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2  This file contains a concatenation of the PCRE man pages, converted to plain  This file contains a concatenation of the PCRE man pages, converted to plain
3  text format for ease of searching with a text editor, or for use on systems  text format for ease of searching with a text editor, or for use on systems
4  that do not have a man page processor. The small individual files that give  that do not have a man page processor. The small individual files that give
5  synopses of each function in the library have not been included. There are  synopses of each function in the library have not been included. Neither has
6  separate text files for the pcregrep and pcretest commands.  the pcredemo program. There are separate text files for the pcregrep and
7    pcretest commands.
8  -----------------------------------------------------------------------------  -----------------------------------------------------------------------------
9    
10    
# Line 18  INTRODUCTION Line 19  INTRODUCTION
19    
20         The  PCRE  library is a set of functions that implement regular expres-         The  PCRE  library is a set of functions that implement regular expres-
21         sion pattern matching using the same syntax and semantics as Perl, with         sion pattern matching using the same syntax and semantics as Perl, with
22         just  a  few  differences.  The current implementation of PCRE (release         just  a few differences. Some features that appeared in Python and PCRE
23         6.x) corresponds approximately with Perl  5.8,  including  support  for         before they appeared in Perl are also available using the  Python  syn-
24         UTF-8 encoded strings and Unicode general category properties. However,         tax,  there  is  some  support for one or two .NET and Oniguruma syntax
25         this support has to be explicitly enabled; it is not the default.         items, and there is an option for requesting some  minor  changes  that
26           give better JavaScript compatibility.
27         In addition to the Perl-compatible matching function,  PCRE  also  con-  
28         tains  an  alternative matching function that matches the same compiled         The  current implementation of PCRE corresponds approximately with Perl
29         patterns in a different way. In certain circumstances, the  alternative         5.10, including support for UTF-8 encoded strings and  Unicode  general
30         function  has  some  advantages.  For  a discussion of the two matching         category  properties.  However,  UTF-8  and  Unicode  support has to be
31         algorithms, see the pcrematching page.         explicitly enabled; it is not the default. The  Unicode  tables  corre-
32           spond to Unicode release 5.2.0.
33         PCRE is written in C and released as a C library. A  number  of  people  
34         have  written  wrappers and interfaces of various kinds. In particular,         In  addition to the Perl-compatible matching function, PCRE contains an
35         Google Inc.  have provided a comprehensive C++  wrapper.  This  is  now         alternative function that matches the same compiled patterns in a  dif-
36           ferent way. In certain circumstances, the alternative function has some
37           advantages.  For a discussion of the two matching algorithms,  see  the
38           pcrematching page.
39    
40           PCRE  is  written  in C and released as a C library. A number of people
41           have written wrappers and interfaces of various kinds.  In  particular,
42           Google  Inc.   have  provided  a comprehensive C++ wrapper. This is now
43         included as part of the PCRE distribution. The pcrecpp page has details         included as part of the PCRE distribution. The pcrecpp page has details
44         of this interface. Other people's contributions can  be  found  in  the         of  this  interface.  Other  people's contributions can be found in the
45         Contrib directory at the primary FTP site, which is:         Contrib directory at the primary FTP site, which is:
46    
47         ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre         ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre
48    
49         Details  of  exactly which Perl regular expression features are and are         Details of exactly which Perl regular expression features are  and  are
50         not supported by PCRE are given in separate documents. See the pcrepat-         not supported by PCRE are given in separate documents. See the pcrepat-
51         tern and pcrecompat pages.         tern and pcrecompat pages. There is a syntax summary in the  pcresyntax
52           page.
53    
54         Some  features  of  PCRE can be included, excluded, or changed when the         Some  features  of  PCRE can be included, excluded, or changed when the
55         library is built. The pcre_config() function makes it  possible  for  a         library is built. The pcre_config() function makes it  possible  for  a
56         client  to  discover  which  features are available. The features them-         client  to  discover  which  features are available. The features them-
57         selves are described in the pcrebuild page. Documentation about  build-         selves are described in the pcrebuild page. Documentation about  build-
58         ing  PCRE for various operating systems can be found in the README file         ing  PCRE  for various operating systems can be found in the README and
59         in the source distribution.         NON-UNIX-USE files in the source distribution.
