866  MULTITHREADING Line 986  MULTITHREADING
986  SAVING PRECOMPILED PATTERNS FOR LATER USE  SAVING PRECOMPILED PATTERNS FOR LATER USE
987    
988         The compiled form of a regular expression can be saved and re-used at a         The compiled form of a regular expression can be saved and re-used at a
989         later time, possibly by a different program, and even on a  host  other         later  time,  possibly by a different program, and even on a host other
990         than  the  one  on  which  it  was  compiled.  Details are given in the         than the one on which  it  was  compiled.  Details  are  given  in  the
991         pcreprecompile documentation.         pcreprecompile  documentation.  However, compiling a regular expression
992           with one version of PCRE for use with a different version is not  guar-
993           anteed to work and may cause crashes.
994    
995    
996  CHECKING BUILD-TIME OPTIONS  CHECKING BUILD-TIME OPTIONS
997    
998         int pcre_config(int what, void *where);         int pcre_config(int what, void *where);
999    
1000         The function pcre_config() makes it possible for a PCRE client to  dis-         The  function pcre_config() makes it possible for a PCRE client to dis-
1001         cover which optional features have been compiled into the PCRE library.         cover which optional features have been compiled into the PCRE library.
1002         The pcrebuild documentation has more details about these optional  fea-         The  pcrebuild documentation has more details about these optional fea-
1003         tures.         tures.
1004    
1005         The  first  argument  for pcre_config() is an integer, specifying which         The first argument for pcre_config() is an  integer,  specifying  which
1006         information is required; the second argument is a pointer to a variable         information is required; the second argument is a pointer to a variable
1007         into  which  the  information  is  placed. The following information is         into which the information is  placed.  The  following  information  is
1008         available:         available:
1009    
1010           PCRE_CONFIG_UTF8           PCRE_CONFIG_UTF8
1011    
1012         The output is an integer that is set to one if UTF-8 support is  avail-         The  output is an integer that is set to one if UTF-8 support is avail-
1013         able; otherwise it is set to zero.         able; otherwise it is set to zero.
1014    
1015           PCRE_CONFIG_UNICODE_PROPERTIES           PCRE_CONFIG_UNICODE_PROPERTIES
1016    
1017         The  output  is  an  integer  that is set to one if support for Unicode         The output is an integer that is set to  one  if  support  for  Unicode
1018         character properties is available; otherwise it is set to zero.         character properties is available; otherwise it is set to zero.
1019    
1020           PCRE_CONFIG_NEWLINE           PCRE_CONFIG_NEWLINE
1021    
1022         The output is an integer whose value specifies  the  default  character         The  output  is  an integer whose value specifies the default character
1023         sequence  that is recognized as meaning "newline". The four values that         sequence that is recognized as meaning "newline". The four values  that
1024         are supported are: 10 for LF, 13 for CR, 3338 for CRLF, and -1 for ANY.         are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,
1025         The default should normally be the standard sequence for your operating         and -1 for ANY. The default should normally be  the  standard  sequence
1026         system.         for your operating system.
1027    
1028             PCRE_CONFIG_BSR
1029    
1030           The output is an integer whose value indicates what character sequences
1031           the \R escape sequence matches by default. A value of 0 means  that  \R
1032           matches  any  Unicode  line ending sequence; a value of 1 means that \R
1033           matches only CR, LF, or CRLF. The default can be overridden when a pat-
1034           tern is compiled or matched.
1035    
1036           PCRE_CONFIG_LINK_SIZE           PCRE_CONFIG_LINK_SIZE
1037    
1038         The output is an integer that contains the number  of  bytes  used  for         The  output  is  an  integer that contains the number of bytes used for
1039         internal linkage in compiled regular expressions. The value is 2, 3, or         internal linkage in compiled regular expressions. The value is 2, 3, or
1040         4. Larger values allow larger regular expressions to  be  compiled,  at         4.  Larger  values  allow larger regular expressions to be compiled, at
1041         the  expense  of  slower matching. The default value of 2 is sufficient         the expense of slower matching. The default value of  2  is  sufficient
1042         for all but the most massive patterns, since  it  allows  the  compiled         for  all  but  the  most massive patterns, since it allows the compiled
1043         pattern to be up to 64K in size.         pattern to be up to 64K in size.
1044    
1045           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
1046    
1047         The  output  is  an integer that contains the threshold above which the         The output is an integer that contains the threshold  above  which  the
1048         POSIX interface uses malloc() for output vectors. Further  details  are         POSIX  interface  uses malloc() for output vectors. Further details are
1049         given in the pcreposix documentation.         given in the pcreposix documentation.
1050    
1051           PCRE_CONFIG_MATCH_LIMIT           PCRE_CONFIG_MATCH_LIMIT
1052    
1053         The output is an integer that gives the default limit for the number of         The output is an integer that gives the default limit for the number of
1054         internal matching function calls in a  pcre_exec()  execution.  Further         internal  matching  function  calls in a pcre_exec() execution. Further
1055         details are given with pcre_exec() below.         details are given with pcre_exec() below.
1056    
1057           PCRE_CONFIG_MATCH_LIMIT_RECURSION           PCRE_CONFIG_MATCH_LIMIT_RECURSION
1058    
1059         The  output is an integer that gives the default limit for the depth of         The output is an integer that gives the default limit for the depth  of
1060         recursion when calling the internal matching function in a  pcre_exec()         recursion  when calling the internal matching function in a pcre_exec()
1061         execution. Further details are given with pcre_exec() below.         execution. Further details are given with pcre_exec() below.
1062    
1063           PCRE_CONFIG_STACKRECURSE           PCRE_CONFIG_STACKRECURSE
1064    
1065         The  output is an integer that is set to one if internal recursion when         The output is an integer that is set to one if internal recursion  when
1066         running pcre_exec() is implemented by recursive function calls that use         running pcre_exec() is implemented by recursive function calls that use
1067         the  stack  to remember their state. This is the usual way that PCRE is         the stack to remember their state. This is the usual way that  PCRE  is
1068         compiled. The output is zero if PCRE was compiled to use blocks of data         compiled. The output is zero if PCRE was compiled to use blocks of data
1069         on  the  heap  instead  of  recursive  function  calls.  In  this case,         on the  heap  instead  of  recursive  function  calls.  In  this  case,
1070         pcre_stack_malloc and  pcre_stack_free  are  called  to  manage  memory         pcre_stack_malloc  and  pcre_stack_free  are  called  to  manage memory
1071         blocks on the heap, thus avoiding the use of the stack.         blocks on the heap, thus avoiding the use of the stack.
1072    
1073    
# Line 954  COMPILING A PATTERN Line 1084  COMPILING A PATTERN
1084    
1085         Either of the functions pcre_compile() or pcre_compile2() can be called         Either of the functions pcre_compile() or pcre_compile2() can be called
1086         to compile a pattern into an internal form. The only difference between         to compile a pattern into an internal form. The only difference between
1087         the  two interfaces is that pcre_compile2() has an additional argument,         the two interfaces is that pcre_compile2() has an additional  argument,
1088         errorcodeptr, via which a numerical error code can be returned.         errorcodeptr, via which a numerical error code can be returned.
1089    
1090         The pattern is a C string terminated by a binary zero, and is passed in         The pattern is a C string terminated by a binary zero, and is passed in
1091         the  pattern  argument.  A  pointer to a single block of memory that is         the pattern argument. A pointer to a single block  of  memory  that  is
1092         obtained via pcre_malloc is returned. This contains the  compiled  code         obtained  via  pcre_malloc is returned. This contains the compiled code
1093         and related data. The pcre type is defined for the returned block; this         and related data. The pcre type is defined for the returned block; this
1094         is a typedef for a structure whose contents are not externally defined.         is a typedef for a structure whose contents are not externally defined.
1095         It is up to the caller to free the memory (via pcre_free) when it is no         It is up to the caller to free the memory (via pcre_free) when it is no
1096         longer required.         longer required.
1097    
1098         Although the compiled code of a PCRE regex is relocatable, that is,  it         Although  the compiled code of a PCRE regex is relocatable, that is, it
1099         does not depend on memory location, the complete pcre data block is not         does not depend on memory location, the complete pcre data block is not
1100         fully relocatable, because it may contain a copy of the tableptr  argu-         fully  relocatable, because it may contain a copy of the tableptr argu-
1101         ment, which is an address (see below).         ment, which is an address (see below).
1102    
1103         The options argument contains various bit settings that affect the com-         The options argument contains various bit settings that affect the com-
1104         pilation. It should be zero if no options are required.  The  available         pilation.  It  should be zero if no options are required. The available
1105         options  are  described  below. Some of them, in particular, those that         options are described below. Some of them, in  particular,  those  that
1106         are compatible with Perl, can also be set and  unset  from  within  the         are  compatible  with  Perl,  can also be set and unset from within the
1107         pattern  (see  the  detailed  description in the pcrepattern documenta-         pattern (see the detailed description  in  the  pcrepattern  documenta-
1108         tion). For these options, the contents of the options  argument  speci-         tion).  For  these options, the contents of the options argument speci-
1109         fies  their initial settings at the start of compilation and execution.         fies their initial settings at the start of compilation and  execution.
1110         The PCRE_ANCHORED and PCRE_NEWLINE_xxx options can be set at  the  time         The  PCRE_ANCHORED  and PCRE_NEWLINE_xxx options can be set at the time
1111         of matching as well as at compile time.         of matching as well as at compile time.
1112    
1113         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
1114         if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and
1115         sets the variable pointed to by errptr to point to a textual error mes-         sets the variable pointed to by errptr to point to a textual error mes-
1116         sage. This is a static string that is part of the library. You must not         sage. This is a static string that is part of the library. You must not
1117         try to free it. The offset from the start of the pattern to the charac-         try to free it. The offset from the start of the pattern to the charac-
1118         ter where the error was discovered is placed in the variable pointed to         ter where the error was discovered is placed in the variable pointed to
1119         by  erroffset,  which must not be NULL. If it is, an immediate error is         by erroffset, which must not be NULL. If it is, an immediate  error  is
1120         given.         given.
1121    
1122         If pcre_compile2() is used instead of pcre_compile(),  and  the  error-         If  pcre_compile2()  is  used instead of pcre_compile(), and the error-
1123         codeptr  argument is not NULL, a non-zero error code number is returned         codeptr argument is not NULL, a non-zero error code number is  returned
1124         via this argument in the event of an error. This is in addition to  the         via  this argument in the event of an error. This is in addition to the
1125         textual error message. Error codes and messages are listed below.         textual error message. Error codes and messages are listed below.
1126    
1127         If  the  final  argument, tableptr, is NULL, PCRE uses a default set of         If the final argument, tableptr, is NULL, PCRE uses a  default  set  of
1128         character tables that are  built  when  PCRE  is  compiled,  using  the         character  tables  that  are  built  when  PCRE  is compiled, using the
1129         default  C  locale.  Otherwise, tableptr must be an address that is the         default C locale. Otherwise, tableptr must be an address  that  is  the
1130         result of a call to pcre_maketables(). This value is  stored  with  the         result  of  a  call to pcre_maketables(). This value is stored with the
1131         compiled  pattern,  and used again by pcre_exec(), unless another table         compiled pattern, and used again by pcre_exec(), unless  another  table
1132         pointer is passed to it. For more discussion, see the section on locale         pointer is passed to it. For more discussion, see the section on locale
1133         support below.         support below.
1134    
1135         This  code  fragment  shows a typical straightforward call to pcre_com-         This code fragment shows a typical straightforward  call  to  pcre_com-
1136         pile():         pile():
1137    
1138           pcre *re;           pcre *re;
# Line 1015  COMPILING A PATTERN Line 1145  COMPILING A PATTERN
1145             &erroffset,       /* for error offset */             &erroffset,       /* for error offset */
1146             NULL);            /* use default character tables */             NULL);            /* use default character tables */
1147    
1148         The following names for option bits are defined in  the  pcre.h  header         The  following  names  for option bits are defined in the pcre.h header
1149         file:         file:
1150    
1151           PCRE_ANCHORED           PCRE_ANCHORED
1152    
1153         If this bit is set, the pattern is forced to be "anchored", that is, it         If this bit is set, the pattern is forced to be "anchored", that is, it
1154         is constrained to match only at the first matching point in the  string         is  constrained to match only at the first matching point in the string
1155         that  is being searched (the "subject string"). This effect can also be         that is being searched (the "subject string"). This effect can also  be
1156         achieved by appropriate constructs in the pattern itself, which is  the         achieved  by appropriate constructs in the pattern itself, which is the
1157         only way to do it in Perl.         only way to do it in Perl.
1158    
1159           PCRE_AUTO_CALLOUT           PCRE_AUTO_CALLOUT
1160    
1161         If this bit is set, pcre_compile() automatically inserts callout items,         If this bit is set, pcre_compile() automatically inserts callout items,
1162         all with number 255, before each pattern item. For  discussion  of  the         all  with  number  255, before each pattern item. For discussion of the
1163         callout facility, see the pcrecallout documentation.         callout facility, see the pcrecallout documentation.
1164    
1165             PCRE_BSR_ANYCRLF
1166             PCRE_BSR_UNICODE
1167    
1168           These options (which are mutually exclusive) control what the \R escape
1169           sequence  matches.  The choice is either to match only CR, LF, or CRLF,
1170           or to match any Unicode newline sequence. The default is specified when
1171           PCRE is built. It can be overridden from within the pattern, or by set-
1172           ting an option when a compiled pattern is matched.
1173    
1174           PCRE_CASELESS           PCRE_CASELESS
1175    
1176         If  this  bit is set, letters in the pattern match both upper and lower         If this bit is set, letters in the pattern match both upper  and  lower
1177         case letters. It is equivalent to Perl's  /i  option,  and  it  can  be         case  letters.  It  is  equivalent  to  Perl's /i option, and it can be
1178         changed  within a pattern by a (?i) option setting. In UTF-8 mode, PCRE         changed within a pattern by a (?i) option setting. In UTF-8 mode,  PCRE
1179         always understands the concept of case for characters whose values  are         always  understands the concept of case for characters whose values are
1180         less  than 128, so caseless matching is always possible. For characters         less than 128, so caseless matching is always possible. For  characters
1181         with higher values, the concept of case is supported if  PCRE  is  com-         with  higher  values,  the concept of case is supported if PCRE is com-
1182         piled  with Unicode property support, but not otherwise. If you want to         piled with Unicode property support, but not otherwise. If you want  to
1183         use caseless matching for characters 128 and  above,  you  must  ensure         use  caseless  matching  for  characters 128 and above, you must ensure
1184         that  PCRE  is  compiled  with Unicode property support as well as with         that PCRE is compiled with Unicode property support  as  well  as  with
1185         UTF-8 support.         UTF-8 support.
1186    
1187           PCRE_DOLLAR_ENDONLY           PCRE_DOLLAR_ENDONLY
1188    
1189         If this bit is set, a dollar metacharacter in the pattern matches  only         If  this bit is set, a dollar metacharacter in the pattern matches only
1190         at  the  end  of the subject string. Without this option, a dollar also         at the end of the subject string. Without this option,  a  dollar  also
1191         matches immediately before a newline at the end of the string (but  not         matches  immediately before a newline at the end of the string (but not
1192         before  any  other newlines). The PCRE_DOLLAR_ENDONLY option is ignored         before any other newlines). The PCRE_DOLLAR_ENDONLY option  is  ignored
1193         if PCRE_MULTILINE is set.  There is no equivalent  to  this  option  in         if  PCRE_MULTILINE  is  set.   There is no equivalent to this option in
1194         Perl, and no way to set it within a pattern.         Perl, and no way to set it within a pattern.
1195    
1196           PCRE_DOTALL           PCRE_DOTALL
1197    
1198         If this bit is set, a dot metacharater in the pattern matches all char-         If this bit is set, a dot metacharater in the pattern matches all char-
1199         acters, including those that indicate newline. Without it, a  dot  does         acters,  including  those that indicate newline. Without it, a dot does
1200         not  match  when  the  current position is at a newline. This option is         not match when the current position is at a  newline.  This  option  is
1201         equivalent to Perl's /s option, and it can be changed within a  pattern         equivalent  to Perl's /s option, and it can be changed within a pattern
1202         by  a (?s) option setting. A negative class such as [^a] always matches         by a (?s) option setting. A negative class such as [^a] always  matches
1203         newline characters, independent of the setting of this option.         newline characters, independent of the setting of this option.
1204    
1205           PCRE_DUPNAMES           PCRE_DUPNAMES
1206    
1207         If this bit is set, names used to identify capturing  subpatterns  need         If  this  bit is set, names used to identify capturing subpatterns need
1208         not be unique. This can be helpful for certain types of pattern when it         not be unique. This can be helpful for certain types of pattern when it
1209         is known that only one instance of the named  subpattern  can  ever  be         is  known  that  only  one instance of the named subpattern can ever be
1210         matched.  There  are  more details of named subpatterns below; see also         matched. There are more details of named subpatterns  below;  see  also
1211         the pcrepattern documentation.         the pcrepattern documentation.
1212    
1213           PCRE_EXTENDED           PCRE_EXTENDED
1214    
1215         If this bit is set, whitespace  data  characters  in  the  pattern  are         If  this  bit  is  set,  whitespace  data characters in the pattern are
1216         totally ignored except when escaped or inside a character class. White-         totally ignored except when escaped or inside a character class. White-
1217         space does not include the VT character (code 11). In addition, charac-         space does not include the VT character (code 11). In addition, charac-
1218         ters between an unescaped # outside a character class and the next new-         ters between an unescaped # outside a character class and the next new-
1219         line, inclusive, are also ignored. This  is  equivalent  to  Perl's  /x         line,  inclusive,  are  also  ignored.  This is equivalent to Perl's /x
1220         option,  and  it  can be changed within a pattern by a (?x) option set-         option, and it can be changed within a pattern by a  (?x)  option  set-
1221         ting.         ting.
1222    
1223         This option makes it possible to include  comments  inside  complicated         This  option  makes  it possible to include comments inside complicated
1224         patterns.   Note,  however,  that this applies only to data characters.         patterns.  Note, however, that this applies only  to  data  characters.
1225         Whitespace  characters  may  never  appear  within  special   character         Whitespace   characters  may  never  appear  within  special  character
1226         sequences  in  a  pattern,  for  example  within the sequence (?( which         sequences in a pattern, for  example  within  the  sequence  (?(  which
1227         introduces a conditional subpattern.         introduces a conditional subpattern.
1228    
1229           PCRE_EXTRA           PCRE_EXTRA
1230    
1231         This option was invented in order to turn on  additional  functionality         This  option  was invented in order to turn on additional functionality
1232         of  PCRE  that  is  incompatible with Perl, but it is currently of very         of PCRE that is incompatible with Perl, but it  is  currently  of  very
1233         little use. When set, any backslash in a pattern that is followed by  a         little  use. When set, any backslash in a pattern that is followed by a
1234         letter  that  has  no  special  meaning causes an error, thus reserving         letter that has no special meaning  causes  an  error,  thus  reserving
1235         these combinations for future expansion. By  default,  as  in  Perl,  a         these  combinations  for  future  expansion.  By default, as in Perl, a
1236         backslash  followed by a letter with no special meaning is treated as a         backslash followed by a letter with no special meaning is treated as  a
1237         literal. (Perl can, however, be persuaded to give a warning for  this.)         literal.  (Perl can, however, be persuaded to give a warning for this.)
1238         There  are  at  present no other features controlled by this option. It         There are at present no other features controlled by  this  option.  It
1239         can also be set by a (?X) option setting within a pattern.         can also be set by a (?X) option setting within a pattern.
