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# Line 18  INTRODUCTION Line 18  INTRODUCTION
18    
19         The  PCRE  library is a set of functions that implement regular expres-         The  PCRE  library is a set of functions that implement regular expres-
20         sion pattern matching using the same syntax and semantics as Perl, with         sion pattern matching using the same syntax and semantics as Perl, with
21         just  a  few  differences.  The current implementation of PCRE (release         just  a  few  differences. Certain features that appeared in Python and
22         6.x) corresponds approximately with Perl  5.8,  including  support  for         PCRE before they appeared in Perl are also available using  the  Python
23         UTF-8 encoded strings and Unicode general category properties. However,         syntax.  There is also some support for certain .NET and Oniguruma syn-
24         this support has to be explicitly enabled; it is not the default.         tax items, and there is an option for  requesting  some  minor  changes
25           that give better JavaScript compatibility.
26         In addition to the Perl-compatible matching function,  PCRE  also  con-  
27         tains  an  alternative matching function that matches the same compiled         The  current  implementation of PCRE (release 7.x) corresponds approxi-
28         patterns in a different way. In certain circumstances, the  alternative         mately with Perl 5.10, including support for UTF-8 encoded strings  and
29         function  has  some  advantages.  For  a discussion of the two matching         Unicode general category properties. However, UTF-8 and Unicode support
30         algorithms, see the pcrematching page.         has to be explicitly enabled; it is not the default. The Unicode tables
31           correspond to Unicode release 5.1.
32         PCRE is written in C and released as a C library. A  number  of  people  
33         have  written  wrappers and interfaces of various kinds. In particular,         In  addition to the Perl-compatible matching function, PCRE contains an
34         Google Inc.  have provided a comprehensive C++  wrapper.  This  is  now         alternative matching function that matches the same  compiled  patterns
35           in  a different way. In certain circumstances, the alternative function
36           has some advantages. For a discussion of the two  matching  algorithms,
37           see the pcrematching page.
38    
39           PCRE  is  written  in C and released as a C library. A number of people
40           have written wrappers and interfaces of various kinds.  In  particular,
41           Google  Inc.   have  provided  a comprehensive C++ wrapper. This is now
42         included as part of the PCRE distribution. The pcrecpp page has details         included as part of the PCRE distribution. The pcrecpp page has details
43         of this interface. Other people's contributions can  be  found  in  the         of  this  interface.  Other  people's contributions can be found in the
44         Contrib directory at the primary FTP site, which is:         Contrib directory at the primary FTP site, which is:
45    
46         ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre         ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre
47    
48         Details  of  exactly which Perl regular expression features are and are         Details of exactly which Perl regular expression features are  and  are
49         not supported by PCRE are given in separate documents. See the pcrepat-         not supported by PCRE are given in separate documents. See the pcrepat-
50         tern and pcrecompat pages.         tern and pcrecompat pages. There is a syntax summary in the  pcresyntax
51           page.
52    
53         Some  features  of  PCRE can be included, excluded, or changed when the         Some  features  of  PCRE can be included, excluded, or changed when the
54         library is built. The pcre_config() function makes it  possible  for  a         library is built. The pcre_config() function makes it  possible  for  a
# Line 67  USER DOCUMENTATION Line 75  USER DOCUMENTATION
75         of searching. The sections are as follows:         of searching. The sections are as follows:
76    
77           pcre              this document           pcre              this document
78             pcre-config       show PCRE installation configuration information
79           pcreapi           details of PCRE's native C API           pcreapi           details of PCRE's native C API
80           pcrebuild         options for building PCRE           pcrebuild         options for building PCRE
81           pcrecallout       details of the callout feature           pcrecallout       details of the callout feature
# Line 77  USER DOCUMENTATION Line 86  USER DOCUMENTATION
86           pcrepartial       details of the partial matching facility           pcrepartial       details of the partial matching facility
87           pcrepattern       syntax and semantics of supported           pcrepattern       syntax and semantics of supported
88                               regular expressions                               regular expressions
89             pcresyntax        quick syntax reference
90           pcreperform       discussion of performance issues           pcreperform       discussion of performance issues
91           pcreposix         the POSIX-compatible C API           pcreposix         the POSIX-compatible C API
92           pcreprecompile    details of saving and re-using precompiled patterns           pcreprecompile    details of saving and re-using precompiled patterns
93           pcresample        discussion of the sample program           pcresample        discussion of the sample program
94             pcrestack         discussion of stack usage
95           pcretest          description of the pcretest testing command           pcretest          description of the pcretest testing command
96    
97         In  addition,  in the "man" and HTML formats, there is a short page for         In addition, in the "man" and HTML formats, there is a short  page  for
98         each C library function, listing its arguments and results.         each C library function, listing its arguments and results.
99    
100    
101  LIMITATIONS  LIMITATIONS
102    
103         There are some size limitations in PCRE but it is hoped that they  will         There  are some size limitations in PCRE but it is hoped that they will
104         never in practice be relevant.         never in practice be relevant.
105    
106         The  maximum  length of a compiled pattern is 65539 (sic) bytes if PCRE         The maximum length of a compiled pattern is 65539 (sic) bytes  if  PCRE
107         is compiled with the default internal linkage size of 2. If you want to         is compiled with the default internal linkage size of 2. If you want to
108         process  regular  expressions  that are truly enormous, you can compile         process regular expressions that are truly enormous,  you  can  compile
109         PCRE with an internal linkage size of 3 or 4 (see the  README  file  in         PCRE  with  an  internal linkage size of 3 or 4 (see the README file in
110         the  source  distribution and the pcrebuild documentation for details).         the source distribution and the pcrebuild documentation  for  details).
111         In these cases the limit is substantially larger.  However,  the  speed         In  these  cases the limit is substantially larger.  However, the speed
112         of execution will be slower.         of execution is slower.
113    
114         All values in repeating quantifiers must be less than 65536.  The maxi-         All values in repeating quantifiers must be less than 65536.
115         mum number of capturing subpatterns is 65535.  
116           There is no limit to the number of parenthesized subpatterns, but there
117         There is no limit to the number of non-capturing subpatterns,  but  the         can be no more than 65535 capturing subpatterns.
        maximum  depth  of  nesting  of  all kinds of parenthesized subpattern,  
        including capturing subpatterns, assertions, and other types of subpat-  
        tern, is 200.  
118    
119         The  maximum  length of a subject string is the largest positive number         The maximum length of name for a named subpattern is 32 characters, and
120         that an integer variable can hold. However, when using the  traditional         the maximum number of named subpatterns is 10000.
121    
122           The maximum length of a subject string is the largest  positive  number
123           that  an integer variable can hold. However, when using the traditional
124         matching function, PCRE uses recursion to handle subpatterns and indef-         matching function, PCRE uses recursion to handle subpatterns and indef-
125         inite repetition.  This means that the available stack space may  limit         inite  repetition.  This means that the available stack space may limit
126         the size of a subject string that can be processed by certain patterns.         the size of a subject string that can be processed by certain patterns.
127           For a discussion of stack issues, see the pcrestack documentation.
128    
129    
130  UTF-8 AND UNICODE PROPERTY SUPPORT  UTF-8 AND UNICODE PROPERTY SUPPORT
131    
132         From release 3.3, PCRE has  had  some  support  for  character  strings         From  release  3.3,  PCRE  has  had  some support for character strings
133         encoded  in the UTF-8 format. For release 4.0 this was greatly extended         encoded in the UTF-8 format. For release 4.0 this was greatly  extended
134         to cover most common requirements, and in release 5.0  additional  sup-         to  cover  most common requirements, and in release 5.0 additional sup-
135         port for Unicode general category properties was added.         port for Unicode general category properties was added.
136    
137         In  order  process  UTF-8 strings, you must build PCRE to include UTF-8         In order process UTF-8 strings, you must build PCRE  to  include  UTF-8
138         support in the code, and, in addition,  you  must  call  pcre_compile()         support  in  the  code,  and, in addition, you must call pcre_compile()
139         with  the PCRE_UTF8 option flag. When you do this, both the pattern and         with the PCRE_UTF8 option flag, or the  pattern  must  start  with  the
140         any subject strings that are matched against it are  treated  as  UTF-8         sequence  (*UTF8).  When  either of these is the case, both the pattern
141         strings instead of just strings of bytes.         and any subject strings that are matched  against  it  are  treated  as
142           UTF-8 strings instead of just strings of bytes.
143    
144         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,
145         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
146         is  limited  to testing the PCRE_UTF8 flag in several places, so should         is limited to testing the PCRE_UTF8 flag occasionally, so should not be
147         not be very large.         very big.
148    
149         If PCRE is built with Unicode character property support (which implies         If PCRE is built with Unicode character property support (which implies
150         UTF-8  support),  the  escape sequences \p{..}, \P{..}, and \X are sup-         UTF-8  support),  the  escape sequences \p{..}, \P{..}, and \X are sup-
151         ported.  The available properties that can be tested are limited to the         ported.  The available properties that can be tested are limited to the
152         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
153         for a decimal number. A full list is given in the pcrepattern  documen-         for a decimal number, the Unicode script names such as Arabic  or  Han,
154         tation. The PCRE library is increased in size by about 90K when Unicode         and  the  derived  properties  Any  and L&. A full list is given in the
155         property support is included.         pcrepattern documentation. Only the short names for properties are sup-
156           ported.  For example, \p{L} matches a letter. Its Perl synonym, \p{Let-
157         The following comments apply when PCRE is running in UTF-8 mode:         ter}, is not supported.  Furthermore,  in  Perl,  many  properties  may
158           optionally  be  prefixed by "Is", for compatibility with Perl 5.6. PCRE
159         1. When you set the PCRE_UTF8 flag, the strings passed as patterns  and         does not support this.
160         subjects  are  checked for validity on entry to the relevant functions.  
161         If an invalid UTF-8 string is passed, an error return is given. In some     Validity of UTF-8 strings
162         situations,  you  may  already  know  that  your strings are valid, and  
163         therefore want to skip these checks in order to improve performance. If         When you set the PCRE_UTF8 flag, the strings  passed  as  patterns  and
164         you  set  the  PCRE_NO_UTF8_CHECK  flag at compile time or at run time,         subjects are (by default) checked for validity on entry to the relevant
165         PCRE assumes that the pattern or subject  it  is  given  (respectively)         functions. From release 7.3 of PCRE, the check is according  the  rules
166         contains  only valid UTF-8 codes. In this case, it does not diagnose an         of  RFC  3629, which are themselves derived from the Unicode specifica-
167         invalid UTF-8 string. If you pass an invalid UTF-8 string to PCRE  when         tion. Earlier releases of PCRE followed the rules of  RFC  2279,  which
168         PCRE_NO_UTF8_CHECK  is set, the results are undefined. Your program may         allows  the  full range of 31-bit values (0 to 0x7FFFFFFF). The current
169         crash.         check allows only values in the range U+0 to U+10FFFF, excluding U+D800
170           to U+DFFF.
171         2. In a pattern, the escape sequence \x{...}, where the contents of the  
172         braces  is  a  string  of hexadecimal digits, is interpreted as a UTF-8         The  excluded  code  points are the "Low Surrogate Area" of Unicode, of
173         character whose code number is the given hexadecimal number, for  exam-         which the Unicode Standard says this: "The Low Surrogate Area does  not
174         ple:  \x{1234}.  If a non-hexadecimal digit appears between the braces,         contain  any  character  assignments,  consequently  no  character code
175         the item is not recognized.  This escape sequence can be used either as         charts or namelists are provided for this area. Surrogates are reserved
176         a literal, or within a character class.         for  use  with  UTF-16 and then must be used in pairs." The code points
177           that are encoded by UTF-16 pairs  are  available  as  independent  code
178           points  in  the  UTF-8  encoding.  (In other words, the whole surrogate
179           thing is a fudge for UTF-16 which unfortunately messes up UTF-8.)
180    
181           If an  invalid  UTF-8  string  is  passed  to  PCRE,  an  error  return
182           (PCRE_ERROR_BADUTF8) is given. In some situations, you may already know
183           that your strings are valid, and therefore want to skip these checks in
184           order to improve performance. If you set the PCRE_NO_UTF8_CHECK flag at
185           compile time or at run time, PCRE assumes that the pattern  or  subject
186           it  is  given  (respectively)  contains only valid UTF-8 codes. In this
187           case, it does not diagnose an invalid UTF-8 string.
188    
189           If you pass an invalid UTF-8 string  when  PCRE_NO_UTF8_CHECK  is  set,
190           what  happens  depends on why the string is invalid. If the string con-
191           forms to the "old" definition of UTF-8 (RFC 2279), it is processed as a
192           string  of  characters  in  the  range 0 to 0x7FFFFFFF. In other words,
193           apart from the initial validity test, PCRE (when in UTF-8 mode) handles
194           strings  according  to  the more liberal rules of RFC 2279. However, if
195           the string does not even conform to RFC 2279, the result is  undefined.
196           Your program may crash.
197    
198           If  you  want  to  process  strings  of  values  in the full range 0 to
199           0x7FFFFFFF, encoded in a UTF-8-like manner as per the old RFC, you  can
200           set PCRE_NO_UTF8_CHECK to bypass the more restrictive test. However, in
201           this situation, you will have to apply your own validity check.
202    
203       General comments about UTF-8 mode
204    
205           1. An unbraced hexadecimal escape sequence (such  as  \xb3)  matches  a
206           two-byte UTF-8 character if the value is greater than 127.
207    
208         3.  The  original hexadecimal escape sequence, \xhh, matches a two-byte         2.  Octal  numbers  up to \777 are recognized, and match two-byte UTF-8
209         UTF-8 character if the value is greater than 127.         characters for values greater than \177.
210    
211         4. Repeat quantifiers apply to complete UTF-8 characters, not to  indi-         3. Repeat quantifiers apply to complete UTF-8 characters, not to  indi-
212         vidual bytes, for example: \x{100}{3}.         vidual bytes, for example: \x{100}{3}.
213    
214         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-
215         gle byte.         gle byte.
216    
217         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
218         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
219         not available in the alternative matching function, pcre_dfa_exec().         not available in the alternative matching function, pcre_dfa_exec().
220    
221         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
222         test  characters of any code value, but the characters that PCRE recog-         test  characters of any code value, but the characters that PCRE recog-
223         nizes as digits, spaces, or word characters  remain  the  same  set  as         nizes as digits, spaces, or word characters  remain  the  same  set  as
224         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
225         includes Unicode property support, because to do otherwise  would  slow         includes Unicode property support, because to do otherwise  would  slow
226         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
227         sense of, say, "digit", you must use Unicode  property  tests  such  as         sense of, say, "digit", you must use Unicode  property  tests  such  as
228         \p{Nd}.         \p{Nd}.  Note  that  this  also applies to \b, because it is defined in
229           terms of \w and \W.
230    
231         8.  Similarly,  characters that match the POSIX named character classes         7. Similarly, characters that match the POSIX named  character  classes
232         are all low-valued characters.         are all low-valued characters.
233    
234         9. Case-insensitive matching applies only to  characters  whose  values         8.  However,  the Perl 5.10 horizontal and vertical whitespace matching
235         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-
236         Even when Unicode property support is available, PCRE  still  uses  its         acters.
237         own  character  tables when checking the case of low-valued characters,  
238         so as not to degrade performance.  The Unicode property information  is         9.  Case-insensitive  matching  applies only to characters whose values
239         used only for characters with higher values.         are less than 128, unless PCRE is built with Unicode property  support.
240           Even  when  Unicode  property support is available, PCRE still uses its
241           own character tables when checking the case of  low-valued  characters,
242           so  as not to degrade performance.  The Unicode property information is
243           used only for characters with higher values. Even when Unicode property
244           support is available, PCRE supports case-insensitive matching only when
245           there is a one-to-one mapping between a letter's  cases.  There  are  a
246           small  number  of  many-to-one  mappings in Unicode; these are not sup-
247           ported by PCRE.
248    
249    
250  AUTHOR  AUTHOR
251    
252         Philip Hazel         Philip Hazel
253         University Computing Service,         University Computing Service
254         Cambridge CB2 3QG, England.         Cambridge CB2 3QH, England.
255    
256           Putting an actual email address here seems to have been a spam  magnet,
257           so  I've  taken  it away. If you want to email me, use my two initials,
258           followed by the two digits 10, at the domain cam.ac.uk.
259    
260    
261         Putting  an actual email address here seems to have been a spam magnet,  REVISION
        so I've taken it away. If you want to email me, use my initial and sur-  
        name, separated by a dot, at the domain ucs.cam.ac.uk.  
262    
263  Last updated: 07 March 2005         Last updated: 11 April 2009
264  Copyright (c) 1997-2005 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
265  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
266    
267    
# Line 220  NAME Line 275  NAME
275  PCRE BUILD-TIME OPTIONS  PCRE BUILD-TIME OPTIONS
276    
277         This  document  describes  the  optional  features  of PCRE that can be         This  document  describes  the  optional  features  of PCRE that can be
278         selected when the library is compiled. They are all selected, or  dese-         selected when the library is compiled. It assumes use of the  configure
279         lected, by providing options to the configure script that is run before         script,  where the optional features are selected or deselected by pro-
280         the make command. The complete list of  options  for  configure  (which         viding options to configure before running the make  command.  However,
281         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
282         directory) can be obtained by running         environments using the GUI facility of  CMakeSetup  if  you  are  using
283           CMake instead of configure to build PCRE.
284    
285           The complete list of options for configure (which includes the standard
286           ones such as the  selection  of  the  installation  directory)  can  be
287           obtained by running
288    
289           ./configure --help           ./configure --help
290    
291         The following sections describe certain options whose names begin  with         The  following  sections  include  descriptions  of options whose names
292         --enable  or  --disable. These settings specify changes to the defaults         begin with --enable or --disable. These settings specify changes to the
293         for the configure command. Because of the  way  that  configure  works,         defaults  for  the configure command. Because of the way that configure
294         --enable  and  --disable  always  come  in  pairs, so the complementary         works, --enable and --disable always come in pairs, so  the  complemen-
295         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
296         not described.         is not described.
297    
298    
299  C++ SUPPORT  C++ SUPPORT
# Line 249  C++ SUPPORT Line 309  C++ SUPPORT
309    
310  UTF-8 SUPPORT  UTF-8 SUPPORT
311    
312         To build PCRE with support for UTF-8 character strings, add         To build PCRE with support for UTF-8 Unicode character strings, add
313    
314           --enable-utf8           --enable-utf8
315    
316         to  the  configure  command.  Of  itself, this does not make PCRE treat         to the configure command. Of itself, this  does  not  make  PCRE  treat
317         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
318         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()
319         function.         function.
320    
321           If  you set --enable-utf8 when compiling in an EBCDIC environment, PCRE
322           expects its input to be either ASCII or UTF-8 (depending on the runtime
323           option).  It  is not possible to support both EBCDIC and UTF-8 codes in
324           the same  version  of  the  library.  Consequently,  --enable-utf8  and
325           --enable-ebcdic are mutually exclusive.
326    
327    
328  UNICODE CHARACTER PROPERTY SUPPORT  UNICODE CHARACTER PROPERTY SUPPORT
329    
330         UTF-8 support allows PCRE to process character values greater than  255         UTF-8  support allows PCRE to process character values greater than 255
331         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-
332         vide any facilities for accessing the properties of such characters. If         vide any facilities for accessing the properties of such characters. If
333         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
334         refer to Unicode character properties, you must add         refer to Unicode character properties, you must add
335    
336           --enable-unicode-properties           --enable-unicode-properties
337    
338         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
339         not explicitly requested it.         not explicitly requested it.
340    
341         Including  Unicode  property  support  adds around 90K of tables to the         Including Unicode property support adds around 30K  of  tables  to  the
342         PCRE library, approximately doubling its size. Only the  general  cate-         PCRE  library.  Only  the general category properties such as Lu and Nd
343         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.  
344    
345    
346  CODE VALUE OF NEWLINE  CODE VALUE OF NEWLINE
347    
348         By default, PCRE treats character 10 (linefeed) as the newline  charac-         By default, PCRE interprets the linefeed (LF) character  as  indicating
349         ter. This is the normal newline character on Unix-like systems. You can         the  end  of  a line. This is the normal newline character on Unix-like
350         compile PCRE to use character 13 (carriage return) instead by adding         systems. You can compile PCRE to use carriage return (CR)  instead,  by
351           adding
352    
353           --enable-newline-is-cr           --enable-newline-is-cr
354    
355         to the configure command. For completeness there is  also  a  --enable-         to  the  configure  command.  There  is  also  a --enable-newline-is-lf
356         newline-is-lf  option,  which explicitly specifies linefeed as the new-         option, which explicitly specifies linefeed as the newline character.
357         line character.  
358           Alternatively, you can specify that line endings are to be indicated by
359           the two character sequence CRLF. If you want this, add
360    
361             --enable-newline-is-crlf
362    
363           to the configure command. There is a fourth option, specified by
364    
365             --enable-newline-is-anycrlf
366    
367           which  causes  PCRE  to recognize any of the three sequences CR, LF, or
368           CRLF as indicating a line ending. Finally, a fifth option, specified by
369    
370             --enable-newline-is-any
371    
372           causes PCRE to recognize any Unicode newline sequence.
373    
374           Whatever line ending convention is selected when PCRE is built  can  be
375           overridden  when  the library functions are called. At build time it is
376           conventional to use the standard for your operating system.
377    
378    
379    WHAT \R MATCHES
380    
381           By default, the sequence \R in a pattern matches  any  Unicode  newline
382           sequence,  whatever  has  been selected as the line ending sequence. If
383           you specify
384    
385             --enable-bsr-anycrlf
386    
387           the default is changed so that \R matches only CR, LF, or  CRLF.  What-
388           ever  is selected when PCRE is built can be overridden when the library
389           functions are called.
390    
391    
392  BUILDING SHARED AND STATIC LIBRARIES  BUILDING SHARED AND STATIC LIBRARIES
# Line 319  POSIX MALLOC USAGE Line 417  POSIX MALLOC USAGE
417         to the configure command.         to the configure command.
418    
419    
 LIMITING PCRE RESOURCE USAGE  
   
        Internally,  PCRE has a function called match(), which it calls repeat-  
        edly  (possibly  recursively)  when  matching  a   pattern   with   the  
        pcre_exec()  function.  By controlling the maximum number of times this  
        function may be called during a single matching operation, a limit  can  
        be  placed  on  the resources used by a single call to pcre_exec(). The  
        limit can be changed at run time, as described in the pcreapi  documen-  
        tation.  The default is 10 million, but this can be changed by adding a  
        setting such as  
   
          --with-match-limit=500000  
   
        to  the  configure  command.  This  setting  has  no  effect   on   the  
        pcre_dfa_exec() matching function.  