60    
61         The library contains a number of undocumented  internal  functions  and         The library contains a number of undocumented  internal  functions  and
62         data  tables  that  are  used by more than one of the exported external         data  tables  that  are  used by more than one of the exported external
# Line 63  USER DOCUMENTATION Line 72  USER DOCUMENTATION
72         The user documentation for PCRE comprises a number  of  different  sec-         The user documentation for PCRE comprises a number  of  different  sec-
73         tions.  In the "man" format, each of these is a separate "man page". In         tions.  In the "man" format, each of these is a separate "man page". In
74         the HTML format, each is a separate page, linked from the  index  page.         the HTML format, each is a separate page, linked from the  index  page.
75         In  the  plain text format, all the sections are concatenated, for ease         In  the  plain  text format, all the sections, except the pcredemo sec-
76         of searching. The sections are as follows:         tion, are concatenated, for ease of searching. The sections are as fol-
77           lows:
78    
79           pcre              this document           pcre              this document
80             pcre-config       show PCRE installation configuration information
81           pcreapi           details of PCRE's native C API           pcreapi           details of PCRE's native C API
82           pcrebuild         options for building PCRE           pcrebuild         options for building PCRE
83           pcrecallout       details of the callout feature           pcrecallout       details of the callout feature
84           pcrecompat        discussion of Perl compatibility           pcrecompat        discussion of Perl compatibility
85           pcrecpp           details of the C++ wrapper           pcrecpp           details of the C++ wrapper
86             pcredemo          a demonstration C program that uses PCRE
87           pcregrep          description of the pcregrep command           pcregrep          description of the pcregrep command
88           pcrematching      discussion of the two matching algorithms           pcrematching      discussion of the two matching algorithms
89           pcrepartial       details of the partial matching facility           pcrepartial       details of the partial matching facility
# Line 80  USER DOCUMENTATION Line 92  USER DOCUMENTATION
92           pcreperform       discussion of performance issues           pcreperform       discussion of performance issues
93           pcreposix         the POSIX-compatible C API           pcreposix         the POSIX-compatible C API
94           pcreprecompile    details of saving and re-using precompiled patterns           pcreprecompile    details of saving and re-using precompiled patterns
95           pcresample        discussion of the sample program           pcresample        discussion of the pcredemo program
96             pcrestack         discussion of stack usage
97             pcresyntax        quick syntax reference
98           pcretest          description of the pcretest testing command           pcretest          description of the pcretest testing command
99    
100         In  addition,  in the "man" and HTML formats, there is a short page for         In  addition,  in the "man" and HTML formats, there is a short page for
# Line 98  LIMITATIONS Line 112  LIMITATIONS
112         PCRE with an internal linkage size of 3 or 4 (see the  README  file  in         PCRE with an internal linkage size of 3 or 4 (see the  README  file  in
113         the  source  distribution and the pcrebuild documentation for details).         the  source  distribution and the pcrebuild documentation for details).
114         In these cases the limit is substantially larger.  However,  the  speed         In these cases the limit is substantially larger.  However,  the  speed
115         of execution will be slower.         of execution is slower.
116    
117         All values in repeating quantifiers must be less than 65536.  The maxi-         All values in repeating quantifiers must be less than 65536.
        mum number of capturing subpatterns is 65535.  
118    
119         There is no limit to the number of non-capturing subpatterns,  but  the         There is no limit to the number of parenthesized subpatterns, but there
120         maximum  depth  of  nesting  of  all kinds of parenthesized subpattern,         can be no more than 65535 capturing subpatterns.
121         including capturing subpatterns, assertions, and other types of subpat-  
122         tern, is 200.         The maximum length of name for a named subpattern is 32 characters, and
123           the maximum number of named subpatterns is 10000.
124    
125         The  maximum  length of a subject string is the largest positive number         The  maximum  length of a subject string is the largest positive number
126         that an integer variable can hold. However, when using the  traditional         that an integer variable can hold. However, when using the  traditional
127         matching function, PCRE uses recursion to handle subpatterns and indef-         matching function, PCRE uses recursion to handle subpatterns and indef-
128         inite repetition.  This means that the available stack space may  limit         inite repetition.  This means that the available stack space may  limit
129         the size of a subject string that can be processed by certain patterns.         the size of a subject string that can be processed by certain patterns.