1240    
1241           PCRE_FIRSTLINE           PCRE_FIRSTLINE
1242    
1243         If this option is set, an  unanchored  pattern  is  required  to  match         If  this  option  is  set,  an  unanchored pattern is required to match
1244         before  or  at  the  first  newline  in  the subject string, though the         before or at the first  newline  in  the  subject  string,  though  the
1245         matched text may continue over the newline.         matched text may continue over the newline.
1246    
1247           PCRE_MULTILINE           PCRE_MULTILINE
1248    
1249         By default, PCRE treats the subject string as consisting  of  a  single         By  default,  PCRE  treats the subject string as consisting of a single
1250         line  of characters (even if it actually contains newlines). The "start         line of characters (even if it actually contains newlines). The  "start
1251         of line" metacharacter (^) matches only at the  start  of  the  string,         of  line"  metacharacter  (^)  matches only at the start of the string,
1252         while  the  "end  of line" metacharacter ($) matches only at the end of         while the "end of line" metacharacter ($) matches only at  the  end  of
1253         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY
1254         is set). This is the same as Perl.         is set). This is the same as Perl.
1255    
1256         When  PCRE_MULTILINE  it  is set, the "start of line" and "end of line"         When PCRE_MULTILINE it is set, the "start of line" and  "end  of  line"
1257         constructs match immediately following or immediately  before  internal         constructs  match  immediately following or immediately before internal
1258         newlines  in  the  subject string, respectively, as well as at the very         newlines in the subject string, respectively, as well as  at  the  very
1259         start and end. This is equivalent to Perl's /m option, and  it  can  be         start  and  end.  This is equivalent to Perl's /m option, and it can be
1260         changed within a pattern by a (?m) option setting. If there are no new-         changed within a pattern by a (?m) option setting. If there are no new-
1261         lines in a subject string, or no occurrences of ^ or $  in  a  pattern,         lines  in  a  subject string, or no occurrences of ^ or $ in a pattern,
1262         setting PCRE_MULTILINE has no effect.         setting PCRE_MULTILINE has no effect.
1263    
1264           PCRE_NEWLINE_CR           PCRE_NEWLINE_CR
1265           PCRE_NEWLINE_LF           PCRE_NEWLINE_LF
1266           PCRE_NEWLINE_CRLF           PCRE_NEWLINE_CRLF
1267             PCRE_NEWLINE_ANYCRLF
1268           PCRE_NEWLINE_ANY           PCRE_NEWLINE_ANY
1269    
1270         These  options  override the default newline definition that was chosen         These options override the default newline definition that  was  chosen
1271         when PCRE was built. Setting the first or the second specifies  that  a         when  PCRE  was built. Setting the first or the second specifies that a
1272         newline  is  indicated  by a single character (CR or LF, respectively).         newline is indicated by a single character (CR  or  LF,  respectively).
1273         Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by  the         Setting  PCRE_NEWLINE_CRLF specifies that a newline is indicated by the
1274         two-character  CRLF  sequence.  Setting PCRE_NEWLINE_ANY specifies that         two-character CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF  specifies
1275         any Unicode newline sequence should be recognized. The Unicode  newline         that any of the three preceding sequences should be recognized. Setting
1276         sequences  are  the three just mentioned, plus the single characters VT         PCRE_NEWLINE_ANY specifies that any Unicode newline sequence should  be
1277         (vertical tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085),         recognized. The Unicode newline sequences are the three just mentioned,
1278         LS  (line separator, U+2028), and PS (paragraph separator, U+2029). The         plus the single characters VT (vertical  tab,  U+000B),  FF  (formfeed,
1279         last two are recognized only in UTF-8 mode.         U+000C),  NEL  (next line, U+0085), LS (line separator, U+2028), and PS
1280           (paragraph separator, U+2029). The last  two  are  recognized  only  in
1281         The newline setting in the  options  word  uses  three  bits  that  are         UTF-8 mode.
1282         treated  as  a  number, giving eight possibilities. Currently only five  
1283         are used (default plus the four values above). This means that  if  you         The  newline  setting  in  the  options  word  uses three bits that are
1284         set  more  than  one  newline option, the combination may or may not be         treated as a number, giving eight possibilities. Currently only six are
1285         sensible. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is  equiva-         used  (default  plus the five values above). This means that if you set
1286         lent  to PCRE_NEWLINE_CRLF, but other combinations yield unused numbers         more than one newline option, the combination may or may not be  sensi-
1287         and cause an error.         ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
1288           PCRE_NEWLINE_CRLF, but other combinations may yield unused numbers  and
1289         The only time that a line break is specially recognized when  compiling         cause an error.
1290         a  pattern  is  if  PCRE_EXTENDED  is set, and an unescaped # outside a  
1291         character class is encountered. This indicates  a  comment  that  lasts         The  only time that a line break is specially recognized when compiling
1292         until  after the next line break sequence. In other circumstances, line         a pattern is if PCRE_EXTENDED is set, and  an  unescaped  #  outside  a
1293         break  sequences  are  treated  as  literal  data,   except   that   in         character  class  is  encountered.  This indicates a comment that lasts
1294           until after the next line break sequence. In other circumstances,  line
1295           break   sequences   are   treated  as  literal  data,  except  that  in
1296         PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters         PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters
1297         and are therefore ignored.         and are therefore ignored.
1298    
1299         The newline option that is set at compile time becomes the default that         The newline option that is set at compile time becomes the default that
1300         is  used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.         is used for pcre_exec() and pcre_dfa_exec(), but it can be  overridden.
1301    
1302           PCRE_NO_AUTO_CAPTURE           PCRE_NO_AUTO_CAPTURE
1303    
1304         If this option is set, it disables the use of numbered capturing paren-         If this option is set, it disables the use of numbered capturing paren-
1305         theses  in the pattern. Any opening parenthesis that is not followed by         theses in the pattern. Any opening parenthesis that is not followed  by
1306         ? behaves as if it were followed by ?: but named parentheses can  still         ?  behaves as if it were followed by ?: but named parentheses can still
1307         be  used  for  capturing  (and  they acquire numbers in the usual way).         be used for capturing (and they acquire  numbers  in  the  usual  way).
1308         There is no equivalent of this option in Perl.         There is no equivalent of this option in Perl.
1309    
1310           PCRE_UNGREEDY           PCRE_UNGREEDY
1311    
1312         This option inverts the "greediness" of the quantifiers  so  that  they         This  option  inverts  the "greediness" of the quantifiers so that they
1313         are  not greedy by default, but become greedy if followed by "?". It is         are not greedy by default, but become greedy if followed by "?". It  is
1314         not compatible with Perl. It can also be set by a (?U)  option  setting         not  compatible  with Perl. It can also be set by a (?U) option setting
1315         within the pattern.         within the pattern.
1316    
1317           PCRE_UTF8           PCRE_UTF8
1318    
1319         This  option  causes PCRE to regard both the pattern and the subject as         This option causes PCRE to regard both the pattern and the  subject  as
1320         strings of UTF-8 characters instead of single-byte  character  strings.         strings  of  UTF-8 characters instead of single-byte character strings.
1321         However,  it is available only when PCRE is built to include UTF-8 sup-         However, it is available only when PCRE is built to include UTF-8  sup-
1322         port. If not, the use of this option provokes an error. Details of  how         port.  If not, the use of this option provokes an error. Details of how
1323         this  option  changes the behaviour of PCRE are given in the section on         this option changes the behaviour of PCRE are given in the  section  on
1324         UTF-8 support in the main pcre page.         UTF-8 support in the main pcre page.
1325    
1326           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
1327    
1328         When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is         When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
1329         automatically  checked. If an invalid UTF-8 sequence of bytes is found,         automatically checked. There is a  discussion  about  the  validity  of
1330         pcre_compile() returns an error. If you already know that your  pattern         UTF-8  strings  in  the main pcre page. If an invalid UTF-8 sequence of
1331         is  valid, and you want to skip this check for performance reasons, you         bytes is found, pcre_compile() returns an error. If  you  already  know
1332         can set the PCRE_NO_UTF8_CHECK option. When it is set,  the  effect  of         that your pattern is valid, and you want to skip this check for perfor-
1333         passing an invalid UTF-8 string as a pattern is undefined. It may cause         mance reasons, you can set the PCRE_NO_UTF8_CHECK option.  When  it  is
1334         your program to crash.  Note that this option can  also  be  passed  to         set,  the  effect  of  passing  an invalid UTF-8 string as a pattern is
1335         pcre_exec()  and pcre_dfa_exec(), to suppress the UTF-8 validity check-         undefined. It may cause your program to crash. Note  that  this  option
1336         ing of subject strings.         can  also be passed to pcre_exec() and pcre_dfa_exec(), to suppress the
1337           UTF-8 validity checking of subject strings.
1338    
1339    
1340  COMPILATION ERROR CODES  COMPILATION ERROR CODES
# Line 1213  COMPILATION ERROR CODES Line 1356  COMPILATION ERROR CODES
1356            9  nothing to repeat            9  nothing to repeat
1357           10  [this code is not in use]           10  [this code is not in use]
1358           11  internal error: unexpected repeat           11  internal error: unexpected repeat
1359           12  unrecognized character after (?           12  unrecognized character after (? or (?-
1360           13  POSIX named classes are supported only within a class           13  POSIX named classes are supported only within a class
1361           14  missing )           14  missing )
1362           15  reference to non-existent subpattern           15  reference to non-existent subpattern
# Line 1221  COMPILATION ERROR CODES Line 1364  COMPILATION ERROR CODES
1364           17  unknown option bit(s) set           17  unknown option bit(s) set
1365           18  missing ) after comment           18  missing ) after comment
1366           19  [this code is not in use]           19  [this code is not in use]
1367           20  regular expression too large           20  regular expression is too large
1368           21  failed to get memory           21  failed to get memory
1369           22  unmatched parentheses           22  unmatched parentheses
1370           23  internal error: code overflow           23  internal error: code overflow
# Line 1230  COMPILATION ERROR CODES Line 1373  COMPILATION ERROR CODES
1373           26  malformed number or name after (?(           26  malformed number or name after (?(
1374           27  conditional group contains more than two branches           27  conditional group contains more than two branches
1375           28  assertion expected after (?(           28  assertion expected after (?(
1376           29  (?R or (?digits must be followed by )           29  (?R or (?[+-]digits must be followed by )
1377           30  unknown POSIX class name           30  unknown POSIX class name
1378           31  POSIX collating elements are not supported           31  POSIX collating elements are not supported
1379           32  this version of PCRE is not compiled with PCRE_UTF8 support           32  this version of PCRE is not compiled with PCRE_UTF8 support
# Line 1250  COMPILATION ERROR CODES Line 1393  COMPILATION ERROR CODES
1393           46  malformed \P or \p sequence           46  malformed \P or \p sequence
1394           47  unknown property name after \P or \p           47  unknown property name after \P or \p
1395           48  subpattern name is too long (maximum 32 characters)           48  subpattern name is too long (maximum 32 characters)
1396           49  too many named subpatterns (maximum 10,000)           49  too many named subpatterns (maximum 10000)
1397           50  repeated subpattern is too long           50  [this code is not in use]
1398           51  octal value is greater than \377 (not in UTF-8 mode)           51  octal value is greater than \377 (not in UTF-8 mode)
1399           52  internal error: overran compiling workspace           52  internal error: overran compiling workspace
1400           53   internal  error:  previously-checked  referenced  subpattern not           53   internal  error:  previously-checked  referenced  subpattern not
1401         found         found
1402           54  DEFINE group contains more than one branch           54  DEFINE group contains more than one branch
1403           55  repeating a DEFINE group is not allowed           55  repeating a DEFINE group is not allowed
1404           56  inconsistent NEWLINE options"           56  inconsistent NEWLINE options
1405             57  \g is not followed by a braced name or an optionally braced
1406                   non-zero number
1407             58  (?+ or (?- or (?(+ or (?(- must be followed by a non-zero number
1408             59  (*VERB) with an argument is not supported
1409             60  (*VERB) not recognized
1410             61  number is too big
1411             62  subpattern name expected
1412             63  digit expected after (?+
1413    
1414           The numbers 32 and 10000 in errors 48 and 49  are  defaults;  different
1415           values may be used if the limits were changed when PCRE was built.
1416    
1417    
1418  STUDYING A PATTERN  STUDYING A PATTERN
# Line 1266  STUDYING A PATTERN Line 1420  STUDYING A PATTERN
1420         pcre_extra *pcre_study(const pcre *code, int options         pcre_extra *pcre_study(const pcre *code, int options
1421              const char **errptr);              const char **errptr);
1422    
1423         If a compiled pattern is going to be used several times,  it  is  worth         If  a  compiled  pattern is going to be used several times, it is worth
1424         spending more time analyzing it in order to speed up the time taken for         spending more time analyzing it in order to speed up the time taken for
1425         matching. The function pcre_study() takes a pointer to a compiled  pat-         matching.  The function pcre_study() takes a pointer to a compiled pat-
1426         tern as its first argument. If studying the pattern produces additional         tern as its first argument. If studying the pattern produces additional
1427         information that will help speed up matching,  pcre_study()  returns  a         information  that  will  help speed up matching, pcre_study() returns a
1428         pointer  to a pcre_extra block, in which the study_data field points to         pointer to a pcre_extra block, in which the study_data field points  to
1429         the results of the study.         the results of the study.
1430    
1431         The  returned  value  from  pcre_study()  can  be  passed  directly  to         The  returned  value  from  pcre_study()  can  be  passed  directly  to
1432         pcre_exec().  However,  a  pcre_extra  block also contains other fields         pcre_exec(). However, a pcre_extra block  also  contains  other  fields
1433         that can be set by the caller before the block  is  passed;  these  are         that  can  be  set  by the caller before the block is passed; these are
1434         described below in the section on matching a pattern.         described below in the section on matching a pattern.
1435    
1436         If  studying  the  pattern  does not produce any additional information         If studying the pattern does not  produce  any  additional  information
1437         pcre_study() returns NULL. In that circumstance, if the calling program         pcre_study() returns NULL. In that circumstance, if the calling program
1438         wants  to  pass  any of the other fields to pcre_exec(), it must set up         wants to pass any of the other fields to pcre_exec(), it  must  set  up
1439         its own pcre_extra block.         its own pcre_extra block.
1440    
1441         The second argument of pcre_study() contains option bits.  At  present,         The  second  argument of pcre_study() contains option bits. At present,
1442         no options are defined, and this argument should always be zero.         no options are defined, and this argument should always be zero.
1443    
1444         The  third argument for pcre_study() is a pointer for an error message.         The third argument for pcre_study() is a pointer for an error  message.
1445         If studying succeeds (even if no data is  returned),  the  variable  it         If  studying  succeeds  (even  if no data is returned), the variable it
1446         points  to  is  set  to NULL. Otherwise it is set to point to a textual         points to is set to NULL. Otherwise it is set to  point  to  a  textual
1447         error message. This is a static string that is part of the library. You         error message. This is a static string that is part of the library. You
1448         must  not  try  to  free it. You should test the error pointer for NULL         must not try to free it. You should test the  error  pointer  for  NULL
1449         after calling pcre_study(), to be sure that it has run successfully.         after calling pcre_study(), to be sure that it has run successfully.
1450    
1451         This is a typical call to pcre_study():         This is a typical call to pcre_study():
# Line 1303  STUDYING A PATTERN Line 1457  STUDYING A PATTERN
1457             &error);        /* set to NULL or points to a message */             &error);        /* set to NULL or points to a message */
1458    
1459         At present, studying a pattern is useful only for non-anchored patterns         At present, studying a pattern is useful only for non-anchored patterns
1460         that  do not have a single fixed starting character. A bitmap of possi-         that do not have a single fixed starting character. A bitmap of  possi-
1461         ble starting bytes is created.         ble starting bytes is created.
1462    
1463    
1464  LOCALE SUPPORT  LOCALE SUPPORT
1465    
1466         PCRE handles caseless matching, and determines whether  characters  are         PCRE  handles  caseless matching, and determines whether characters are
1467         letters  digits,  or whatever, by reference to a set of tables, indexed         letters, digits, or whatever, by reference to a set of tables,  indexed
1468         by character value. When running in UTF-8 mode, this  applies  only  to         by  character  value.  When running in UTF-8 mode, this applies only to
1469         characters  with  codes  less than 128. Higher-valued codes never match         characters with codes less than 128. Higher-valued  codes  never  match
1470         escapes such as \w or \d, but can be tested with \p if  PCRE  is  built         escapes  such  as  \w or \d, but can be tested with \p if PCRE is built
1471         with  Unicode  character property support. The use of locales with Uni-         with Unicode character property support. The use of locales  with  Uni-
1472         code is discouraged.         code  is discouraged. If you are handling characters with codes greater
1473           than 128, you should either use UTF-8 and Unicode, or use locales,  but
1474         An internal set of tables is created in the default C locale when  PCRE         not try to mix the two.
1475         is  built.  This  is  used when the final argument of pcre_compile() is  
1476         NULL, and is sufficient for many applications. An  alternative  set  of         PCRE  contains  an  internal set of tables that are used when the final
1477         tables  can,  however, be supplied. These may be created in a different         argument of pcre_compile() is  NULL.  These  are  sufficient  for  many
1478         locale from the default. As more and more applications change to  using         applications.  Normally, the internal tables recognize only ASCII char-
1479         Unicode, the need for this locale support is expected to die away.         acters. However, when PCRE is built, it is possible to cause the inter-
1480           nal tables to be rebuilt in the default "C" locale of the local system,
1481           which may cause them to be different.
1482    
1483           The internal tables can always be overridden by tables supplied by  the
1484           application that calls PCRE. These may be created in a different locale
1485           from the default. As more and more applications change  to  using  Uni-
1486           code, the need for this locale support is expected to die away.
1487    
1488         External  tables  are  built by calling the pcre_maketables() function,         External  tables  are  built by calling the pcre_maketables() function,
1489         which has no arguments, in the relevant locale. The result can then  be         which has no arguments, in the relevant locale. The result can then  be
# Line 1335  LOCALE SUPPORT Line 1496  LOCALE SUPPORT
1496           tables = pcre_maketables();           tables = pcre_maketables();
1497           re = pcre_compile(..., tables);           re = pcre_compile(..., tables);
1498    
1499         When pcre_maketables() runs, the tables are built  in  memory  that  is         The locale name "fr_FR" is used on Linux and other  Unix-like  systems;
1500         obtained  via  pcre_malloc. It is the caller's responsibility to ensure         if you are using Windows, the name for the French locale is "french".
1501         that the memory containing the tables remains available for as long  as  
1502           When  pcre_maketables()  runs,  the  tables are built in memory that is
1503           obtained via pcre_malloc. It is the caller's responsibility  to  ensure
1504           that  the memory containing the tables remains available for as long as
1505         it is needed.         it is needed.
1506    
1507         The pointer that is passed to pcre_compile() is saved with the compiled         The pointer that is passed to pcre_compile() is saved with the compiled
1508         pattern, and the same tables are used via this pointer by  pcre_study()         pattern,  and the same tables are used via this pointer by pcre_study()
1509         and normally also by pcre_exec(). Thus, by default, for any single pat-         and normally also by pcre_exec(). Thus, by default, for any single pat-
1510         tern, compilation, studying and matching all happen in the same locale,         tern, compilation, studying and matching all happen in the same locale,
1511         but different patterns can be compiled in different locales.         but different patterns can be compiled in different locales.