   
   
420  HANDLING VERY LARGE PATTERNS  HANDLING VERY LARGE PATTERNS
421    
422         Within  a  compiled  pattern,  offset values are used to point from one         Within  a  compiled  pattern,  offset values are used to point from one
# Line 353  HANDLING VERY LARGE PATTERNS Line 434  HANDLING VERY LARGE PATTERNS
434         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
435         additional bytes when handling them.         additional bytes when handling them.
436    
        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.  
   
437    
438  AVOIDING EXCESSIVE STACK USAGE  AVOIDING EXCESSIVE STACK USAGE
439    
440         When matching with the pcre_exec() function, PCRE implements backtrack-         When matching with the pcre_exec() function, PCRE implements backtrack-
441         ing by making recursive calls to an internal function  called  match().         ing  by  making recursive calls to an internal function called match().
442         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-
443         verely limit PCRE's operation. (The Unix environment does  not  usually         verely  limit  PCRE's operation. (The Unix environment does not usually
444         suffer  from  this  problem.)  An alternative approach that uses memory         suffer from this problem, but it may sometimes be necessary to increase
445         from the heap to remember data, instead  of  using  recursive  function         the  maximum  stack size.  There is a discussion in the pcrestack docu-
446         calls,  has been implemented to work round this problem. If you want to         mentation.) An alternative approach to recursion that uses memory  from
447         build a version of PCRE that works this way, add         the  heap  to remember data, instead of using recursive function calls,
448           has been implemented to work round the problem of limited  stack  size.
449           If you want to build a version of PCRE that works this way, add
450    
451           --disable-stack-for-recursion           --disable-stack-for-recursion
452    
453         to the configure command. With this configuration, PCRE  will  use  the         to  the  configure  command. With this configuration, PCRE will use the
454         pcre_stack_malloc  and pcre_stack_free variables to call memory manage-         pcre_stack_malloc and pcre_stack_free variables to call memory  manage-
455         ment functions. Separate functions are provided because  the  usage  is         ment  functions. By default these point to malloc() and free(), but you
456         very  predictable:  the  block sizes requested are always the same, and         can replace the pointers so that your own functions are used.
457         the blocks are always freed in reverse order. A calling  program  might  
458         be  able  to implement optimized functions that perform better than the         Separate functions are  provided  rather  than  using  pcre_malloc  and
459         standard malloc() and  free()  functions.  PCRE  runs  noticeably  more         pcre_free  because  the  usage  is  very  predictable:  the block sizes
460         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
461         function; it is not relevant for the the pcre_dfa_exec() function.         reverse  order.  A calling program might be able to implement optimized
462           functions that perform better  than  malloc()  and  free().  PCRE  runs
463           noticeably more slowly when built in this way. This option affects only
464           the  pcre_exec()  function;  it   is   not   relevant   for   the   the
465           pcre_dfa_exec() function.
466    
467    
468    LIMITING PCRE RESOURCE USAGE
469    
470           Internally,  PCRE has a function called match(), which it calls repeat-
471           edly  (sometimes  recursively)  when  matching  a  pattern   with   the
472           pcre_exec()  function.  By controlling the maximum number of times this
473           function may be called during a single matching operation, a limit  can
474           be  placed  on  the resources used by a single call to pcre_exec(). The
475           limit can be changed at run time, as described in the pcreapi  documen-
476           tation.  The default is 10 million, but this can be changed by adding a
477           setting such as
478    
479             --with-match-limit=500000
480    
481           to  the  configure  command.  This  setting  has  no  effect   on   the
482           pcre_dfa_exec() matching function.
483    
484           In  some  environments  it is desirable to limit the depth of recursive
485           calls of match() more strictly than the total number of calls, in order
486           to  restrict  the maximum amount of stack (or heap, if --disable-stack-
487           for-recursion is specified) that is used. A second limit controls this;
488           it  defaults  to  the  value  that is set for --with-match-limit, which
489           imposes no additional constraints. However, you can set a  lower  limit
490           by adding, for example,
491    
492             --with-match-limit-recursion=10000
493    
494           to  the  configure  command.  This  value can also be overridden at run
495           time.
496    
497    
498    CREATING CHARACTER TABLES AT BUILD TIME
499    
500           PCRE uses fixed tables for processing characters whose code values  are
501           less  than 256. By default, PCRE is built with a set of tables that are
502           distributed in the file pcre_chartables.c.dist. These  tables  are  for
503           ASCII codes only. If you add
504    
505             --enable-rebuild-chartables
506    
507           to  the  configure  command, the distributed tables are no longer used.
508           Instead, a program called dftables is compiled and  run.  This  outputs
509           the source for new set of tables, created in the default locale of your
510           C runtime system. (This method of replacing the tables does not work if
511           you  are cross compiling, because dftables is run on the local host. If
512           you need to create alternative tables when cross  compiling,  you  will
513           have to do so "by hand".)
514    
515    
516  USING EBCDIC CODE  USING EBCDIC CODE
517    
518         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
519         character  code  is  ASCII  (or Unicode, which is a superset of ASCII).         character code is ASCII (or Unicode, which is  a  superset  of  ASCII).
520         PCRE can, however, be compiled to  run  in  an  EBCDIC  environment  by         This  is  the  case for most computer operating systems. PCRE can, how-
521         adding         ever, be compiled to run in an EBCDIC environment by adding
522    
523           --enable-ebcdic           --enable-ebcdic
524    
525         to the configure command.         to the configure command. This setting implies --enable-rebuild-charta-
526           bles.  You  should  only  use  it if you know that you are in an EBCDIC
527           environment (for example,  an  IBM  mainframe  operating  system).  The
528           --enable-ebcdic option is incompatible with --enable-utf8.
529    
530    
531    PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT
532    
533           By default, pcregrep reads all files as plain text. You can build it so
534           that it recognizes files whose names end in .gz or .bz2, and reads them
535           with libz or libbz2, respectively, by adding one or both of
536    
537             --enable-pcregrep-libz
538             --enable-pcregrep-libbz2
539    
540           to the configure command. These options naturally require that the rel-
541           evant libraries are installed on your system. Configuration  will  fail
542           if they are not.
543    
544    
545    PCRETEST OPTION FOR LIBREADLINE SUPPORT
546    
547           If you add
548    
549             --enable-pcretest-libreadline
550    
551           to  the  configure  command,  pcretest  is  linked with the libreadline
552           library, and when its input is from a terminal, it reads it  using  the
553           readline() function. This provides line-editing and history facilities.
554           Note that libreadline is GPL-licenced, so if you distribute a binary of
555           pcretest linked in this way, there may be licensing issues.
556    
557           Setting  this  option  causes  the -lreadline option to be added to the
558           pcretest build. In many operating environments with  a  sytem-installed
559           libreadline this is sufficient. However, in some environments (e.g.  if
560           an unmodified distribution version of readline is in use),  some  extra
561           configuration  may  be necessary. The INSTALL file for libreadline says
562           this:
563    
564             "Readline uses the termcap functions, but does not link with the
565             termcap or curses library itself, allowing applications which link
566             with readline the to choose an appropriate library."
567    
568           If your environment has not been set up so that an appropriate  library
569           is automatically included, you may need to add something like
570    
571             LIBS="-ncurses"
572    
573           immediately before the configure command.
574    
575    
576    SEE ALSO
577    
578           pcreapi(3), pcre_config(3).
579    
580    
581  Last updated: 15 August 2005  AUTHOR
582  Copyright (c) 1997-2005 University of Cambridge.  
583           Philip Hazel
584           University Computing Service
585           Cambridge CB2 3QH, England.
586    
587    
588    REVISION
589    
590           Last updated: 17 March 2009
591           Copyright (c) 1997-2009 University of Cambridge.
592  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
593    
594    
# Line 431  PCRE MATCHING ALGORITHMS Line 624  PCRE MATCHING ALGORITHMS
624           <something> <something else> <something further>           <something> <something else> <something further>
625    
626         there are three possible answers. The standard algorithm finds only one         there are three possible answers. The standard algorithm finds only one
627         of them, whereas the DFA algorithm finds all three.         of them, whereas the alternative algorithm finds all three.
628    
629    
630  REGULAR EXPRESSIONS AS TREES  REGULAR EXPRESSIONS AS TREES
# Line 440  REGULAR EXPRESSIONS AS TREES Line 633  REGULAR EXPRESSIONS AS TREES
633         resented  as  a  tree structure. An unlimited repetition in the pattern         resented  as  a  tree structure. An unlimited repetition in the pattern
634         makes the tree of infinite size, but it is still a tree.  Matching  the         makes the tree of infinite size, but it is still a tree.  Matching  the
635         pattern  to a given subject string (from a given starting point) can be         pattern  to a given subject string (from a given starting point) can be
636         thought of as a search of the tree.  There are  two  standard  ways  to         thought of as a search of the tree.  There are two  ways  to  search  a
637         search  a  tree: depth-first and breadth-first, and these correspond to         tree:  depth-first  and  breadth-first, and these correspond to the two
638         the two matching algorithms provided by PCRE.         matching algorithms provided by PCRE.
639    
640    
641  THE STANDARD MATCHING ALGORITHM  THE STANDARD MATCHING ALGORITHM
642    
643         In the terminology of Jeffrey Friedl's book Mastering  Regular  Expres-         In the terminology of Jeffrey Friedl's book "Mastering Regular  Expres-
644         sions,  the  standard  algorithm  is  an "NFA algorithm". It conducts a         sions",  the  standard  algorithm  is an "NFA algorithm". It conducts a
645         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
646         single path through the tree, checking that the subject matches what is         single path through the tree, checking that the subject matches what is
647         required. When there is a mismatch, the algorithm  tries  any  alterna-         required. When there is a mismatch, the algorithm  tries  any  alterna-
# Line 472  THE STANDARD MATCHING ALGORITHM Line 665  THE STANDARD MATCHING ALGORITHM
665         This provides support for capturing parentheses and back references.         This provides support for capturing parentheses and back references.
666    
667    
668  THE DFA MATCHING ALGORITHM  THE ALTERNATIVE MATCHING ALGORITHM
669    
670         DFA stands for "deterministic finite automaton", but you do not need to         This algorithm conducts a breadth-first search of  the  tree.  Starting
671         understand the origins of that name. This algorithm conducts a breadth-         from  the  first  matching  point  in the subject, it scans the subject
672         first search of the tree. Starting from the first matching point in the         string from left to right, once, character by character, and as it does
673         subject,  it scans the subject string from left to right, once, charac-         this,  it remembers all the paths through the tree that represent valid
674         ter by character, and as it does  this,  it  remembers  all  the  paths         matches. In Friedl's terminology, this is a kind  of  "DFA  algorithm",
675         through the tree that represent valid matches.         though  it is not implemented as a traditional finite state machine (it
676           keeps multiple states active simultaneously).
677         The  scan  continues until either the end of the subject is reached, or  
678         there are no more unterminated paths. At this point,  terminated  paths         The scan continues until either the end of the subject is  reached,  or
679         represent  the different matching possibilities (if there are none, the         there  are  no more unterminated paths. At this point, terminated paths
680         match has failed).  Thus, if there is more  than  one  possible  match,         represent the different matching possibilities (if there are none,  the
681           match  has  failed).   Thus,  if there is more than one possible match,
682         this algorithm finds all of them, and in particular, it finds the long-         this algorithm finds all of them, and in particular, it finds the long-
683         est. In PCRE, there is an option to stop the algorithm after the  first         est.  In PCRE, there is an option to stop the algorithm after the first
684         match (which is necessarily the shortest) has been found.         match (which is necessarily the shortest) has been found.
685    
686         Note that all the matches that are found start at the same point in the         Note that all the matches that are found start at the same point in the
# Line 494  THE DFA MATCHING ALGORITHM Line 688  THE DFA MATCHING ALGORITHM
688    
689           cat(er(pillar)?)           cat(er(pillar)?)
690    
691         is matched against the string "the caterpillar catchment",  the  result         is  matched  against the string "the caterpillar catchment", the result
692         will  be the three strings "cat", "cater", and "caterpillar" that start         will be the three strings "cat", "cater", and "caterpillar" that  start
693         at the fourth character of the subject. The algorithm does not automat-         at the fourth character of the subject. The algorithm does not automat-
694         ically move on to find matches that start at later positions.         ically move on to find matches that start at later positions.
695    
696         There are a number of features of PCRE regular expressions that are not         There are a number of features of PCRE regular expressions that are not
697         supported by the DFA matching algorithm. They are as follows:         supported by the alternative matching algorithm. They are as follows:
698    
699         1. Because the algorithm finds all  possible  matches,  the  greedy  or         1.  Because  the  algorithm  finds  all possible matches, the greedy or
700         ungreedy  nature  of repetition quantifiers is not relevant. Greedy and         ungreedy nature of repetition quantifiers is not relevant.  Greedy  and
701         ungreedy quantifiers are treated in exactly the same way.         ungreedy quantifiers are treated in exactly the same way. However, pos-
702           sessive quantifiers can make a difference when what follows could  also
703           match what is quantified, for example in a pattern like this:
704    
705             ^a++\w!
706    
707           This  pattern matches "aaab!" but not "aaa!", which would be matched by
708           a non-possessive quantifier. Similarly, if an atomic group is  present,
709           it  is matched as if it were a standalone pattern at the current point,
710           and the longest match is then "locked in" for the rest of  the  overall
711           pattern.
712    
713         2. When dealing with multiple paths through the tree simultaneously, it         2. When dealing with multiple paths through the tree simultaneously, it
714         is  not  straightforward  to  keep track of captured substrings for the         is not straightforward to keep track of  captured  substrings  for  the
715         different matching possibilities, and  PCRE's  implementation  of  this         different  matching  possibilities,  and  PCRE's implementation of this
716         algorithm does not attempt to do this. This means that no captured sub-         algorithm does not attempt to do this. This means that no captured sub-
717         strings are available.         strings are available.
718    
719         3. Because no substrings are captured, back references within the  pat-         3.  Because no substrings are captured, back references within the pat-
720         tern are not supported, and cause errors if encountered.         tern are not supported, and cause errors if encountered.
721    
722         4.  For  the same reason, conditional expressions that use a backrefer-         4. For the same reason, conditional expressions that use  a  backrefer-
723         ence as the condition are not supported.         ence  as  the  condition or test for a specific group recursion are not
724           supported.
725    
726           5. Because many paths through the tree may be  active,  the  \K  escape
727           sequence, which resets the start of the match when encountered (but may
728           be on some paths and not on others), is not  supported.  It  causes  an
729           error if encountered.
730    
731         5. Callouts are supported, but the value of the  capture_top  field  is         6.  Callouts  are  supported, but the value of the capture_top field is
732         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.
733    
734         6.  The \C escape sequence, which (in the standard algorithm) matches a         7. The \C escape sequence, which (in the standard algorithm) matches  a
735         single byte, even in UTF-8 mode, is not supported because the DFA algo-         single  byte, even in UTF-8 mode, is not supported because the alterna-
736         rithm moves through the subject string one character at a time, for all         tive algorithm moves through the subject  string  one  character  at  a
737         active paths through the tree.         time, for all active paths through the tree.
738    
739           8.  Except for (*FAIL), the backtracking control verbs such as (*PRUNE)
740           are not supported. (*FAIL) is supported, and  behaves  like  a  failing
741           negative assertion.
742    
743    
744  ADVANTAGES OF THE DFA ALGORITHM  ADVANTAGES OF THE ALTERNATIVE ALGORITHM
745    
746         Using the DFA matching algorithm provides the following advantages:         Using  the alternative matching algorithm provides the following advan-
747           tages:
748    
749         1. All possible matches (at a single point in the subject) are automat-         1. All possible matches (at a single point in the subject) are automat-
750         ically  found,  and  in particular, the longest match is found. To find         ically  found,  and  in particular, the longest match is found. To find
# Line 538  ADVANTAGES OF THE DFA ALGORITHM Line 753  ADVANTAGES OF THE DFA ALGORITHM
753    
754         2.  There is much better support for partial matching. The restrictions         2.  There is much better support for partial matching. The restrictions
755         on the content of the pattern that apply when using the standard  algo-         on the content of the pattern that apply when using the standard  algo-
756         rithm  for partial matching do not apply to the DFA algorithm. For non-         rithm  for  partial matching do not apply to the alternative algorithm.
757         anchored patterns, the starting position of a partial match  is  avail-         For non-anchored patterns, the starting position of a partial match  is
758         able.         available.
759    
760         3.  Because  the  DFA algorithm scans the subject string just once, and         3.  Because  the  alternative  algorithm  scans the subject string just
761         never needs to backtrack, it is possible  to  pass  very  long  subject         once, and never needs to backtrack, it is possible to  pass  very  long
762         strings  to  the matching function in several pieces, checking for par-         subject  strings  to  the matching function in several pieces, checking
763         tial matching each time.         for partial matching each time.
764    
765    
766  DISADVANTAGES OF THE DFA ALGORITHM  DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
767    
768         The DFA algorithm suffers from a number of disadvantages:         The alternative algorithm suffers from a number of disadvantages:
769    
770         1. It is substantially slower than  the  standard  algorithm.  This  is         1. It is substantially slower than  the  standard  algorithm.  This  is
771         partly  because  it has to search for all possible matches, but is also         partly  because  it has to search for all possible matches, but is also
# Line 558  DISADVANTAGES OF THE DFA ALGORITHM Line 773  DISADVANTAGES OF THE DFA ALGORITHM
773    
774         2. Capturing parentheses and back references are not supported.         2. Capturing parentheses and back references are not supported.
775    
776         3. The "atomic group" feature of PCRE regular expressions is supported,         3. Although atomic groups are supported, their use does not provide the
777         but  does not provide the advantage that it does for the standard algo-         performance advantage that it does for the standard algorithm.
778         rithm.  
779    
780    AUTHOR
781    
782           Philip Hazel
783           University Computing Service
784           Cambridge CB2 3QH, England.
785    
786    
787  Last updated: 28 February 2005  REVISION
788  Copyright (c) 1997-2005 University of Cambridge.  
789           Last updated: 19 April 2008
790           Copyright (c) 1997-2008 University of Cambridge.
791  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
792    
793    
# Line 616  PCRE NATIVE API Line 840  PCRE NATIVE API
840         int pcre_get_stringnumber(const pcre *code,         int pcre_get_stringnumber(const pcre *code,
841              const char *name);              const char *name);
842    
843           int pcre_get_stringtable_entries(const pcre *code,
844                const char *name, char **first, char **last);
845    
846         int pcre_get_substring(const char *subject, int *ovector,         int pcre_get_substring(const char *subject, int *ovector,
847              int stringcount, int stringnumber,              int stringcount, int stringnumber,
848              const char **stringptr);              const char **stringptr);
# Line 654  PCRE NATIVE API Line 881  PCRE NATIVE API
881  PCRE API OVERVIEW  PCRE API OVERVIEW
882    
883         PCRE has its own native API, which is described in this document. There         PCRE has its own native API, which is described in this document. There
884         is also a set of wrapper functions that correspond to the POSIX regular         are also some wrapper functions that correspond to  the  POSIX  regular
885         expression  API.  These  are  described in the pcreposix documentation.         expression  API.  These  are  described in the pcreposix documentation.
886         Both of these APIs define a set of C function calls. A C++  wrapper  is         Both of these APIs define a set of C function calls. A C++  wrapper  is
887         distributed with PCRE. It is documented in the pcrecpp page.         distributed with PCRE. It is documented in the pcrecpp page.
# Line 672  PCRE API OVERVIEW Line 899  PCRE API OVERVIEW
899         a  Perl-compatible  manner. A sample program that demonstrates the sim-         a  Perl-compatible  manner. A sample program that demonstrates the sim-
900         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
901         the  source distribution. The pcresample documentation describes how to         the  source distribution. The pcresample documentation describes how to
902         run it.         compile and run it.
903    
904         A second matching function, pcre_dfa_exec(), which is not Perl-compati-         A second matching function, pcre_dfa_exec(), which is not Perl-compati-
905         ble,  is  also provided. This uses a different algorithm for the match-         ble,  is  also provided. This uses a different algorithm for the match-
906         ing. This allows it to find all possible matches (at a given  point  in         ing. The alternative algorithm finds all possible matches (at  a  given
907         the  subject),  not  just  one. However, this algorithm does not return         point  in  the subject), and scans the subject just once. However, this
908         captured substrings. A description of the two matching  algorithms  and         algorithm does not return captured substrings. A description of the two
909         their  advantages  and disadvantages is given in the pcrematching docu-         matching  algorithms and their advantages and disadvantages is given in
910         mentation.         the pcrematching documentation.
911    
912         In addition to the main compiling and  matching  functions,  there  are         In addition to the main compiling and  matching  functions,  there  are
913         convenience functions for extracting captured substrings from a subject         convenience functions for extracting captured substrings from a subject
# Line 692  PCRE API OVERVIEW Line 919  PCRE API OVERVIEW
919           pcre_get_named_substring()           pcre_get_named_substring()
920           pcre_get_substring_list()           pcre_get_substring_list()
921           pcre_get_stringnumber()           pcre_get_stringnumber()
922             pcre_get_stringtable_entries()
923    
924         pcre_free_substring() and pcre_free_substring_list() are also provided,         pcre_free_substring() and pcre_free_substring_list() are also provided,
925         to free the memory used for extracted strings.         to free the memory used for extracted strings.
# Line 723  PCRE API OVERVIEW Line 951  PCRE API OVERVIEW
951         indirections  to  memory  management functions. These special functions         indirections  to  memory  management functions. These special functions
952         are used only when PCRE is compiled to use  the  heap  for  remembering         are used only when PCRE is compiled to use  the  heap  for  remembering
953         data, instead of recursive function calls, when running the pcre_exec()         data, instead of recursive function calls, when running the pcre_exec()
954         function. This is a non-standard way of building PCRE, for use in envi-         function. See the pcrebuild documentation for  details  of  how  to  do
955         ronments that have limited stacks. Because of the greater use of memory         this.  It  is  a non-standard way of building PCRE, for use in environ-
956         management, it runs more slowly.  Separate functions  are  provided  so         ments that have limited stacks. Because of the greater  use  of  memory
957         that  special-purpose  external  code  can  be used for this case. When         management,  it  runs  more  slowly. Separate functions are provided so
958         used, these functions are always called in a  stack-like  manner  (last         that special-purpose external code can be  used  for  this  case.  When
959         obtained,  first freed), and always for memory blocks of the same size.         used,  these  functions  are always called in a stack-like manner (last
960           obtained, first freed), and always for memory blocks of the same  size.
961           There  is  a discussion about PCRE's stack usage in the pcrestack docu-
962           mentation.