130           For a discussion of stack issues, see the pcrestack documentation.
131    
132    
133  UTF-8 AND UNICODE PROPERTY SUPPORT  UTF-8 AND UNICODE PROPERTY SUPPORT
# Line 124  UTF-8 AND UNICODE PROPERTY SUPPORT Line 139  UTF-8 AND UNICODE PROPERTY SUPPORT
139    
140         In  order  process  UTF-8 strings, you must build PCRE to include UTF-8         In  order  process  UTF-8 strings, you must build PCRE to include UTF-8
141         support in the code, and, in addition,  you  must  call  pcre_compile()         support in the code, and, in addition,  you  must  call  pcre_compile()
142         with  the PCRE_UTF8 option flag. When you do this, both the pattern and         with  the  PCRE_UTF8  option  flag,  or the pattern must start with the
143         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
144         strings instead of just strings of bytes.         and  any  subject  strings  that  are matched against it are treated as
145           UTF-8 strings instead of strings of 1-byte characters.
146         If  you compile PCRE with UTF-8 support, but do not use it at run time,  
147         the library will be a bit bigger, but the additional run time  overhead         If you compile PCRE with UTF-8 support, but do not use it at run  time,
148         is  limited  to testing the PCRE_UTF8 flag in several places, so should         the  library will be a bit bigger, but the additional run time overhead
149         not be very large.         is limited to testing the PCRE_UTF8 flag occasionally, so should not be
150           very big.
151    
152         If PCRE is built with Unicode character property support (which implies         If PCRE is built with Unicode character property support (which implies
153         UTF-8  support),  the  escape sequences \p{..}, \P{..}, and \X are sup-         UTF-8 support), the escape sequences \p{..}, \P{..}, and  \X  are  sup-
154         ported.  The available properties that can be tested are limited to the         ported.  The available properties that can be tested are limited to the
155         general  category  properties such as Lu for an upper case letter or Nd         general category properties such as Lu for an upper case letter  or  Nd
156         for a decimal number. A full list is given in the pcrepattern  documen-         for  a  decimal number, the Unicode script names such as Arabic or Han,
157         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
158         property support is included.         pcrepattern documentation. Only the short names for properties are sup-
159           ported. For example, \p{L} matches a letter. Its Perl synonym,  \p{Let-
160         The following comments apply when PCRE is running in UTF-8 mode:         ter},  is  not  supported.   Furthermore,  in Perl, many properties may
161           optionally be prefixed by "Is", for compatibility with Perl  5.6.  PCRE
162         1. When you set the PCRE_UTF8 flag, the strings passed as patterns  and         does not support this.
163         subjects  are  checked for validity on entry to the relevant functions.  
164         If an invalid UTF-8 string is passed, an error return is given. In some     Validity of UTF-8 strings
165         situations,  you  may  already  know  that  your strings are valid, and  
166         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
167         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
168         PCRE assumes that the pattern or subject  it  is  given  (respectively)         functions.  From  release 7.3 of PCRE, the check is according the rules
169         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-
170         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
171         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
172         crash.         check allows only values in the range U+0 to U+10FFFF, excluding U+D800
173           to U+DFFF.
174         2. In a pattern, the escape sequence \x{...}, where the contents of the  
175         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
176         character whose code number is the given hexadecimal number, for  exam-         which  the Unicode Standard says this: "The Low Surrogate Area does not
177         ple:  \x{1234}.  If a non-hexadecimal digit appears between the braces,         contain any  character  assignments,  consequently  no  character  code
178         the item is not recognized.  This escape sequence can be used either as         charts or namelists are provided for this area. Surrogates are reserved
179         a literal, or within a character class.         for use with UTF-16 and then must be used in pairs."  The  code  points
180           that  are  encoded  by  UTF-16  pairs are available as independent code
181           points in the UTF-8 encoding. (In  other  words,  the  whole  surrogate
182           thing is a fudge for UTF-16 which unfortunately messes up UTF-8.)
183    
184           If  an  invalid  UTF-8  string  is  passed  to  PCRE,  an  error return
185           (PCRE_ERROR_BADUTF8) is given. In some situations, you may already know
186           that your strings are valid, and therefore want to skip these checks in
187           order to improve performance. If you set the PCRE_NO_UTF8_CHECK flag at
188           compile  time  or at run time, PCRE assumes that the pattern or subject
189           it is given (respectively) contains only valid  UTF-8  codes.  In  this
190           case, it does not diagnose an invalid UTF-8 string.