1512    
1513         It  is  possible to pass a table pointer or NULL (indicating the use of         It is possible to pass a table pointer or NULL (indicating the  use  of
1514         the internal tables) to pcre_exec(). Although  not  intended  for  this         the  internal  tables)  to  pcre_exec(). Although not intended for this
1515         purpose,  this facility could be used to match a pattern in a different         purpose, this facility could be used to match a pattern in a  different
1516         locale from the one in which it was compiled. Passing table pointers at         locale from the one in which it was compiled. Passing table pointers at
1517         run time is discussed below in the section on matching a pattern.         run time is discussed below in the section on matching a pattern.
1518    
# Line 1358  INFORMATION ABOUT A PATTERN Line 1522  INFORMATION ABOUT A PATTERN
1522         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
1523              int what, void *where);              int what, void *where);
1524    
1525         The  pcre_fullinfo() function returns information about a compiled pat-         The pcre_fullinfo() function returns information about a compiled  pat-
1526         tern. It replaces the obsolete pcre_info() function, which is neverthe-         tern. It replaces the obsolete pcre_info() function, which is neverthe-
1527         less retained for backwards compability (and is documented below).         less retained for backwards compability (and is documented below).
1528    
1529         The  first  argument  for  pcre_fullinfo() is a pointer to the compiled         The first argument for pcre_fullinfo() is a  pointer  to  the  compiled
1530         pattern. The second argument is the result of pcre_study(), or NULL  if         pattern.  The second argument is the result of pcre_study(), or NULL if
1531         the  pattern  was not studied. The third argument specifies which piece         the pattern was not studied. The third argument specifies  which  piece
1532         of information is required, and the fourth argument is a pointer  to  a         of  information  is required, and the fourth argument is a pointer to a
1533         variable  to  receive  the  data. The yield of the function is zero for         variable to receive the data. The yield of the  function  is  zero  for
1534         success, or one of the following negative numbers:         success, or one of the following negative numbers:
1535    
1536           PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_NULL       the argument code was NULL
# Line 1374  INFORMATION ABOUT A PATTERN Line 1538  INFORMATION ABOUT A PATTERN
1538           PCRE_ERROR_BADMAGIC   the "magic number" was not found           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1539           PCRE_ERROR_BADOPTION  the value of what was invalid           PCRE_ERROR_BADOPTION  the value of what was invalid
1540    
1541         The "magic number" is placed at the start of each compiled  pattern  as         The  "magic  number" is placed at the start of each compiled pattern as
1542         an  simple check against passing an arbitrary memory pointer. Here is a         an simple check against passing an arbitrary memory pointer. Here is  a
1543         typical call of pcre_fullinfo(), to obtain the length of  the  compiled         typical  call  of pcre_fullinfo(), to obtain the length of the compiled
1544         pattern:         pattern:
1545    
1546           int rc;           int rc;
# Line 1387  INFORMATION ABOUT A PATTERN Line 1551  INFORMATION ABOUT A PATTERN
1551             PCRE_INFO_SIZE,   /* what is required */             PCRE_INFO_SIZE,   /* what is required */
1552             &length);         /* where to put the data */             &length);         /* where to put the data */
1553    
1554         The  possible  values for the third argument are defined in pcre.h, and         The possible values for the third argument are defined in  pcre.h,  and
1555         are as follows:         are as follows:
1556    
1557           PCRE_INFO_BACKREFMAX           PCRE_INFO_BACKREFMAX
1558    
1559         Return the number of the highest back reference  in  the  pattern.  The         Return  the  number  of  the highest back reference in the pattern. The
1560         fourth  argument  should  point to an int variable. Zero is returned if         fourth argument should point to an int variable. Zero  is  returned  if
1561         there are no back references.         there are no back references.
1562    
1563           PCRE_INFO_CAPTURECOUNT           PCRE_INFO_CAPTURECOUNT
1564    
1565         Return the number of capturing subpatterns in the pattern.  The  fourth         Return  the  number of capturing subpatterns in the pattern. The fourth
1566         argument should point to an int variable.         argument should point to an int variable.
1567    
1568           PCRE_INFO_DEFAULT_TABLES           PCRE_INFO_DEFAULT_TABLES
1569    
1570         Return  a pointer to the internal default character tables within PCRE.         Return a pointer to the internal default character tables within  PCRE.
1571         The fourth argument should point to an unsigned char *  variable.  This         The  fourth  argument should point to an unsigned char * variable. This
1572         information call is provided for internal use by the pcre_study() func-         information call is provided for internal use by the pcre_study() func-
1573         tion. External callers can cause PCRE to use  its  internal  tables  by         tion.  External  callers  can  cause PCRE to use its internal tables by
1574         passing a NULL table pointer.         passing a NULL table pointer.
1575    
1576           PCRE_INFO_FIRSTBYTE           PCRE_INFO_FIRSTBYTE
1577    
1578         Return  information  about  the first byte of any matched string, for a         Return information about the first byte of any matched  string,  for  a
1579         non-anchored pattern. The fourth argument should point to an int  vari-         non-anchored  pattern. The fourth argument should point to an int vari-
1580         able.  (This option used to be called PCRE_INFO_FIRSTCHAR; the old name         able. (This option used to be called PCRE_INFO_FIRSTCHAR; the old  name
1581         is still recognized for backwards compatibility.)         is still recognized for backwards compatibility.)
1582    
1583         If there is a fixed first byte, for example, from  a  pattern  such  as         If  there  is  a  fixed first byte, for example, from a pattern such as
1584         (cat|cow|coyote), its value is returned. Otherwise, if either         (cat|cow|coyote), its value is returned. Otherwise, if either
1585    
1586         (a)  the pattern was compiled with the PCRE_MULTILINE option, and every         (a) the pattern was compiled with the PCRE_MULTILINE option, and  every
1587         branch starts with "^", or         branch starts with "^", or
1588    
1589         (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not         (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
1590         set (if it were set, the pattern would be anchored),         set (if it were set, the pattern would be anchored),
1591    
1592         -1  is  returned, indicating that the pattern matches only at the start         -1 is returned, indicating that the pattern matches only at  the  start
1593         of a subject string or after any newline within the  string.  Otherwise         of  a  subject string or after any newline within the string. Otherwise
1594         -2 is returned. For anchored patterns, -2 is returned.         -2 is returned. For anchored patterns, -2 is returned.
1595    
1596           PCRE_INFO_FIRSTTABLE           PCRE_INFO_FIRSTTABLE
1597    
1598         If  the pattern was studied, and this resulted in the construction of a         If the pattern was studied, and this resulted in the construction of  a
1599         256-bit table indicating a fixed set of bytes for the first byte in any         256-bit table indicating a fixed set of bytes for the first byte in any
1600         matching  string, a pointer to the table is returned. Otherwise NULL is         matching string, a pointer to the table is returned. Otherwise NULL  is
1601         returned. The fourth argument should point to an unsigned char *  vari-         returned.  The fourth argument should point to an unsigned char * vari-
1602         able.         able.
1603    
1604             PCRE_INFO_HASCRORLF
1605    
1606           Return 1 if the pattern contains any explicit  matches  for  CR  or  LF
1607           characters,  otherwise  0.  The  fourth argument should point to an int
1608           variable. An explicit match is either a literal CR or LF character,  or
1609           \r or \n.
1610    
1611             PCRE_INFO_JCHANGED
1612    
1613           Return  1  if  the (?J) or (?-J) option setting is used in the pattern,
1614           otherwise 0. The fourth argument should point to an int variable.  (?J)
1615           and (?-J) set and unset the local PCRE_DUPNAMES option, respectively.
1616    
1617           PCRE_INFO_LASTLITERAL           PCRE_INFO_LASTLITERAL
1618    
1619         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
# Line 1491  INFORMATION ABOUT A PATTERN Line 1668  INFORMATION ABOUT A PATTERN
1668         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
1669         to be different for each compiled pattern.         to be different for each compiled pattern.
1670    
1671             PCRE_INFO_OKPARTIAL
1672    
1673           Return  1 if the pattern can be used for partial matching, otherwise 0.
1674           The fourth argument should point to an int  variable.  The  pcrepartial
1675           documentation  lists  the restrictions that apply to patterns when par-
1676           tial matching is used.
1677    
1678           PCRE_INFO_OPTIONS           PCRE_INFO_OPTIONS
1679    
1680         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
1681         fourth argument should point to an unsigned long  int  variable.  These         fourth  argument  should  point to an unsigned long int variable. These
1682         option bits are those specified in the call to pcre_compile(), modified         option bits are those specified in the call to pcre_compile(), modified
1683         by any top-level option settings within the pattern itself.         by any top-level option settings at the start of the pattern itself. In
1684           other words, they are the options that will be in force  when  matching
1685           starts.  For  example, if the pattern /(?im)abc(?-i)d/ is compiled with
1686           the PCRE_EXTENDED option, the result is PCRE_CASELESS,  PCRE_MULTILINE,
1687           and PCRE_EXTENDED.
1688    
1689         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
1690         alternatives begin with one of the following:         alternatives begin with one of the following:
1691    
1692           ^     unless PCRE_MULTILINE is set           ^     unless PCRE_MULTILINE is set
# Line 1512  INFORMATION ABOUT A PATTERN Line 1700  INFORMATION ABOUT A PATTERN
1700    
1701           PCRE_INFO_SIZE           PCRE_INFO_SIZE
1702    
1703         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
1704         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
1705         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
1706         size_t variable.         size_t variable.
# Line 1520  INFORMATION ABOUT A PATTERN Line 1708  INFORMATION ABOUT A PATTERN
1708           PCRE_INFO_STUDYSIZE           PCRE_INFO_STUDYSIZE
1709    
1710         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
1711         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
1712         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
1713         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
1714         variable.         variable.
1715    
1716    
# Line 1530  OBSOLETE INFO FUNCTION Line 1718  OBSOLETE INFO FUNCTION
1718    
1719         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
1720    
1721         The  pcre_info()  function is now obsolete because its interface is too         The pcre_info() function is now obsolete because its interface  is  too
1722         restrictive to return all the available data about a compiled  pattern.         restrictive  to return all the available data about a compiled pattern.
1723         New   programs   should  use  pcre_fullinfo()  instead.  The  yield  of         New  programs  should  use  pcre_fullinfo()  instead.  The   yield   of
1724         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-
1725         lowing negative numbers:         lowing negative numbers:
1726    
1727           PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_NULL       the argument code was NULL
1728           PCRE_ERROR_BADMAGIC   the "magic number" was not found           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1729    
1730         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
1731         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
1732         PCRE_INFO_OPTIONS above).         PCRE_INFO_OPTIONS above).
1733    
1734         If  the  pattern  is  not anchored and the firstcharptr argument is not         If the pattern is not anchored and the  firstcharptr  argument  is  not
1735         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
1736         any matched string (see PCRE_INFO_FIRSTBYTE above).         any matched string (see PCRE_INFO_FIRSTBYTE above).
1737    
1738    
# Line 1552  REFERENCE COUNTS Line 1740  REFERENCE COUNTS
1740    
1741         int pcre_refcount(pcre *code, int adjust);         int pcre_refcount(pcre *code, int adjust);
1742    
1743         The  pcre_refcount()  function is used to maintain a reference count in         The pcre_refcount() function is used to maintain a reference  count  in
1744         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
1745         benefit  of  applications  that  operate  in an object-oriented manner,         benefit of applications that  operate  in  an  object-oriented  manner,
1746         where different parts of the application may be using the same compiled         where different parts of the application may be using the same compiled
1747         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.
1748    
1749         When a pattern is compiled, the reference count field is initialized to         When a pattern is compiled, the reference count field is initialized to
1750         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
1751         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
1752         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
1753         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
1754         is outside these limits, it is forced to the appropriate limit value.         is outside these limits, it is forced to the appropriate limit value.
1755    
1756         Except when it is zero, the reference count is not correctly  preserved         Except  when it is zero, the reference count is not correctly preserved
1757         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
1758         whose byte-order is different. (This seems a highly unlikely scenario.)         whose byte-order is different. (This seems a highly unlikely scenario.)
1759    
1760    
# Line 1576  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1764  MATCHING A PATTERN: THE TRADITIONAL FUNC
1764              const char *subject, int length, int startoffset,              const char *subject, int length, int startoffset,
1765              int options, int *ovector, int ovecsize);              int options, int *ovector, int ovecsize);
1766    
1767         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
1768         compiled pattern, which is passed in the code argument. If the  pattern         compiled  pattern, which is passed in the code argument. If the pattern
1769         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
1770         argument. This function is the main matching facility of  the  library,         argument.  This  function is the main matching facility of the library,
1771         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
1772         an alternative matching function, which is described below in the  sec-         an  alternative matching function, which is described below in the sec-
1773         tion about the pcre_dfa_exec() function.         tion about the pcre_dfa_exec() function.
1774    
1775         In  most applications, the pattern will have been compiled (and option-         In most applications, the pattern will have been compiled (and  option-
1776         ally studied) in the same process that calls pcre_exec().  However,  it         ally  studied)  in the same process that calls pcre_exec(). However, it
1777         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
1778         later in different processes, possibly even on different hosts.  For  a         later  in  different processes, possibly even on different hosts. For a
1779         discussion about this, see the pcreprecompile documentation.         discussion about this, see the pcreprecompile documentation.
1780    
1781         Here is an example of a simple call to pcre_exec():         Here is an example of a simple call to pcre_exec():
# Line 1606  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1794  MATCHING A PATTERN: THE TRADITIONAL FUNC
1794    
1795     Extra data for pcre_exec()     Extra data for pcre_exec()
1796    
1797         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
1798         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
1799         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-
1800         tional information in it. The pcre_extra block contains  the  following         tional  information  in it. The pcre_extra block contains the following
1801         fields (not necessarily in this order):         fields (not necessarily in this order):
1802    
1803           unsigned long int flags;           unsigned long int flags;
# Line 1619  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1807  MATCHING A PATTERN: THE TRADITIONAL FUNC
1807           void *callout_data;           void *callout_data;
1808           const unsigned char *tables;           const unsigned char *tables;
1809    
1810         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
1811         are set. The flag bits are:         are set. The flag bits are:
1812    
1813           PCRE_EXTRA_STUDY_DATA           PCRE_EXTRA_STUDY_DATA
# Line 1628  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1816  MATCHING A PATTERN: THE TRADITIONAL FUNC
1816           PCRE_EXTRA_CALLOUT_DATA           PCRE_EXTRA_CALLOUT_DATA
1817           PCRE_EXTRA_TABLES           PCRE_EXTRA_TABLES
1818    
1819         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
1820         the  pcre_extra  block  that is returned by pcre_study(), together with         the pcre_extra block that is returned by  pcre_study(),  together  with
1821         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
1822         add  to  the  block by setting the other fields and their corresponding         add to the block by setting the other fields  and  their  corresponding
1823         flag bits.         flag bits.
1824    
1825         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
1826         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
1827         match, but which have a very large number  of  possibilities  in  their         match,  but  which  have  a very large number of possibilities in their
1828         search  trees.  The  classic  example  is  the  use of nested unlimited         search trees. The classic  example  is  the  use  of  nested  unlimited
1829         repeats.         repeats.
1830    
1831         Internally, PCRE uses a function called match() which it calls  repeat-         Internally,  PCRE uses a function called match() which it calls repeat-
1832         edly  (sometimes  recursively). The limit set by match_limit is imposed         edly (sometimes recursively). The limit set by match_limit  is  imposed
1833         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
1834         has  the  effect  of  limiting the amount of backtracking that can take         has the effect of limiting the amount of  backtracking  that  can  take
1835         place. For patterns that are not anchored, the count restarts from zero         place. For patterns that are not anchored, the count restarts from zero
1836         for each position in the subject string.         for each position in the subject string.
1837    
1838         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
1839         default default is 10 million, which handles all but the  most  extreme         default  default  is 10 million, which handles all but the most extreme
1840         cases.  You  can  override  the  default by suppling pcre_exec() with a         cases. You can override the default  by  suppling  pcre_exec()  with  a
1841         pcre_extra    block    in    which    match_limit    is    set,     and         pcre_extra     block    in    which    match_limit    is    set,    and
1842         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
1843         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1844    
1845         The match_limit_recursion field is similar to match_limit, but  instead         The  match_limit_recursion field is similar to match_limit, but instead
1846         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
1847         the depth of recursion. The recursion depth is a  smaller  number  than         the  depth  of  recursion. The recursion depth is a smaller number than
1848         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-
1849         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.
1850    
1851         Limiting  the  recursion  depth  limits the amount of stack that can be         Limiting the recursion depth limits the amount of  stack  that  can  be
1852         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
1853         of the stack, the amount of heap memory that can be used.         of the stack, the amount of heap memory that can be used.
1854    
1855         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
1856         built; the default default  is  the  same  value  as  the  default  for         built;  the  default  default  is  the  same  value  as the default for
1857         match_limit.  You can override the default by suppling pcre_exec() with         match_limit. You can override the default by suppling pcre_exec()  with
1858         a  pcre_extra  block  in  which  match_limit_recursion  is   set,   and         a   pcre_extra   block  in  which  match_limit_recursion  is  set,  and
1859         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
1860         limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.         limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1861    
1862         The pcre_callout field is used in conjunction with the  "callout"  fea-         The  pcre_callout  field is used in conjunction with the "callout" fea-
1863         ture, which is described in the pcrecallout documentation.         ture, which is described in the pcrecallout documentation.
1864    
1865         The  tables  field  is  used  to  pass  a  character  tables pointer to         The tables field  is  used  to  pass  a  character  tables  pointer  to
1866         pcre_exec(); this overrides the value that is stored with the  compiled         pcre_exec();  this overrides the value that is stored with the compiled
1867         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
1868         custom tables were supplied to pcre_compile() via  its  tableptr  argu-         custom  tables  were  supplied to pcre_compile() via its tableptr argu-
1869         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
1870         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-
1871         using  patterns  that  have been saved after compiling with an external         using patterns that have been saved after compiling  with  an  external
1872         set of tables, because the external tables  might  be  at  a  different         set  of  tables,  because  the  external tables might be at a different
1873         address  when  pcre_exec() is called. See the pcreprecompile documenta-         address when pcre_exec() is called. See the  pcreprecompile  documenta-
1874         tion for a discussion of saving compiled patterns for later use.         tion for a discussion of saving compiled patterns for later use.
1875    
1876     Option bits for pcre_exec()     Option bits for pcre_exec()
1877    
1878         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.
1879         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,
1880         PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and         PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and
1881         PCRE_PARTIAL.         PCRE_PARTIAL.
1882    
1883           PCRE_ANCHORED           PCRE_ANCHORED
1884    
1885         The  PCRE_ANCHORED  option  limits pcre_exec() to matching at the first         The PCRE_ANCHORED option limits pcre_exec() to matching  at  the  first
1886         matching position. If a pattern was  compiled  with  PCRE_ANCHORED,  or         matching  position.  If  a  pattern was compiled with PCRE_ANCHORED, or
1887         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
1888         unachored at matching time.         unachored at matching time.
1889    
1890             PCRE_BSR_ANYCRLF
1891             PCRE_BSR_UNICODE
1892    
1893           These options (which are mutually exclusive) control what the \R escape
1894           sequence matches. The choice is either to match only CR, LF,  or  CRLF,
1895           or  to  match  any Unicode newline sequence. These options override the
1896           choice that was made or defaulted when the pattern was compiled.