963    
964         The global variable pcre_callout initially contains NULL. It can be set         The global variable pcre_callout initially contains NULL. It can be set
965         by  the  caller  to  a "callout" function, which PCRE will then call at         by  the  caller  to  a "callout" function, which PCRE will then call at
# Line 736  PCRE API OVERVIEW Line 967  PCRE API OVERVIEW
967         pcrecallout documentation.         pcrecallout documentation.
968    
969    
970    NEWLINES
971    
972           PCRE  supports five different conventions for indicating line breaks in
973           strings: a single CR (carriage return) character, a  single  LF  (line-
974           feed) character, the two-character sequence CRLF, any of the three pre-
975           ceding, or any Unicode newline sequence. The Unicode newline  sequences
976           are  the  three just mentioned, plus the single characters VT (vertical
977           tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS  (line
978           separator, U+2028), and PS (paragraph separator, U+2029).
979    
980           Each  of  the first three conventions is used by at least one operating
981           system as its standard newline sequence. When PCRE is built, a  default
982           can  be  specified.  The default default is LF, which is the Unix stan-
983           dard. When PCRE is run, the default can be overridden,  either  when  a
984           pattern is compiled, or when it is matched.
985    
986           At compile time, the newline convention can be specified by the options
987           argument of pcre_compile(), or it can be specified by special  text  at
988           the start of the pattern itself; this overrides any other settings. See
989           the pcrepattern page for details of the special character sequences.
990    
991           In the PCRE documentation the word "newline" is used to mean "the char-
992           acter  or pair of characters that indicate a line break". The choice of
993           newline convention affects the handling of  the  dot,  circumflex,  and
994           dollar metacharacters, the handling of #-comments in /x mode, and, when
995           CRLF is a recognized line ending sequence, the match position  advance-
996           ment for a non-anchored pattern. There is more detail about this in the
997           section on pcre_exec() options below.
998    
999           The choice of newline convention does not affect the interpretation  of
1000           the  \n  or  \r  escape  sequences, nor does it affect what \R matches,
1001           which is controlled in a similar way, but by separate options.
1002    
1003    
1004  MULTITHREADING  MULTITHREADING
1005    
1006         The  PCRE  functions  can be used in multi-threading applications, with         The PCRE functions can be used in  multi-threading  applications,  with
1007         the  proviso  that  the  memory  management  functions  pointed  to  by         the  proviso  that  the  memory  management  functions  pointed  to  by
1008         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
1009         callout function pointed to by pcre_callout, are shared by all threads.         callout function pointed to by pcre_callout, are shared by all threads.
# Line 753  SAVING PRECOMPILED PATTERNS FOR LATER US Line 1018  SAVING PRECOMPILED PATTERNS FOR LATER US
1018         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
1019         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
1020         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
1021         pcreprecompile documentation.         pcreprecompile documentation. However, compiling a  regular  expression
1022           with  one version of PCRE for use with a different version is not guar-
1023           anteed to work and may cause crashes.
1024    
1025    
1026  CHECKING BUILD-TIME OPTIONS  CHECKING BUILD-TIME OPTIONS
# Line 782  CHECKING BUILD-TIME OPTIONS Line 1049  CHECKING BUILD-TIME OPTIONS
1049    
1050           PCRE_CONFIG_NEWLINE           PCRE_CONFIG_NEWLINE
1051    
1052         The output is an integer that is set to the value of the code  that  is         The output is an integer whose value specifies  the  default  character
1053         used  for the newline character. It is either linefeed (10) or carriage         sequence  that is recognized as meaning "newline". The four values that
1054         return (13), and should normally be the  standard  character  for  your         are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,
1055         operating system.         and  -1  for  ANY.  Though they are derived from ASCII, the same values
1056           are returned in EBCDIC environments. The default should normally corre-
1057           spond to the standard sequence for your operating system.
1058    
1059             PCRE_CONFIG_BSR
1060    
1061           The output is an integer whose value indicates what character sequences
1062           the \R escape sequence matches by default. A value of 0 means  that  \R
1063           matches  any  Unicode  line ending sequence; a value of 1 means that \R
1064           matches only CR, LF, or CRLF. The default can be overridden when a pat-
1065           tern is compiled or matched.
1066    
1067           PCRE_CONFIG_LINK_SIZE           PCRE_CONFIG_LINK_SIZE
1068    
# Line 804  CHECKING BUILD-TIME OPTIONS Line 1081  CHECKING BUILD-TIME OPTIONS
1081    
1082           PCRE_CONFIG_MATCH_LIMIT           PCRE_CONFIG_MATCH_LIMIT
1083    
1084         The output is an integer that gives the default limit for the number of         The output is a long integer that gives the default limit for the  num-
1085         internal  matching  function  calls in a pcre_exec() execution. Further         ber  of  internal  matching  function calls in a pcre_exec() execution.
1086         details are given with pcre_exec() below.         Further details are given with pcre_exec() below.
1087    
1088             PCRE_CONFIG_MATCH_LIMIT_RECURSION
1089    
1090           The output is a long integer that gives the default limit for the depth
1091           of   recursion  when  calling  the  internal  matching  function  in  a
1092           pcre_exec() execution.  Further  details  are  given  with  pcre_exec()
1093           below.
1094    
1095           PCRE_CONFIG_STACKRECURSE           PCRE_CONFIG_STACKRECURSE
1096    
1097         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
1098         running pcre_exec() is implemented by recursive function calls that use         running pcre_exec() is implemented by recursive function calls that use
1099         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
1100         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
1101         on the  heap  instead  of  recursive  function  calls.  In  this  case,         on  the  heap  instead  of  recursive  function  calls.  In  this case,
1102         pcre_stack_malloc  and  pcre_stack_free  are  called  to  manage memory         pcre_stack_malloc and  pcre_stack_free  are  called  to  manage  memory
1103         blocks on the heap, thus avoiding the use of the stack.         blocks on the heap, thus avoiding the use of the stack.
1104    
1105    
# Line 832  COMPILING A PATTERN Line 1116  COMPILING A PATTERN
1116    
1117         Either of the functions pcre_compile() or pcre_compile2() can be called         Either of the functions pcre_compile() or pcre_compile2() can be called
1118         to compile a pattern into an internal form. The only difference between         to compile a pattern into an internal form. The only difference between
1119         the two interfaces is that pcre_compile2() has an additional  argument,         the  two interfaces is that pcre_compile2() has an additional argument,
1120         errorcodeptr, via which a numerical error code can be returned.         errorcodeptr, via which a numerical error code can be returned.
1121    
1122         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
1123         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
1124         obtained  via  pcre_malloc is returned. This contains the compiled code         obtained via pcre_malloc is returned. This contains the  compiled  code
1125         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
1126         is a typedef for a structure whose contents are not externally defined.         is a typedef for a structure whose contents are not externally defined.
1127         It is up to the caller  to  free  the  memory  when  it  is  no  longer         It is up to the caller to free the memory (via pcre_free) when it is no
1128         required.         longer required.
1129    
1130         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
1131         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
1132         fully  relocatable, because it may contain a copy of the tableptr argu-         fully relocatable, because it may contain a copy of the tableptr  argu-
1133         ment, which is an address (see below).         ment, which is an address (see below).
1134    
1135         The options argument contains independent bits that affect the compila-         The options argument contains various bit settings that affect the com-
1136         tion.  It  should  be  zero  if  no options are required. The available         pilation. It should be zero if no options are required.  The  available
1137         options are described below. Some of them, in  particular,  those  that         options  are  described  below. Some of them (in particular, those that
1138         are  compatible  with  Perl,  can also be set and unset from within the         are compatible with Perl, but also some others) can  also  be  set  and
1139         pattern (see the detailed description  in  the  pcrepattern  documenta-         unset  from  within  the  pattern  (see the detailed description in the
1140         tion).  For  these options, the contents of the options argument speci-         pcrepattern documentation). For those options that can be different  in
1141         fies their initial settings at the start of compilation and  execution.         different  parts  of  the pattern, the contents of the options argument
1142         The  PCRE_ANCHORED option can be set at the time of matching as well as         specifies their initial settings at the start of compilation and execu-
1143         at compile time.         tion.  The PCRE_ANCHORED and PCRE_NEWLINE_xxx options can be set at the
1144           time of matching as well as at compile time.
1145    
1146         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
1147         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and
1148         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-
1149         sage.  The  offset from the start of the pattern to the character where         sage. This is a static string that is part of the library. You must not
1150         the error was discovered is  placed  in  the  variable  pointed  to  by         try to free it. The offset from the start of the pattern to the charac-
1151         erroffset,  which  must  not  be  NULL. If it is, an immediate error is         ter where the error was discovered is placed in the variable pointed to
1152           by erroffset, which must not be NULL. If it is, an immediate  error  is
1153         given.         given.
1154    
1155         If pcre_compile2() is used instead of pcre_compile(),  and  the  error-         If  pcre_compile2()  is  used instead of pcre_compile(), and the error-
1156         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
1157         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
1158         textual error message. Error codes and messages are listed below.         textual error message. Error codes and messages are listed below.
1159    
1160         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
1161         character tables that are  built  when  PCRE  is  compiled,  using  the         character  tables  that  are  built  when  PCRE  is compiled, using the
1162         default  C  locale.  Otherwise, tableptr must be an address that is the         default C locale. Otherwise, tableptr must be an address  that  is  the
1163         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
1164         compiled  pattern,  and used again by pcre_exec(), unless another table         compiled pattern, and used again by pcre_exec(), unless  another  table
1165         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
1166         support below.         support below.
1167    
1168         This  code  fragment  shows a typical straightforward call to pcre_com-         This code fragment shows a typical straightforward  call  to  pcre_com-
1169         pile():         pile():
1170    
1171           pcre *re;           pcre *re;
# Line 892  COMPILING A PATTERN Line 1178  COMPILING A PATTERN
1178             &erroffset,       /* for error offset */             &erroffset,       /* for error offset */
1179             NULL);            /* use default character tables */             NULL);            /* use default character tables */
1180    
1181         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
1182         file:         file:
1183    
1184           PCRE_ANCHORED           PCRE_ANCHORED
1185    
1186         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
1187         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
1188         that  is being searched (the "subject string"). This effect can also be         that is being searched (the "subject string"). This effect can also  be
1189         achieved by appropriate constructs in the pattern itself, which is  the         achieved  by appropriate constructs in the pattern itself, which is the
1190         only way to do it in Perl.         only way to do it in Perl.
1191    
1192           PCRE_AUTO_CALLOUT           PCRE_AUTO_CALLOUT
1193    
1194         If this bit is set, pcre_compile() automatically inserts callout items,         If this bit is set, pcre_compile() automatically inserts callout items,
1195         all with number 255, before each pattern item. For  discussion  of  the         all  with  number  255, before each pattern item. For discussion of the
1196         callout facility, see the pcrecallout documentation.         callout facility, see the pcrecallout documentation.
1197    
1198             PCRE_BSR_ANYCRLF
1199             PCRE_BSR_UNICODE
1200    
1201           These options (which are mutually exclusive) control what the \R escape
1202           sequence  matches.  The choice is either to match only CR, LF, or CRLF,
1203           or to match any Unicode newline sequence. The default is specified when
1204           PCRE is built. It can be overridden from within the pattern, or by set-
1205           ting an option when a compiled pattern is matched.
1206    
1207           PCRE_CASELESS           PCRE_CASELESS
1208    
1209         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
1210         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
1211         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
1212         always understands the concept of case for characters whose values  are         always  understands the concept of case for characters whose values are
1213         less  than 128, so caseless matching is always possible. For characters         less than 128, so caseless matching is always possible. For  characters
1214         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-
1215         piled  with Unicode property support, but not otherwise. If you want to         piled with Unicode property support, but not otherwise. If you want  to
1216         use caseless matching for characters 128 and  above,  you  must  ensure         use  caseless  matching  for  characters 128 and above, you must ensure
1217         that  PCRE  is  compiled  with Unicode property support as well as with         that PCRE is compiled with Unicode property support  as  well  as  with
1218         UTF-8 support.         UTF-8 support.
1219    
1220           PCRE_DOLLAR_ENDONLY           PCRE_DOLLAR_ENDONLY
1221    
1222         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
1223         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
1224         matches immediately before the final character if it is a newline  (but         matches  immediately before a newline at the end of the string (but not
1225         not  before  any  other  newlines).  The  PCRE_DOLLAR_ENDONLY option is         before any other newlines). The PCRE_DOLLAR_ENDONLY option  is  ignored
1226         ignored if PCRE_MULTILINE is set. There is no equivalent to this option         if  PCRE_MULTILINE  is  set.   There is no equivalent to this option in
1227         in Perl, and no way to set it within a pattern.         Perl, and no way to set it within a pattern.
1228    
1229           PCRE_DOTALL           PCRE_DOTALL
1230    
1231         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-
1232         acters, including newlines. Without it,  newlines  are  excluded.  This         acters,  including  those that indicate newline. Without it, a dot does
1233         option  is equivalent to Perl's /s option, and it can be changed within         not match when the current position is at a  newline.  This  option  is
1234         a pattern by a (?s) option setting.  A  negative  class  such  as  [^a]         equivalent  to Perl's /s option, and it can be changed within a pattern
1235         always  matches a newline character, independent of the setting of this         by a (?s) option setting. A negative class such as [^a] always  matches
1236         option.         newline characters, independent of the setting of this option.
1237    
1238             PCRE_DUPNAMES
1239    
1240           If  this  bit is set, names used to identify capturing subpatterns need
1241           not be unique. This can be helpful for certain types of pattern when it
1242           is  known  that  only  one instance of the named subpattern can ever be
1243           matched. There are more details of named subpatterns  below;  see  also
1244           the pcrepattern documentation.
1245    
1246           PCRE_EXTENDED           PCRE_EXTENDED
1247    
1248         If this bit is set, whitespace  data  characters  in  the  pattern  are         If  this  bit  is  set,  whitespace  data characters in the pattern are
1249         totally ignored except when escaped or inside a character class. White-         totally ignored except when escaped or inside a character class. White-
1250         space does not include the VT character (code 11). In addition, charac-         space does not include the VT character (code 11). In addition, charac-
1251         ters between an unescaped # outside a character class and the next new-         ters between an unescaped # outside a character class and the next new-
1252         line character, inclusive, are also  ignored.  This  is  equivalent  to         line,  inclusive,  are  also  ignored.  This is equivalent to Perl's /x
1253         Perl's  /x  option,  and  it  can be changed within a pattern by a (?x)         option, and it can be changed within a pattern by a  (?x)  option  set-
1254         option setting.         ting.
1255    
1256         This option makes it possible to include  comments  inside  complicated         This  option  makes  it possible to include comments inside complicated
1257         patterns.   Note,  however,  that this applies only to data characters.         patterns.  Note, however, that this applies only  to  data  characters.
1258         Whitespace  characters  may  never  appear  within  special   character         Whitespace   characters  may  never  appear  within  special  character
1259         sequences  in  a  pattern,  for  example  within the sequence (?( which         sequences in a pattern, for  example  within  the  sequence  (?(  which
1260         introduces a conditional subpattern.         introduces a conditional subpattern.
1261    
1262           PCRE_EXTRA           PCRE_EXTRA
1263    
1264         This option was invented in order to turn on  additional  functionality         This  option  was invented in order to turn on additional functionality
1265         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
1266         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
1267         letter  that  has  no  special  meaning causes an error, thus reserving         letter that has no special meaning  causes  an  error,  thus  reserving
1268         these combinations for future expansion. By  default,  as  in  Perl,  a         these  combinations  for  future  expansion.  By default, as in Perl, a
1269         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
1270         literal. There are at present no  other  features  controlled  by  this         literal.  (Perl can, however, be persuaded to give a warning for this.)
1271         option. It can also be set by a (?X) option setting within a pattern.         There are at present no other features controlled by  this  option.  It
1272           can also be set by a (?X) option setting within a pattern.
1273    
1274           PCRE_FIRSTLINE           PCRE_FIRSTLINE
1275    
1276         If  this  option  is  set,  an  unanchored pattern is required to match         If  this  option  is  set,  an  unanchored pattern is required to match
1277         before or at the first newline character in the subject string,  though         before or at the first  newline  in  the  subject  string,  though  the
1278         the matched text may continue over the newline.         matched text may continue over the newline.
1279    
1280             PCRE_JAVASCRIPT_COMPAT
1281    
1282           If this option is set, PCRE's behaviour is changed in some ways so that
1283           it is compatible with JavaScript rather than Perl. The changes  are  as
1284           follows:
1285    
1286           (1)  A  lone  closing square bracket in a pattern causes a compile-time
1287           error, because this is illegal in JavaScript (by default it is  treated
1288           as a data character). Thus, the pattern AB]CD becomes illegal when this
1289           option is set.
1290    
1291           (2) At run time, a back reference to an unset subpattern group  matches
1292           an  empty  string (by default this causes the current matching alterna-
1293           tive to fail). A pattern such as (\1)(a) succeeds when this  option  is
1294           set  (assuming  it can find an "a" in the subject), whereas it fails by
1295           default, for Perl compatibility.
1296    
1297           PCRE_MULTILINE           PCRE_MULTILINE
1298    
1299         By  default,  PCRE  treats the subject string as consisting of a single         By default, PCRE treats the subject string as consisting  of  a  single
1300         line of characters (even if it actually contains newlines). The  "start         line  of characters (even if it actually contains newlines). The "start
1301         of  line"  metacharacter  (^)  matches only at the start of the string,         of line" metacharacter (^) matches only at the  start  of  the  string,
1302         while the "end of line" metacharacter ($) matches only at  the  end  of         while  the  "end  of line" metacharacter ($) matches only at the end of
1303         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY
1304         is set). This is the same as Perl.         is set). This is the same as Perl.
1305    
1306         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"
1307         constructs  match  immediately following or immediately before any new-         constructs match immediately following or immediately  before  internal
1308         line in the subject string, respectively, as well as at the very  start         newlines  in  the  subject string, respectively, as well as at the very
1309         and  end. This is equivalent to Perl's /m option, and it can be changed         start and end. This is equivalent to Perl's /m option, and  it  can  be
1310         within a pattern by a (?m) option setting. If there are no "\n" charac-         changed within a pattern by a (?m) option setting. If there are no new-
1311         ters  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,
1312         setting PCRE_MULTILINE has no effect.         setting PCRE_MULTILINE has no effect.
1313    
1314             PCRE_NEWLINE_CR
1315             PCRE_NEWLINE_LF
1316             PCRE_NEWLINE_CRLF
1317             PCRE_NEWLINE_ANYCRLF
1318             PCRE_NEWLINE_ANY
1319    
1320           These  options  override the default newline definition that was chosen
1321           when PCRE was built. Setting the first or the second specifies  that  a
1322           newline  is  indicated  by a single character (CR or LF, respectively).
1323           Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by  the
1324           two-character  CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF specifies
1325           that any of the three preceding sequences should be recognized. Setting
1326           PCRE_NEWLINE_ANY  specifies that any Unicode newline sequence should be
1327           recognized. The Unicode newline sequences are the three just mentioned,
1328           plus  the  single  characters  VT (vertical tab, U+000B), FF (formfeed,
1329           U+000C), NEL (next line, U+0085), LS (line separator, U+2028),  and  PS
1330           (paragraph  separator,  U+2029).  The  last  two are recognized only in
1331           UTF-8 mode.
1332    
1333           The newline setting in the  options  word  uses  three  bits  that  are
1334           treated as a number, giving eight possibilities. Currently only six are
1335           used (default plus the five values above). This means that if  you  set
1336           more  than one newline option, the combination may or may not be sensi-
1337           ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
1338           PCRE_NEWLINE_CRLF,  but other combinations may yield unused numbers and
1339           cause an error.
1340    
1341           The only time that a line break is specially recognized when  compiling
1342           a  pattern  is  if  PCRE_EXTENDED  is set, and an unescaped # outside a
1343           character class is encountered. This indicates  a  comment  that  lasts
1344           until  after the next line break sequence. In other circumstances, line
1345           break  sequences  are  treated  as  literal  data,   except   that   in
1346           PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters
1347           and are therefore ignored.
1348    
1349           The newline option that is set at compile time becomes the default that
1350           is used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
1351    
1352           PCRE_NO_AUTO_CAPTURE           PCRE_NO_AUTO_CAPTURE
1353    
1354         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-
1355         theses  in the pattern. Any opening parenthesis that is not followed by         theses in the pattern. Any opening parenthesis that is not followed  by
1356         ? behaves as if it were followed by ?: but named parentheses can  still         ?  behaves as if it were followed by ?: but named parentheses can still
1357         be  used  for  capturing  (and  they acquire numbers in the usual way).         be used for capturing (and they acquire  numbers  in  the  usual  way).
1358         There is no equivalent of this option in Perl.         There is no equivalent of this option in Perl.
1359    
1360           PCRE_UNGREEDY           PCRE_UNGREEDY
1361    
1362         This option inverts the "greediness" of the quantifiers  so  that  they         This  option  inverts  the "greediness" of the quantifiers so that they
1363         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
1364         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
1365         within the pattern.         within the pattern.
1366    
1367           PCRE_UTF8           PCRE_UTF8
1368    
1369         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
1370         strings of UTF-8 characters instead of single-byte  character  strings.         strings  of  UTF-8 characters instead of single-byte character strings.
1371         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-
1372         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
1373         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
1374         UTF-8 support in the main pcre page.         UTF-8 support in the main pcre page.
1375    
1376           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
1377    
1378         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
1379         automatically  checked. If an invalid UTF-8 sequence of bytes is found,         automatically checked. There is a  discussion  about  the  validity  of
1380         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
1381         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
1382         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-
1383         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
1384         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
1385         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
1386         ing of subject strings.         can  also be passed to pcre_exec() and pcre_dfa_exec(), to suppress the
1387           UTF-8 validity checking of subject strings.
1388    
1389    
1390  COMPILATION ERROR CODES  COMPILATION ERROR CODES
1391    
1392         The following table lists the error  codes  than  may  be  returned  by         The following table lists the error  codes  than  may  be  returned  by
1393         pcre_compile2(),  along with the error messages that may be returned by         pcre_compile2(),  along with the error messages that may be returned by
1394         both compiling functions.         both compiling functions. As PCRE has developed, some error codes  have
1395           fallen out of use. To avoid confusion, they have not been re-used.