191    
192           If  you  pass  an  invalid UTF-8 string when PCRE_NO_UTF8_CHECK is set,
193           what happens depends on why the string is invalid. If the  string  con-
194           forms to the "old" definition of UTF-8 (RFC 2279), it is processed as a
195           string of characters in the range 0  to  0x7FFFFFFF.  In  other  words,
196           apart from the initial validity test, PCRE (when in UTF-8 mode) handles
197           strings according to the more liberal rules of RFC  2279.  However,  if
198           the  string does not even conform to RFC 2279, the result is undefined.
199           Your program may crash.
200    
201           If you want to process strings  of  values  in  the  full  range  0  to
202           0x7FFFFFFF,  encoded in a UTF-8-like manner as per the old RFC, you can
203           set PCRE_NO_UTF8_CHECK to bypass the more restrictive test. However, in
204           this situation, you will have to apply your own validity check.
205    
206       General comments about UTF-8 mode
207    
208           1.  An  unbraced  hexadecimal  escape sequence (such as \xb3) matches a
209           two-byte UTF-8 character if the value is greater than 127.
210    
211         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
212         UTF-8 character if the value is greater than 127.         characters for values greater than \177.
213    
214         4. Repeat quantifiers apply to complete UTF-8 characters, not to  indi-         3.  Repeat quantifiers apply to complete UTF-8 characters, not to indi-
215         vidual bytes, for example: \x{100}{3}.         vidual bytes, for example: \x{100}{3}.
216    
217         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-
218         gle byte.         gle byte.
219    
220         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
221         mode,  but  its  use can lead to some strange effects. This facility is         mode, but its use can lead to some strange effects.  This  facility  is
222         not available in the alternative matching function, pcre_dfa_exec().         not available in the alternative matching function, pcre_dfa_exec().
223    
224         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
225         test  characters of any code value, but the characters that PCRE recog-         test characters of any code value, but the characters that PCRE  recog-
226         nizes as digits, spaces, or word characters  remain  the  same  set  as         nizes  as  digits,  spaces,  or  word characters remain the same set as
227         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
228         includes Unicode property support, because to do otherwise  would  slow         includes  Unicode  property support, because to do otherwise would slow
229         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
230         sense of, say, "digit", you must use Unicode  property  tests  such  as         sense  of,  say,  "digit",  you must use Unicode property tests such as
231         \p{Nd}.         \p{Nd}. Note that this also applies to \b, because  it  is  defined  in
232           terms of \w and \W.
233    
234         8.  Similarly,  characters that match the POSIX named character classes         7.  Similarly,  characters that match the POSIX named character classes
235         are all low-valued characters.         are all low-valued characters.
236    
237           8. However, the Perl 5.10 horizontal and vertical  whitespace  matching
238           escapes (\h, \H, \v, and \V) do match all the appropriate Unicode char-
239           acters.
240    
241         9. Case-insensitive matching applies only to  characters  whose  values         9. Case-insensitive matching applies only to  characters  whose  values
242         are  less than 128, unless PCRE is built with Unicode property support.         are  less than 128, unless PCRE is built with Unicode property support.
243         Even when Unicode property support is available, PCRE  still  uses  its         Even when Unicode property support is available, PCRE  still  uses  its
244         own  character  tables when checking the case of low-valued characters,         own  character  tables when checking the case of low-valued characters,
245         so as not to degrade performance.  The Unicode property information  is         so as not to degrade performance.  The Unicode property information  is
246         used only for characters with higher values.         used only for characters with higher values. Even when Unicode property
247           support is available, PCRE supports case-insensitive matching only when
248           there  is  a  one-to-one  mapping between a letter's cases. There are a
249           small number of many-to-one mappings in Unicode;  these  are  not  sup-
250           ported by PCRE.
251    
252    
253  AUTHOR  AUTHOR
254    
255         Philip Hazel         Philip Hazel
256         University Computing Service,         University Computing Service
257         Cambridge CB2 3QG, England.         Cambridge CB2 3QH, England.
258    
259         Putting  an actual email address here seems to have been a spam magnet,         Putting  an actual email address here seems to have been a spam magnet,
260         so I've taken it away. If you want to email me, use my initial and sur-         so I've taken it away. If you want to email me, use  my  two  initials,
261         name, separated by a dot, at the domain ucs.cam.ac.uk.         followed by the two digits 10, at the domain cam.ac.uk.