1897    
1898           PCRE_NEWLINE_CR           PCRE_NEWLINE_CR
1899           PCRE_NEWLINE_LF           PCRE_NEWLINE_LF
1900           PCRE_NEWLINE_CRLF           PCRE_NEWLINE_CRLF
1901             PCRE_NEWLINE_ANYCRLF
1902           PCRE_NEWLINE_ANY           PCRE_NEWLINE_ANY
1903    
1904         These options override  the  newline  definition  that  was  chosen  or         These options override  the  newline  definition  that  was  chosen  or
# Line 1709  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1906  MATCHING A PATTERN: THE TRADITIONAL FUNC
1906         tion of pcre_compile()  above.  During  matching,  the  newline  choice         tion of pcre_compile()  above.  During  matching,  the  newline  choice
1907         affects  the  behaviour  of the dot, circumflex, and dollar metacharac-         affects  the  behaviour  of the dot, circumflex, and dollar metacharac-
1908         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
1909         match  failure  for  an  unanchored  pattern. When PCRE_NEWLINE_CRLF or         match failure for an unanchored pattern.
1910         PCRE_NEWLINE_ANY is set, and a match attempt  fails  when  the  current  
1911         position  is  at a CRLF sequence, the match position is advanced by two         When  PCRE_NEWLINE_CRLF,  PCRE_NEWLINE_ANYCRLF,  or PCRE_NEWLINE_ANY is
1912         characters instead of one, in other words, to after the CRLF.         set, and a match attempt for an unanchored pattern fails when the  cur-
1913           rent  position  is  at  a  CRLF  sequence,  and the pattern contains no
1914           explicit matches for  CR  or  LF  characters,  the  match  position  is
1915           advanced by two characters instead of one, in other words, to after the
1916           CRLF.
1917    
1918           The above rule is a compromise that makes the most common cases work as
1919           expected.  For  example,  if  the  pattern  is .+A (and the PCRE_DOTALL
1920           option is not set), it does not match the string "\r\nA" because, after
1921           failing  at the start, it skips both the CR and the LF before retrying.
1922           However, the pattern [\r\n]A does match that string,  because  it  con-
1923           tains an explicit CR or LF reference, and so advances only by one char-
1924           acter after the first failure.
1925    
1926           An explicit match for CR of LF is either a literal appearance of one of
1927           those  characters,  or  one  of the \r or \n escape sequences. Implicit
1928           matches such as [^X] do not count, nor does \s (which includes  CR  and
1929           LF in the characters that it matches).
1930    
1931           Notwithstanding  the above, anomalous effects may still occur when CRLF
1932           is a valid newline sequence and explicit \r or \n escapes appear in the
1933           pattern.
1934    
1935           PCRE_NOTBOL           PCRE_NOTBOL
1936    
1937         This option specifies that first character of the subject string is not         This option specifies that first character of the subject string is not
1938         the  beginning  of  a  line, so the circumflex metacharacter should not         the beginning of a line, so the  circumflex  metacharacter  should  not
1939         match before it. Setting this without PCRE_MULTILINE (at compile  time)         match  before it. Setting this without PCRE_MULTILINE (at compile time)
1940         causes  circumflex  never to match. This option affects only the behav-         causes circumflex never to match. This option affects only  the  behav-
1941         iour of the circumflex metacharacter. It does not affect \A.         iour of the circumflex metacharacter. It does not affect \A.
1942    
1943           PCRE_NOTEOL           PCRE_NOTEOL
1944    
1945         This option specifies that the end of the subject string is not the end         This option specifies that the end of the subject string is not the end
1946         of  a line, so the dollar metacharacter should not match it nor (except         of a line, so the dollar metacharacter should not match it nor  (except
1947         in multiline mode) a newline immediately before it. Setting this  with-         in  multiline mode) a newline immediately before it. Setting this with-
1948         out PCRE_MULTILINE (at compile time) causes dollar never to match. This         out PCRE_MULTILINE (at compile time) causes dollar never to match. This
1949         option affects only the behaviour of the dollar metacharacter. It  does         option  affects only the behaviour of the dollar metacharacter. It does
1950         not affect \Z or \z.         not affect \Z or \z.
1951    
1952           PCRE_NOTEMPTY           PCRE_NOTEMPTY
1953    
1954         An empty string is not considered to be a valid match if this option is         An empty string is not considered to be a valid match if this option is
1955         set. If there are alternatives in the pattern, they are tried.  If  all         set.  If  there are alternatives in the pattern, they are tried. If all
1956         the  alternatives  match  the empty string, the entire match fails. For         the alternatives match the empty string, the entire  match  fails.  For
1957         example, if the pattern         example, if the pattern
1958    
1959           a?b?           a?b?
1960    
1961         is applied to a string not beginning with "a" or "b",  it  matches  the         is  applied  to  a string not beginning with "a" or "b", it matches the
1962         empty  string at the start of the subject. With PCRE_NOTEMPTY set, this         empty string at the start of the subject. With PCRE_NOTEMPTY set,  this
1963         match is not valid, so PCRE searches further into the string for occur-         match is not valid, so PCRE searches further into the string for occur-
1964         rences of "a" or "b".         rences of "a" or "b".
1965    
1966         Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a spe-         Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a spe-
1967         cial case of a pattern match of the empty  string  within  its  split()         cial  case  of  a  pattern match of the empty string within its split()
1968         function,  and  when  using  the /g modifier. It is possible to emulate         function, and when using the /g modifier. It  is  possible  to  emulate
1969         Perl's behaviour after matching a null string by first trying the match         Perl's behaviour after matching a null string by first trying the match
1970         again at the same offset with PCRE_NOTEMPTY and PCRE_ANCHORED, and then         again at the same offset with PCRE_NOTEMPTY and PCRE_ANCHORED, and then
1971         if that fails by advancing the starting offset (see below)  and  trying         if  that  fails by advancing the starting offset (see below) and trying
1972         an ordinary match again. There is some code that demonstrates how to do         an ordinary match again. There is some code that demonstrates how to do
1973         this in the pcredemo.c sample program.         this in the pcredemo.c sample program.
1974    
1975           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
1976    
1977         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
1978         UTF-8  string is automatically checked when pcre_exec() is subsequently         UTF-8 string is automatically checked when pcre_exec() is  subsequently
1979         called.  The value of startoffset is also checked  to  ensure  that  it         called.   The  value  of  startoffset is also checked to ensure that it
1980         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
1981         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
1982         startoffset  contains  an  invalid  value, PCRE_ERROR_BADUTF8_OFFSET is         main pcre page. If  an  invalid  UTF-8  sequence  of  bytes  is  found,
1983         returned.         pcre_exec()  returns  the error PCRE_ERROR_BADUTF8. If startoffset con-
1984           tains an invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.
1985    
1986         If you already know that your subject is valid, and you  want  to  skip         If you already know that your subject is valid, and you  want  to  skip
1987         these    checks    for   performance   reasons,   you   can   set   the         these    checks    for   performance   reasons,   you   can   set   the
# Line 1985  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2204  MATCHING A PATTERN: THE TRADITIONAL FUNC
2204         field  in  a  pcre_extra  structure (or defaulted) was reached. See the         field  in  a  pcre_extra  structure (or defaulted) was reached. See the
2205         description above.         description above.
2206    
          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.  
   
2207           PCRE_ERROR_BADNEWLINE     (-23)           PCRE_ERROR_BADNEWLINE     (-23)
2208    
2209         An invalid combination of PCRE_NEWLINE_xxx options was given.         An invalid combination of PCRE_NEWLINE_xxx options was given.
2210    
2211         Error numbers -16 to -20 are not used by pcre_exec().         Error numbers -16 to -20 and -22 are not used by pcre_exec().
2212    
2213    
2214  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
# Line 2132  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2343  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2343    
2344         These  functions call pcre_get_stringnumber(), and if it succeeds, they         These  functions call pcre_get_stringnumber(), and if it succeeds, they
2345         then call pcre_copy_substring() or pcre_get_substring(),  as  appropri-         then call pcre_copy_substring() or pcre_get_substring(),  as  appropri-
2346         ate.         ate.  NOTE:  If PCRE_DUPNAMES is set and there are duplicate names, the
2347           behaviour may not be what you want (see the next section).
2348    
2349    
2350  DUPLICATE SUBPATTERN NAMES  DUPLICATE SUBPATTERN NAMES
# Line 2140  DUPLICATE SUBPATTERN NAMES Line 2352  DUPLICATE SUBPATTERN NAMES
2352         int pcre_get_stringtable_entries(const pcre *code,         int pcre_get_stringtable_entries(const pcre *code,
2353              const char *name, char **first, char **last);              const char *name, char **first, char **last);
2354    
2355         When  a  pattern  is  compiled with the PCRE_DUPNAMES option, names for         When a pattern is compiled with the  PCRE_DUPNAMES  option,  names  for
2356         subpatterns are not required to  be  unique.  Normally,  patterns  with         subpatterns  are  not  required  to  be unique. Normally, patterns with
2357         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
2358         subpatterns participates. An example is shown in the pcrepattern  docu-         subpatterns  participates. An example is shown in the pcrepattern docu-
2359         mentation. When duplicates are present, pcre_copy_named_substring() and         mentation.
2360         pcre_get_named_substring() return the first substring corresponding  to  
2361         the  given  name  that  is  set.  If  none  are set, an empty string is         When   duplicates   are   present,   pcre_copy_named_substring()    and
2362         returned.  The pcre_get_stringnumber() function returns one of the num-         pcre_get_named_substring()  return the first substring corresponding to
2363         bers  that are associated with the name, but it is not defined which it         the given name that is set. If  none  are  set,  PCRE_ERROR_NOSUBSTRING
2364         is.         (-7)  is  returned;  no  data  is returned. The pcre_get_stringnumber()
2365           function returns one of the numbers that are associated with the  name,
2366           but it is not defined which it is.
2367    
2368         If you want to get full details of all captured substrings for a  given         If  you want to get full details of all captured substrings for a given
2369         name,  you  must  use  the pcre_get_stringtable_entries() function. The         name, you must use  the  pcre_get_stringtable_entries()  function.  The
2370         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
2371         third  and  fourth  are  pointers to variables which are updated by the         third and fourth are pointers to variables which  are  updated  by  the
2372         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
2373         the  name-to-number  table  for  the  given  name.  The function itself         the name-to-number table  for  the  given  name.  The  function  itself
2374         returns the length of each entry,  or  PCRE_ERROR_NOSUBSTRING  (-7)  if         returns  the  length  of  each entry, or PCRE_ERROR_NOSUBSTRING (-7) if
2375         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-
2376         tion entitled Information about a  pattern.   Given  all  the  relevant         tion  entitled  Information  about  a  pattern.  Given all the relevant
2377         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
2378         the captured data, if any.         the captured data, if any.
2379    
2380    
2381  FINDING ALL POSSIBLE MATCHES  FINDING ALL POSSIBLE MATCHES
2382    
2383         The traditional matching function uses a  similar  algorithm  to  Perl,         The  traditional  matching  function  uses a similar algorithm to Perl,
2384         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
2385         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
2386         possible  match,  consider using the alternative matching function (see         possible match, consider using the alternative matching  function  (see
2387         below) instead. If you cannot use the alternative function,  but  still         below)  instead.  If you cannot use the alternative function, but still
2388         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
2389         of the callout facility, which is described in the pcrecallout documen-         of the callout facility, which is described in the pcrecallout documen-
2390         tation.         tation.
2391    
2392         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-
2393         tern.  When your callout function is called, extract and save the  cur-         tern.   When your callout function is called, extract and save the cur-
2394         rent  matched  substring.  Then  return  1, which forces pcre_exec() to         rent matched substring. Then return  1,  which  forces  pcre_exec()  to
2395         backtrack and try other alternatives. Ultimately, when it runs  out  of         backtrack  and  try other alternatives. Ultimately, when it runs out of
2396         matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.         matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
2397    
2398    
# Line 2189  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2403  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2403              int options, int *ovector, int ovecsize,              int options, int *ovector, int ovecsize,
2404              int *workspace, int wscount);              int *workspace, int wscount);
2405    
2406         The  function  pcre_dfa_exec()  is  called  to  match  a subject string         The function pcre_dfa_exec()  is  called  to  match  a  subject  string
2407         against a compiled pattern, using a matching algorithm that  scans  the         against  a  compiled pattern, using a matching algorithm that scans the
2408         subject  string  just  once, and does not backtrack. This has different         subject string just once, and does not backtrack.  This  has  different
2409         characteristics to the normal algorithm, and  is  not  compatible  with         characteristics  to  the  normal  algorithm, and is not compatible with
2410         Perl.  Some  of the features of PCRE patterns are not supported. Never-         Perl. Some of the features of PCRE patterns are not  supported.  Never-
2411         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
2412         a discussion of the two matching algorithms, see the pcrematching docu-         a discussion of the two matching algorithms, see the pcrematching docu-
2413         mentation.         mentation.
2414    
2415         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
2416         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-
2417         ent way, and this is described below. The other  common  arguments  are         ent  way,  and  this is described below. The other common arguments are
2418         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
2419         repeated here.         repeated here.
2420    
2421         The two additional arguments provide workspace for  the  function.  The         The  two  additional  arguments provide workspace for the function. The
2422         workspace  vector  should  contain at least 20 elements. It is used for         workspace vector should contain at least 20 elements. It  is  used  for
2423         keeping  track  of  multiple  paths  through  the  pattern  tree.  More         keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2424         workspace  will  be  needed for patterns and subjects where there are a         workspace will be needed for patterns and subjects where  there  are  a
2425         lot of potential matches.         lot of potential matches.
2426    
2427         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 2229  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2443  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2443    
2444     Option bits for pcre_dfa_exec()     Option bits for pcre_dfa_exec()
2445    
2446         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
2447         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-
2448         LINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,  PCRE_NO_UTF8_CHECK,         LINE_xxx,  PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK,
2449         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
2450         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
2451         not repeated here.         not repeated here.
2452    
2453           PCRE_PARTIAL           PCRE_PARTIAL
2454    
2455         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
2456         details  are  slightly  different.  When  PCRE_PARTIAL   is   set   for         details   are   slightly   different.  When  PCRE_PARTIAL  is  set  for
2457         pcre_dfa_exec(),  the  return code PCRE_ERROR_NOMATCH is converted into         pcre_dfa_exec(), the return code PCRE_ERROR_NOMATCH is  converted  into
2458         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
2459         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-
2460         sibility. The portion of the string that provided the partial match  is         sibility.  The portion of the string that provided the partial match is
2461         set as the first matching string.         set as the first matching string.
2462    
2463           PCRE_DFA_SHORTEST           PCRE_DFA_SHORTEST
2464    
2465         Setting  the  PCRE_DFA_SHORTEST option causes the matching algorithm to         Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to
2466         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-
2467         tive  algorithm  works, this is necessarily the shortest possible match         tive algorithm works, this is necessarily the shortest  possible  match
2468         at the first possible matching point in the subject string.         at the first possible matching point in the subject string.
2469    
2470           PCRE_DFA_RESTART           PCRE_DFA_RESTART
2471    
2472         When pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option,  and         When  pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option, and
2473         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-
2474         tional subject characters, and have it continue with  the  same  match.         tional  subject  characters,  and have it continue with the same match.
2475         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
2476         workspace and wscount options must reference the same vector as  before         workspace  and wscount options must reference the same vector as before
2477         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
2478         match. There is more discussion of this  facility  in  the  pcrepartial         match.  There  is  more  discussion of this facility in the pcrepartial
2479         documentation.         documentation.
2480    
2481     Successful returns from pcre_dfa_exec()     Successful returns from pcre_dfa_exec()
2482    
2483         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-
2484         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
2485         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
2486         matches are all initial substrings of the longer matches. For  example,         matches  are all initial substrings of the longer matches. For example,
2487         if the pattern         if the pattern
2488    
2489           <.*>           <.*>
# Line 2284  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2498  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2498           <something> <something else>           <something> <something else>
2499           <something> <something else> <something further>           <something> <something else> <something further>
2500    
2501         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,
2502         which is the number of matched substrings.  The  substrings  themselves         which  is  the  number of matched substrings. The substrings themselves
2503         are  returned  in  ovector. Each string uses two elements; the first is         are returned in ovector. Each string uses two elements;  the  first  is
2504         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
2505         fact,  all  the  strings  have the same start offset. (Space could have         fact, all the strings have the same start  offset.  (Space  could  have
2506         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
2507         compatibility  with  the  way pcre_exec() returns data, even though the         compatibility with the way pcre_exec() returns data,  even  though  the
2508         meaning of the strings is different.)         meaning of the strings is different.)
2509    
2510         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-
2511         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
2512         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
2513         filled with the longest matches.         filled with the longest matches.
2514    
2515     Error returns from pcre_dfa_exec()     Error returns from pcre_dfa_exec()
2516    
2517         The  pcre_dfa_exec()  function returns a negative number when it fails.         The pcre_dfa_exec() function returns a negative number when  it  fails.
2518         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
2519         described  above.   There are in addition the following errors that are         described above.  There are in addition the following errors  that  are
2520         specific to pcre_dfa_exec():         specific to pcre_dfa_exec():
2521    
2522           PCRE_ERROR_DFA_UITEM      (-16)           PCRE_ERROR_DFA_UITEM      (-16)
2523    
2524         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-
2525         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
2526         reference.         reference.
2527    
2528           PCRE_ERROR_DFA_UCOND      (-17)           PCRE_ERROR_DFA_UCOND      (-17)
2529    
2530         This return is given if pcre_dfa_exec()  encounters  a  condition  item         This  return  is  given  if pcre_dfa_exec() encounters a condition item
2531         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
2532         in a specific group. These are not supported.         in a specific group. These are not supported.
2533    
2534           PCRE_ERROR_DFA_UMLIMIT    (-18)           PCRE_ERROR_DFA_UMLIMIT    (-18)
2535    
2536         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
2537         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
2538         (it is meaningless).         (it is meaningless).
2539    
2540           PCRE_ERROR_DFA_WSSIZE     (-19)           PCRE_ERROR_DFA_WSSIZE     (-19)
2541    
2542         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
2543         workspace vector.         workspace vector.
2544    
2545           PCRE_ERROR_DFA_RECURSE    (-20)           PCRE_ERROR_DFA_RECURSE    (-20)
2546    
2547         When  a  recursive subpattern is processed, the matching function calls         When a recursive subpattern is processed, the matching  function  calls
2548         itself recursively, using private vectors for  ovector  and  workspace.         itself  recursively,  using  private vectors for ovector and workspace.
2549         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
2550         should be extremely rare, as a vector of size 1000 is used.         should be extremely rare, as a vector of size 1000 is used.
2551    
2552    
2553  SEE ALSO  SEE ALSO
2554    
2555         pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3),  pcrepar-         pcrebuild(3),  pcrecallout(3), pcrecpp(3)(3), pcrematching(3), pcrepar-
2556         tial(3),  pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).         tial(3), pcreposix(3), pcreprecompile(3), pcresample(3),  pcrestack(3).
2557    
2558    
2559  AUTHOR  AUTHOR
# Line 2351  AUTHOR Line 2565  AUTHOR
2565    
2566  REVISION  REVISION
2567    
2568         Last updated: 06 March 2007         Last updated: 23 January 2008
2569         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2008 University of Cambridge.
2570  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2571    
2572    
# Line 2379  PCRE CALLOUTS Line 2593  PCRE CALLOUTS
2593         default value is zero.  For  example,  this  pattern  has  two  callout         default value is zero.  For  example,  this  pattern  has  two  callout
2594         points:         points:
2595    
2596           (?C1)eabc(?C2)def           (?C1)abc(?C2)def
2597    
2598         If  the  PCRE_AUTO_CALLOUT  option  bit  is  set when pcre_compile() is         If  the  PCRE_AUTO_CALLOUT  option  bit  is  set when pcre_compile() is
2599         called, PCRE automatically  inserts  callouts,  all  with  number  255,         called, PCRE automatically  inserts  callouts,  all  with  number  255,
# Line 2454  THE CALLOUT INTERFACE Line 2668  THE CALLOUT INTERFACE
2668         The subject and subject_length fields contain copies of the values that         The subject and subject_length fields contain copies of the values that
2669         were passed to pcre_exec().         were passed to pcre_exec().