1396    
1397            0  no error            0  no error
1398            1  \ at end of pattern            1  \ at end of pattern
# Line 1043  COMPILATION ERROR CODES Line 1404  COMPILATION ERROR CODES
1404            7  invalid escape sequence in character class            7  invalid escape sequence in character class
1405            8  range out of order in character class            8  range out of order in character class
1406            9  nothing to repeat            9  nothing to repeat
1407           10  operand of unlimited repeat could match the empty string           10  [this code is not in use]
1408           11  internal error: unexpected repeat           11  internal error: unexpected repeat
1409           12  unrecognized character after (?           12  unrecognized character after (? or (?-
1410           13  POSIX named classes are supported only within a class           13  POSIX named classes are supported only within a class
1411           14  missing )           14  missing )
1412           15  reference to non-existent subpattern           15  reference to non-existent subpattern
1413           16  erroffset passed as NULL           16  erroffset passed as NULL
1414           17  unknown option bit(s) set           17  unknown option bit(s) set
1415           18  missing ) after comment           18  missing ) after comment
1416           19  parentheses nested too deeply           19  [this code is not in use]
1417           20  regular expression too large           20  regular expression is too large
1418           21  failed to get memory           21  failed to get memory
1419           22  unmatched parentheses           22  unmatched parentheses
1420           23  internal error: code overflow           23  internal error: code overflow
1421           24  unrecognized character after (?<           24  unrecognized character after (?<
1422           25  lookbehind assertion is not fixed length           25  lookbehind assertion is not fixed length
1423           26  malformed number after (?(           26  malformed number or name after (?(
1424           27  conditional group contains more than two branches           27  conditional group contains more than two branches
1425           28  assertion expected after (?(           28  assertion expected after (?(
1426           29  (?R or (?digits must be followed by )           29  (?R or (?[+-]digits must be followed by )
1427           30  unknown POSIX class name           30  unknown POSIX class name
1428           31  POSIX collating elements are not supported           31  POSIX collating elements are not supported
1429           32  this version of PCRE is not compiled with PCRE_UTF8 support           32  this version of PCRE is not compiled with PCRE_UTF8 support
1430           33  spare error           33  [this code is not in use]
1431           34  character value in \x{...} sequence is too large           34  character value in \x{...} sequence is too large
1432           35  invalid condition (?(0)           35  invalid condition (?(0)
1433           36  \C not allowed in lookbehind assertion           36  \C not allowed in lookbehind assertion
# Line 1075  COMPILATION ERROR CODES Line 1436  COMPILATION ERROR CODES
1436           39  closing ) for (?C expected           39  closing ) for (?C expected
1437           40  recursive call could loop indefinitely           40  recursive call could loop indefinitely
1438           41  unrecognized character after (?P           41  unrecognized character after (?P
1439           42  syntax error after (?P           42  syntax error in subpattern name (missing terminator)
1440           43  two named groups have the same name           43  two named subpatterns have the same name
1441           44  invalid UTF-8 string           44  invalid UTF-8 string
1442           45  support for \P, \p, and \X has not been compiled           45  support for \P, \p, and \X has not been compiled
1443           46  malformed \P or \p sequence           46  malformed \P or \p sequence
1444           47  unknown property name after \P or \p           47  unknown property name after \P or \p
1445             48  subpattern name is too long (maximum 32 characters)
1446             49  too many named subpatterns (maximum 10000)
1447             50  [this code is not in use]
1448             51  octal value is greater than \377 (not in UTF-8 mode)
1449             52  internal error: overran compiling workspace
1450             53   internal  error:  previously-checked  referenced  subpattern not
1451           found
1452             54  DEFINE group contains more than one branch
1453             55  repeating a DEFINE group is not allowed
1454             56  inconsistent NEWLINE options
1455             57  \g is not followed by a braced, angle-bracketed, or quoted
1456                   name/number or by a plain number
1457             58  a numbered reference must not be zero
1458             59  (*VERB) with an argument is not supported
1459             60  (*VERB) not recognized
1460             61  number is too big
1461             62  subpattern name expected
1462             63  digit expected after (?+
1463             64  ] is an invalid data character in JavaScript compatibility mode
1464    
1465           The numbers 32 and 10000 in errors 48 and 49  are  defaults;  different
1466           values may be used if the limits were changed when PCRE was built.
1467    
1468    
1469  STUDYING A PATTERN  STUDYING A PATTERN
# Line 1088  STUDYING A PATTERN Line 1471  STUDYING A PATTERN
1471         pcre_extra *pcre_study(const pcre *code, int options         pcre_extra *pcre_study(const pcre *code, int options
1472              const char **errptr);              const char **errptr);
1473    
1474         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
1475         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
1476         matching. The function pcre_study() takes a pointer to a compiled  pat-         matching.  The function pcre_study() takes a pointer to a compiled pat-
1477         tern as its first argument. If studying the pattern produces additional         tern as its first argument. If studying the pattern produces additional
1478         information that will help speed up matching,  pcre_study()  returns  a         information  that  will  help speed up matching, pcre_study() returns a
1479         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
1480         the results of the study.         the results of the study.
1481    
1482         The  returned  value  from  pcre_study()  can  be  passed  directly  to         The  returned  value  from  pcre_study()  can  be  passed  directly  to
1483         pcre_exec().  However,  a  pcre_extra  block also contains other fields         pcre_exec(). However, a pcre_extra block  also  contains  other  fields
1484         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
1485         described below in the section on matching a pattern.         described below in the section on matching a pattern.
1486    
1487         If  studying  the  pattern  does not produce any additional information         If studying the pattern does not  produce  any  additional  information
1488         pcre_study() returns NULL. In that circumstance, if the calling program         pcre_study() returns NULL. In that circumstance, if the calling program
1489         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
1490         its own pcre_extra block.         its own pcre_extra block.
1491    
1492         The second argument of pcre_study() contains option bits.  At  present,         The  second  argument of pcre_study() contains option bits. At present,
1493         no options are defined, and this argument should always be zero.         no options are defined, and this argument should always be zero.
1494    
1495         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.
1496         If studying succeeds (even if no data is  returned),  the  variable  it         If  studying  succeeds  (even  if no data is returned), the variable it
1497         points  to  is set to NULL. Otherwise it points to a textual error mes-         points to is set to NULL. Otherwise it is set to  point  to  a  textual
1498         sage. You should therefore test the error pointer for NULL after  call-         error message. This is a static string that is part of the library. You
1499         ing pcre_study(), to be sure that it has run successfully.         must not try to free it. You should test the  error  pointer  for  NULL
1500           after calling pcre_study(), to be sure that it has run successfully.
1501    
1502         This is a typical call to pcre_study():         This is a typical call to pcre_study():
1503    
# Line 1131  STUDYING A PATTERN Line 1515  STUDYING A PATTERN
1515  LOCALE SUPPORT  LOCALE SUPPORT
1516    
1517         PCRE  handles  caseless matching, and determines whether characters are         PCRE  handles  caseless matching, and determines whether characters are
1518         letters digits, or whatever, by reference to a set of  tables,  indexed         letters, digits, or whatever, by reference to a set of tables,  indexed
1519         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
1520         characters with codes less than 128. Higher-valued  codes  never  match         characters with codes less than 128. Higher-valued  codes  never  match
1521         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
1522         with Unicode character property support.         with Unicode character property support. The use of locales  with  Uni-
1523           code  is discouraged. If you are handling characters with codes greater
1524         An internal set of tables is created in the default C locale when  PCRE         than 128, you should either use UTF-8 and Unicode, or use locales,  but
1525         is  built.  This  is  used when the final argument of pcre_compile() is         not try to mix the two.
1526         NULL, and is sufficient for many applications. An  alternative  set  of  
1527         tables  can,  however, be supplied. These may be created in a different         PCRE  contains  an  internal set of tables that are used when the final
1528         locale from the default. As more and more applications change to  using         argument of pcre_compile() is  NULL.  These  are  sufficient  for  many
1529         Unicode, the need for this locale support is expected to die away.         applications.  Normally, the internal tables recognize only ASCII char-
1530           acters. However, when PCRE is built, it is possible to cause the inter-
1531           nal tables to be rebuilt in the default "C" locale of the local system,
1532           which may cause them to be different.
1533    
1534           The internal tables can always be overridden by tables supplied by  the
1535           application that calls PCRE. These may be created in a different locale
1536           from the default. As more and more applications change  to  using  Uni-
1537           code, the need for this locale support is expected to die away.
1538    
1539         External  tables  are  built by calling the pcre_maketables() function,         External  tables  are  built by calling the pcre_maketables() function,
1540         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 1155  LOCALE SUPPORT Line 1547  LOCALE SUPPORT
1547           tables = pcre_maketables();           tables = pcre_maketables();
1548           re = pcre_compile(..., tables);           re = pcre_compile(..., tables);
1549    
1550         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;
1551         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".
1552         that the memory containing the tables remains available for as long  as  
1553           When  pcre_maketables()  runs,  the  tables are built in memory that is
1554           obtained via pcre_malloc. It is the caller's responsibility  to  ensure
1555           that  the memory containing the tables remains available for as long as
1556         it is needed.         it is needed.
1557    
1558         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
1559         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()
1560         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-
1561         tern, compilation, studying and matching all happen in the same locale,         tern, compilation, studying and matching all happen in the same locale,
1562         but different patterns can be compiled in different locales.         but different patterns can be compiled in different locales.
1563    
1564         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
1565         the internal tables) to pcre_exec(). Although  not  intended  for  this         the  internal  tables)  to  pcre_exec(). Although not intended for this
1566         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
1567         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
1568         run time is discussed below in the section on matching a pattern.         run time is discussed below in the section on matching a pattern.
1569    
# Line 1178  INFORMATION ABOUT A PATTERN Line 1573  INFORMATION ABOUT A PATTERN
1573         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
1574              int what, void *where);              int what, void *where);
1575    
1576         The  pcre_fullinfo() function returns information about a compiled pat-         The pcre_fullinfo() function returns information about a compiled  pat-
1577         tern. It replaces the obsolete pcre_info() function, which is neverthe-         tern. It replaces the obsolete pcre_info() function, which is neverthe-
1578         less retained for backwards compability (and is documented below).         less retained for backwards compability (and is documented below).
1579    
1580         The  first  argument  for  pcre_fullinfo() is a pointer to the compiled         The first argument for pcre_fullinfo() is a  pointer  to  the  compiled
1581         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
1582         the  pattern  was not studied. The third argument specifies which piece         the pattern was not studied. The third argument specifies  which  piece
1583         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
1584         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
1585         success, or one of the following negative numbers:         success, or one of the following negative numbers:
1586    
1587           PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_NULL       the argument code was NULL
# Line 1194  INFORMATION ABOUT A PATTERN Line 1589  INFORMATION ABOUT A PATTERN
1589           PCRE_ERROR_BADMAGIC   the "magic number" was not found           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1590           PCRE_ERROR_BADOPTION  the value of what was invalid           PCRE_ERROR_BADOPTION  the value of what was invalid
1591    
1592         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
1593         an  simple check against passing an arbitrary memory pointer. Here is a         an simple check against passing an arbitrary memory pointer. Here is  a
1594         typical call of pcre_fullinfo(), to obtain the length of  the  compiled         typical  call  of pcre_fullinfo(), to obtain the length of the compiled
1595         pattern:         pattern:
1596    
1597           int rc;           int rc;
1598           unsigned long int length;           size_t length;
1599           rc = pcre_fullinfo(           rc = pcre_fullinfo(
1600             re,               /* result of pcre_compile() */             re,               /* result of pcre_compile() */
1601             pe,               /* result of pcre_study(), or NULL */             pe,               /* result of pcre_study(), or NULL */
1602             PCRE_INFO_SIZE,   /* what is required */             PCRE_INFO_SIZE,   /* what is required */
1603             &length);         /* where to put the data */             &length);         /* where to put the data */
1604    
1605         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
1606         are as follows:         are as follows:
1607    
1608           PCRE_INFO_BACKREFMAX           PCRE_INFO_BACKREFMAX
1609    
1610         Return the number of the highest back reference  in  the  pattern.  The         Return  the  number  of  the highest back reference in the pattern. The
1611         fourth  argument  should  point to an int variable. Zero is returned if         fourth argument should point to an int variable. Zero  is  returned  if
1612         there are no back references.         there are no back references.
1613    
1614           PCRE_INFO_CAPTURECOUNT           PCRE_INFO_CAPTURECOUNT
1615    
1616         Return the number of capturing subpatterns in the pattern.  The  fourth         Return  the  number of capturing subpatterns in the pattern. The fourth
1617         argument should point to an int variable.         argument should point to an int variable.
1618    
1619           PCRE_INFO_DEFAULT_TABLES           PCRE_INFO_DEFAULT_TABLES
1620    
1621         Return  a pointer to the internal default character tables within PCRE.         Return a pointer to the internal default character tables within  PCRE.
1622         The fourth argument should point to an unsigned char *  variable.  This         The  fourth  argument should point to an unsigned char * variable. This
1623         information call is provided for internal use by the pcre_study() func-         information call is provided for internal use by the pcre_study() func-
1624         tion. External callers can cause PCRE to use  its  internal  tables  by         tion.  External  callers  can  cause PCRE to use its internal tables by
1625         passing a NULL table pointer.         passing a NULL table pointer.
1626    
1627           PCRE_INFO_FIRSTBYTE           PCRE_INFO_FIRSTBYTE
1628    
1629         Return  information  about  the first byte of any matched string, for a         Return information about the first byte of any matched  string,  for  a
1630         non-anchored   pattern.   (This    option    used    to    be    called         non-anchored  pattern. The fourth argument should point to an int vari-
1631         PCRE_INFO_FIRSTCHAR;  the  old  name  is still recognized for backwards         able. (This option used to be called PCRE_INFO_FIRSTCHAR; the old  name
1632         compatibility.)         is still recognized for backwards compatibility.)
1633    
1634         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
1635         (cat|cow|coyote),  it  is  returned in the integer pointed to by where.         (cat|cow|coyote), its value is returned. Otherwise, if either
        Otherwise, if either  
1636    
1637         (a) the pattern was compiled with the PCRE_MULTILINE option, and  every         (a) the pattern was compiled with the PCRE_MULTILINE option, and  every
1638         branch starts with "^", or         branch starts with "^", or
# Line 1258  INFORMATION ABOUT A PATTERN Line 1652  INFORMATION ABOUT A PATTERN
1652         returned.  The fourth argument should point to an unsigned char * vari-         returned.  The fourth argument should point to an unsigned char * vari-
1653         able.         able.
1654    
1655             PCRE_INFO_HASCRORLF
1656    
1657           Return 1 if the pattern contains any explicit  matches  for  CR  or  LF
1658           characters,  otherwise  0.  The  fourth argument should point to an int
1659           variable. An explicit match is either a literal CR or LF character,  or
1660           \r or \n.
1661    
1662             PCRE_INFO_JCHANGED
1663    
1664           Return  1  if  the (?J) or (?-J) option setting is used in the pattern,
1665           otherwise 0. The fourth argument should point to an int variable.  (?J)
1666           and (?-J) set and unset the local PCRE_DUPNAMES option, respectively.
1667    
1668           PCRE_INFO_LASTLITERAL           PCRE_INFO_LASTLITERAL
1669    
1670         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
1671         matched  string,  other  than  at  its  start,  if such a byte has been         matched string, other than at its  start,  if  such  a  byte  has  been
1672         recorded. The fourth argument should point to an int variable. If there         recorded. The fourth argument should point to an int variable. If there
1673         is  no such byte, -1 is returned. For anchored patterns, a last literal         is no such byte, -1 is returned. For anchored patterns, a last  literal
1674         byte is recorded only if it follows something of variable  length.  For         byte  is  recorded only if it follows something of variable length. For
1675         example, for the pattern /^a\d+z\d+/ the returned value is "z", but for         example, for the pattern /^a\d+z\d+/ the returned value is "z", but for
1676         /^a\dz\d/ the returned value is -1.         /^a\dz\d/ the returned value is -1.
1677    
# Line 1272  INFORMATION ABOUT A PATTERN Line 1679  INFORMATION ABOUT A PATTERN
1679           PCRE_INFO_NAMEENTRYSIZE           PCRE_INFO_NAMEENTRYSIZE
1680           PCRE_INFO_NAMETABLE           PCRE_INFO_NAMETABLE
1681    
1682         PCRE supports the use of named as well as numbered capturing  parenthe-         PCRE  supports the use of named as well as numbered capturing parenthe-
1683         ses.  The names are just an additional way of identifying the parenthe-         ses. The names are just an additional way of identifying the  parenthe-
1684         ses,  which  still  acquire  numbers.  A  convenience  function  called         ses, which still acquire numbers. Several convenience functions such as
1685         pcre_get_named_substring()  is  provided  for  extracting an individual         pcre_get_named_substring() are provided for  extracting  captured  sub-
1686         captured substring by name. It is also possible  to  extract  the  data         strings  by  name. It is also possible to extract the data directly, by
1687         directly,  by  first converting the name to a number in order to access         first converting the name to a number in order to  access  the  correct
1688         the correct pointers in the output vector (described  with  pcre_exec()         pointers in the output vector (described with pcre_exec() below). To do
1689         below).  To  do the conversion, you need to use the name-to-number map,         the conversion, you need  to  use  the  name-to-number  map,  which  is
1690         which is described by these three values.         described by these three values.
1691    
1692         The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT         The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT
1693         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
1694         of each entry; both of these  return  an  int  value.  The  entry  size         of  each  entry;  both  of  these  return  an int value. The entry size
1695         depends  on the length of the longest name. PCRE_INFO_NAMETABLE returns         depends on the length of the longest name. PCRE_INFO_NAMETABLE  returns
1696         a pointer to the first entry of the table  (a  pointer  to  char).  The         a  pointer  to  the  first  entry of the table (a pointer to char). The
1697         first two bytes of each entry are the number of the capturing parenthe-         first two bytes of each entry are the number of the capturing parenthe-
1698         sis, most significant byte first. The rest of the entry is  the  corre-         sis,  most  significant byte first. The rest of the entry is the corre-
1699         sponding  name,  zero  terminated. The names are in alphabetical order.         sponding name, zero terminated. The names are  in  alphabetical  order.
1700         For example, consider the following pattern  (assume  PCRE_EXTENDED  is         When PCRE_DUPNAMES is set, duplicate names are in order of their paren-
1701         set, so white space - including newlines - is ignored):         theses numbers. For example, consider  the  following  pattern  (assume
1702           PCRE_EXTENDED  is  set,  so  white  space  -  including  newlines  - is
1703           ignored):
1704    
1705           (?P<date> (?P<year>(\d\d)?\d\d) -           (?<date> (?<year>(\d\d)?\d\d) -
1706           (?P<month>\d\d) - (?P<day>\d\d) )           (?<month>\d\d) - (?<day>\d\d) )
1707    
1708         There  are  four  named subpatterns, so the table has four entries, and         There are four named subpatterns, so the table has  four  entries,  and
1709         each entry in the table is eight bytes long. The table is  as  follows,         each  entry  in the table is eight bytes long. The table is as follows,
1710         with non-printing bytes shows in hexadecimal, and undefined bytes shown         with non-printing bytes shows in hexadecimal, and undefined bytes shown
1711         as ??:         as ??:
1712    
# Line 1306  INFORMATION ABOUT A PATTERN Line 1715  INFORMATION ABOUT A PATTERN
1715           00 04 m  o  n  t  h  00           00 04 m  o  n  t  h  00
1716           00 02 y  e  a  r  00 ??           00 02 y  e  a  r  00 ??
1717    
1718         When writing code to extract data  from  named  subpatterns  using  the         When  writing  code  to  extract  data from named subpatterns using the
1719         name-to-number map, remember that the length of each entry is likely to         name-to-number map, remember that the length of the entries  is  likely
1720         be different for each compiled pattern.         to be different for each compiled pattern.
1721    
1722             PCRE_INFO_OKPARTIAL
1723    
1724           Return  1 if the pattern can be used for partial matching, otherwise 0.
1725           The fourth argument should point to an int  variable.  The  pcrepartial
1726           documentation  lists  the restrictions that apply to patterns when par-
1727           tial matching is used.
1728    
1729           PCRE_INFO_OPTIONS           PCRE_INFO_OPTIONS
1730    
1731         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
1732         fourth  argument  should  point to an unsigned long int variable. These         fourth  argument  should  point to an unsigned long int variable. These
1733         option bits are those specified in the call to pcre_compile(), modified         option bits are those specified in the call to pcre_compile(), modified
1734         by any top-level option settings within the pattern itself.         by any top-level option settings at the start of the pattern itself. In
1735           other words, they are the options that will be in force  when  matching
1736           starts.  For  example, if the pattern /(?im)abc(?-i)d/ is compiled with
1737           the PCRE_EXTENDED option, the result is PCRE_CASELESS,  PCRE_MULTILINE,
1738           and PCRE_EXTENDED.
1739    
1740         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
1741         alternatives begin with one of the following:         alternatives begin with one of the following:
# Line 1395  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1815  MATCHING A PATTERN: THE TRADITIONAL FUNC
1815              const char *subject, int length, int startoffset,              const char *subject, int length, int startoffset,
1816              int options, int *ovector, int ovecsize);              int options, int *ovector, int ovecsize);
1817    
1818         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
1819         compiled  pattern, which is passed in the code argument. If the pattern         compiled pattern, which is passed in the code argument. If the  pattern
1820         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
1821         argument.  This  function is the main matching facility of the library,         argument. This function is the main matching facility of  the  library,
1822         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
1823         an  alternative matching function, which is described below in the sec-         an alternative matching function, which is described below in the  sec-
1824         tion about the pcre_dfa_exec() function.         tion about the pcre_dfa_exec() function.
1825    
1826         In most applications, the pattern will have been compiled (and  option-         In  most applications, the pattern will have been compiled (and option-
1827         ally  studied)  in the same process that calls pcre_exec(). However, it         ally studied) in the same process that calls pcre_exec().  However,  it
1828         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
1829         later  in  different processes, possibly even on different hosts. For a         later in different processes, possibly even on different hosts.  For  a
1830         discussion about this, see the pcreprecompile documentation.         discussion about this, see the pcreprecompile documentation.
1831    
1832         Here is an example of a simple call to pcre_exec():         Here is an example of a simple call to pcre_exec():
# Line 1425  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1845  MATCHING A PATTERN: THE TRADITIONAL FUNC
1845    
1846     Extra data for pcre_exec()     Extra data for pcre_exec()
1847    
1848         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
1849         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
1850         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-
1851         tional  information in it. The fields in a pcre_extra block are as fol-         tional information in it. The pcre_extra block contains  the  following
1852         lows:         fields (not necessarily in this order):
1853    
1854           unsigned long int flags;           unsigned long int flags;
1855           void *study_data;           void *study_data;
1856           unsigned long int match_limit;           unsigned long int match_limit;
1857             unsigned long int match_limit_recursion;
1858           void *callout_data;           void *callout_data;
1859           const unsigned char *tables;           const unsigned char *tables;
1860    
1861         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
1862         are set. The flag bits are:         are set. The flag bits are:
1863    
1864           PCRE_EXTRA_STUDY_DATA           PCRE_EXTRA_STUDY_DATA
1865           PCRE_EXTRA_MATCH_LIMIT           PCRE_EXTRA_MATCH_LIMIT
1866             PCRE_EXTRA_MATCH_LIMIT_RECURSION
1867           PCRE_EXTRA_CALLOUT_DATA           PCRE_EXTRA_CALLOUT_DATA
1868           PCRE_EXTRA_TABLES           PCRE_EXTRA_TABLES
1869    
1870         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
1871         the pcre_extra block that is returned by  pcre_study(),  together  with         the  pcre_extra  block  that is returned by pcre_study(), together with
1872         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
1873         add to the block by setting the other fields  and  their  corresponding         add  to  the  block by setting the other fields and their corresponding
1874         flag bits.         flag bits.