262    
263    
264  Last updated: 07 March 2005  REVISION
265  Copyright (c) 1997-2005 University of Cambridge.  
266           Last updated: 01 March 2010
267           Copyright (c) 1997-2010 University of Cambridge.
268  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
269    
270    
# Line 220  NAME Line 278  NAME
278  PCRE BUILD-TIME OPTIONS  PCRE BUILD-TIME OPTIONS
279    
280         This  document  describes  the  optional  features  of PCRE that can be         This  document  describes  the  optional  features  of PCRE that can be
281         selected when the library is compiled. They are all selected, or  dese-         selected when the library is compiled. It assumes use of the  configure
282         lected, by providing options to the configure script that is run before         script,  where the optional features are selected or deselected by pro-
283         the make command. The complete list of  options  for  configure  (which         viding options to configure before running the make  command.  However,
284         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
285         directory) can be obtained by running         environments using the GUI facility of cmake-gui if you are using CMake
286           instead of configure to build PCRE.
287    
288           There  is  a  lot more information about building PCRE in non-Unix-like
289           environments in the file called NON_UNIX_USE, which is part of the PCRE
290           distribution.  You  should consult this file as well as the README file
291           if you are building in a non-Unix-like environment.
292    
293           The complete list of options for configure (which includes the standard
294           ones  such  as  the  selection  of  the  installation directory) can be
295           obtained by running
296    
297           ./configure --help           ./configure --help
298    
299         The following sections describe certain options whose names begin  with         The following sections include  descriptions  of  options  whose  names
300         --enable  or  --disable. These settings specify changes to the defaults         begin with --enable or --disable. These settings specify changes to the
301         for the configure command. Because of the  way  that  configure  works,         defaults for the configure command. Because of the way  that  configure
302         --enable  and  --disable  always  come  in  pairs, so the complementary         works,  --enable  and --disable always come in pairs, so the complemen-
303         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
304         not described.         is not described.
305    
306    
307  C++ SUPPORT  C++ SUPPORT
# Line 249  C++ SUPPORT Line 317  C++ SUPPORT
317    
318  UTF-8 SUPPORT  UTF-8 SUPPORT
319    
320         To build PCRE with support for UTF-8 character strings, add         To build PCRE with support for UTF-8 Unicode character strings, add
321    
322           --enable-utf8           --enable-utf8
323    
324         to  the  configure  command.  Of  itself, this does not make PCRE treat         to  the  configure  command.  Of  itself, this does not make PCRE treat
325         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
326         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()
327         function.         or pcre_compile2() functions.
328    
329           If you set --enable-utf8 when compiling in an EBCDIC environment,  PCRE
330           expects its input to be either ASCII or UTF-8 (depending on the runtime
331           option). It is not possible to support both EBCDIC and UTF-8  codes  in
332           the  same  version  of  the  library.  Consequently,  --enable-utf8 and
333           --enable-ebcdic are mutually exclusive.
334    
335    
336  UNICODE CHARACTER PROPERTY SUPPORT  UNICODE CHARACTER PROPERTY SUPPORT
# Line 272  UNICODE CHARACTER PROPERTY SUPPORT Line 346  UNICODE CHARACTER PROPERTY SUPPORT
346         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
347         not explicitly requested it.         not explicitly requested it.
348    
349         Including  Unicode  property  support  adds around 90K of tables to the         Including  Unicode  property  support  adds around 30K of tables to the
350         PCRE library, approximately doubling its size. Only the  general  cate-         PCRE library. Only the general category properties such as  Lu  and  Nd
351         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.  
352    
353    
354  CODE VALUE OF NEWLINE  CODE VALUE OF NEWLINE
355    
356         By default, PCRE treats character 10 (linefeed) as the newline  charac-         By  default,  PCRE interprets the linefeed (LF) character as indicating
357         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
358         compile PCRE to use character 13 (carriage return) instead by adding         systems.  You  can compile PCRE to use carriage return (CR) instead, by
359           adding
360    
361           --enable-newline-is-cr           --enable-newline-is-cr
362    
363         to the configure command. For completeness there is  also  a  --enable-         to the  configure  command.  There  is  also  a  --enable-newline-is-lf
364         newline-is-lf  option,  which explicitly specifies linefeed as the new-         option, which explicitly specifies linefeed as the newline character.
365         line character.  