2670    
2671         The start_match field contains the offset within the subject  at  which         The start_match field normally contains the offset within  the  subject
2672         the  current match attempt started. If the pattern is not anchored, the         at  which  the  current  match  attempt started. However, if the escape
2673         callout function may be called several times from the same point in the         sequence \K has been encountered, this value is changed to reflect  the
2674         pattern for different starting points in the subject.         modified  starting  point.  If the pattern is not anchored, the callout
2675           function may be called several times from the same point in the pattern
2676           for different starting points in the subject.
2677    
2678         The  current_position  field  contains the offset within the subject of         The  current_position  field  contains the offset within the subject of
2679         the current match pointer.         the current match pointer.
# Line 2520  AUTHOR Line 2736  AUTHOR
2736    
2737  REVISION  REVISION
2738    
2739         Last updated: 06 March 2007         Last updated: 29 May 2007
2740         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
2741  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2742    
# Line 2536  DIFFERENCES BETWEEN PCRE AND PERL Line 2752  DIFFERENCES BETWEEN PCRE AND PERL
2752    
2753         This  document describes the differences in the ways that PCRE and Perl         This  document describes the differences in the ways that PCRE and Perl
2754         handle regular expressions. The differences described here  are  mainly         handle regular expressions. The differences described here  are  mainly
2755         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
2756         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.
2757    
2758         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
2759         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 2602  DIFFERENCES BETWEEN PCRE AND PERL Line 2818  DIFFERENCES BETWEEN PCRE AND PERL
2818         matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2         matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2
2819         unset, but in PCRE it is set to "b".         unset, but in PCRE it is set to "b".
2820    
2821         11. PCRE provides some extensions to the Perl regular expression facil-         11.  PCRE  does  support  Perl  5.10's  backtracking  verbs  (*ACCEPT),
2822           (*FAIL),  (*F),  (*COMMIT), (*PRUNE), (*SKIP), and (*THEN), but only in
2823           the forms without an  argument.  PCRE  does  not  support  (*MARK).  If
2824           (*ACCEPT)  is within capturing parentheses, PCRE does not set that cap-
2825           ture group; this is different to Perl.
2826    
2827           12. PCRE provides some extensions to the Perl regular expression facil-
2828         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
2829         versions, some of which (such as named parentheses) have been  in  PCRE         versions, some of which (such as named parentheses) have been  in  PCRE
2830         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 2615  DIFFERENCES BETWEEN PCRE AND PERL Line 2837  DIFFERENCES BETWEEN PCRE AND PERL
2837         meta-character matches only at the very end of the string.         meta-character matches only at the very end of the string.
2838    
2839         (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-
2840         cial  meaning  is  faulted.  Otherwise,  like  Perl,  the  backslash is         cial meaning is faulted. Otherwise, like Perl, the backslash is quietly
2841         ignored. (Perl can be made to issue a warning.)         ignored.  (Perl can be made to issue a warning.)
2842    
2843         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-
2844         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 2628  DIFFERENCES BETWEEN PCRE AND PERL Line 2850  DIFFERENCES BETWEEN PCRE AND PERL
2850         (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-
2851         TURE options for pcre_exec() have no Perl equivalents.         TURE options for pcre_exec() have no Perl equivalents.
2852    
2853         (g) The callout facility is PCRE-specific.         (g) The \R escape sequence can be restricted to match only CR,  LF,  or
2854           CRLF by the PCRE_BSR_ANYCRLF option.
2855    
2856           (h) The callout facility is PCRE-specific.
2857    
2858         (h) The partial matching facility is PCRE-specific.         (i) The partial matching facility is PCRE-specific.
2859    
2860         (i) Patterns compiled by PCRE can be saved and re-used at a later time,         (j) Patterns compiled by PCRE can be saved and re-used at a later time,
2861         even on different hosts that have the other endianness.         even on different hosts that have the other endianness.
2862    
2863         (j)  The  alternative  matching function (pcre_dfa_exec()) matches in a         (k) The alternative matching function (pcre_dfa_exec())  matches  in  a
2864         different way and is not Perl-compatible.         different way and is not Perl-compatible.
2865    
2866           (l)  PCRE  recognizes some special sequences such as (*CR) at the start
2867           of a pattern that set overall options that cannot be changed within the
2868           pattern.
2869    
2870    
2871  AUTHOR  AUTHOR
2872    
# Line 2648  AUTHOR Line 2877  AUTHOR
2877    
2878  REVISION  REVISION
2879    
2880         Last updated: 06 March 2007         Last updated: 11 September 2007
2881         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
2882  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2883    
# Line 2662  NAME Line 2891  NAME
2891    
2892  PCRE REGULAR EXPRESSION DETAILS  PCRE REGULAR EXPRESSION DETAILS
2893    
2894         The  syntax  and semantics of the regular expressions supported by PCRE         The  syntax and semantics of the regular expressions that are supported
2895         are described below. Regular expressions are also described in the Perl         by PCRE are described in detail below. There is a quick-reference  syn-
2896         documentation  and  in  a  number  of books, some of which have copious         tax  summary  in  the  pcresyntax  page. Perl's regular expressions are
2897         examples.  Jeffrey Friedl's "Mastering Regular Expressions",  published         described in its own documentation, and regular expressions in  general
2898         by  O'Reilly, covers regular expressions in great detail. This descrip-         are  covered in a number of books, some of which have copious examples.
2899         tion of PCRE's regular expressions is intended as reference material.         Jeffrey  Friedl's  "Mastering  Regular   Expressions",   published   by
2900           O'Reilly,  covers regular expressions in great detail. This description
2901           of PCRE's regular expressions is intended as reference material.
2902    
2903         The original operation of PCRE was on strings of  one-byte  characters.         The original operation of PCRE was on strings of  one-byte  characters.
2904         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 2681  PCRE REGULAR EXPRESSION DETAILS Line 2912  PCRE REGULAR EXPRESSION DETAILS
2912         ported  by  PCRE when its main matching function, pcre_exec(), is used.         ported  by  PCRE when its main matching function, pcre_exec(), is used.
2913         From  release  6.0,   PCRE   offers   a   second   matching   function,         From  release  6.0,   PCRE   offers   a   second   matching   function,
2914         pcre_dfa_exec(),  which matches using a different algorithm that is not         pcre_dfa_exec(),  which matches using a different algorithm that is not
2915         Perl-compatible. The advantages and disadvantages  of  the  alternative         Perl-compatible. Some of the features discussed below are not available
2916         function, and how it differs from the normal function, are discussed in         when  pcre_dfa_exec()  is used. The advantages and disadvantages of the
2917         the pcrematching page.         alternative function, and how it differs from the normal function,  are
2918           discussed in the pcrematching page.
2919    
2920    
2921    NEWLINE CONVENTIONS
2922    
2923           PCRE  supports five different conventions for indicating line breaks in
2924           strings: a single CR (carriage return) character, a  single  LF  (line-
2925           feed) character, the two-character sequence CRLF, any of the three pre-
2926           ceding, or any Unicode newline sequence. The pcreapi page  has  further
2927           discussion  about newlines, and shows how to set the newline convention
2928           in the options arguments for the compiling and matching functions.
2929    
2930           It is also possible to specify a newline convention by starting a  pat-
2931           tern string with one of the following five sequences:
2932    
2933             (*CR)        carriage return
2934             (*LF)        linefeed
2935             (*CRLF)      carriage return, followed by linefeed
2936             (*ANYCRLF)   any of the three above
2937             (*ANY)       all Unicode newline sequences
2938    
2939           These override the default and the options given to pcre_compile(). For
2940           example, on a Unix system where LF is the default newline sequence, the
2941           pattern
2942    
2943             (*CR)a.b
2944    
2945           changes the convention to CR. That pattern matches "a\nb" because LF is
2946           no longer a newline. Note that these special settings,  which  are  not
2947           Perl-compatible,  are  recognized  only at the very start of a pattern,
2948           and that they must be in upper case.  If  more  than  one  of  them  is
2949           present, the last one is used.
2950    
2951           The  newline  convention  does  not  affect what the \R escape sequence
2952           matches. By default, this is any Unicode  newline  sequence,  for  Perl
2953           compatibility.  However, this can be changed; see the description of \R
2954           in the section entitled "Newline sequences" below. A change of \R  set-
2955           ting can be combined with a change of newline convention.
2956    
2957    
2958  CHARACTERS AND METACHARACTERS  CHARACTERS AND METACHARACTERS
2959    
2960         A regular expression is a pattern that is  matched  against  a  subject         A  regular  expression  is  a pattern that is matched against a subject
2961         string  from  left  to right. Most characters stand for themselves in a         string from left to right. Most characters stand for  themselves  in  a
2962         pattern, and match the corresponding characters in the  subject.  As  a         pattern,  and  match  the corresponding characters in the subject. As a
2963         trivial example, the pattern         trivial example, the pattern
2964    
2965           The quick brown fox           The quick brown fox
2966    
2967         matches a portion of a subject string that is identical to itself. When         matches a portion of a subject string that is identical to itself. When
2968         caseless matching is specified (the PCRE_CASELESS option), letters  are         caseless  matching is specified (the PCRE_CASELESS option), letters are
2969         matched  independently  of case. In UTF-8 mode, PCRE always understands         matched independently of case. In UTF-8 mode, PCRE  always  understands
2970         the concept of case for characters whose values are less than  128,  so         the  concept  of case for characters whose values are less than 128, so
2971         caseless  matching  is always possible. For characters with higher val-         caseless matching is always possible. For characters with  higher  val-
2972         ues, the concept of case is supported if PCRE is compiled with  Unicode         ues,  the concept of case is supported if PCRE is compiled with Unicode
2973         property  support,  but  not  otherwise.   If  you want to use caseless         property support, but not otherwise.   If  you  want  to  use  caseless
2974         matching for characters 128 and above, you must  ensure  that  PCRE  is         matching  for  characters  128  and above, you must ensure that PCRE is
2975         compiled with Unicode property support as well as with UTF-8 support.         compiled with Unicode property support as well as with UTF-8 support.
2976    
2977         The  power  of  regular  expressions  comes from the ability to include         The power of regular expressions comes  from  the  ability  to  include
2978         alternatives and repetitions in the pattern. These are encoded  in  the         alternatives  and  repetitions in the pattern. These are encoded in the
2979         pattern by the use of metacharacters, which do not stand for themselves         pattern by the use of metacharacters, which do not stand for themselves
2980         but instead are interpreted in some special way.         but instead are interpreted in some special way.
2981    
2982         There are two different sets of metacharacters: those that  are  recog-         There  are  two different sets of metacharacters: those that are recog-
2983         nized  anywhere in the pattern except within square brackets, and those         nized anywhere in the pattern except within square brackets, and  those
2984         that are recognized within square brackets.  Outside  square  brackets,         that  are  recognized  within square brackets. Outside square brackets,
2985         the metacharacters are as follows:         the metacharacters are as follows:
2986    
2987           \      general escape character with several uses           \      general escape character with several uses
# Line 2731  CHARACTERS AND METACHARACTERS Line 3000  CHARACTERS AND METACHARACTERS
3000                  also "possessive quantifier"                  also "possessive quantifier"
3001           {      start min/max quantifier           {      start min/max quantifier
3002    
3003         Part  of  a  pattern  that is in square brackets is called a "character         Part of a pattern that is in square brackets  is  called  a  "character
3004         class". In a character class the only metacharacters are:         class". In a character class the only metacharacters are:
3005    
3006           \      general escape character           \      general escape character
# Line 2741  CHARACTERS AND METACHARACTERS Line 3010  CHARACTERS AND METACHARACTERS
3010                    syntax)                    syntax)
3011           ]      terminates the character class           ]      terminates the character class
3012    
3013         The following sections describe the use of each of the  metacharacters.         The  following sections describe the use of each of the metacharacters.
3014    
3015    
3016  BACKSLASH  BACKSLASH
3017    
3018         The backslash character has several uses. Firstly, if it is followed by         The backslash character has several uses. Firstly, if it is followed by
3019         a non-alphanumeric character, it takes away any  special  meaning  that         a  non-alphanumeric  character,  it takes away any special meaning that
3020         character  may  have.  This  use  of  backslash  as an escape character         character may have. This  use  of  backslash  as  an  escape  character
3021         applies both inside and outside character classes.         applies both inside and outside character classes.
3022    
3023         For example, if you want to match a * character, you write  \*  in  the         For  example,  if  you want to match a * character, you write \* in the
3024         pattern.   This  escaping  action  applies whether or not the following         pattern.  This escaping action applies whether  or  not  the  following
3025         character would otherwise be interpreted as a metacharacter, so  it  is         character  would  otherwise be interpreted as a metacharacter, so it is
3026         always  safe  to  precede  a non-alphanumeric with backslash to specify         always safe to precede a non-alphanumeric  with  backslash  to  specify
3027         that it stands for itself. In particular, if you want to match a  back-         that  it stands for itself. In particular, if you want to match a back-
3028         slash, you write \\.         slash, you write \\.
3029    
3030         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in         If a pattern is compiled with the PCRE_EXTENDED option,  whitespace  in
3031         the pattern (other than in a character class) and characters between  a         the  pattern (other than in a character class) and characters between a
3032         # outside a character class and the next newline are ignored. An escap-         # outside a character class and the next newline are ignored. An escap-
3033         ing backslash can be used to include a whitespace  or  #  character  as         ing  backslash  can  be  used to include a whitespace or # character as
3034         part of the pattern.         part of the pattern.
3035    
3036         If  you  want  to remove the special meaning from a sequence of charac-         If you want to remove the special meaning from a  sequence  of  charac-
3037         ters, you can do so by putting them between \Q and \E. This is  differ-         ters,  you can do so by putting them between \Q and \E. This is differ-
3038         ent  from  Perl  in  that  $  and  @ are handled as literals in \Q...\E         ent from Perl in that $ and  @  are  handled  as  literals  in  \Q...\E
3039         sequences in PCRE, whereas in Perl, $ and @ cause  variable  interpola-         sequences  in  PCRE, whereas in Perl, $ and @ cause variable interpola-
3040         tion. Note the following examples:         tion. Note the following examples:
3041    
3042           Pattern            PCRE matches   Perl matches           Pattern            PCRE matches   Perl matches
# Line 2777  BACKSLASH Line 3046  BACKSLASH
3046           \Qabc\$xyz\E       abc\$xyz       abc\$xyz           \Qabc\$xyz\E       abc\$xyz       abc\$xyz
3047           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz
3048    
3049         The  \Q...\E  sequence  is recognized both inside and outside character         The \Q...\E sequence is recognized both inside  and  outside  character
3050         classes.         classes.
3051    
3052     Non-printing characters     Non-printing characters
3053    
3054         A second use of backslash provides a way of encoding non-printing char-         A second use of backslash provides a way of encoding non-printing char-
3055         acters  in patterns in a visible manner. There is no restriction on the         acters in patterns in a visible manner. There is no restriction on  the
3056         appearance of non-printing characters, apart from the binary zero  that         appearance  of non-printing characters, apart from the binary zero that
3057         terminates  a  pattern,  but  when  a pattern is being prepared by text         terminates a pattern, but when a pattern  is  being  prepared  by  text
3058         editing, it is usually easier  to  use  one  of  the  following  escape         editing,  it  is  usually  easier  to  use  one of the following escape
3059         sequences than the binary character it represents:         sequences than the binary character it represents:
3060    
3061           \a        alarm, that is, the BEL character (hex 07)           \a        alarm, that is, the BEL character (hex 07)
3062           \cx       "control-x", where x is any character           \cx       "control-x", where x is any character
3063           \e        escape (hex 1B)           \e        escape (hex 1B)
3064           \f        formfeed (hex 0C)           \f        formfeed (hex 0C)
3065           \n        newline (hex 0A)           \n        linefeed (hex 0A)
3066           \r        carriage return (hex 0D)           \r        carriage return (hex 0D)
3067           \t        tab (hex 09)           \t        tab (hex 09)
3068           \ddd      character with octal code ddd, or backreference           \ddd      character with octal code ddd, or backreference
3069           \xhh      character with hex code hh           \xhh      character with hex code hh
3070           \x{hhh..} character with hex code hhh..           \x{hhh..} character with hex code hhh..
3071    
3072         The  precise  effect of \cx is as follows: if x is a lower case letter,         The precise effect of \cx is as follows: if x is a lower  case  letter,
3073         it is converted to upper case. Then bit 6 of the character (hex 40)  is         it  is converted to upper case. Then bit 6 of the character (hex 40) is
3074         inverted.   Thus  \cz becomes hex 1A, but \c{ becomes hex 3B, while \c;         inverted.  Thus \cz becomes hex 1A, but \c{ becomes hex 3B,  while  \c;
3075         becomes hex 7B.         becomes hex 7B.
3076    
3077         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
3078         in  upper  or  lower case). Any number of hexadecimal digits may appear         in upper or lower case). Any number of hexadecimal  digits  may  appear
3079         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
3080         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,
3081         the maximum hexadecimal value is 7FFFFFFF). If  characters  other  than         the  maximum value in hexadecimal is 7FFFFFFF. Note that this is bigger
3082         hexadecimal  digits  appear between \x{ and }, or if there is no termi-         than the largest Unicode code point, which is 10FFFF.
3083         nating }, this form of escape is not recognized.  Instead, the  initial  
3084         \x will be interpreted as a basic hexadecimal escape, with no following         If characters other than hexadecimal digits appear between \x{  and  },
3085         digits, giving a character whose value is zero.         or if there is no terminating }, this form of escape is not recognized.
3086           Instead, the initial \x will be  interpreted  as  a  basic  hexadecimal
3087           escape,  with  no  following  digits, giving a character whose value is
3088           zero.
3089    
3090         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
3091         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-
# Line 2868  BACKSLASH Line 3140  BACKSLASH
3140    
3141     Absolute and relative back references     Absolute and relative back references
3142    
3143         The sequence \g followed by a positive or negative  number,  optionally         The sequence \g followed by an unsigned or a negative  number,  option-
3144         enclosed  in  braces,  is  an absolute or relative back reference. Back         ally  enclosed  in braces, is an absolute or relative back reference. A
3145         references are discussed later, following the discussion  of  parenthe-         named back reference can be coded as \g{name}. Back references are dis-
3146         sized subpatterns.         cussed later, following the discussion of parenthesized subpatterns.
3147    
3148     Generic character types     Generic character types
3149    
# Line 2880  BACKSLASH Line 3152  BACKSLASH
3152    
3153           \d     any decimal digit           \d     any decimal digit
3154           \D     any character that is not a decimal digit           \D     any character that is not a decimal digit
3155             \h     any horizontal whitespace character
3156             \H     any character that is not a horizontal whitespace character
3157           \s     any whitespace character           \s     any whitespace character
3158           \S     any character that is not a whitespace character           \S     any character that is not a whitespace character
3159             \v     any vertical whitespace character
3160             \V     any character that is not a vertical whitespace character
3161           \w     any "word" character           \w     any "word" character
3162           \W     any "non-word" character           \W     any "non-word" character
3163    
# Line 2896  BACKSLASH Line 3172  BACKSLASH
3172    
3173         For  compatibility  with Perl, \s does not match the VT character (code         For  compatibility  with Perl, \s does not match the VT character (code
3174         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
3175         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
3176         "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-
3177         ter. In PCRE, it never does.)         ter. In PCRE, it never does.