1875    
1876         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
1877         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
1878         match,  but  which  have  a very large number of possibilities in their         match, but which have a very large number  of  possibilities  in  their
1879         search trees. The classic  example  is  the  use  of  nested  unlimited         search  trees.  The  classic  example  is  the  use of nested unlimited
1880         repeats.         repeats.
1881    
1882         Internally,  PCRE uses a function called match() which it calls repeat-         Internally, PCRE uses a function called match() which it calls  repeat-
1883         edly (sometimes recursively). The limit is imposed  on  the  number  of         edly  (sometimes  recursively). The limit set by match_limit is imposed
1884         times  this  function is called during a match, which has the effect of         on the number of times this function is called during  a  match,  which
1885         limiting the amount of recursion and backtracking that can take  place.         has  the  effect  of  limiting the amount of backtracking that can take
1886         For patterns that are not anchored, the count starts from zero for each         place. For patterns that are not anchored, the count restarts from zero
1887         position in the subject string.         for each position in the subject string.
1888    
1889         The default limit for the library can be set when PCRE  is  built;  the         The  default  value  for  the  limit can be set when PCRE is built; the
1890         default  default  is 10 million, which handles all but the most extreme         default default is 10 million, which handles all but the  most  extreme
1891         cases. You can reduce  the  default  by  suppling  pcre_exec()  with  a         cases.  You  can  override  the  default by suppling pcre_exec() with a
1892         pcre_extra  block  in  which match_limit is set to a smaller value, and         pcre_extra    block    in    which    match_limit    is    set,     and
1893         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
1894         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1895    
1896           The match_limit_recursion field is similar to match_limit, but  instead
1897           of limiting the total number of times that match() is called, it limits
1898           the depth of recursion. The recursion depth is a  smaller  number  than
1899           the  total number of calls, because not all calls to match() are recur-
1900           sive.  This limit is of use only if it is set smaller than match_limit.
1901    
1902           Limiting the recursion depth limits the amount of  stack  that  can  be
1903           used, or, when PCRE has been compiled to use memory on the heap instead
1904           of the stack, the amount of heap memory that can be used.
1905    
1906           The default value for match_limit_recursion can be  set  when  PCRE  is
1907           built;  the  default  default  is  the  same  value  as the default for
1908           match_limit. You can override the default by suppling pcre_exec()  with
1909           a   pcre_extra   block  in  which  match_limit_recursion  is  set,  and
1910           PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in  the  flags  field.  If  the
1911           limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1912    
1913         The  pcre_callout  field is used in conjunction with the "callout" fea-         The  pcre_callout  field is used in conjunction with the "callout" fea-
1914         ture, which is described in the pcrecallout documentation.         ture, which is described in the pcrecallout documentation.
1915    
# Line 1488  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1927  MATCHING A PATTERN: THE TRADITIONAL FUNC
1927     Option bits for pcre_exec()     Option bits for pcre_exec()
1928    
1929         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.
1930         The  only  bits  that  may  be  set  are  PCRE_ANCHORED,   PCRE_NOTBOL,         The only bits that may  be  set  are  PCRE_ANCHORED,  PCRE_NEWLINE_xxx,
1931         PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK and PCRE_PARTIAL.         PCRE_NOTBOL,    PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_START_OPTIMIZE,
1932           PCRE_NO_UTF8_CHECK and PCRE_PARTIAL.
1933    
1934           PCRE_ANCHORED           PCRE_ANCHORED
1935    
1936         The  PCRE_ANCHORED  option  limits pcre_exec() to matching at the first         The PCRE_ANCHORED option limits pcre_exec() to matching  at  the  first
1937         matching position. If a pattern was  compiled  with  PCRE_ANCHORED,  or         matching  position.  If  a  pattern was compiled with PCRE_ANCHORED, or
1938         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
1939         unachored at matching time.         unachored at matching time.
1940    
1941             PCRE_BSR_ANYCRLF
1942             PCRE_BSR_UNICODE
1943    
1944           These options (which are mutually exclusive) control what the \R escape
1945           sequence matches. The choice is either to match only CR, LF,  or  CRLF,
1946           or  to  match  any Unicode newline sequence. These options override the
1947           choice that was made or defaulted when the pattern was compiled.
1948    
1949             PCRE_NEWLINE_CR
1950             PCRE_NEWLINE_LF
1951             PCRE_NEWLINE_CRLF
1952             PCRE_NEWLINE_ANYCRLF
1953             PCRE_NEWLINE_ANY
1954    
1955           These options override  the  newline  definition  that  was  chosen  or
1956           defaulted  when the pattern was compiled. For details, see the descrip-
1957           tion of pcre_compile()  above.  During  matching,  the  newline  choice
1958           affects  the  behaviour  of the dot, circumflex, and dollar metacharac-
1959           ters. It may also alter the way the match position is advanced after  a
1960           match failure for an unanchored pattern.
1961    
1962           When  PCRE_NEWLINE_CRLF,  PCRE_NEWLINE_ANYCRLF,  or PCRE_NEWLINE_ANY is
1963           set, and a match attempt for an unanchored pattern fails when the  cur-
1964           rent  position  is  at  a  CRLF  sequence,  and the pattern contains no
1965           explicit matches for  CR  or  LF  characters,  the  match  position  is
1966           advanced by two characters instead of one, in other words, to after the
1967           CRLF.
1968    
1969           The above rule is a compromise that makes the most common cases work as
1970           expected.  For  example,  if  the  pattern  is .+A (and the PCRE_DOTALL
1971           option is not set), it does not match the string "\r\nA" because, after
1972           failing  at the start, it skips both the CR and the LF before retrying.
1973           However, the pattern [\r\n]A does match that string,  because  it  con-
1974           tains an explicit CR or LF reference, and so advances only by one char-
1975           acter after the first failure.
1976    
1977           An explicit match for CR of LF is either a literal appearance of one of
1978           those  characters,  or  one  of the \r or \n escape sequences. Implicit
1979           matches such as [^X] do not count, nor does \s (which includes  CR  and
1980           LF in the characters that it matches).
1981    
1982           Notwithstanding  the above, anomalous effects may still occur when CRLF
1983           is a valid newline sequence and explicit \r or \n escapes appear in the
1984           pattern.
1985    
1986           PCRE_NOTBOL           PCRE_NOTBOL
1987    
1988         This option specifies that first character of the subject string is not         This option specifies that first character of the subject string is not
1989         the  beginning  of  a  line, so the circumflex metacharacter should not         the beginning of a line, so the  circumflex  metacharacter  should  not
1990         match before it. Setting this without PCRE_MULTILINE (at compile  time)         match  before it. Setting this without PCRE_MULTILINE (at compile time)
1991         causes  circumflex  never to match. This option affects only the behav-         causes circumflex never to match. This option affects only  the  behav-
1992         iour of the circumflex metacharacter. It does not affect \A.         iour of the circumflex metacharacter. It does not affect \A.
1993    
1994           PCRE_NOTEOL           PCRE_NOTEOL
1995    
1996         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
1997         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
1998         in multiline mode) a newline immediately before it. Setting this  with-         in  multiline mode) a newline immediately before it. Setting this with-
1999         out PCRE_MULTILINE (at compile time) causes dollar never to match. This         out PCRE_MULTILINE (at compile time) causes dollar never to match. This
2000         option affects only the behaviour of the dollar metacharacter. It  does         option  affects only the behaviour of the dollar metacharacter. It does
2001         not affect \Z or \z.         not affect \Z or \z.
2002    
2003           PCRE_NOTEMPTY           PCRE_NOTEMPTY
2004    
2005         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
2006         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
2007         the  alternatives  match  the empty string, the entire match fails. For         the alternatives match the empty string, the entire  match  fails.  For
2008         example, if the pattern         example, if the pattern
2009    
2010           a?b?           a?b?
2011    
2012         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
2013         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
2014         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-
2015         rences of "a" or "b".         rences of "a" or "b".
2016    
2017         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-
2018         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()
2019         function,  and  when  using  the /g modifier. It is possible to emulate         function, and when using the /g modifier. It  is  possible  to  emulate
2020         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
2021         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
2022         if that fails by advancing the starting offset (see below)  and  trying         if  that  fails by advancing the starting offset (see below) and trying
2023         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
2024         this in the pcredemo.c sample program.         this in the pcredemo.c sample program.
2025    
2026             PCRE_NO_START_OPTIMIZE
2027    
2028           There  are a number of optimizations that pcre_exec() uses at the start
2029           of a match, in order to speed up the process. For  example,  if  it  is
2030           known  that  a  match must start with a specific character, it searches
2031           the subject for that character, and fails immediately if it cannot find
2032           it,  without actually running the main matching function. When callouts
2033           are in use, these optimizations can cause  them  to  be  skipped.  This
2034           option  disables  the  "start-up" optimizations, causing performance to
2035           suffer, but ensuring that the callouts do occur.
2036    
2037           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
2038    
2039         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
2040         UTF-8  string is automatically checked when pcre_exec() is subsequently         UTF-8  string is automatically checked when pcre_exec() is subsequently
2041         called.  The value of startoffset is also checked  to  ensure  that  it         called.  The value of startoffset is also checked  to  ensure  that  it
2042         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
2043         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
2044         startoffset  contains  an  invalid  value, PCRE_ERROR_BADUTF8_OFFSET is         main  pcre  page.  If  an  invalid  UTF-8  sequence  of bytes is found,
2045         returned.         pcre_exec() returns the error PCRE_ERROR_BADUTF8. If  startoffset  con-
2046           tains an invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.
2047         If you already know that your subject is valid, and you  want  to  skip  
2048         these    checks    for   performance   reasons,   you   can   set   the         If  you  already  know that your subject is valid, and you want to skip
2049         PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might  want  to         these   checks   for   performance   reasons,   you   can    set    the
2050         do  this  for the second and subsequent calls to pcre_exec() if you are         PCRE_NO_UTF8_CHECK  option  when calling pcre_exec(). You might want to
2051         making repeated calls to find all  the  matches  in  a  single  subject         do this for the second and subsequent calls to pcre_exec() if  you  are
2052         string.  However,  you  should  be  sure  that the value of startoffset         making  repeated  calls  to  find  all  the matches in a single subject
2053         points to the start of a UTF-8 character.  When  PCRE_NO_UTF8_CHECK  is         string. However, you should be  sure  that  the  value  of  startoffset
2054         set,  the  effect of passing an invalid UTF-8 string as a subject, or a         points  to  the  start of a UTF-8 character. When PCRE_NO_UTF8_CHECK is
2055         value of startoffset that does not point to the start of a UTF-8  char-         set, the effect of passing an invalid UTF-8 string as a subject,  or  a
2056           value  of startoffset that does not point to the start of a UTF-8 char-
2057         acter, is undefined. Your program may crash.         acter, is undefined. Your program may crash.
2058    
2059           PCRE_PARTIAL           PCRE_PARTIAL
2060    
2061         This  option  turns  on  the  partial  matching feature. If the subject         This option turns on the  partial  matching  feature.  If  the  subject
2062         string fails to match the pattern, but at some point during the  match-         string  fails to match the pattern, but at some point during the match-
2063         ing  process  the  end of the subject was reached (that is, the subject         ing process the end of the subject was reached (that  is,  the  subject
2064         partially matches the pattern and the failure to  match  occurred  only         partially  matches  the  pattern and the failure to match occurred only
2065         because  there were not enough subject characters), pcre_exec() returns         because there were not enough subject characters), pcre_exec()  returns
2066         PCRE_ERROR_PARTIAL instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL  is         PCRE_ERROR_PARTIAL  instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is
2067         used,  there  are restrictions on what may appear in the pattern. These         used, there are restrictions on what may appear in the  pattern.  These
2068         are discussed in the pcrepartial documentation.         are discussed in the pcrepartial documentation.
2069    
2070     The string to be matched by pcre_exec()     The string to be matched by pcre_exec()
2071    
2072         The subject string is passed to pcre_exec() as a pointer in subject,  a         The  subject string is passed to pcre_exec() as a pointer in subject, a
2073         length  in  length, and a starting byte offset in startoffset. In UTF-8         length (in bytes) in length, and a starting byte offset in startoffset.
2074         mode, the byte offset must point to the start  of  a  UTF-8  character.         In UTF-8 mode, the byte offset must point to the start of a UTF-8 char-
2075         Unlike  the  pattern string, the subject may contain binary zero bytes.         acter. Unlike the pattern string, the subject may contain  binary  zero
2076         When the starting offset is zero, the search for a match starts at  the         bytes.  When the starting offset is zero, the search for a match starts
2077         beginning of the subject, and this is by far the most common case.         at the beginning of the subject, and this is by  far  the  most  common
2078           case.
2079    
2080         A  non-zero  starting offset is useful when searching for another match         A  non-zero  starting offset is useful when searching for another match
2081         in the same subject by calling pcre_exec() again after a previous  suc-         in the same subject by calling pcre_exec() again after a previous  suc-
# Line 1613  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2111  MATCHING A PATTERN: THE TRADITIONAL FUNC
2111         string. PCRE supports several other kinds of  parenthesized  subpattern         string. PCRE supports several other kinds of  parenthesized  subpattern
2112         that do not cause substrings to be captured.         that do not cause substrings to be captured.
2113    
2114         Captured  substrings are returned to the caller via a vector of integer         Captured substrings are returned to the caller via a vector of integers
2115         offsets whose address is passed in ovector. The number of  elements  in         whose address is passed in ovector. The number of elements in the  vec-
2116         the  vector is passed in ovecsize, which must be a non-negative number.         tor  is  passed in ovecsize, which must be a non-negative number. Note:
2117         Note: this argument is NOT the size of ovector in bytes.         this argument is NOT the size of ovector in bytes.
2118    
2119         The first two-thirds of the vector is used to pass back  captured  sub-         The first two-thirds of the vector is used to pass back  captured  sub-
2120         strings,  each  substring using a pair of integers. The remaining third         strings,  each  substring using a pair of integers. The remaining third
2121         of the vector is used as workspace by pcre_exec() while  matching  cap-         of the vector is used as workspace by pcre_exec() while  matching  cap-
2122         turing  subpatterns, and is not available for passing back information.         turing  subpatterns, and is not available for passing back information.
2123         The length passed in ovecsize should always be a multiple of three.  If         The number passed in ovecsize should always be a multiple of three.  If
2124         it is not, it is rounded down.         it is not, it is rounded down.
2125    
2126         When  a  match  is successful, information about captured substrings is         When  a  match  is successful, information about captured substrings is
2127         returned in pairs of integers, starting at the  beginning  of  ovector,         returned in pairs of integers, starting at the  beginning  of  ovector,
2128         and  continuing  up  to two-thirds of its length at the most. The first         and  continuing  up  to two-thirds of its length at the most. The first
2129         element of a pair is set to the offset of the first character in a sub-         element of each pair is set to the byte offset of the  first  character
2130         string,  and  the  second  is  set to the offset of the first character         in  a  substring, and the second is set to the byte offset of the first
2131         after the end of a substring. The  first  pair,  ovector[0]  and  ovec-         character after the end of a substring. Note: these values  are  always
2132         tor[1],  identify  the  portion  of  the  subject string matched by the         byte offsets, even in UTF-8 mode. They are not character counts.
2133         entire pattern. The next pair is used for the first  capturing  subpat-  
2134         tern,  and  so  on.  The value returned by pcre_exec() is the number of         The  first  pair  of  integers, ovector[0] and ovector[1], identify the
2135         pairs that have been set. If there are no  capturing  subpatterns,  the         portion of the subject string matched by the entire pattern.  The  next
2136         return  value  from  a  successful match is 1, indicating that just the         pair  is  used for the first capturing subpattern, and so on. The value
2137         first pair of offsets has been set.         returned by pcre_exec() is one more than the highest numbered pair that
2138           has  been  set.  For example, if two substrings have been captured, the
2139         Some convenience functions are provided  for  extracting  the  captured         returned value is 3. If there are no capturing subpatterns, the  return
2140         substrings  as  separate  strings. These are described in the following         value from a successful match is 1, indicating that just the first pair
2141         section.         of offsets has been set.
   
        It is possible for an capturing subpattern number  n+1  to  match  some  
        part  of  the  subject  when subpattern n has not been used at all. For  
        example, if the string "abc" is matched against the pattern (a|(z))(bc)  
        subpatterns  1 and 3 are matched, but 2 is not. When this happens, both  
        offset values corresponding to the unused subpattern are set to -1.  
2142    
2143         If a capturing subpattern is matched repeatedly, it is the last portion         If a capturing subpattern is matched repeatedly, it is the last portion
2144         of the string that it matched that is returned.         of the string that it matched that is returned.
2145    
2146         If  the vector is too small to hold all the captured substring offsets,         If  the vector is too small to hold all the captured substring offsets,
2147         it is used as far as possible (up to two-thirds of its length), and the         it is used as far as possible (up to two-thirds of its length), and the
2148         function  returns a value of zero. In particular, if the substring off-         function  returns  a value of zero. If the substring offsets are not of
2149         sets are not of interest, pcre_exec() may be called with ovector passed         interest, pcre_exec() may be called with ovector  passed  as  NULL  and
2150         as  NULL  and  ovecsize  as zero. However, if the pattern contains back         ovecsize  as zero. However, if the pattern contains back references and
2151         references and the ovector is not big enough to  remember  the  related         the ovector is not big enough to remember the related substrings,  PCRE
2152         substrings,  PCRE has to get additional memory for use during matching.         has  to  get additional memory for use during matching. Thus it is usu-
2153         Thus it is usually advisable to supply an ovector.         ally advisable to supply an ovector.
2154    
2155         Note that pcre_info() can be used to find out how many  capturing  sub-         The pcre_info() function can be used to find  out  how  many  capturing
2156         patterns there are in a compiled pattern. The smallest size for ovector         subpatterns  there  are  in  a  compiled pattern. The smallest size for
2157         that will allow for n captured substrings, in addition to  the  offsets         ovector that will allow for n captured substrings, in addition  to  the
2158         of the substring matched by the whole pattern, is (n+1)*3.         offsets of the substring matched by the whole pattern, is (n+1)*3.
2159    
2160           It  is  possible for capturing subpattern number n+1 to match some part
2161           of the subject when subpattern n has not been used at all. For example,
2162           if  the  string  "abc"  is  matched against the pattern (a|(z))(bc) the
2163           return from the function is 4, and subpatterns 1 and 3 are matched, but
2164           2  is  not.  When  this happens, both values in the offset pairs corre-
2165           sponding to unused subpatterns are set to -1.
2166    
2167           Offset values that correspond to unused subpatterns at the end  of  the
2168           expression  are  also  set  to  -1. For example, if the string "abc" is
2169           matched against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are  not
2170           matched.  The  return  from the function is 2, because the highest used
2171           capturing subpattern number is 1. However, you can refer to the offsets
2172           for  the  second  and third capturing subpatterns if you wish (assuming
2173           the vector is large enough, of course).
2174    
2175     Return values from pcre_exec()         Some convenience functions are provided  for  extracting  the  captured
2176           substrings as separate strings. These are described below.
2177    
2178       Error return values from pcre_exec()
2179    
2180         If  pcre_exec()  fails, it returns a negative number. The following are         If  pcre_exec()  fails, it returns a negative number. The following are
2181         defined in the header file:         defined in the header file:
# Line 1691  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2201  MATCHING A PATTERN: THE TRADITIONAL FUNC
2201         an environment with the other endianness. This is the error  that  PCRE         an environment with the other endianness. This is the error  that  PCRE
2202         gives when the magic number is not present.         gives when the magic number is not present.
2203    
2204           PCRE_ERROR_UNKNOWN_NODE   (-5)           PCRE_ERROR_UNKNOWN_OPCODE (-5)
2205    
2206         While running the pattern match, an unknown item was encountered in the         While running the pattern match, an unknown item was encountered in the
2207         compiled pattern. This error could be caused by a bug  in  PCRE  or  by         compiled pattern. This error could be caused by a bug  in  PCRE  or  by
# Line 1713  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2223  MATCHING A PATTERN: THE TRADITIONAL FUNC
2223    
2224           PCRE_ERROR_MATCHLIMIT     (-8)           PCRE_ERROR_MATCHLIMIT     (-8)
2225    
2226         The  recursion  and backtracking limit, as specified by the match_limit         The  backtracking  limit,  as  specified  by the match_limit field in a
2227         field in a pcre_extra structure (or defaulted)  was  reached.  See  the         pcre_extra structure (or defaulted) was reached.  See  the  description
2228         description above.         above.
2229    
2230           PCRE_ERROR_CALLOUT        (-9)           PCRE_ERROR_CALLOUT        (-9)
2231    
# Line 1752  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2262  MATCHING A PATTERN: THE TRADITIONAL FUNC
2262    
2263           PCRE_ERROR_BADCOUNT       (-15)           PCRE_ERROR_BADCOUNT       (-15)
2264    
2265         This error is given if the value of the ovecsize argument is  negative.         This error is given if the value of the ovecsize argument is negative.
2266    
2267             PCRE_ERROR_RECURSIONLIMIT (-21)
2268    
2269           The internal recursion limit, as specified by the match_limit_recursion
2270           field  in  a  pcre_extra  structure (or defaulted) was reached. See the
2271           description above.
2272    
2273             PCRE_ERROR_BADNEWLINE     (-23)
2274    
2275           An invalid combination of PCRE_NEWLINE_xxx options was given.
2276    
2277           Error numbers -16 to -20 and -22 are not used by pcre_exec().
2278    
2279    
2280  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
# Line 1768  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2290  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2290         int pcre_get_substring_list(const char *subject,         int pcre_get_substring_list(const char *subject,
2291              int *ovector, int stringcount, const char ***listptr);              int *ovector, int stringcount, const char ***listptr);
2292    
2293         Captured  substrings  can  be  accessed  directly  by using the offsets         Captured substrings can be  accessed  directly  by  using  the  offsets
2294         returned by pcre_exec() in  ovector.  For  convenience,  the  functions         returned  by  pcre_exec()  in  ovector.  For convenience, the functions
2295         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-
2296         string_list() are provided for extracting captured substrings  as  new,         string_list()  are  provided for extracting captured substrings as new,
2297         separate,  zero-terminated strings. These functions identify substrings         separate, zero-terminated strings. These functions identify  substrings
2298         by number. The next section describes functions  for  extracting  named         by  number.  The  next section describes functions for extracting named
2299         substrings.  A  substring  that  contains  a  binary  zero is correctly         substrings.