3178    
3179           In  UTF-8 mode, characters with values greater than 128 never match \d,
3180           \s, or \w, and always match \D, \S, and \W. This is true even when Uni-
3181           code  character  property  support is available. These sequences retain
3182           their original meanings from before UTF-8 support was available, mainly
3183           for efficiency reasons.
3184    
3185           The sequences \h, \H, \v, and \V are Perl 5.10 features. In contrast to
3186           the other sequences, these do match certain high-valued  codepoints  in
3187           UTF-8 mode.  The horizontal space characters are:
3188    
3189             U+0009     Horizontal tab
3190             U+0020     Space
3191             U+00A0     Non-break space
3192             U+1680     Ogham space mark
3193             U+180E     Mongolian vowel separator
3194             U+2000     En quad
3195             U+2001     Em quad
3196             U+2002     En space
3197             U+2003     Em space
3198             U+2004     Three-per-em space
3199             U+2005     Four-per-em space
3200             U+2006     Six-per-em space
3201             U+2007     Figure space
3202             U+2008     Punctuation space
3203             U+2009     Thin space
3204             U+200A     Hair space
3205             U+202F     Narrow no-break space
3206             U+205F     Medium mathematical space
3207             U+3000     Ideographic space
3208    
3209           The vertical space characters are:
3210    
3211             U+000A     Linefeed
3212             U+000B     Vertical tab
3213             U+000C     Formfeed
3214             U+000D     Carriage return
3215             U+0085     Next line
3216             U+2028     Line separator
3217             U+2029     Paragraph separator
3218    
3219         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
3220         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-
3221         trolled  by PCRE's low-valued character tables, and may vary if locale-         trolled  by PCRE's low-valued character tables, and may vary if locale-
3222         specific matching is taking place (see "Locale support" in the  pcreapi         specific matching is taking place (see "Locale support" in the  pcreapi
3223         page).  For  example,  in  the  "fr_FR" (French) locale, some character         page).  For  example,  in  a French locale such as "fr_FR" in Unix-like
3224         codes greater than 128 are used for accented  letters,  and  these  are         systems, or "french" in Windows, some character codes greater than  128
3225         matched by \w.         are  used for accented letters, and these are matched by \w. The use of
3226           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.  
3227    
3228     Newline sequences     Newline sequences
3229    
3230         Outside a character class, the escape sequence \R matches  any  Unicode         Outside a character class, by default, the escape sequence  \R  matches
3231         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
3232         equivalent to the following:         mode \R is equivalent to the following:
3233    
3234           (?>\r\n|\n|\x0b|\f|\r|\x85)           (?>\r\n|\n|\x0b|\f|\r|\x85)
3235    
# Line 2933  BACKSLASH Line 3245  BACKSLASH
3245         rator,  U+2029).   Unicode character property support is not needed for         rator,  U+2029).   Unicode character property support is not needed for
3246         these characters to be recognized.         these characters to be recognized.
3247    
3248           It is possible to restrict \R to match only CR, LF, or CRLF (instead of
3249           the  complete  set  of  Unicode  line  endings)  by  setting the option
3250           PCRE_BSR_ANYCRLF either at compile time or when the pattern is matched.
3251           (BSR is an abbrevation for "backslash R".) This can be made the default
3252           when PCRE is built; if this is the case, the  other  behaviour  can  be
3253           requested  via  the  PCRE_BSR_UNICODE  option.   It is also possible to
3254           specify these settings by starting a pattern string  with  one  of  the
3255           following sequences:
3256    
3257             (*BSR_ANYCRLF)   CR, LF, or CRLF only
3258             (*BSR_UNICODE)   any Unicode newline sequence
3259    
3260           These override the default and the options given to pcre_compile(), but
3261           they can be overridden by options given to pcre_exec(). Note that these
3262           special settings, which are not Perl-compatible, are recognized only at
3263           the very start of a pattern, and that they must be in  upper  case.  If
3264           more  than  one  of  them is present, the last one is used. They can be
3265           combined with a change of newline convention, for  example,  a  pattern
3266           can start with:
3267    
3268             (*ANY)(*BSR_ANYCRLF)
3269    
3270         Inside a character class, \R matches the letter "R".         Inside a character class, \R matches the letter "R".
3271    
3272     Unicode character properties     Unicode character properties
3273    
3274         When PCRE is built with Unicode character property support, three addi-         When PCRE is built with Unicode character property support, three addi-
3275         tional  escape  sequences  to  match character properties are available         tional escape sequences that match characters with specific  properties
3276         when UTF-8 mode is selected. They are:         are  available.   When not in UTF-8 mode, these sequences are of course
3277           limited to testing characters whose codepoints are less than  256,  but
3278           they do work in this mode.  The extra escape sequences are:
3279    
3280           \p{xx}   a character with the xx property           \p{xx}   a character with the xx property
3281           \P{xx}   a character without the xx property           \P{xx}   a character without the xx property
3282           \X       an extended Unicode sequence           \X       an extended Unicode sequence
3283    
3284         The property names represented by xx above are limited to  the  Unicode         The  property  names represented by xx above are limited to the Unicode
3285         script names, the general category properties, and "Any", which matches         script names, the general category properties, and "Any", which matches
3286         any character (including newline). Other properties such as "InMusical-         any character (including newline). Other properties such as "InMusical-
3287         Symbols"  are  not  currently supported by PCRE. Note that \P{Any} does         Symbols" are not currently supported by PCRE. Note  that  \P{Any}  does
3288         not match any characters, so always causes a match failure.         not match any characters, so always causes a match failure.
3289    
3290         Sets of Unicode characters are defined as belonging to certain scripts.         Sets of Unicode characters are defined as belonging to certain scripts.
3291         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.
3292         For example:         For example:
3293    
3294           \p{Greek}           \p{Greek}
3295           \P{Han}           \P{Han}
3296    
3297         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
3298         "Common". The current list of scripts is:         "Common". The current list of scripts is:
3299    
3300         Arabic,  Armenian,  Balinese,  Bengali,  Bopomofo,  Braille,  Buginese,         Arabic,  Armenian,  Balinese,  Bengali,  Bopomofo,  Braille,  Buginese,
3301         Buhid,  Canadian_Aboriginal,  Cherokee,  Common,   Coptic,   Cuneiform,         Buhid,   Canadian_Aboriginal,   Cherokee,  Common,  Coptic,  Cuneiform,
3302         Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,         Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,
3303         Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew,  Hira-         Gothic,  Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hira-
3304         gana,  Inherited,  Kannada,  Katakana,  Kharoshthi,  Khmer, Lao, Latin,         gana, Inherited, Kannada,  Katakana,  Kharoshthi,  Khmer,  Lao,  Latin,
3305         Limbu,  Linear_B,  Malayalam,  Mongolian,  Myanmar,  New_Tai_Lue,  Nko,         Limbu,  Linear_B,  Malayalam,  Mongolian,  Myanmar,  New_Tai_Lue,  Nko,
3306         Ogham,  Old_Italic,  Old_Persian, Oriya, Osmanya, Phags_Pa, Phoenician,         Ogham, Old_Italic, Old_Persian, Oriya, Osmanya,  Phags_Pa,  Phoenician,
3307         Runic,  Shavian,  Sinhala,  Syloti_Nagri,  Syriac,  Tagalog,  Tagbanwa,         Runic,  Shavian,  Sinhala,  Syloti_Nagri,  Syriac,  Tagalog,  Tagbanwa,
3308         Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.         Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.
3309    
3310         Each  character has exactly one general category property, specified by         Each character has exactly one general category property, specified  by
3311         a two-letter abbreviation. For compatibility with Perl, negation can be         a two-letter abbreviation. For compatibility with Perl, negation can be
3312         specified  by  including a circumflex between the opening brace and the         specified by including a circumflex between the opening brace  and  the
3313         property name. For example, \p{^Lu} is the same as \P{Lu}.         property name. For example, \p{^Lu} is the same as \P{Lu}.
3314    
3315         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-
3316         eral  category properties that start with that letter. In this case, in         eral category properties that start with that letter. In this case,  in
3317         the absence of negation, the curly brackets in the escape sequence  are         the  absence of negation, the curly brackets in the escape sequence are
3318         optional; these two examples have the same effect:         optional; these two examples have the same effect:
3319    
3320           \p{L}           \p{L}
# Line 3030  BACKSLASH Line 3366  BACKSLASH
3366           Zp    Paragraph separator           Zp    Paragraph separator
3367           Zs    Space separator           Zs    Space separator
3368    
3369         The  special property L& is also supported: it matches a character that         The special property L& is also supported: it matches a character  that
3370         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
3371         classified as a modifier or "other".         classified as a modifier or "other".
3372    
3373         The  long  synonyms  for  these  properties that Perl supports (such as         The Cs (Surrogate) property applies only to  characters  in  the  range
3374         \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
3375           RFC 3629) and so cannot be tested by PCRE, unless UTF-8 validity check-
3376           ing  has  been  turned off (see the discussion of PCRE_NO_UTF8_CHECK in
3377           the pcreapi page).
3378    
3379           The long synonyms for these properties  that  Perl  supports  (such  as
3380           \p{Letter})  are  not  supported by PCRE, nor is it permitted to prefix
3381         any of these properties with "Is".         any of these properties with "Is".
3382    
3383         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-
3384         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
3385         in the Unicode table.         in the Unicode table.
3386    
3387         Specifying  caseless  matching  does not affect these escape sequences.         Specifying caseless matching does not affect  these  escape  sequences.
3388         For example, \p{Lu} always matches only upper case letters.         For example, \p{Lu} always matches only upper case letters.
3389    
3390         The \X escape matches any number of Unicode  characters  that  form  an         The  \X  escape  matches  any number of Unicode characters that form an
3391         extended Unicode sequence. \X is equivalent to         extended Unicode sequence. \X is equivalent to
3392    
3393           (?>\PM\pM*)           (?>\PM\pM*)
3394    
3395         That  is,  it matches a character without the "mark" property, followed         That is, it matches a character without the "mark"  property,  followed
3396         by zero or more characters with the "mark"  property,  and  treats  the         by  zero  or  more  characters with the "mark" property, and treats the
3397         sequence  as  an  atomic group (see below).  Characters with the "mark"         sequence as an atomic group (see below).  Characters  with  the  "mark"
3398         property are typically accents that affect the preceding character.         property  are  typically  accents  that affect the preceding character.
3399           None of them have codepoints less than 256, so  in  non-UTF-8  mode  \X
3400           matches any one character.
3401    
3402         Matching characters by Unicode property is not fast, because  PCRE  has         Matching  characters  by Unicode property is not fast, because PCRE has
3403         to  search  a  structure  that  contains data for over fifteen thousand         to search a structure that contains  data  for  over  fifteen  thousand
3404         characters. That is why the traditional escape sequences such as \d and         characters. That is why the traditional escape sequences such as \d and
3405         \w do not use Unicode properties in PCRE.         \w do not use Unicode properties in PCRE.
3406    
3407       Resetting the match start
3408    
3409           The escape sequence \K, which is a Perl 5.10 feature, causes any previ-
3410           ously  matched  characters  not  to  be  included  in the final matched
3411           sequence. For example, the pattern:
3412    
3413             foo\Kbar
3414    
3415           matches "foobar", but reports that it has matched "bar".  This  feature
3416           is  similar  to  a lookbehind assertion (described below).  However, in
3417           this case, the part of the subject before the real match does not  have
3418           to  be of fixed length, as lookbehind assertions do. The use of \K does
3419           not interfere with the setting of captured  substrings.   For  example,
3420           when the pattern
3421    
3422             (foo)\Kbar
3423    
3424           matches "foobar", the first substring is still set to "foo".
3425    
3426     Simple assertions     Simple assertions
3427    
3428         The  final use of backslash is for certain simple assertions. An asser-         The  final use of backslash is for certain simple assertions. An asser-
# Line 3275  SQUARE BRACKETS AND CHARACTER CLASSES Line 3638  SQUARE BRACKETS AND CHARACTER CLASSES
3638         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,
3639         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
3640         to  [][\\^_`wxyzabc],  matched  caselessly,  and  in non-UTF-8 mode, if         to  [][\\^_`wxyzabc],  matched  caselessly,  and  in non-UTF-8 mode, if
3641         character tables for the "fr_FR" locale are in use, [\xc8-\xcb] matches         character tables for a French locale are in  use,  [\xc8-\xcb]  matches
3642         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
3643         concept of case for characters with values greater than 128  only  when         concept of case for characters with values greater than 128  only  when
3644         it is compiled with Unicode property support.         it is compiled with Unicode property support.
# Line 3359  VERTICAL BAR Line 3722  VERTICAL BAR
3722  INTERNAL OPTION SETTING  INTERNAL OPTION SETTING
3723    
3724         The  settings  of  the  PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and         The  settings  of  the  PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and
3725         PCRE_EXTENDED options can be changed  from  within  the  pattern  by  a         PCRE_EXTENDED options (which are Perl-compatible) can be  changed  from
3726         sequence  of  Perl  option  letters  enclosed between "(?" and ")". The         within  the  pattern  by  a  sequence  of  Perl option letters enclosed
3727         option letters are         between "(?" and ")".  The option letters are
3728    
3729           i  for PCRE_CASELESS           i  for PCRE_CASELESS
3730           m  for PCRE_MULTILINE           m  for PCRE_MULTILINE
# Line 3375  INTERNAL OPTION SETTING Line 3738  INTERNAL OPTION SETTING
3738         is also permitted. If a  letter  appears  both  before  and  after  the         is also permitted. If a  letter  appears  both  before  and  after  the
3739         hyphen, the option is unset.         hyphen, the option is unset.
3740    
3741           The  PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and PCRE_EXTRA
3742           can be changed in the same way as the Perl-compatible options by  using
3743           the characters J, U and X respectively.
3744    
3745         When  an option change occurs at top level (that is, not inside subpat-         When  an option change occurs at top level (that is, not inside subpat-
3746         tern parentheses), the change applies to the remainder of  the  pattern         tern parentheses), the change applies to the remainder of  the  pattern
3747         that follows.  If the change is placed right at the start of a pattern,         that follows.  If the change is placed right at the start of a pattern,
# Line 3400  INTERNAL OPTION SETTING Line 3767  INTERNAL OPTION SETTING
3767         the  effects  of option settings happen at compile time. There would be         the  effects  of option settings happen at compile time. There would be
3768         some very weird behaviour otherwise.         some very weird behaviour otherwise.
3769    
3770         The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and  PCRE_EXTRA         Note: There are other PCRE-specific options that  can  be  set  by  the
3771         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
3772         the characters J, U and X respectively.         cases the pattern can contain special  leading  sequences  to  override
3773           what  the  application  has set or what has been defaulted. Details are
3774           given in the section entitled "Newline sequences" above.
3775    
3776    
3777  SUBPATTERNS  SUBPATTERNS
# Line 3460  SUBPATTERNS Line 3829  SUBPATTERNS
3829         "Saturday".         "Saturday".
3830    
3831    
3832    DUPLICATE SUBPATTERN NUMBERS
3833    
3834           Perl 5.10 introduced a feature whereby each alternative in a subpattern
3835           uses the same numbers for its capturing parentheses. Such a  subpattern
3836           starts  with (?| and is itself a non-capturing subpattern. For example,
3837           consider this pattern:
3838    
3839             (?|(Sat)ur|(Sun))day
3840    
3841           Because the two alternatives are inside a (?| group, both sets of  cap-
3842           turing  parentheses  are  numbered one. Thus, when the pattern matches,
3843           you can look at captured substring number  one,  whichever  alternative
3844           matched.  This  construct  is useful when you want to capture part, but
3845           not all, of one of a number of alternatives. Inside a (?| group, paren-
3846           theses  are  numbered as usual, but the number is reset at the start of
3847           each branch. The numbers of any capturing buffers that follow the  sub-
3848           pattern  start after the highest number used in any branch. The follow-
3849           ing example is taken from the Perl documentation.  The  numbers  under-
3850           neath show in which buffer the captured content will be stored.
3851    
3852             # before  ---------------branch-reset----------- after
3853             / ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x
3854             # 1            2         2  3        2     3     4
3855    
3856           A  backreference  or  a  recursive call to a numbered subpattern always
3857           refers to the first one in the pattern with the given number.
3858    
3859           An alternative approach to using this "branch reset" feature is to  use
3860           duplicate named subpatterns, as described in the next section.
3861    
3862    
3863  NAMED SUBPATTERNS  NAMED SUBPATTERNS
3864    
3865         Identifying  capturing  parentheses  by number is simple, but it can be         Identifying  capturing  parentheses  by number is simple, but it can be
# Line 3499  NAMED SUBPATTERNS Line 3899  NAMED SUBPATTERNS
3899           (?<DN>Sat)(?:urday)?           (?<DN>Sat)(?:urday)?
3900    
3901         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
3902         match.  The convenience  function  for  extracting  the  data  by  name         match.  (An alternative way of solving this problem is to use a "branch
3903         returns  the  substring  for  the first (and in this example, the only)         reset" subpattern, as described in the previous section.)
3904         subpattern of that name that matched.  This  saves  searching  to  find  
3905         which  numbered  subpattern  it  was. If you make a reference to a non-         The  convenience  function  for extracting the data by name returns the
3906         unique named subpattern from elsewhere in the  pattern,  the  one  that         substring for the first (and in this example, the only)  subpattern  of
3907         corresponds  to  the  lowest number is used. For further details of the         that  name  that  matched.  This saves searching to find which numbered
3908         interfaces for handling named subpatterns, see the  pcreapi  documenta-         subpattern it was. If you make a reference to a non-unique  named  sub-
3909         tion.         pattern  from elsewhere in the pattern, the one that corresponds to the
3910           lowest number is used. For further details of the interfaces  for  han-
3911           dling named subpatterns, see the pcreapi documentation.
3912    
3913    
3914  REPETITION  REPETITION
# Line 3711  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE Line 4113  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
4113    
4114           \d++foo           \d++foo
4115    
4116         Possessive  quantifiers  are  always  greedy;  the   setting   of   the         Note that a possessive quantifier can be used with an entire group, for
4117           example:
4118    
4119             (abc|xyz){2,3}+
4120    
4121           Possessive   quantifiers   are   always  greedy;  the  setting  of  the
4122         PCRE_UNGREEDY option is ignored. They are a convenient notation for the         PCRE_UNGREEDY option is ignored. They are a convenient notation for the
4123         simpler forms of atomic group. However, there is no difference  in  the         simpler  forms  of atomic group. However, there is no difference in the
4124         meaning  of  a  possessive  quantifier and the equivalent atomic group,         meaning of a possessive quantifier and  the  equivalent  atomic  group,
4125         though there may be a performance  difference;  possessive  quantifiers         though  there  may  be a performance difference; possessive quantifiers
4126         should be slightly faster.         should be slightly faster.
4127    
4128         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-
4129         tax.  Jeffrey Friedl originated the idea (and the name)  in  the  first         tax.   Jeffrey  Friedl  originated the idea (and the name) in the first
4130         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
4131         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
4132         found its way into Perl at release 5.10.         found its way into Perl at release 5.10.
4133    
4134         PCRE has an optimization that automatically "possessifies" certain sim-         PCRE has an optimization that automatically "possessifies" certain sim-
4135         ple pattern constructs. For example, the sequence  A+B  is  treated  as         ple  pattern  constructs.  For  example, the sequence A+B is treated as
4136         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
4137         when B must follow.         when B must follow.
4138    
4139         When a pattern contains an unlimited repeat inside  a  subpattern  that         When  a  pattern  contains an unlimited repeat inside a subpattern that
4140         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
4141         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
4142         very long time indeed. The pattern         very long time indeed. The pattern
4143    
4144           (\D+|<\d+>)*[!?]           (\D+|<\d+>)*[!?]
4145    
4146         matches  an  unlimited number of substrings that either consist of non-         matches an unlimited number of substrings that either consist  of  non-
4147         digits, or digits enclosed in <>, followed by either ! or  ?.  When  it         digits,  or  digits  enclosed in <>, followed by either ! or ?. When it
4148         matches, it runs quickly. However, if it is applied to         matches, it runs quickly. However, if it is applied to
4149    
4150           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
4151    
4152         it  takes  a  long  time  before reporting failure. This is because the         it takes a long time before reporting  failure.  This  is  because  the
4153         string can be divided between the internal \D+ repeat and the  external         string  can be divided between the internal \D+ repeat and the external
4154         *  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
4155         example uses [!?] rather than a single character at  the  end,  because         example  uses  [!?]  rather than a single character at the end, because
4156         both  PCRE  and  Perl have an optimization that allows for fast failure         both PCRE and Perl have an optimization that allows  for  fast  failure
4157         when a single character is used. They remember the last single  charac-         when  a single character is used. They remember the last single charac-
4158         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
4159         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
4160         group, like this:         group, like this:
4161    
4162           ((?>\D+)|<\d+>)*[!?]           ((?>\D+)|<\d+>)*[!?]
4163    
4164         sequences  of non-digits cannot be broken, and failure happens quickly.         sequences of non-digits cannot be broken, and failure happens  quickly.
4165    
4166    
4167  BACK REFERENCES  BACK REFERENCES
4168    
4169         Outside a character class, a backslash followed by a digit greater than         Outside a character class, a backslash followed by a digit greater than
4170         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-
4171         pattern earlier (that is, to its left) in the pattern,  provided  there         pattern  earlier  (that is, to its left) in the pattern, provided there
4172         have been that many previous capturing left parentheses.         have been that many previous capturing left parentheses.
4173    
4174         However, if the decimal number following the backslash is less than 10,         However, if the decimal number following the backslash is less than 10,
4175         it is always taken as a back reference, and causes  an  error  only  if         it  is  always  taken  as a back reference, and causes an error only if
4176         there  are  not that many capturing left parentheses in the entire pat-         there are not that many capturing left parentheses in the  entire  pat-
4177         tern. In other words, the parentheses that are referenced need  not  be         tern.  In  other words, the parentheses that are referenced need not be
4178         to  the left of the reference for numbers less than 10. A "forward back         to the left of the reference for numbers less than 10. A "forward  back
4179         reference" of this type can make sense when a  repetition  is  involved         reference"  of  this  type can make sense when a repetition is involved
4180         and  the  subpattern to the right has participated in an earlier itera-         and the subpattern to the right has participated in an  earlier  itera-
4181         tion.         tion.
4182    
4183         It is not possible to have a numerical "forward back  reference"  to  a         It  is  not  possible to have a numerical "forward back reference" to a
4184         subpattern  whose  number  is  10  or  more using this syntax because a         subpattern whose number is 10 or  more  using  this  syntax  because  a
4185         sequence such as \50 is interpreted as a character  defined  in  octal.         sequence  such  as  \50 is interpreted as a character defined in octal.
4186         See the subsection entitled "Non-printing characters" above for further         See the subsection entitled "Non-printing characters" above for further
4187         details of the handling of digits following a backslash.  There  is  no         details  of  the  handling of digits following a backslash. There is no
4188         such  problem  when named parentheses are used. A back reference to any         such problem when named parentheses are used. A back reference  to  any
4189         subpattern is possible using named parentheses (see below).         subpattern is possible using named parentheses (see below).
4190    
4191         Another way of avoiding the ambiguity inherent in  the  use  of  digits         Another  way  of  avoiding  the ambiguity inherent in the use of digits
4192         following a backslash is to use the \g escape sequence, which is a fea-         following a backslash is to use the \g escape sequence, which is a fea-
4193         ture introduced in Perl 5.10. This escape must be followed by  a  posi-         ture  introduced  in  Perl  5.10.  This  escape  must be followed by an
4194         tive  or  a negative number, optionally enclosed in braces. These exam-         unsigned number or a negative number, optionally  enclosed  in  braces.
4195         ples are all identical:         These examples are all identical:
4196    
4197           (ring), \1           (ring), \1
4198           (ring), \g1           (ring), \g1
4199           (ring), \g{1}           (ring), \g{1}
4200    
4201         A positive number specifies an absolute reference without the ambiguity         An  unsigned number specifies an absolute reference without the ambigu-
4202         that  is  present  in  the older syntax. It is also useful when literal         ity that is present in the older syntax. It is also useful when literal
4203         digits follow the reference. A negative number is a relative reference.         digits follow the reference. A negative number is a relative reference.
4204         Consider this example:         Consider this example:
4205    
4206           (abc(def)ghi)\g{-1}           (abc(def)ghi)\g{-1}
4207    
4208         The sequence \g{-1} is a reference to the most recently started captur-         The sequence \g{-1} is a reference to the most recently started captur-
4209         ing subpattern before \g, that is, is it equivalent to  \2.  Similarly,         ing  subpattern  before \g, that is, is it equivalent to \2. Similarly,
4210         \g{-2} would be equivalent to \1. The use of relative references can be         \g{-2} would be equivalent to \1. The use of relative references can be
4211         helpful in long patterns, and also in  patterns  that  are  created  by         helpful  in  long  patterns,  and  also in patterns that are created by
4212         joining together fragments that contain references within themselves.         joining together fragments that contain references within themselves.
4213    
4214         A  back  reference matches whatever actually matched the capturing sub-         A back reference matches whatever actually matched the  capturing  sub-
4215         pattern in the current subject string, rather  than  anything  matching         pattern  in  the  current subject string, rather than anything matching
4216         the subpattern itself (see "Subpatterns as subroutines" below for a way         the subpattern itself (see "Subpatterns as subroutines" below for a way
4217         of doing that). So the pattern         of doing that). So the pattern
4218    
4219           (sens|respons)e and \1ibility           (sens|respons)e and \1ibility
4220    
4221         matches "sense and sensibility" and "response and responsibility",  but         matches  "sense and sensibility" and "response and responsibility", but
4222         not  "sense and responsibility". If caseful matching is in force at the         not "sense and responsibility". If caseful matching is in force at  the
4223         time of the back reference, the case of letters is relevant. For  exam-         time  of the back reference, the case of letters is relevant. For exam-
4224         ple,         ple,
4225    
4226           ((?i)rah)\s+\1           ((?i)rah)\s+\1
4227    
4228         matches  "rah  rah"  and  "RAH RAH", but not "RAH rah", even though the         matches "rah rah" and "RAH RAH", but not "RAH  rah",  even  though  the
4229         original capturing subpattern is matched caselessly.         original capturing subpattern is matched caselessly.
4230    
4231         Back references to named subpatterns use the Perl  syntax  \k<name>  or         There  are  several  different ways of writing back references to named
4232         \k'name'  or  the  Python  syntax (?P=name). We could rewrite the above         subpatterns. The .NET syntax \k{name} and the Perl syntax  \k<name>  or
4233         example in either of the following ways:         \k'name'  are supported, as is the Python syntax (?P=name). Perl 5.10's
4234           unified back reference syntax, in which \g can be used for both numeric
4235           and  named  references,  is  also supported. We could rewrite the above
4236           example in any of the following ways:
4237    
4238           (?<p1>(?i)rah)\s+\k<p1>           (?<p1>(?i)rah)\s+\k<p1>
4239             (?'p1'(?i)rah)\s+\k{p1}
4240           (?P<p1>(?i)rah)\s+(?P=p1)           (?P<p1>(?i)rah)\s+(?P=p1)
4241             (?<p1>(?i)rah)\s+\g{p1}
4242    
4243         A subpattern that is referenced by  name  may  appear  in  the  pattern         A subpattern that is referenced by  name  may  appear  in  the  pattern
4244         before or after the reference.         before or after the reference.
# Line 3941  ASSERTIONS Line 4353  ASSERTIONS
4353    
4354           (?<=abc|abde)           (?<=abc|abde)
4355    
4356           In some cases, the Perl 5.10 escape sequence \K (see above) can be used
4357           instead  of  a lookbehind assertion; this is not restricted to a fixed-
4358           length.
4359    
4360         The implementation of lookbehind assertions is, for  each  alternative,         The implementation of lookbehind assertions is, for  each  alternative,
4361         to  temporarily  move the current position back by the fixed length and         to  temporarily  move the current position back by the fixed length and
4362         then try to match. If there are insufficient characters before the cur-         then try to match. If there are insufficient characters before the cur-
# Line 4034  CONDITIONAL SUBPATTERNS Line 4450  CONDITIONAL SUBPATTERNS
4450    
4451         If  the  text between the parentheses consists of a sequence of digits,         If  the  text between the parentheses consists of a sequence of digits,
4452         the condition is true if the capturing subpattern of  that  number  has         the condition is true if the capturing subpattern of  that  number  has
4453         previously matched.         previously  matched.  An  alternative notation is to precede the digits
4454           with a plus or minus sign. In this case, the subpattern number is rela-
4455           tive rather than absolute.  The most recently opened parentheses can be
4456           referenced by (?(-1), the next most recent by (?(-2),  and  so  on.  In
4457           looping constructs it can also make sense to refer to subsequent groups
4458           with constructs such as (?(+2).
4459    
4460         Consider  the  following  pattern, which contains non-significant white         Consider the following pattern, which  contains  non-significant  white
4461         space to make it more readable (assume the PCRE_EXTENDED option) and to         space to make it more readable (assume the PCRE_EXTENDED option) and to
4462         divide it into three parts for ease of discussion:         divide it into three parts for ease of discussion:
4463    
4464           ( \( )?    [^()]+    (?(1) \) )           ( \( )?    [^()]+    (?(1) \) )
4465    
4466         The  first  part  matches  an optional opening parenthesis, and if that         The first part matches an optional opening  parenthesis,  and  if  that
4467         character is present, sets it as the first captured substring. The sec-         character is present, sets it as the first captured substring. The sec-
4468         ond  part  matches one or more characters that are not parentheses. The         ond part matches one or more characters that are not  parentheses.  The
4469         third part is a conditional subpattern that tests whether the first set         third part is a conditional subpattern that tests whether the first set
4470         of parentheses matched or not. If they did, that is, if subject started         of parentheses matched or not. If they did, that is, if subject started
4471         with an opening parenthesis, the condition is true, and so the yes-pat-         with an opening parenthesis, the condition is true, and so the yes-pat-
4472         tern  is  executed  and  a  closing parenthesis is required. Otherwise,         tern is executed and a  closing  parenthesis  is  required.  Otherwise,
4473         since no-pattern is not present, the  subpattern  matches  nothing.  In         since  no-pattern  is  not  present, the subpattern matches nothing. In
4474         other  words,  this  pattern  matches  a  sequence  of non-parentheses,         other words,  this  pattern  matches  a  sequence  of  non-parentheses,
4475         optionally enclosed in parentheses.         optionally enclosed in parentheses.
4476    
4477           If  you  were  embedding  this pattern in a larger one, you could use a
4478           relative reference:
4479    
4480             ...other stuff... ( \( )?    [^()]+    (?(-1) \) ) ...
4481    
4482           This makes the fragment independent of the parentheses  in  the  larger
4483           pattern.
4484    
4485     Checking for a used subpattern by name     Checking for a used subpattern by name
4486    
4487         Perl uses the syntax (?(<name>)...) or (?('name')...)  to  test  for  a         Perl  uses  the  syntax  (?(<name>)...) or (?('name')...) to test for a
4488         used  subpattern  by  name.  For compatibility with earlier versions of         used subpattern by name. For compatibility  with  earlier  versions  of
4489         PCRE, which had this facility before Perl, the syntax  (?(name)...)  is         PCRE,  which  had this facility before Perl, the syntax (?(name)...) is
4490         also  recognized. However, there is a possible ambiguity with this syn-         also recognized. However, there is a possible ambiguity with this  syn-
4491         tax, because subpattern names may  consist  entirely  of  digits.  PCRE         tax,  because  subpattern  names  may  consist entirely of digits. PCRE
4492         looks  first for a named subpattern; if it cannot find one and the name         looks first for a named subpattern; if it cannot find one and the  name
4493         consists entirely of digits, PCRE looks for a subpattern of  that  num-         consists  entirely  of digits, PCRE looks for a subpattern of that num-
4494         ber,  which must be greater than zero. Using subpattern names that con-         ber, which must be greater than zero. Using subpattern names that  con-
4495         sist entirely of digits is not recommended.         sist entirely of digits is not recommended.
4496    
4497         Rewriting the above example to use a named subpattern gives this:         Rewriting the above example to use a named subpattern gives this:
# Line 4073  CONDITIONAL SUBPATTERNS Line 4502  CONDITIONAL SUBPATTERNS
4502     Checking for pattern recursion     Checking for pattern recursion
4503    
4504         If the condition is the string (R), and there is no subpattern with the         If the condition is the string (R), and there is no subpattern with the
4505         name  R, the condition is true if a recursive call to the whole pattern         name R, the condition is true if a recursive call to the whole  pattern
4506         or any subpattern has been made. If digits or a name preceded by amper-         or any subpattern has been made. If digits or a name preceded by amper-
4507         sand follow the letter R, for example:         sand follow the letter R, for example:
4508    
4509           (?(R3)...) or (?(R&name)...)           (?(R3)...) or (?(R&name)...)
4510    
4511         the  condition is true if the most recent recursion is into the subpat-         the condition is true if the most recent recursion is into the  subpat-
4512         tern whose number or name is given. This condition does not  check  the         tern  whose  number or name is given. This condition does not check the
4513         entire recursion stack.         entire recursion stack.
4514    
4515         At  "top  level", all these recursion test conditions are false. Recur-         At "top level", all these recursion test conditions are  false.  Recur-
4516         sive patterns are described below.         sive patterns are described below.
4517    
4518     Defining subpatterns for use by reference only     Defining subpatterns for use by reference only
4519    
4520         If the condition is the string (DEFINE), and  there  is  no  subpattern         If  the  condition  is  the string (DEFINE), and there is no subpattern
4521         with  the  name  DEFINE,  the  condition is always false. In this case,         with the name DEFINE, the condition is  always  false.  In  this  case,
4522         there may be only one alternative  in  the  subpattern.  It  is  always         there  may  be  only  one  alternative  in the subpattern. It is always
4523         skipped  if  control  reaches  this  point  in the pattern; the idea of         skipped if control reaches this point  in  the  pattern;  the  idea  of
4524         DEFINE is that it can be used to define "subroutines" that can be  ref-         DEFINE  is that it can be used to define "subroutines" that can be ref-
4525         erenced  from elsewhere. (The use of "subroutines" is described below.)         erenced from elsewhere. (The use of "subroutines" is described  below.)
4526         For example, a pattern to match an IPv4 address could be  written  like         For  example,  a pattern to match an IPv4 address could be written like
4527         this (ignore whitespace and line breaks):         this (ignore whitespace and line breaks):
4528    
4529           (?(DEFINE) (?<byte> 2[0-4]\d | 25[0-5] | 1\d\d | [1-9]?\d) )           (?(DEFINE) (?<byte> 2[0-4]\d | 25[0-5] | 1\d\d | [1-9]?\d) )
4530           \b (?&byte) (\.(?&byte)){3} \b           \b (?&byte) (\.(?&byte)){3} \b
4531    
4532         The  first part of the pattern is a DEFINE group inside which a another         The first part of the pattern is a DEFINE group inside which a  another
4533         group named "byte" is defined. This matches an individual component  of         group  named "byte" is defined. This matches an individual component of
4534         an  IPv4  address  (a number less than 256). When matching takes place,         an IPv4 address (a number less than 256). When  matching  takes  place,
4535         this part of the pattern is skipped because DEFINE acts  like  a  false         this  part  of  the pattern is skipped because DEFINE acts like a false
4536         condition.         condition.
4537    
4538         The rest of the pattern uses references to the named group to match the         The rest of the pattern uses references to the named group to match the
4539         four dot-separated components of an IPv4 address, insisting on  a  word         four  dot-separated  components of an IPv4 address, insisting on a word
4540         boundary at each end.         boundary at each end.
4541    
4542     Assertion conditions     Assertion conditions
4543    
4544         If  the  condition  is  not  in any of the above formats, it must be an         If the condition is not in any of the above  formats,  it  must  be  an
4545         assertion.  This may be a positive or negative lookahead or  lookbehind         assertion.   This may be a positive or negative lookahead or lookbehind
4546         assertion.  Consider  this  pattern,  again  containing non-significant         assertion. Consider  this  pattern,  again  containing  non-significant
4547         white space, and with the two alternatives on the second line:         white space, and with the two alternatives on the second line:
4548    
4549           (?(?=[^a-z]*[a-z])           (?(?=[^a-z]*[a-z])
4550           \d{2}-[a-z]{3}-\d{2}  |  \d{2}-\d{2}-\d{2} )           \d{2}-[a-z]{3}-\d{2}  |  \d{2}-\d{2}-\d{2} )
4551    
4552         The condition  is  a  positive  lookahead  assertion  that  matches  an         The  condition  is  a  positive  lookahead  assertion  that  matches an
4553         optional  sequence of non-letters followed by a letter. In other words,         optional sequence of non-letters followed by a letter. In other  words,
4554         it tests for the presence of at least one letter in the subject.  If  a         it  tests  for the presence of at least one letter in the subject. If a
4555         letter  is found, the subject is matched against the first alternative;         letter is found, the subject is matched against the first  alternative;
4556         otherwise it is  matched  against  the  second.  This  pattern  matches         otherwise  it  is  matched  against  the  second.  This pattern matches
4557         strings  in  one  of the two forms dd-aaa-dd or dd-dd-dd, where aaa are         strings in one of the two forms dd-aaa-dd or dd-dd-dd,  where  aaa  are
4558         letters and dd are digits.         letters and dd are digits.
4559    
4560    
4561  COMMENTS  COMMENTS
4562    
4563         The sequence (?# marks the start of a comment that continues up to  the         The  sequence (?# marks the start of a comment that continues up to the
4564         next  closing  parenthesis.  Nested  parentheses are not permitted. The         next closing parenthesis. Nested parentheses  are  not  permitted.  The
4565         characters that make up a comment play no part in the pattern  matching         characters  that make up a comment play no part in the pattern matching
4566         at all.         at all.
4567    
4568         If  the PCRE_EXTENDED option is set, an unescaped # character outside a         If the PCRE_EXTENDED option is set, an unescaped # character outside  a
4569         character class introduces a  comment  that  continues  to  immediately         character  class  introduces  a  comment  that continues to immediately
4570         after the next newline in the pattern.         after the next newline in the pattern.
4571    
4572    
4573  RECURSIVE PATTERNS  RECURSIVE PATTERNS
4574    
4575         Consider  the problem of matching a string in parentheses, allowing for         Consider the problem of matching a string in parentheses, allowing  for
4576         unlimited nested parentheses. Without the use of  recursion,  the  best         unlimited  nested  parentheses.  Without the use of recursion, the best
4577         that  can  be  done  is  to use a pattern that matches up to some fixed         that can be done is to use a pattern that  matches  up  to  some  fixed
4578         depth of nesting. It is not possible to  handle  an  arbitrary  nesting         depth  of  nesting.  It  is not possible to handle an arbitrary nesting
4579         depth.         depth.