2300         extracted and has a further zero added on the end, but  the  result  is  
2301         not, of course, a C string.         A substring that contains a binary zero is correctly extracted and  has
2302           a  further zero added on the end, but the result is not, of course, a C
2303           string.  However, you can process such a string  by  referring  to  the
2304           length  that  is  returned  by  pcre_copy_substring() and pcre_get_sub-
2305           string().  Unfortunately, the interface to pcre_get_substring_list() is
2306           not  adequate for handling strings containing binary zeros, because the
2307           end of the final string is not independently indicated.
2308    
2309         The  first  three  arguments  are the same for all three of these func-         The first three arguments are the same for all  three  of  these  func-
2310         tions: subject is the subject string that has  just  been  successfully         tions:  subject  is  the subject string that has just been successfully
2311         matched, ovector is a pointer to the vector of integer offsets that was         matched, ovector is a pointer to the vector of integer offsets that was
2312         passed to pcre_exec(), and stringcount is the number of substrings that         passed to pcre_exec(), and stringcount is the number of substrings that
2313         were  captured  by  the match, including the substring that matched the         were captured by the match, including the substring  that  matched  the
2314         entire regular expression. This is the value returned by pcre_exec() if         entire regular expression. This is the value returned by pcre_exec() if
2315         it  is greater than zero. If pcre_exec() returned zero, indicating that         it is greater than zero. If pcre_exec() returned zero, indicating  that
2316         it ran out of space in ovector, the value passed as stringcount  should         it  ran out of space in ovector, the value passed as stringcount should
2317         be the number of elements in the vector divided by three.         be the number of elements in the vector divided by three.
2318    
2319         The  functions pcre_copy_substring() and pcre_get_substring() extract a         The functions pcre_copy_substring() and pcre_get_substring() extract  a
2320         single substring, whose number is given as  stringnumber.  A  value  of         single  substring,  whose  number  is given as stringnumber. A value of
2321         zero  extracts  the  substring that matched the entire pattern, whereas         zero extracts the substring that matched the  entire  pattern,  whereas
2322         higher values  extract  the  captured  substrings.  For  pcre_copy_sub-         higher  values  extract  the  captured  substrings.  For pcre_copy_sub-
2323         string(),  the  string  is  placed  in buffer, whose length is given by         string(), the string is placed in buffer,  whose  length  is  given  by
2324         buffersize, while for pcre_get_substring() a new  block  of  memory  is         buffersize,  while  for  pcre_get_substring()  a new block of memory is
2325         obtained  via  pcre_malloc,  and its address is returned via stringptr.         obtained via pcre_malloc, and its address is  returned  via  stringptr.
2326         The yield of the function is the length of the  string,  not  including         The  yield  of  the function is the length of the string, not including
2327         the terminating zero, or one of         the terminating zero, or one of these error codes:
2328    
2329           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2330    
2331         The  buffer  was too small for pcre_copy_substring(), or the attempt to         The buffer was too small for pcre_copy_substring(), or the  attempt  to
2332         get memory failed for pcre_get_substring().         get memory failed for pcre_get_substring().
2333    
2334           PCRE_ERROR_NOSUBSTRING    (-7)           PCRE_ERROR_NOSUBSTRING    (-7)
2335    
2336         There is no substring whose number is stringnumber.         There is no substring whose number is stringnumber.
2337    
2338         The pcre_get_substring_list()  function  extracts  all  available  sub-         The  pcre_get_substring_list()  function  extracts  all  available sub-
2339         strings  and  builds  a list of pointers to them. All this is done in a         strings and builds a list of pointers to them. All this is  done  in  a
2340         single block of memory that is obtained via pcre_malloc. The address of         single block of memory that is obtained via pcre_malloc. The address of
2341         the  memory  block  is returned via listptr, which is also the start of         the memory block is returned via listptr, which is also  the  start  of
2342         the list of string pointers. The end of the list is marked  by  a  NULL         the  list  of  string pointers. The end of the list is marked by a NULL
2343         pointer. The yield of the function is zero if all went well, or         pointer. The yield of the function is zero if all  went  well,  or  the
2344           error code
2345    
2346           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2347    
# Line 1831  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2360  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2360         tively.  They  do  nothing  more  than  call the function pointed to by         tively.  They  do  nothing  more  than  call the function pointed to by
2361         pcre_free, which of course could be called directly from a  C  program.         pcre_free, which of course could be called directly from a  C  program.
2362         However,  PCRE is used in some situations where it is linked via a spe-         However,  PCRE is used in some situations where it is linked via a spe-
2363         cial  interface  to  another  programming  language  which  cannot  use         cial  interface  to  another  programming  language  that  cannot   use
2364         pcre_free  directly;  it is for these cases that the functions are pro-         pcre_free  directly;  it is for these cases that the functions are pro-
2365         vided.         vided.
2366    
# Line 1854  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2383  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2383         To extract a substring by name, you first have to find associated  num-         To extract a substring by name, you first have to find associated  num-
2384         ber.  For example, for this pattern         ber.  For example, for this pattern
2385    
2386           (a+)b(?P<xxx>\d+)...           (a+)b(?<xxx>\d+)...
2387    
2388         the number of the subpattern called "xxx" is 2. You can find the number         the number of the subpattern called "xxx" is 2. If the name is known to
2389         from the name by calling pcre_get_stringnumber(). The first argument is         be unique (PCRE_DUPNAMES was not set), you can find the number from the
2390         the  compiled  pattern,  and  the  second is the name. The yield of the         name by calling pcre_get_stringnumber(). The first argument is the com-
2391         function is the subpattern number, or  PCRE_ERROR_NOSUBSTRING  (-7)  if         piled pattern, and the second is the name. The yield of the function is
2392         there is no subpattern of that name.         the  subpattern  number,  or PCRE_ERROR_NOSUBSTRING (-7) if there is no
2393           subpattern of that name.
2394    
2395         Given the number, you can extract the substring directly, or use one of         Given the number, you can extract the substring directly, or use one of
2396         the functions described in the previous section. For convenience, there         the functions described in the previous section. For convenience, there
2397         are also two functions that do the whole job.         are also two functions that do the whole job.
2398    
2399         Most    of    the    arguments   of   pcre_copy_named_substring()   and         Most   of   the   arguments    of    pcre_copy_named_substring()    and
2400         pcre_get_named_substring() are the same  as  those  for  the  similarly         pcre_get_named_substring()  are  the  same  as  those for the similarly
2401         named  functions  that extract by number. As these are described in the         named functions that extract by number. As these are described  in  the
2402         previous section, they are not re-described here. There  are  just  two         previous  section,  they  are not re-described here. There are just two
2403         differences:         differences:
2404    
2405         First,  instead  of a substring number, a substring name is given. Sec-         First, instead of a substring number, a substring name is  given.  Sec-
2406         ond, there is an extra argument, given at the start, which is a pointer         ond, there is an extra argument, given at the start, which is a pointer
2407         to  the compiled pattern. This is needed in order to gain access to the         to the compiled pattern. This is needed in order to gain access to  the
2408         name-to-number translation table.         name-to-number translation table.
2409    
2410         These functions call pcre_get_stringnumber(), and if it succeeds,  they         These  functions call pcre_get_stringnumber(), and if it succeeds, they
2411         then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-         then call pcre_copy_substring() or pcre_get_substring(),  as  appropri-
2412         ate.         ate.  NOTE:  If PCRE_DUPNAMES is set and there are duplicate names, the
2413           behaviour may not be what you want (see the next section).
2414    
2415           Warning: If the pattern uses the "(?|" feature to set up multiple  sub-
2416           patterns  with  the  same  number,  you cannot use names to distinguish
2417           them, because names are not included in the compiled code. The matching
2418           process uses only numbers.
2419    
2420    
2421    DUPLICATE SUBPATTERN NAMES
2422    
2423           int pcre_get_stringtable_entries(const pcre *code,
2424                const char *name, char **first, char **last);
2425    
2426           When  a  pattern  is  compiled with the PCRE_DUPNAMES option, names for
2427           subpatterns are not required to  be  unique.  Normally,  patterns  with
2428           duplicate  names  are such that in any one match, only one of the named
2429           subpatterns participates. An example is shown in the pcrepattern  docu-
2430           mentation.
2431    
2432           When    duplicates   are   present,   pcre_copy_named_substring()   and
2433           pcre_get_named_substring() return the first substring corresponding  to
2434           the  given  name  that  is set. If none are set, PCRE_ERROR_NOSUBSTRING
2435           (-7) is returned; no  data  is  returned.  The  pcre_get_stringnumber()
2436           function  returns one of the numbers that are associated with the name,
2437           but it is not defined which it is.
2438    
2439           If you want to get full details of all captured substrings for a  given
2440           name,  you  must  use  the pcre_get_stringtable_entries() function. The
2441           first argument is the compiled pattern, and the second is the name. The
2442           third  and  fourth  are  pointers to variables which are updated by the
2443           function. After it has run, they point to the first and last entries in
2444           the  name-to-number  table  for  the  given  name.  The function itself
2445           returns the length of each entry,  or  PCRE_ERROR_NOSUBSTRING  (-7)  if
2446           there  are none. The format of the table is described above in the sec-
2447           tion entitled Information about a  pattern.   Given  all  the  relevant
2448           entries  for the name, you can extract each of their numbers, and hence
2449           the captured data, if any.
2450    
2451    
2452  FINDING ALL POSSIBLE MATCHES  FINDING ALL POSSIBLE MATCHES
# Line 1908  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2475  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2475              int *workspace, int wscount);              int *workspace, int wscount);
2476    
2477         The  function  pcre_dfa_exec()  is  called  to  match  a subject string         The  function  pcre_dfa_exec()  is  called  to  match  a subject string
2478         against a compiled pattern, using a "DFA" matching algorithm. This  has         against a compiled pattern, using a matching algorithm that  scans  the
2479         different  characteristics to the normal algorithm, and is not compati-         subject  string  just  once, and does not backtrack. This has different
2480         ble with Perl. Some of the features of PCRE patterns are not supported.         characteristics to the normal algorithm, and  is  not  compatible  with
2481         Nevertheless, there are times when this kind of matching can be useful.         Perl.  Some  of the features of PCRE patterns are not supported. Never-
2482         For a discussion of the two matching algorithms, see  the  pcrematching         theless, there are times when this kind of matching can be useful.  For
2483         documentation.         a discussion of the two matching algorithms, see the pcrematching docu-
2484           mentation.
2485    
2486         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
2487         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-
2488         ent  way,  and  this is described below. The other common arguments are         ent way, and this is described below. The other  common  arguments  are
2489         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
2490         repeated here.         repeated here.
2491    
2492         The  two  additional  arguments provide workspace for the function. The         The two additional arguments provide workspace for  the  function.  The
2493         workspace vector should contain at least 20 elements. It  is  used  for         workspace  vector  should  contain at least 20 elements. It is used for
2494         keeping  track  of  multiple  paths  through  the  pattern  tree.  More         keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2495         workspace will be needed for patterns and subjects where  there  are  a         workspace  will  be  needed for patterns and subjects where there are a
2496         lot of possible matches.         lot of potential matches.
2497    
2498         Here is an example of a simple call to pcre_exec():         Here is an example of a simple call to pcre_dfa_exec():
2499    
2500           int rc;           int rc;
2501           int ovector[10];           int ovector[10];
2502           int wspace[20];           int wspace[20];
2503           rc = pcre_exec(           rc = pcre_dfa_exec(
2504             re,             /* result of pcre_compile() */             re,             /* result of pcre_compile() */
2505             NULL,           /* we didn't study the pattern */             NULL,           /* we didn't study the pattern */
2506             "some string",  /* the subject string */             "some string",  /* the subject string */
# Line 1946  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2514  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2514    
2515     Option bits for pcre_dfa_exec()     Option bits for pcre_dfa_exec()
2516    
2517         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
2518         zero. The only bits that may be  set  are  PCRE_ANCHORED,  PCRE_NOTBOL,         zero.  The  only  bits  that  may  be  set are PCRE_ANCHORED, PCRE_NEW-
2519         PCRE_NOTEOL,     PCRE_NOTEMPTY,    PCRE_NO_UTF8_CHECK,    PCRE_PARTIAL,         LINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,  PCRE_NO_UTF8_CHECK,
2520         PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All  but  the  last  three  of         PCRE_PARTIAL, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last
2521         these  are  the  same  as  for pcre_exec(), so their description is not         three of these are the same as for pcre_exec(), so their description is
2522         repeated here.         not repeated here.
2523    
2524           PCRE_PARTIAL           PCRE_PARTIAL
2525    
2526         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
2527         details   are   slightly   different.  When  PCRE_PARTIAL  is  set  for         details  are  slightly  different.  When  PCRE_PARTIAL   is   set   for
2528         pcre_dfa_exec(), the return code PCRE_ERROR_NOMATCH is  converted  into         pcre_dfa_exec(),  the  return code PCRE_ERROR_NOMATCH is converted into
2529         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
2530         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-
2531         sibility.  The portion of the string that provided the partial match is         sibility. The portion of the string that provided the partial match  is
2532         set as the first matching string.         set as the first matching string.
2533    
2534           PCRE_DFA_SHORTEST           PCRE_DFA_SHORTEST
2535    
2536         Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to         Setting  the  PCRE_DFA_SHORTEST option causes the matching algorithm to
2537         stop  as  soon  as  it  has found one match. Because of the way the DFA         stop as soon as it has found one match. Because of the way the alterna-
2538         algorithm works, this is necessarily the shortest possible match at the         tive  algorithm  works, this is necessarily the shortest possible match
2539         first possible matching point in the subject string.         at the first possible matching point in the subject string.
2540    
2541           PCRE_DFA_RESTART           PCRE_DFA_RESTART
2542    
2543         When  pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option, and         When pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option,  and
2544         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-
2545         tional  subject  characters,  and have it continue with the same match.         tional subject characters, and have it continue with  the  same  match.
2546         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
2547         workspace  and wscount options must reference the same vector as before         workspace and wscount options must reference the same vector as  before
2548         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
2549         match.  There  is  more  discussion of this facility in the pcrepartial         match. There is more discussion of this  facility  in  the  pcrepartial
2550         documentation.         documentation.
2551    
2552     Successful returns from pcre_dfa_exec()     Successful returns from pcre_dfa_exec()
2553    
2554         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-
2555         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
2556         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
2557         matches  are all initial substrings of the longer matches. For example,         matches are all initial substrings of the longer matches. For  example,
2558         if the pattern         if the pattern
2559    
2560           <.*>           <.*>
# Line 2001  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2569  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2569           <something> <something else>           <something> <something else>
2570           <something> <something else> <something further>           <something> <something else> <something further>
2571    
2572         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,
2573         which  is  the  number of matched substrings. The substrings themselves         which is the number of matched substrings.  The  substrings  themselves
2574         are returned in ovector. Each string uses two elements;  the  first  is         are  returned  in  ovector. Each string uses two elements; the first is
2575         the  offset  to the start, and the second is the offset to the end. All         the offset to the start, and the second is the offset to  the  end.  In
2576         the strings have the same start offset. (Space could have been saved by         fact,  all  the  strings  have the same start offset. (Space could have
2577         giving  this only once, but it was decided to retain some compatibility         been saved by giving this only once, but it was decided to retain  some
2578         with the way pcre_exec() returns data, even though the meaning  of  the         compatibility  with  the  way pcre_exec() returns data, even though the
2579         strings is different.)         meaning of the strings is different.)
2580    
2581         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-
2582         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
2583         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
2584         filled with the longest matches.         filled with the longest matches.
2585    
2586     Error returns from pcre_dfa_exec()     Error returns from pcre_dfa_exec()
2587    
2588         The pcre_dfa_exec() function returns a negative number when  it  fails.         The  pcre_dfa_exec()  function returns a negative number when it fails.
2589         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
2590         described above.  There are in addition the following errors  that  are         described  above.   There are in addition the following errors that are
2591         specific to pcre_dfa_exec():         specific to pcre_dfa_exec():
2592    
2593           PCRE_ERROR_DFA_UITEM      (-16)           PCRE_ERROR_DFA_UITEM      (-16)
2594    
2595         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-
2596         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
2597         reference.         reference.
2598    
2599           PCRE_ERROR_DFA_UCOND      (-17)           PCRE_ERROR_DFA_UCOND      (-17)
2600    
2601         This  return is given if pcre_dfa_exec() encounters a condition item in         This return is given if pcre_dfa_exec()  encounters  a  condition  item
2602         a pattern that uses a back reference for the  condition.  This  is  not         that  uses  a back reference for the condition, or a test for recursion
2603         supported.         in a specific group. These are not supported.
2604    
2605           PCRE_ERROR_DFA_UMLIMIT    (-18)           PCRE_ERROR_DFA_UMLIMIT    (-18)
2606    
2607         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
2608         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
2609         (it is meaningless).         (it is meaningless).
2610    
2611           PCRE_ERROR_DFA_WSSIZE     (-19)           PCRE_ERROR_DFA_WSSIZE     (-19)
2612    
2613         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
2614         workspace vector.         workspace vector.
2615    
2616           PCRE_ERROR_DFA_RECURSE    (-20)           PCRE_ERROR_DFA_RECURSE    (-20)
2617    
2618         When a recursive subpattern is processed, the matching  function  calls         When  a  recursive subpattern is processed, the matching function calls
2619         itself  recursively,  using  private vectors for ovector and workspace.         itself recursively, using private vectors for  ovector  and  workspace.
2620         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
2621         should be extremely rare, as a vector of size 1000 is used.         should be extremely rare, as a vector of size 1000 is used.
2622    
2623  Last updated: 16 May 2005  
2624  Copyright (c) 1997-2005 University of Cambridge.  SEE ALSO
2625    
2626           pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3),  pcrepar-
2627           tial(3), pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
2628    
2629    
2630    AUTHOR
2631    
2632           Philip Hazel
2633           University Computing Service
2634           Cambridge CB2 3QH, England.
2635    
2636    
2637    REVISION
2638    
2639           Last updated: 11 April 2009
2640           Copyright (c) 1997-2009 University of Cambridge.
2641  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2642    
2643    
# Line 2080  PCRE CALLOUTS Line 2664  PCRE CALLOUTS
2664         default value is zero.  For  example,  this  pattern  has  two  callout         default value is zero.  For  example,  this  pattern  has  two  callout
2665         points:         points:
2666    
2667           (?C1)eabc(?C2)def           (?C1)abc(?C2)def
2668    
2669         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
2670         called, PCRE automatically  inserts  callouts,  all  with  number  255,         called, PCRE automatically  inserts  callouts,  all  with  number  255,
# Line 2104  PCRE CALLOUTS Line 2688  PCRE CALLOUTS
2688  MISSING CALLOUTS  MISSING CALLOUTS
2689    
2690         You  should  be  aware  that,  because of optimizations in the way PCRE         You  should  be  aware  that,  because of optimizations in the way PCRE
2691         matches patterns, callouts sometimes do not happen. For example, if the         matches patterns by default, callouts  sometimes  do  not  happen.  For
2692         pattern is         example, if the pattern is
2693    
2694           ab(?C4)cd           ab(?C4)cd
2695    
# Line 2114  MISSING CALLOUTS Line 2698  MISSING CALLOUTS
2698         ever  start,  and  the  callout is never reached. However, with "abyd",         ever  start,  and  the  callout is never reached. However, with "abyd",
2699         though the result is still no match, the callout is obeyed.         though the result is still no match, the callout is obeyed.
2700    
2701           You can disable these optimizations by passing the  PCRE_NO_START_OPTI-
2702           MIZE  option  to  pcre_exec()  or  pcre_dfa_exec(). This slows down the
2703           matching process, but does ensure that callouts  such  as  the  example
2704           above are obeyed.
2705    
2706    
2707  THE CALLOUT INTERFACE  THE CALLOUT INTERFACE
2708    
2709         During matching, when PCRE reaches a callout point, the external  func-         During  matching, when PCRE reaches a callout point, the external func-
2710         tion  defined by pcre_callout is called (if it is set). This applies to         tion defined by pcre_callout is called (if it is set). This applies  to
2711         both the pcre_exec() and the pcre_dfa_exec()  matching  functions.  The         both  the  pcre_exec()  and the pcre_dfa_exec() matching functions. The
2712         only  argument  to  the callout function is a pointer to a pcre_callout         only argument to the callout function is a pointer  to  a  pcre_callout
2713         block. This structure contains the following fields:         block. This structure contains the following fields:
2714    
2715           int          version;           int          version;
# Line 2136  THE CALLOUT INTERFACE Line 2725  THE CALLOUT INTERFACE
2725           int          pattern_position;           int          pattern_position;
2726           int          next_item_length;           int          next_item_length;
2727    
2728         The version field is an integer containing the version  number  of  the         The  version  field  is an integer containing the version number of the
2729         block  format. The initial version was 0; the current version is 1. The         block format. The initial version was 0; the current version is 1.  The
2730         version number will change again in future  if  additional  fields  are         version  number  will  change  again in future if additional fields are
2731         added, but the intention is never to remove any of the existing fields.         added, but the intention is never to remove any of the existing fields.
2732    
2733         The callout_number field contains the number of the  callout,  as  com-         The callout_number field contains the number of the  callout,  as  com-
# Line 2155  THE CALLOUT INTERFACE Line 2744  THE CALLOUT INTERFACE
2744         The subject and subject_length fields contain copies of the values that         The subject and subject_length fields contain copies of the values that
2745         were passed to pcre_exec().         were passed to pcre_exec().
2746    
2747         The start_match field contains the offset within the subject  at  which         The start_match field normally contains the offset within  the  subject
2748         the  current match attempt started. If the pattern is not anchored, the         at  which  the  current  match  attempt started. However, if the escape
2749         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
2750         pattern for different starting points in the subject.         modified  starting  point.  If the pattern is not anchored, the callout
2751           function may be called several times from the same point in the pattern
2752           for different starting points in the subject.
2753    
2754         The  current_position  field  contains the offset within the subject of         The  current_position  field  contains the offset within the subject of
2755         the current match pointer.         the current match pointer.
# Line 2211  RETURN VALUES Line 2802  RETURN VALUES
2802         reserved for use by callout functions; it will never be  used  by  PCRE         reserved for use by callout functions; it will never be  used  by  PCRE
2803         itself.         itself.
2804    
2805  Last updated: 28 February 2005  
2806  Copyright (c) 1997-2005 University of Cambridge.  AUTHOR
2807    
2808           Philip Hazel
2809           University Computing Service
2810           Cambridge CB2 3QH, England.
2811    
2812    
2813    REVISION
2814    
2815           Last updated: 15 March 2009
2816           Copyright (c) 1997-2009 University of Cambridge.
2817  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2818    
2819    
# Line 2226  NAME Line 2827  NAME
2827  DIFFERENCES BETWEEN PCRE AND PERL  DIFFERENCES BETWEEN PCRE AND PERL
2828    
2829         This  document describes the differences in the ways that PCRE and Perl         This  document describes the differences in the ways that PCRE and Perl
2830         handle regular expressions. The differences  described  here  are  with         handle regular expressions. The differences described here  are  mainly
2831         respect to Perl 5.8.         with  respect  to  Perl 5.8, though PCRE versions 7.0 and later contain
2832           some features that are expected to be in the forthcoming Perl 5.10.
2833         1.  PCRE does not have full UTF-8 support. Details of what it does have  
2834         are given in the section on UTF-8 support in the main pcre page.         1. PCRE has only a subset of Perl's UTF-8 and Unicode support.  Details
2835           of  what  it does have are given in the section on UTF-8 support in the
2836           main pcre page.
2837    
2838         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl
2839         permits  them,  but they do not mean what you might think. For example,         permits  them,  but they do not mean what you might think. For example,
# Line 2257  DIFFERENCES BETWEEN PCRE AND PERL Line 2860  DIFFERENCES BETWEEN PCRE AND PERL
2860         6. The Perl escape sequences \p, \P, and \X are supported only if  PCRE         6. The Perl escape sequences \p, \P, and \X are supported only if  PCRE
2861         is  built  with Unicode character property support. The properties that         is  built  with Unicode character property support. The properties that
2862         can be tested with \p and \P are limited to the general category  prop-         can be tested with \p and \P are limited to the general category  prop-
2863         erties such as Lu and Nd.         erties  such  as  Lu and Nd, script names such as Greek or Han, and the
2864           derived properties Any and L&.
2865    
2866         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
2867         ters in between are treated as literals.  This  is  slightly  different         ters  in  between  are  treated as literals. This is slightly different
2868         from  Perl  in  that  $  and  @ are also handled as literals inside the         from Perl in that $ and @ are  also  handled  as  literals  inside  the
2869         quotes. In Perl, they cause variable interpolation (but of course  PCRE         quotes.  In Perl, they cause variable interpolation (but of course PCRE
2870         does not have variables). Note the following examples:         does not have variables). Note the following examples:
2871    
2872             Pattern            PCRE matches      Perl matches             Pattern            PCRE matches      Perl matches
# Line 2272  DIFFERENCES BETWEEN PCRE AND PERL Line 2876  DIFFERENCES BETWEEN PCRE AND PERL
2876             \Qabc\$xyz\E       abc\$xyz          abc\$xyz             \Qabc\$xyz\E       abc\$xyz          abc\$xyz
2877             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz
2878    
2879         The  \Q...\E  sequence  is recognized both inside and outside character         The \Q...\E sequence is recognized both inside  and  outside  character
2880         classes.         classes.
2881    
2882         8. Fairly obviously, PCRE does not support the (?{code}) and (?p{code})         8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
2883         constructions.  However,  there is support for recursive patterns using         constructions. However, there is support for recursive  patterns.  This
2884         the non-Perl items (?R),  (?number),  and  (?P>name).  Also,  the  PCRE         is  not available in Perl 5.8, but will be in Perl 5.10. Also, the PCRE
2885         "callout"  feature allows an external function to be called during pat-         "callout" feature allows an external function to be called during  pat-
2886         tern matching. See the pcrecallout documentation for details.         tern matching. See the pcrecallout documentation for details.
2887    
2888         9. There are some differences that are concerned with the  settings  of         9.  Subpatterns  that  are  called  recursively or as "subroutines" are
2889         captured  strings  when  part  of  a  pattern is repeated. For example,         always treated as atomic groups in  PCRE.  This  is  like  Python,  but
2890         matching "aba" against the  pattern  /^(a(b)?)+$/  in  Perl  leaves  $2         unlike Perl.
2891    
2892           10.  There are some differences that are concerned with the settings of
2893           captured strings when part of  a  pattern  is  repeated.  For  example,
2894           matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2
2895         unset, but in PCRE it is set to "b".         unset, but in PCRE it is set to "b".
2896    
2897         10. PCRE provides some extensions to the Perl regular expression facil-         11.  PCRE  does  support  Perl  5.10's  backtracking  verbs  (*ACCEPT),
2898         ities:         (*FAIL),  (*F),  (*COMMIT), (*PRUNE), (*SKIP), and (*THEN), but only in
2899           the forms without an  argument.  PCRE  does  not  support  (*MARK).  If
2900           (*ACCEPT)  is within capturing parentheses, PCRE does not set that cap-
2901           ture group; this is different to Perl.
2902    
2903           12. PCRE provides some extensions to the Perl regular expression facil-
2904           ities.   Perl  5.10  will  include new features that are not in earlier
2905           versions, some of which (such as named parentheses) have been  in  PCRE
2906           for some time. This list is with respect to Perl 5.10:
2907    
2908         (a) Although lookbehind assertions must  match  fixed  length  strings,         (a)  Although  lookbehind  assertions  must match fixed length strings,
2909         each alternative branch of a lookbehind assertion can match a different         each alternative branch of a lookbehind assertion can match a different
2910         length of string. Perl requires them all to have the same length.         length of string. Perl requires them all to have the same length.
2911    
2912         (b) If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the  $         (b)  If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the $
2913         meta-character matches only at the very end of the string.         meta-character matches only at the very end of the string.
2914    
2915         (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-
2916         cial meaning is faulted.         cial meaning is faulted. Otherwise, like Perl, the backslash is quietly
2917           ignored.  (Perl can be made to issue a warning.)
2918    
2919         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-
2920         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 2309  DIFFERENCES BETWEEN PCRE AND PERL Line 2926  DIFFERENCES BETWEEN PCRE AND PERL
2926         (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-
2927         TURE options for pcre_exec() have no Perl equivalents.         TURE options for pcre_exec() have no Perl equivalents.
2928    
2929         (g) The (?R), (?number), and (?P>name) constructs allows for  recursive         (g) The \R escape sequence can be restricted to match only CR,  LF,  or
2930         pattern  matching  (Perl  can  do  this using the (?p{code}) construct,         CRLF by the PCRE_BSR_ANYCRLF option.
        which PCRE cannot support.)  
2931    
2932         (h) PCRE supports named capturing substrings, using the Python  syntax.         (h) The callout facility is PCRE-specific.
2933    
2934         (i)  PCRE  supports  the  possessive quantifier "++" syntax, taken from         (i) The partial matching facility is PCRE-specific.
        Sun's Java package.  
2935    
2936         (j) The (R) condition, for testing recursion, is a PCRE extension.         (j) Patterns compiled by PCRE can be saved and re-used at a later time,
2937           even on different hosts that have the other endianness.
2938    
2939         (k) The callout facility is PCRE-specific.         (k) The alternative matching function (pcre_dfa_exec())  matches  in  a
2940           different way and is not Perl-compatible.
2941    
2942         (l) The partial matching facility is PCRE-specific.         (l)  PCRE  recognizes some special sequences such as (*CR) at the start
2943           of a pattern that set overall options that cannot be changed within the
2944           pattern.
2945    
        (m) Patterns compiled by PCRE can be saved and re-used at a later time,  
        even on different hosts that have the other endianness.  
2946    
2947         (n)  The  alternative  matching function (pcre_dfa_exec()) matches in a  AUTHOR
2948         different way and is not Perl-compatible.  
2949           Philip Hazel
2950           University Computing Service
2951           Cambridge CB2 3QH, England.
2952    
2953  Last updated: 28 February 2005  
2954  Copyright (c) 1997-2005 University of Cambridge.  REVISION
2955    
2956           Last updated: 11 September 2007
2957           Copyright (c) 1997-2007 University of Cambridge.
2958  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2959    
2960    
# Line 2344  NAME Line 2967  NAME
2967    
2968  PCRE REGULAR EXPRESSION DETAILS  PCRE REGULAR EXPRESSION DETAILS
2969    
2970         The  syntax  and semantics of the regular expressions supported by PCRE         The  syntax and semantics of the regular expressions that are supported
2971         are described below. Regular expressions are also described in the Perl         by PCRE are described in detail below. There is a quick-reference  syn-
2972         documentation  and  in  a  number  of books, some of which have copious         tax summary in the pcresyntax page. PCRE tries to match Perl syntax and
2973         examples.  Jeffrey Friedl's "Mastering Regular Expressions",  published         semantics as closely as it can. PCRE  also  supports  some  alternative
2974         by  O'Reilly, covers regular expressions in great detail. This descrip-         regular  expression  syntax (which does not conflict with the Perl syn-
2975         tion of PCRE's regular expressions is intended as reference material.         tax) in order to provide some compatibility with regular expressions in
2976           Python, .NET, and Oniguruma.
2977    
2978           Perl's  regular expressions are described in its own documentation, and
2979           regular expressions in general are covered in a number of  books,  some
2980           of  which  have  copious  examples. Jeffrey Friedl's "Mastering Regular
2981           Expressions", published by  O'Reilly,  covers  regular  expressions  in
2982           great  detail.  This  description  of  PCRE's  regular  expressions  is
2983           intended as reference material.
2984    
2985         The original operation of PCRE was on strings of  one-byte  characters.         The original operation of PCRE was on strings of  one-byte  characters.
2986         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
2987         this, you must build PCRE to  include  UTF-8  support,  and  then  call         this, you must build PCRE to  include  UTF-8  support,  and  then  call
2988         pcre_compile()  with  the  PCRE_UTF8  option.  How this affects pattern         pcre_compile()  with  the  PCRE_UTF8  option.  There  is also a special
2989         matching is mentioned in several places below. There is also a  summary         sequence that can be given at the start of a pattern:
2990         of  UTF-8  features  in  the  section on UTF-8 support in the main pcre  
2991         page.           (*UTF8)
2992    
2993           Starting a pattern with this sequence  is  equivalent  to  setting  the
2994           PCRE_UTF8  option.  This  feature  is  not Perl-compatible. How setting
2995           UTF-8 mode affects pattern matching  is  mentioned  in  several  places
2996           below.  There  is  also  a  summary of UTF-8 features in the section on
2997           UTF-8 support in the main pcre page.
2998    
2999         The remainder of this document discusses the  patterns  that  are  sup-         The remainder of this document discusses the  patterns  that  are  sup-
3000         ported  by  PCRE when its main matching function, pcre_exec(), is used.         ported  by  PCRE when its main matching function, pcre_exec(), is used.
3001         From  release  6.0,   PCRE   offers   a   second   matching   function,         From  release  6.0,   PCRE   offers   a   second   matching   function,
3002         pcre_dfa_exec(),  which matches using a different algorithm that is not         pcre_dfa_exec(),  which matches using a different algorithm that is not
3003         Perl-compatible. The advantages and disadvantages  of  the  alternative         Perl-compatible. Some of the features discussed below are not available
3004         function, and how it differs from the normal function, are discussed in         when  pcre_dfa_exec()  is used. The advantages and disadvantages of the
3005         the pcrematching page.         alternative function, and how it differs from the normal function,  are
3006           discussed in the pcrematching page.
3007         A regular expression is a pattern that is  matched  against  a  subject  
3008         string  from  left  to right. Most characters stand for themselves in a  
3009         pattern, and match the corresponding characters in the  subject.  As  a  NEWLINE CONVENTIONS
3010    
3011           PCRE  supports five different conventions for indicating line breaks in
3012           strings: a single CR (carriage return) character, a  single  LF  (line-
3013           feed) character, the two-character sequence CRLF, any of the three pre-
3014           ceding, or any Unicode newline sequence. The pcreapi page  has  further
3015           discussion  about newlines, and shows how to set the newline convention
3016           in the options arguments for the compiling and matching functions.
3017    
3018           It is also possible to specify a newline convention by starting a  pat-
3019           tern string with one of the following five sequences:
3020    
3021             (*CR)        carriage return
3022             (*LF)        linefeed
3023             (*CRLF)      carriage return, followed by linefeed
3024             (*ANYCRLF)   any of the three above
3025             (*ANY)       all Unicode newline sequences
3026    
3027           These override the default and the options given to pcre_compile(). For
3028           example, on a Unix system where LF is the default newline sequence, the
3029           pattern
3030    
3031             (*CR)a.b
3032    
3033           changes the convention to CR. That pattern matches "a\nb" because LF is
3034           no longer a newline. Note that these special settings,  which  are  not
3035           Perl-compatible,  are  recognized  only at the very start of a pattern,
3036           and that they must be in upper case.  If  more  than  one  of  them  is
3037           present, the last one is used.
3038    
3039           The  newline  convention  does  not  affect what the \R escape sequence
3040           matches. By default, this is any Unicode  newline  sequence,  for  Perl
3041           compatibility.  However, this can be changed; see the description of \R
3042           in the section entitled "Newline sequences" below. A change of \R  set-
3043           ting can be combined with a change of newline convention.
3044    
3045    
3046    CHARACTERS AND METACHARACTERS
3047    
3048           A  regular  expression  is  a pattern that is matched against a subject
3049           string from left to right. Most characters stand for  themselves  in  a
3050           pattern,  and  match  the corresponding characters in the subject. As a
3051         trivial example, the pattern         trivial example, the pattern
3052    
3053           The quick brown fox           The quick brown fox
3054    
3055         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
3056         caseless matching is specified (the PCRE_CASELESS option), letters  are         caseless  matching is specified (the PCRE_CASELESS option), letters are
3057         matched  independently  of case. In UTF-8 mode, PCRE always understands         matched independently of case. In UTF-8 mode, PCRE  always  understands
3058         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
3059         caseless  matching  is always possible. For characters with higher val-         caseless matching is always possible. For characters with  higher  val-
3060         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
3061         property  support,  but  not  otherwise.   If  you want to use caseless         property support, but not otherwise.   If  you  want  to  use  caseless
3062         matching for characters 128 and above, you must  ensure  that  PCRE  is         matching  for  characters  128  and above, you must ensure that PCRE is
3063         compiled with Unicode property support as well as with UTF-8 support.         compiled with Unicode property support as well as with UTF-8 support.
3064    
3065         The  power  of  regular  expressions  comes from the ability to include         The power of regular expressions comes  from  the  ability  to  include
3066         alternatives and repetitions in the pattern. These are encoded  in  the         alternatives  and  repetitions in the pattern. These are encoded in the
3067         pattern by the use of metacharacters, which do not stand for themselves         pattern by the use of metacharacters, which do not stand for themselves
3068         but instead are interpreted in some special way.         but instead are interpreted in some special way.
3069    
3070         There are two different sets of metacharacters: those that  are  recog-         There  are  two different sets of metacharacters: those that are recog-
3071         nized  anywhere in the pattern except within square brackets, and those         nized anywhere in the pattern except within square brackets, and  those
3072         that are recognized in square brackets. Outside  square  brackets,  the         that  are  recognized  within square brackets. Outside square brackets,
3073         metacharacters are as follows:         the metacharacters are as follows:
3074    
3075           \      general escape character with several uses           \      general escape character with several uses
3076           ^      assert start of string (or line, in multiline mode)           ^      assert start of string (or line, in multiline mode)
# Line 2410  PCRE REGULAR EXPRESSION DETAILS Line 3088  PCRE REGULAR EXPRESSION DETAILS
3088                  also "possessive quantifier"                  also "possessive quantifier"
3089           {      start min/max quantifier           {      start min/max quantifier
3090    
3091         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
3092         class". In a character class the only metacharacters are:         class". In a character class the only metacharacters are:
3093    
3094           \      general escape character           \      general escape character
# Line 2420  PCRE REGULAR EXPRESSION DETAILS Line 3098  PCRE REGULAR EXPRESSION DETAILS
3098                    syntax)                    syntax)
3099           ]      terminates the character class           ]      terminates the character class
3100    
3101         The following sections describe the use of each of the  metacharacters.         The following sections describe the use of each of the metacharacters.
3102    
3103    
3104  BACKSLASH  BACKSLASH
# Line 2439  BACKSLASH Line 3117  BACKSLASH
3117    
3118         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in
3119         the pattern (other than in a character class) and characters between  a         the pattern (other than in a character class) and characters between  a
3120         # outside a character class and the next newline character are ignored.         # outside a character class and the next newline are ignored. An escap-
3121         An escaping backslash can be used to include a whitespace or #  charac-         ing backslash can be used to include a whitespace  or  #  character  as
3122         ter as part of the pattern.         part of the pattern.
3123    
3124         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-
3125         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-
# Line 2472  BACKSLASH Line 3150  BACKSLASH
3150           \cx       "control-x", where x is any character           \cx       "control-x", where x is any character
3151           \e        escape (hex 1B)           \e        escape (hex 1B)
3152           \f        formfeed (hex 0C)           \f        formfeed (hex 0C)
3153           \n        newline (hex 0A)           \n        linefeed (hex 0A)
3154           \r        carriage return (hex 0D)           \r        carriage return (hex 0D)
3155           \t        tab (hex 09)           \t        tab (hex 09)
3156           \ddd      character with octal code ddd, or backreference           \ddd      character with octal code ddd, or backreference
3157           \xhh      character with hex code hh           \xhh      character with hex code hh
3158           \x{hhh..} character with hex code hhh... (UTF-8 mode only)           \x{hhh..} character with hex code hhh..
3159    
3160         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,
3161         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
# Line 2485  BACKSLASH Line 3163  BACKSLASH
3163         becomes hex 7B.         becomes hex 7B.
3164    
3165         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
3166         in  upper or lower case). In UTF-8 mode, any number of hexadecimal dig-         in  upper  or  lower case). Any number of hexadecimal digits may appear
3167         its may appear between \x{ and }, but the value of the  character  code         between \x{ and }, but the value of the character  code  must  be  less
3168         must  be  less  than  2**31  (that is, the maximum hexadecimal value is         than 256 in non-UTF-8 mode, and less than 2**31 in UTF-8 mode. That is,
3169         7FFFFFFF). If characters other than hexadecimal digits  appear  between         the maximum value in hexadecimal is 7FFFFFFF. Note that this is  bigger
3170         \x{  and }, or if there is no terminating }, this form of escape is not         than the largest Unicode code point, which is 10FFFF.
3171         recognized. Instead, the initial \x will  be  interpreted  as  a  basic  
3172         hexadecimal  escape, with no following digits, giving a character whose         If  characters  other than hexadecimal digits appear between \x{ and },
3173         value is zero.         or if there is no terminating }, this form of escape is not recognized.
3174           Instead,  the  initial  \x  will  be interpreted as a basic hexadecimal
3175           escape, with no following digits, giving a  character  whose  value  is
3176           zero.
3177    
3178         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
3179         two  syntaxes for \x when PCRE is in UTF-8 mode. There is no difference         two syntaxes for \x. There is no difference in the way  they  are  han-
3180         in the way they are handled. For example, \xdc is exactly the  same  as         dled. For example, \xdc is exactly the same as \x{dc}.
3181         \x{dc}.  
3182           After  \0  up  to two further octal digits are read. If there are fewer
3183         After  \0  up  to  two further octal digits are read. In both cases, if         than two digits, just  those  that  are  present  are  used.  Thus  the
3184         there are fewer than two digits, just those that are present are  used.         sequence \0\x\07 specifies two binary zeros followed by a BEL character
3185         Thus  the sequence \0\x\07 specifies two binary zeros followed by a BEL         (code value 7). Make sure you supply two digits after the initial  zero
3186         character (code value 7). Make sure you supply  two  digits  after  the         if the pattern character that follows is itself an octal digit.
        initial  zero  if the pattern character that follows is itself an octal  
        digit.  
3187    
3188         The handling of a backslash followed by a digit other than 0 is compli-         The handling of a backslash followed by a digit other than 0 is compli-
3189         cated.  Outside a character class, PCRE reads it and any following dig-         cated.  Outside a character class, PCRE reads it and any following dig-
3190         its as a decimal number. If the number is less than  10,  or  if  there         its  as  a  decimal  number. If the number is less than 10, or if there
3191         have been at least that many previous capturing left parentheses in the         have been at least that many previous capturing left parentheses in the
3192         expression, the entire  sequence  is  taken  as  a  back  reference.  A         expression,  the  entire  sequence  is  taken  as  a  back reference. A
3193         description  of how this works is given later, following the discussion         description of how this works is given later, following the  discussion
3194         of parenthesized subpatterns.         of parenthesized subpatterns.
3195    
3196         Inside a character class, or if the decimal number is  greater  than  9         Inside  a  character  class, or if the decimal number is greater than 9
3197         and  there have not been that many capturing subpatterns, PCRE re-reads         and there have not been that many capturing subpatterns, PCRE  re-reads
3198         up to three octal digits following the backslash, and generates a  sin-         up to three octal digits following the backslash, and uses them to gen-
3199         gle byte from the least significant 8 bits of the value. Any subsequent         erate a data character. Any subsequent digits stand for themselves.  In
3200         digits stand for themselves.  For example:         non-UTF-8  mode,  the  value  of a character specified in octal must be
3201           less than \400. In UTF-8 mode, values up to  \777  are  permitted.  For
3202           example:
3203    
3204           \040   is another way of writing a space           \040   is another way of writing a space
3205           \40    is the same, provided there are fewer than 40           \40    is the same, provided there are fewer than 40
# Line 2535  BACKSLASH Line 3216  BACKSLASH
3216           \81    is either a back reference, or a binary zero           \81    is either a back reference, or a binary zero
3217                     followed by the two characters "8" and "1"                     followed by the two characters "8" and "1"
3218    
3219         Note that octal values of 100 or greater must not be  introduced  by  a         Note  that  octal  values of 100 or greater must not be introduced by a
3220         leading zero, because no more than three octal digits are ever read.         leading zero, because no more than three octal digits are ever read.
3221    
3222         All  the  sequences  that  define a single byte value or a single UTF-8         All the sequences that define a single character value can be used both
3223         character (in UTF-8 mode) can be used both inside and outside character         inside  and  outside character classes. In addition, inside a character
3224         classes.  In  addition,  inside  a  character class, the sequence \b is         class, the sequence \b is interpreted as the backspace  character  (hex
3225         interpreted as the backspace character (hex 08), and the sequence \X is         08),  and the sequences \R and \X are interpreted as the characters "R"
3226         interpreted  as  the  character  "X".  Outside a character class, these         and "X", respectively. Outside a character class, these sequences  have
3227         sequences have different meanings (see below).         different meanings (see below).
3228    
3229       Absolute and relative back references
3230    
3231           The  sequence  \g followed by an unsigned or a negative number, option-
3232           ally enclosed in braces, is an absolute or relative back  reference.  A
3233           named back reference can be coded as \g{name}. Back references are dis-
3234           cussed later, following the discussion of parenthesized subpatterns.