4580    
4581         For some time, Perl has provided a facility that allows regular expres-         For some time, Perl has provided a facility that allows regular expres-
4582         sions to recurse (amongst other things). It does this by  interpolating         sions  to recurse (amongst other things). It does this by interpolating
4583         Perl  code in the expression at run time, and the code can refer to the         Perl code in the expression at run time, and the code can refer to  the
4584         expression itself. A Perl pattern using code interpolation to solve the         expression itself. A Perl pattern using code interpolation to solve the
4585         parentheses problem can be created like this:         parentheses problem can be created like this:
4586    
# Line 4161  RECURSIVE PATTERNS Line 4590  RECURSIVE PATTERNS
4590         refers recursively to the pattern in which it appears.         refers recursively to the pattern in which it appears.
4591    
4592         Obviously, PCRE cannot support the interpolation of Perl code. Instead,         Obviously, PCRE cannot support the interpolation of Perl code. Instead,
4593         it  supports  special  syntax  for recursion of the entire pattern, and         it supports special syntax for recursion of  the  entire  pattern,  and
4594         also for individual subpattern recursion.  After  its  introduction  in         also  for  individual  subpattern  recursion. After its introduction in
4595         PCRE  and  Python,  this  kind of recursion was introduced into Perl at         PCRE and Python, this kind of recursion was  introduced  into  Perl  at
4596         release 5.10.         release 5.10.
4597    
4598         A special item that consists of (? followed by a  number  greater  than         A  special  item  that consists of (? followed by a number greater than
4599         zero and a closing parenthesis is a recursive call of the subpattern of         zero and a closing parenthesis is a recursive call of the subpattern of
4600         the given number, provided that it occurs inside that  subpattern.  (If         the  given  number, provided that it occurs inside that subpattern. (If
4601         not,  it  is  a  "subroutine" call, which is described in the next sec-         not, it is a "subroutine" call, which is described  in  the  next  sec-
4602         tion.) The special item (?R) or (?0) is a recursive call of the  entire         tion.)  The special item (?R) or (?0) is a recursive call of the entire
4603         regular expression.         regular expression.
4604    
4605         In  PCRE (like Python, but unlike Perl), a recursive subpattern call is         In PCRE (like Python, but unlike Perl), a recursive subpattern call  is
4606         always treated as an atomic group. That is, once it has matched some of         always treated as an atomic group. That is, once it has matched some of
4607         the subject string, it is never re-entered, even if it contains untried         the subject string, it is never re-entered, even if it contains untried
4608         alternatives and there is a subsequent matching failure.         alternatives and there is a subsequent matching failure.
4609    
4610         This PCRE pattern solves the nested  parentheses  problem  (assume  the         This  PCRE  pattern  solves  the nested parentheses problem (assume the
4611         PCRE_EXTENDED option is set so that white space is ignored):         PCRE_EXTENDED option is set so that white space is ignored):
4612    
4613           \( ( (?>[^()]+) | (?R) )* \)           \( ( (?>[^()]+) | (?R) )* \)
4614    
4615         First  it matches an opening parenthesis. Then it matches any number of         First it matches an opening parenthesis. Then it matches any number  of
4616         substrings which can either be a  sequence  of  non-parentheses,  or  a         substrings  which  can  either  be  a sequence of non-parentheses, or a
4617         recursive  match  of the pattern itself (that is, a correctly parenthe-         recursive match of the pattern itself (that is, a  correctly  parenthe-
4618         sized substring).  Finally there is a closing parenthesis.         sized substring).  Finally there is a closing parenthesis.
4619    
4620         If this were part of a larger pattern, you would not  want  to  recurse         If  this  were  part of a larger pattern, you would not want to recurse
4621         the entire pattern, so instead you could use this:         the entire pattern, so instead you could use this:
4622    
4623           ( \( ( (?>[^()]+) | (?1) )* \) )           ( \( ( (?>[^()]+) | (?1) )* \) )
4624    
4625         We  have  put the pattern into parentheses, and caused the recursion to         We have put the pattern into parentheses, and caused the  recursion  to
4626         refer to them instead of the whole pattern. In a larger pattern,  keep-         refer to them instead of the whole pattern.
4627         ing  track  of parenthesis numbers can be tricky. It may be more conve-  
4628         nient to use named parentheses instead. The Perl  syntax  for  this  is         In  a  larger  pattern,  keeping  track  of  parenthesis numbers can be
4629         (?&name);  PCRE's  earlier syntax (?P>name) is also supported. We could         tricky. This is made easier by the use of relative references. (A  Perl
4630         rewrite the above example as follows:         5.10  feature.)   Instead  of  (?1)  in the pattern above you can write
4631           (?-2) to refer to the second most recently opened parentheses preceding
4632           the  recursion.  In  other  words,  a  negative number counts capturing
4633           parentheses leftwards from the point at which it is encountered.
4634    
4635           It is also possible to refer to  subsequently  opened  parentheses,  by
4636           writing  references  such  as (?+2). However, these cannot be recursive
4637           because the reference is not inside the  parentheses  that  are  refer-
4638           enced.  They  are  always  "subroutine" calls, as described in the next
4639           section.
4640    
4641           An alternative approach is to use named parentheses instead.  The  Perl
4642           syntax  for  this  is (?&name); PCRE's earlier syntax (?P>name) is also
4643           supported. We could rewrite the above example as follows:
4644    
4645           (?<pn> \( ( (?>[^()]+) | (?&pn) )* \) )           (?<pn> \( ( (?>[^()]+) | (?&pn) )* \) )
4646    
4647         If there is more than one subpattern with the same name,  the  earliest         If there is more than one subpattern with the same name,  the  earliest
4648         one  is used. This particular example pattern contains nested unlimited         one is used.
4649         repeats, and so the use of atomic grouping for matching strings of non-  
4650         parentheses  is  important when applying the pattern to strings that do         This  particular  example pattern that we have been looking at contains
4651         not match. For example, when this pattern is applied to         nested unlimited repeats, and so the use of atomic grouping for  match-
4652           ing  strings  of non-parentheses is important when applying the pattern
4653           to strings that do not match. For example, when this pattern is applied
4654           to
4655    
4656           (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa()           (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa()
4657    
4658         it yields "no match" quickly. However, if atomic grouping is not  used,         it  yields "no match" quickly. However, if atomic grouping is not used,
4659         the  match  runs  for a very long time indeed because there are so many         the match runs for a very long time indeed because there  are  so  many
4660         different ways the + and * repeats can carve up the  subject,  and  all         different  ways  the  + and * repeats can carve up the subject, and all
4661         have to be tested before failure can be reported.         have to be tested before failure can be reported.
4662    
4663         At the end of a match, the values set for any capturing subpatterns are         At the end of a match, the values set for any capturing subpatterns are
4664         those from the outermost level of the recursion at which the subpattern         those from the outermost level of the recursion at which the subpattern
4665         value  is  set.   If  you want to obtain intermediate values, a callout         value is set.  If you want to obtain  intermediate  values,  a  callout
4666         function can be used (see below and the pcrecallout documentation).  If         function  can be used (see below and the pcrecallout documentation). If
4667         the pattern above is matched against         the pattern above is matched against
4668    
4669           (ab(cd)ef)           (ab(cd)ef)
4670    
4671         the  value  for  the  capturing  parentheses is "ef", which is the last         the value for the capturing parentheses is  "ef",  which  is  the  last
4672         value taken on at the top level. If additional parentheses  are  added,         value  taken  on at the top level. If additional parentheses are added,
4673         giving         giving
4674    
4675           \( ( ( (?>[^()]+) | (?R) )* ) \)           \( ( ( (?>[^()]+) | (?R) )* ) \)
4676              ^                        ^              ^                        ^
4677              ^                        ^              ^                        ^
4678    
4679         the  string  they  capture is "ab(cd)ef", the contents of the top level         the string they capture is "ab(cd)ef", the contents of  the  top  level
4680         parentheses. If there are more than 15 capturing parentheses in a  pat-         parentheses.  If there are more than 15 capturing parentheses in a pat-
4681         tern, PCRE has to obtain extra memory to store data during a recursion,         tern, PCRE has to obtain extra memory to store data during a recursion,
4682         which it does by using pcre_malloc, freeing  it  via  pcre_free  after-         which  it  does  by  using pcre_malloc, freeing it via pcre_free after-
4683         wards.  If  no  memory  can  be  obtained,  the  match  fails  with the         wards. If  no  memory  can  be  obtained,  the  match  fails  with  the
4684         PCRE_ERROR_NOMEMORY error.         PCRE_ERROR_NOMEMORY error.
4685    
4686         Do not confuse the (?R) item with the condition (R),  which  tests  for         Do  not  confuse  the (?R) item with the condition (R), which tests for
4687         recursion.   Consider  this pattern, which matches text in angle brack-         recursion.  Consider this pattern, which matches text in  angle  brack-
4688         ets, allowing for arbitrary nesting. Only digits are allowed in  nested         ets,  allowing for arbitrary nesting. Only digits are allowed in nested
4689         brackets  (that is, when recursing), whereas any characters are permit-         brackets (that is, when recursing), whereas any characters are  permit-
4690         ted at the outer level.         ted at the outer level.
4691    
4692           < (?: (?(R) \d++  | [^<>]*+) | (?R)) * >           < (?: (?(R) \d++  | [^<>]*+) | (?R)) * >
4693    
4694         In this pattern, (?(R) is the start of a conditional  subpattern,  with         In  this  pattern, (?(R) is the start of a conditional subpattern, with
4695         two  different  alternatives for the recursive and non-recursive cases.         two different alternatives for the recursive and  non-recursive  cases.
4696         The (?R) item is the actual recursive call.         The (?R) item is the actual recursive call.
4697    
4698    
4699  SUBPATTERNS AS SUBROUTINES  SUBPATTERNS AS SUBROUTINES
4700    
4701         If the syntax for a recursive subpattern reference (either by number or         If the syntax for a recursive subpattern reference (either by number or
4702         by  name)  is used outside the parentheses to which it refers, it oper-         by name) is used outside the parentheses to which it refers,  it  oper-
4703         ates like a subroutine in a programming language. The "called"  subpat-         ates  like a subroutine in a programming language. The "called" subpat-
4704         tern  may  be defined before or after the reference. An earlier example         tern may be defined before or after the reference. A numbered reference
4705         pointed out that the pattern         can be absolute or relative, as in these examples:
4706    
4707             (...(absolute)...)...(?2)...
4708             (...(relative)...)...(?-1)...
4709             (...(?+1)...(relative)...
4710    
4711           An earlier example pointed out that the pattern
4712    
4713           (sens|respons)e and \1ibility           (sens|respons)e and \1ibility
4714    
4715         matches "sense and sensibility" and "response and responsibility",  but         matches  "sense and sensibility" and "response and responsibility", but
4716         not "sense and responsibility". If instead the pattern         not "sense and responsibility". If instead the pattern
4717    
4718           (sens|respons)e and (?1)ibility           (sens|respons)e and (?1)ibility
4719    
4720         is  used, it does match "sense and responsibility" as well as the other         is used, it does match "sense and responsibility" as well as the  other
4721         two strings. Another example is  given  in  the  discussion  of  DEFINE         two  strings.  Another  example  is  given  in the discussion of DEFINE
4722         above.         above.
4723    
4724         Like recursive subpatterns, a "subroutine" call is always treated as an         Like recursive subpatterns, a "subroutine" call is always treated as an
4725         atomic group. That is, once it has matched some of the subject  string,         atomic  group. That is, once it has matched some of the subject string,
4726         it  is  never  re-entered, even if it contains untried alternatives and         it is never re-entered, even if it contains  untried  alternatives  and
4727         there is a subsequent matching failure.         there is a subsequent matching failure.
4728    
4729         When a subpattern is used as a subroutine, processing options  such  as         When  a  subpattern is used as a subroutine, processing options such as
4730         case-independence are fixed when the subpattern is defined. They cannot         case-independence are fixed when the subpattern is defined. They cannot
4731         be changed for different calls. For example, consider this pattern:         be changed for different calls. For example, consider this pattern:
4732    
4733           (abc)(?i:(?1))           (abc)(?i:(?-1))
4734    
4735         It matches "abcabc". It does not match "abcABC" because the  change  of         It  matches  "abcabc". It does not match "abcABC" because the change of
4736         processing option does not affect the called subpattern.         processing option does not affect the called subpattern.
4737    
4738    
4739  CALLOUTS  CALLOUTS
4740    
4741         Perl has a feature whereby using the sequence (?{...}) causes arbitrary         Perl has a feature whereby using the sequence (?{...}) causes arbitrary
4742         Perl code to be obeyed in the middle of matching a regular  expression.         Perl  code to be obeyed in the middle of matching a regular expression.
4743         This makes it possible, amongst other things, to extract different sub-         This makes it possible, amongst other things, to extract different sub-
4744         strings that match the same pair of parentheses when there is a repeti-         strings that match the same pair of parentheses when there is a repeti-
4745         tion.         tion.
4746    
4747         PCRE provides a similar feature, but of course it cannot obey arbitrary         PCRE provides a similar feature, but of course it cannot obey arbitrary
4748         Perl code. The feature is called "callout". The caller of PCRE provides         Perl code. The feature is called "callout". The caller of PCRE provides
4749         an  external function by putting its entry point in the global variable         an external function by putting its entry point in the global  variable
4750         pcre_callout.  By default, this variable contains NULL, which  disables         pcre_callout.   By default, this variable contains NULL, which disables
4751         all calling out.         all calling out.
4752    
4753         Within  a  regular  expression,  (?C) indicates the points at which the         Within a regular expression, (?C) indicates the  points  at  which  the
4754         external function is to be called. If you want  to  identify  different         external  function  is  to be called. If you want to identify different
4755         callout  points, you can put a number less than 256 after the letter C.         callout points, you can put a number less than 256 after the letter  C.
4756         The default value is zero.  For example, this pattern has  two  callout         The  default  value is zero.  For example, this pattern has two callout
4757         points:         points:
4758    
4759           (?C1)abc(?C2)def           (?C1)abc(?C2)def
4760    
4761         If the PCRE_AUTO_CALLOUT flag is passed to pcre_compile(), callouts are         If the PCRE_AUTO_CALLOUT flag is passed to pcre_compile(), callouts are
4762         automatically installed before each item in the pattern. They  are  all         automatically  installed  before each item in the pattern. They are all
4763         numbered 255.         numbered 255.
4764    
4765         During matching, when PCRE reaches a callout point (and pcre_callout is         During matching, when PCRE reaches a callout point (and pcre_callout is
4766         set), the external function is called. It is provided with  the  number         set),  the  external function is called. It is provided with the number
4767         of  the callout, the position in the pattern, and, optionally, one item         of the callout, the position in the pattern, and, optionally, one  item
4768         of data originally supplied by the caller of pcre_exec().  The  callout         of  data  originally supplied by the caller of pcre_exec(). The callout
4769         function  may cause matching to proceed, to backtrack, or to fail alto-         function may cause matching to proceed, to backtrack, or to fail  alto-
4770         gether. A complete description of the interface to the callout function         gether. A complete description of the interface to the callout function
4771         is given in the pcrecallout documentation.         is given in the pcrecallout documentation.
4772    
4773    
4774    BACKTRACKING CONTROL
4775    
4776           Perl 5.10 introduced a number of "Special Backtracking Control  Verbs",
4777           which are described in the Perl documentation as "experimental and sub-
4778           ject to change or removal in a future version of Perl". It goes  on  to
4779           say:  "Their usage in production code should be noted to avoid problems
4780           during upgrades." The same remarks apply to the PCRE features described
4781           in this section.
4782    
4783           Since these verbs are specifically related to backtracking, they can be
4784           used only when the pattern is to be matched  using  pcre_exec(),  which
4785           uses  a  backtracking  algorithm. They cause an error if encountered by
4786           pcre_dfa_exec().
4787    
4788           The new verbs make use of what was previously invalid syntax: an  open-
4789           ing parenthesis followed by an asterisk. In Perl, they are generally of
4790           the form (*VERB:ARG) but PCRE does not support the use of arguments, so
4791           its  general  form is just (*VERB). Any number of these verbs may occur
4792           in a pattern. There are two kinds:
4793    
4794       Verbs that act immediately
4795    
4796           The following verbs act as soon as they are encountered:
4797    
4798              (*ACCEPT)
4799    
4800           This verb causes the match to end successfully, skipping the  remainder
4801           of  the pattern. When inside a recursion, only the innermost pattern is
4802           ended immediately. PCRE differs  from  Perl  in  what  happens  if  the
4803           (*ACCEPT)  is inside capturing parentheses. In Perl, the data so far is
4804           captured: in PCRE no data is captured. For example:
4805    
4806             A(A|B(*ACCEPT)|C)D
4807    
4808           This matches "AB", "AAD", or "ACD", but when it matches "AB",  no  data
4809           is captured.
4810    
4811             (*FAIL) or (*F)
4812    
4813           This  verb  causes the match to fail, forcing backtracking to occur. It
4814           is equivalent to (?!) but easier to read. The Perl documentation  notes
4815           that  it  is  probably  useful only when combined with (?{}) or (??{}).
4816           Those are, of course, Perl features that are not present in  PCRE.  The
4817           nearest  equivalent is the callout feature, as for example in this pat-
4818           tern:
4819    
4820             a+(?C)(*FAIL)
4821    
4822           A match with the string "aaaa" always fails, but the callout  is  taken
4823           before each backtrack happens (in this example, 10 times).
4824    
4825       Verbs that act after backtracking
4826    
4827           The following verbs do nothing when they are encountered. Matching con-
4828           tinues with what follows, but if there is no subsequent match, a  fail-
4829           ure  is  forced.   The  verbs  differ  in  exactly what kind of failure
4830           occurs.
4831    
4832             (*COMMIT)
4833    
4834           This verb causes the whole match to fail outright if the  rest  of  the
4835           pattern  does  not match. Even if the pattern is unanchored, no further
4836           attempts to find a match by advancing the start point take place.  Once
4837           (*COMMIT)  has been passed, pcre_exec() is committed to finding a match
4838           at the current starting point, or not at all. For example:
4839    
4840             a+(*COMMIT)b
4841    
4842           This matches "xxaab" but not "aacaab". It can be thought of as  a  kind
4843           of dynamic anchor, or "I've started, so I must finish."
4844    
4845             (*PRUNE)
4846    
4847           This  verb causes the match to fail at the current position if the rest
4848           of the pattern does not match. If the pattern is unanchored, the normal
4849           "bumpalong"  advance to the next starting character then happens. Back-
4850           tracking can occur as usual to the left of (*PRUNE), or  when  matching
4851           to  the right of (*PRUNE), but if there is no match to the right, back-
4852           tracking cannot cross (*PRUNE).  In simple cases, the use  of  (*PRUNE)
4853           is just an alternative to an atomic group or possessive quantifier, but
4854           there are some uses of (*PRUNE) that cannot be expressed in  any  other
4855           way.
4856    
4857             (*SKIP)
4858    
4859           This  verb  is like (*PRUNE), except that if the pattern is unanchored,
4860           the "bumpalong" advance is not to the next character, but to the  posi-
4861           tion  in  the  subject where (*SKIP) was encountered. (*SKIP) signifies
4862           that whatever text was matched leading up to it cannot  be  part  of  a
4863           successful match. Consider:
4864    
4865             a+(*SKIP)b
4866    
4867           If  the  subject  is  "aaaac...",  after  the first match attempt fails
4868           (starting at the first character in the  string),  the  starting  point
4869           skips on to start the next attempt at "c". Note that a possessive quan-
4870           tifer does not have the same effect in this example; although it  would
4871           suppress  backtracking  during  the  first  match  attempt,  the second
4872           attempt would start at the second character instead of skipping  on  to
4873           "c".
4874    
4875             (*THEN)