3235    
3236       Absolute and relative subroutine calls
3237    
3238           For compatibility with Oniguruma, the non-Perl syntax \g followed by  a
3239           name or a number enclosed either in angle brackets or single quotes, is
3240           an alternative syntax for referencing a subpattern as  a  "subroutine".
3241           Details  are  discussed  later.   Note  that  \g{...} (Perl syntax) and
3242           \g<...> (Oniguruma syntax) are not synonymous. The  former  is  a  back
3243           reference; the latter is a subroutine call.
3244    
3245     Generic character types     Generic character types
3246    
3247         The third use of backslash is for specifying generic  character  types.         Another use of backslash is for specifying generic character types. The
3248         The following are always recognized:         following are always recognized:
3249    
3250           \d     any decimal digit           \d     any decimal digit
3251           \D     any character that is not a decimal digit           \D     any character that is not a decimal digit
3252             \h     any horizontal whitespace character
3253             \H     any character that is not a horizontal whitespace character
3254           \s     any whitespace character           \s     any whitespace character
3255           \S     any character that is not a whitespace character           \S     any character that is not a whitespace character
3256             \v     any vertical whitespace character
3257             \V     any character that is not a vertical whitespace character
3258           \w     any "word" character           \w     any "word" character
3259           \W     any "non-word" character           \W     any "non-word" character
3260    
3261         Each pair of escape sequences partitions the complete set of characters         Each pair of escape sequences partitions the complete set of characters
3262         into two disjoint sets. Any given character matches one, and only  one,         into  two disjoint sets. Any given character matches one, and only one,
3263         of each pair.         of each pair.
3264    
3265         These character type sequences can appear both inside and outside char-         These character type sequences can appear both inside and outside char-
3266         acter classes. They each match one character of the  appropriate  type.         acter  classes.  They each match one character of the appropriate type.
3267         If  the current matching point is at the end of the subject string, all         If the current matching point is at the end of the subject string,  all
3268         of them fail, since there is no character to match.         of them fail, since there is no character to match.
3269    
3270         For compatibility with Perl, \s does not match the VT  character  (code         For  compatibility  with Perl, \s does not match the VT character (code
3271         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
3272         characters are HT (9), LF (10), FF (12), CR (13), and space (32).         characters  are  HT  (9), LF (10), FF (12), CR (13), and space (32). If
3273           "use locale;" is included in a Perl script, \s may match the VT charac-
3274           ter. In PCRE, it never does.
3275    
3276           In  UTF-8 mode, characters with values greater than 128 never match \d,
3277           \s, or \w, and always match \D, \S, and \W. This is true even when Uni-
3278           code  character  property  support is available. These sequences retain
3279           their original meanings from before UTF-8 support was available, mainly
3280           for  efficiency  reasons. Note that this also affects \b, because it is
3281           defined in terms of \w and \W.
3282    
3283           The sequences \h, \H, \v, and \V are Perl 5.10 features. In contrast to
3284           the  other  sequences, these do match certain high-valued codepoints in
3285           UTF-8 mode.  The horizontal space characters are:
3286    
3287             U+0009     Horizontal tab
3288             U+0020     Space
3289             U+00A0     Non-break space
3290             U+1680     Ogham space mark
3291             U+180E     Mongolian vowel separator
3292             U+2000     En quad
3293             U+2001     Em quad
3294             U+2002     En space
3295             U+2003     Em space
3296             U+2004     Three-per-em space
3297             U+2005     Four-per-em space
3298             U+2006     Six-per-em space
3299             U+2007     Figure space
3300             U+2008     Punctuation space
3301             U+2009     Thin space
3302             U+200A     Hair space
3303             U+202F     Narrow no-break space
3304             U+205F     Medium mathematical space
3305             U+3000     Ideographic space
3306    
3307           The vertical space characters are:
3308    
3309             U+000A     Linefeed
3310             U+000B     Vertical tab
3311             U+000C     Formfeed
3312             U+000D     Carriage return
3313             U+0085     Next line
3314             U+2028     Line separator
3315             U+2029     Paragraph separator
3316    
3317         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
3318         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-
3319         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-
3320         specific  matching is taking place (see "Locale support" in the pcreapi         specific  matching is taking place (see "Locale support" in the pcreapi
3321         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
3322         codes  greater  than  128  are used for accented letters, and these are         systems,  or "french" in Windows, some character codes greater than 128
3323         matched by \w.         are used for accented letters, and these are matched by \w. The use  of
3324           locales with Unicode is discouraged.
3325    
3326       Newline sequences
3327    
3328           Outside  a  character class, by default, the escape sequence \R matches
3329           any Unicode newline sequence. This is a Perl 5.10 feature. In non-UTF-8
3330           mode \R is equivalent to the following:
3331    
3332             (?>\r\n|\n|\x0b|\f|\r|\x85)
3333    
3334           This  is  an  example  of an "atomic group", details of which are given
3335           below.  This particular group matches either the two-character sequence
3336           CR  followed  by  LF,  or  one  of  the single characters LF (linefeed,
3337           U+000A), VT (vertical tab, U+000B), FF (formfeed, U+000C), CR (carriage
3338           return, U+000D), or NEL (next line, U+0085). The two-character sequence
3339           is treated as a single unit that cannot be split.
3340    
3341           In UTF-8 mode, two additional characters whose codepoints  are  greater
3342           than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa-
3343           rator, U+2029).  Unicode character property support is not  needed  for
3344           these characters to be recognized.
3345    
3346           It is possible to restrict \R to match only CR, LF, or CRLF (instead of
3347           the complete set  of  Unicode  line  endings)  by  setting  the  option
3348           PCRE_BSR_ANYCRLF either at compile time or when the pattern is matched.
3349           (BSR is an abbrevation for "backslash R".) This can be made the default
3350           when  PCRE  is  built;  if this is the case, the other behaviour can be
3351           requested via the PCRE_BSR_UNICODE option.   It  is  also  possible  to
3352           specify  these  settings  by  starting a pattern string with one of the
3353           following sequences:
3354    
3355             (*BSR_ANYCRLF)   CR, LF, or CRLF only
3356             (*BSR_UNICODE)   any Unicode newline sequence
3357    
3358           These override the default and the options given to pcre_compile(), but
3359           they can be overridden by options given to pcre_exec(). Note that these
3360           special settings, which are not Perl-compatible, are recognized only at
3361           the  very  start  of a pattern, and that they must be in upper case. If
3362           more than one of them is present, the last one is  used.  They  can  be
3363           combined  with  a  change of newline convention, for example, a pattern
3364           can start with:
3365    
3366         In UTF-8 mode, characters with values greater than 128 never match  \d,           (*ANY)(*BSR_ANYCRLF)
3367         \s, or \w, and always match \D, \S, and \W. This is true even when Uni-  
3368         code character property support is available.         Inside a character class, \R matches the letter "R".
3369    
3370     Unicode character properties     Unicode character properties
3371    
3372         When PCRE is built with Unicode character property support, three addi-         When PCRE is built with Unicode character property support, three addi-
3373         tional  escape sequences to match generic character types are available         tional  escape sequences that match characters with specific properties
3374         when UTF-8 mode is selected. They are:         are available.  When not in UTF-8 mode, these sequences are  of  course
3375           limited  to  testing characters whose codepoints are less than 256, but
3376          \p{xx}   a character with the xx property         they do work in this mode.  The extra escape sequences are:
3377          \P{xx}   a character without the xx property  
3378          \X       an extended Unicode sequence           \p{xx}   a character with the xx property
3379             \P{xx}   a character without the xx property
3380             \X       an extended Unicode sequence
3381    
3382         The property names represented by xx above are limited to  the  Unicode         The property names represented by xx above are limited to  the  Unicode
3383         general  category properties. Each character has exactly one such prop-         script names, the general category properties, and "Any", which matches
3384         erty, specified by a two-letter abbreviation.  For  compatibility  with         any character (including newline). Other properties such as "InMusical-
3385         Perl,  negation  can be specified by including a circumflex between the         Symbols"  are  not  currently supported by PCRE. Note that \P{Any} does
3386         opening brace and the property name. For example, \p{^Lu} is  the  same         not match any characters, so always causes a match failure.
3387         as \P{Lu}.  
3388           Sets of Unicode characters are defined as belonging to certain scripts.
3389         If  only  one  letter  is  specified with \p or \P, it includes all the         A  character from one of these sets can be matched using a script name.
3390         properties that start with that letter. In this case, in the absence of         For example:
3391         negation, the curly brackets in the escape sequence are optional; these  
3392         two examples have the same effect:           \p{Greek}
3393             \P{Han}
3394    
3395           Those that are not part of an identified script are lumped together  as
3396           "Common". The current list of scripts is:
3397    
3398           Arabic,  Armenian,  Balinese,  Bengali,  Bopomofo,  Braille,  Buginese,
3399           Buhid,  Canadian_Aboriginal,  Cherokee,  Common,   Coptic,   Cuneiform,
3400           Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,
3401           Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew,  Hira-
3402           gana,  Inherited,  Kannada,  Katakana,  Kharoshthi,  Khmer, Lao, Latin,
3403           Limbu,  Linear_B,  Malayalam,  Mongolian,  Myanmar,  New_Tai_Lue,  Nko,
3404           Ogham,  Old_Italic,  Old_Persian, Oriya, Osmanya, Phags_Pa, Phoenician,
3405           Runic,  Shavian,  Sinhala,  Syloti_Nagri,  Syriac,  Tagalog,  Tagbanwa,
3406           Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.
3407    
3408           Each  character has exactly one general category property, specified by
3409           a two-letter abbreviation. For compatibility with Perl, negation can be
3410           specified  by  including a circumflex between the opening brace and the
3411           property name. For example, \p{^Lu} is the same as \P{Lu}.
3412    
3413           If only one letter is specified with \p or \P, it includes all the gen-
3414           eral  category properties that start with that letter. In this case, in
3415           the absence of negation, the curly brackets in the escape sequence  are
3416           optional; these two examples have the same effect:
3417    
3418           \p{L}           \p{L}
3419           \pL           \pL
3420    
3421         The following property codes are supported:         The following general category property codes are supported:
3422    
3423           C     Other           C     Other
3424           Cc    Control           Cc    Control
# Line 2653  BACKSLASH Line 3464  BACKSLASH
3464           Zp    Paragraph separator           Zp    Paragraph separator
3465           Zs    Space separator           Zs    Space separator
3466    
3467         Extended properties such as "Greek" or "InMusicalSymbols" are not  sup-         The  special property L& is also supported: it matches a character that
3468         ported by PCRE.         has the Lu, Ll, or Lt property, in other words, a letter  that  is  not
3469           classified as a modifier or "other".
3470    
3471           The  Cs  (Surrogate)  property  applies only to characters in the range
3472           U+D800 to U+DFFF. Such characters are not valid in UTF-8  strings  (see
3473           RFC 3629) and so cannot be tested by PCRE, unless UTF-8 validity check-
3474           ing has been turned off (see the discussion  of  PCRE_NO_UTF8_CHECK  in
3475           the pcreapi page).
3476    
3477           The  long  synonyms  for  these  properties that Perl supports (such as
3478           \p{Letter}) are not supported by PCRE, nor is it  permitted  to  prefix
3479           any of these properties with "Is".
3480    
3481           No character that is in the Unicode table has the Cn (unassigned) prop-
3482           erty.  Instead, this property is assumed for any code point that is not
3483           in the Unicode table.
3484    
3485         Specifying  caseless  matching  does not affect these escape sequences.         Specifying  caseless  matching  does not affect these escape sequences.
3486         For example, \p{Lu} always matches only upper case letters.         For example, \p{Lu} always matches only upper case letters.
# Line 2667  BACKSLASH Line 3493  BACKSLASH
3493         That  is,  it matches a character without the "mark" property, followed         That  is,  it matches a character without the "mark" property, followed
3494         by zero or more characters with the "mark"  property,  and  treats  the         by zero or more characters with the "mark"  property,  and  treats  the
3495         sequence  as  an  atomic group (see below).  Characters with the "mark"         sequence  as  an  atomic group (see below).  Characters with the "mark"
3496         property are typically accents that affect the preceding character.         property are typically accents that  affect  the  preceding  character.
3497           None  of  them  have  codepoints less than 256, so in non-UTF-8 mode \X
3498           matches any one character.
3499    
3500         Matching characters by Unicode property is not fast, because  PCRE  has         Matching characters by Unicode property is not fast, because  PCRE  has
3501         to  search  a  structure  that  contains data for over fifteen thousand         to  search  a  structure  that  contains data for over fifteen thousand
3502         characters. That is why the traditional escape sequences such as \d and         characters. That is why the traditional escape sequences such as \d and
3503         \w do not use Unicode properties in PCRE.         \w do not use Unicode properties in PCRE.
3504    
3505       Resetting the match start
3506    
3507           The escape sequence \K, which is a Perl 5.10 feature, causes any previ-
3508           ously matched characters not  to  be  included  in  the  final  matched
3509           sequence. For example, the pattern:
3510    
3511             foo\Kbar
3512    
3513           matches  "foobar",  but reports that it has matched "bar". This feature
3514           is similar to a lookbehind assertion (described  below).   However,  in
3515           this  case, the part of the subject before the real match does not have
3516           to be of fixed length, as lookbehind assertions do. The use of \K  does
3517           not  interfere  with  the setting of captured substrings.  For example,
3518           when the pattern
3519    
3520             (foo)\Kbar
3521    
3522           matches "foobar", the first substring is still set to "foo".
3523    
3524     Simple assertions     Simple assertions
3525    
3526         The fourth use of backslash is for certain simple assertions. An asser-         The final use of backslash is for certain simple assertions. An  asser-
3527         tion specifies a condition that has to be met at a particular point  in         tion  specifies a condition that has to be met at a particular point in
3528         a  match, without consuming any characters from the subject string. The         a match, without consuming any characters from the subject string.  The
3529         use of subpatterns for more complicated assertions is described  below.         use  of subpatterns for more complicated assertions is described below.
3530         The backslashed assertions are:         The backslashed assertions are:
3531    
3532           \b     matches at a word boundary           \b     matches at a word boundary
3533           \B     matches when not at a word boundary           \B     matches when not at a word boundary
3534           \A     matches at start of subject           \A     matches at the start of the subject
3535           \Z     matches at end of subject or before newline at end           \Z     matches at the end of the subject
3536           \z     matches at end of subject                   also matches before a newline at the end of the subject
3537           \G     matches at first matching position in subject           \z     matches only at the end of the subject
3538             \G     matches at the first matching position in the subject
3539    
3540         These  assertions may not appear in character classes (but note that \b         These assertions may not appear in character classes (but note that  \b
3541         has a different meaning, namely the backspace character, inside a char-         has a different meaning, namely the backspace character, inside a char-
3542         acter class).         acter class).
3543    
3544         A  word  boundary is a position in the subject string where the current         A word boundary is a position in the subject string where  the  current
3545         character and the previous character do not both match \w or  \W  (i.e.         character  and  the previous character do not both match \w or \W (i.e.
3546         one  matches  \w  and the other matches \W), or the start or end of the         one matches \w and the other matches \W), or the start or  end  of  the
3547         string if the first or last character matches \w, respectively.         string if the first or last character matches \w, respectively.
3548    
3549         The \A, \Z, and \z assertions differ from  the  traditional  circumflex         The  \A,  \Z,  and \z assertions differ from the traditional circumflex
3550         and dollar (described in the next section) in that they only ever match         and dollar (described in the next section) in that they only ever match
3551         at the very start and end of the subject string, whatever  options  are         at  the  very start and end of the subject string, whatever options are
3552         set.  Thus,  they are independent of multiline mode. These three asser-         set. Thus, they are independent of multiline mode. These  three  asser-
3553         tions are not affected by the PCRE_NOTBOL or PCRE_NOTEOL options, which         tions are not affected by the PCRE_NOTBOL or PCRE_NOTEOL options, which
3554         affect  only the behaviour of the circumflex and dollar metacharacters.         affect only the behaviour of the circumflex and dollar  metacharacters.
3555         However, if the startoffset argument of pcre_exec() is non-zero,  indi-         However,  if the startoffset argument of pcre_exec() is non-zero, indi-
3556         cating that matching is to start at a point other than the beginning of         cating that matching is to start at a point other than the beginning of
3557         the subject, \A can never match. The difference between \Z  and  \z  is         the  subject,  \A  can never match. The difference between \Z and \z is
3558         that  \Z  matches  before  a  newline that is the last character of the         that \Z matches before a newline at the end of the string as well as at
3559         string as well as at the end of the string, whereas \z matches only  at         the very end, whereas \z matches only at the end.
        the end.  
3560    
3561         The  \G assertion is true only when the current matching position is at         The  \G assertion is true only when the current matching position is at
3562         the start point of the match, as specified by the startoffset  argument         the start point of the match, as specified by the startoffset  argument
# Line 2748  CIRCUMFLEX AND DOLLAR Line 3595  CIRCUMFLEX AND DOLLAR
3595    
3596         A  dollar  character  is  an assertion that is true only if the current         A  dollar  character  is  an assertion that is true only if the current
3597         matching point is at the end of  the  subject  string,  or  immediately         matching point is at the end of  the  subject  string,  or  immediately
3598         before a newline character that is the last character in the string (by         before a newline at the end of the string (by default). Dollar need not
3599         default). Dollar need not be the last character of  the  pattern  if  a         be the last character of the pattern if a number  of  alternatives  are
3600         number  of alternatives are involved, but it should be the last item in         involved,  but  it  should  be  the last item in any branch in which it
3601         any branch in which it appears.  Dollar has no  special  meaning  in  a         appears. Dollar has no special meaning in a character class.
        character class.  
3602    
3603         The  meaning  of  dollar  can be changed so that it matches only at the         The meaning of dollar can be changed so that it  matches  only  at  the
3604         very end of the string, by setting the  PCRE_DOLLAR_ENDONLY  option  at         very  end  of  the string, by setting the PCRE_DOLLAR_ENDONLY option at
3605         compile time. This does not affect the \Z assertion.         compile time. This does not affect the \Z assertion.
3606    
3607         The meanings of the circumflex and dollar characters are changed if the         The meanings of the circumflex and dollar characters are changed if the
3608         PCRE_MULTILINE option is set. When this is the case, they match immedi-         PCRE_MULTILINE  option  is  set.  When  this  is the case, a circumflex
3609         ately  after  and  immediately  before  an  internal newline character,         matches immediately after internal newlines as well as at the start  of
3610         respectively, in addition to matching at the start and end of the  sub-         the  subject  string.  It  does not match after a newline that ends the
3611         ject  string.  For  example,  the  pattern  /^abc$/ matches the subject         string. A dollar matches before any newlines in the string, as well  as
3612         string "def\nabc" (where \n represents a newline character)  in  multi-         at  the very end, when PCRE_MULTILINE is set. When newline is specified
3613         line mode, but not otherwise.  Consequently, patterns that are anchored         as the two-character sequence CRLF, isolated CR and  LF  characters  do
3614         in single line mode because all branches start with ^ are not  anchored         not indicate newlines.
3615         in  multiline  mode,  and  a  match for circumflex is possible when the  
3616         startoffset  argument  of  pcre_exec()  is  non-zero.   The   PCRE_DOL-         For  example, the pattern /^abc$/ matches the subject string "def\nabc"
3617         LAR_ENDONLY option is ignored if PCRE_MULTILINE is set.         (where \n represents a newline) in multiline mode, but  not  otherwise.
3618           Consequently,  patterns  that  are anchored in single line mode because
3619           all branches start with ^ are not anchored in  multiline  mode,  and  a
3620           match  for  circumflex  is  possible  when  the startoffset argument of
3621           pcre_exec() is non-zero. The PCRE_DOLLAR_ENDONLY option is  ignored  if
3622           PCRE_MULTILINE is set.
3623    
3624         Note  that  the sequences \A, \Z, and \z can be used to match the start         Note  that  the sequences \A, \Z, and \z can be used to match the start
3625         and end of the subject in both modes, and if all branches of a  pattern         and end of the subject in both modes, and if all branches of a  pattern
3626         start  with  \A it is always anchored, whether PCRE_MULTILINE is set or         start  with  \A it is always anchored, whether or not PCRE_MULTILINE is
3627         not.         set.
3628    
3629    
3630  FULL STOP (PERIOD, DOT)  FULL STOP (PERIOD, DOT)
3631    
3632         Outside a character class, a dot in the pattern matches any one charac-         Outside a character class, a dot in the pattern matches any one charac-
3633         ter  in  the  subject,  including a non-printing character, but not (by         ter  in  the subject string except (by default) a character that signi-
3634         default) newline.  In UTF-8 mode, a dot matches  any  UTF-8  character,         fies the end of a line. In UTF-8 mode, the  matched  character  may  be
3635         which might be more than one byte long, except (by default) newline. If         more than one byte long.
3636         the PCRE_DOTALL option is set, dots match newlines as  well.  The  han-  
3637         dling  of dot is entirely independent of the handling of circumflex and         When  a line ending is defined as a single character, dot never matches
3638         dollar, the only relationship being  that  they  both  involve  newline         that character; when the two-character sequence CRLF is used, dot  does
3639         characters. Dot has no special meaning in a character class.         not  match  CR  if  it  is immediately followed by LF, but otherwise it
3640           matches all characters (including isolated CRs and LFs). When any  Uni-
3641           code  line endings are being recognized, dot does not match CR or LF or
3642           any of the other line ending characters.
3643    
3644           The behaviour of dot with regard to newlines can  be  changed.  If  the
3645           PCRE_DOTALL  option  is  set,  a dot matches any one character, without
3646           exception. If the two-character sequence CRLF is present in the subject
3647           string, it takes two dots to match it.
3648    
3649           The  handling of dot is entirely independent of the handling of circum-
3650           flex and dollar, the only relationship being  that  they  both  involve
3651           newlines. Dot has no special meaning in a character class.
3652    
3653    
3654  MATCHING A SINGLE BYTE  MATCHING A SINGLE BYTE
3655    
3656         Outside a character class, the escape sequence \C matches any one byte,         Outside a character class, the escape sequence \C matches any one byte,
3657         both in and out of UTF-8 mode. Unlike a dot, it can  match  a  newline.         both in and out of UTF-8 mode. Unlike a  dot,  it  always  matches  any
3658         The  feature  is provided in Perl in order to match individual bytes in         line-ending  characters.  The  feature  is provided in Perl in order to
3659         UTF-8 mode. Because it  breaks  up  UTF-8  characters  into  individual         match individual bytes in UTF-8 mode. Because it breaks up UTF-8  char-
3660         bytes,  what remains in the string may be a malformed UTF-8 string. For         acters  into individual bytes, what remains