366           Alternatively, you can specify that line endings are to be indicated by
367           the two character sequence CRLF. If you want this, add
368    
369             --enable-newline-is-crlf
370    
371           to the configure command. There is a fourth option, specified by
372    
373             --enable-newline-is-anycrlf
374    
375           which causes PCRE to recognize any of the three sequences  CR,  LF,  or
376           CRLF as indicating a line ending. Finally, a fifth option, specified by
377    
378             --enable-newline-is-any
379    
380           causes PCRE to recognize any Unicode newline sequence.
381    
382           Whatever  line  ending convention is selected when PCRE is built can be
383           overridden when the library functions are called. At build time  it  is
384           conventional to use the standard for your operating system.
385    
386    
387    WHAT \R MATCHES
388    
389           By  default,  the  sequence \R in a pattern matches any Unicode newline
390           sequence, whatever has been selected as the line  ending  sequence.  If
391           you specify
392    
393             --enable-bsr-anycrlf
394    
395           the  default  is changed so that \R matches only CR, LF, or CRLF. What-
396           ever is selected when PCRE is built can be overridden when the  library
397           functions are called.
398    
399    
400  BUILDING SHARED AND STATIC LIBRARIES  BUILDING SHARED AND STATIC LIBRARIES
401    
402         The PCRE building process uses libtool to build both shared and  static         The  PCRE building process uses libtool to build both shared and static
403         Unix  libraries by default. You can suppress one of these by adding one         Unix libraries by default. You can suppress one of these by adding  one
404         of         of
405    
406           --disable-shared           --disable-shared
# Line 306  BUILDING SHARED AND STATIC LIBRARIES Line 412  BUILDING SHARED AND STATIC LIBRARIES
412  POSIX MALLOC USAGE  POSIX MALLOC USAGE
413    
414         When PCRE is called through the POSIX interface (see the pcreposix doc-         When PCRE is called through the POSIX interface (see the pcreposix doc-
415         umentation),  additional  working  storage  is required for holding the         umentation), additional working storage is  required  for  holding  the
416         pointers to capturing substrings, because PCRE requires three  integers         pointers  to capturing substrings, because PCRE requires three integers
417         per  substring,  whereas  the POSIX interface provides only two. If the         per substring, whereas the POSIX interface provides only  two.  If  the
418         number of expected substrings is small, the wrapper function uses space         number of expected substrings is small, the wrapper function uses space
419         on the stack, because this is faster than using malloc() for each call.         on the stack, because this is faster than using malloc() for each call.
420         The default threshold above which the stack is no longer used is 10; it         The default threshold above which the stack is no longer used is 10; it
# Line 319  POSIX MALLOC USAGE Line 425  POSIX MALLOC USAGE
425         to the configure command.         to the configure command.
426    
427    
428    HANDLING VERY LARGE PATTERNS
429    
430           Within a compiled pattern, offset values are used  to  point  from  one
431           part  to another (for example, from an opening parenthesis to an alter-
432           nation metacharacter). By default, two-byte values are used  for  these
433           offsets,  leading  to  a  maximum size for a compiled pattern of around
434           64K. This is sufficient to handle all but the most  gigantic  patterns.
435           Nevertheless,  some  people do want to process truyl enormous patterns,
436           so it is possible to compile PCRE to use three-byte or  four-byte  off-
437           sets by adding a setting such as
438    
439             --with-link-size=3
440    
441           to  the  configure  command.  The value given must be 2, 3, or 4. Using
442           longer offsets slows down the operation of PCRE because it has to  load
443           additional bytes when handling them.
444    
445    
446    AVOIDING EXCESSIVE STACK USAGE
447    
448           When matching with the pcre_exec() function, PCRE implements backtrack-
449           ing by making recursive calls to an internal function  called  match().
450           In  environments  where  the size of the stack is limited, this can se-
451           verely limit PCRE's operation. (The Unix environment does  not  usually
452           suffer from this problem, but it may sometimes be necessary to increase
453           the maximum stack size.  There is a discussion in the  pcrestack  docu-
454           mentation.)  An alternative approach to recursion that uses memory from
455           the heap to remember data, instead of using recursive  function  calls,
456           has  been  implemented to work round the problem of limited stack size.
457           If you want to build a version of PCRE that works this way, add
458    
459             --disable-stack-for-recursion
460    
461           to the configure command. With this configuration, PCRE  will  use  the
462           pcre_stack_malloc  and pcre_stack_free variables to call memory manage-
463           ment functions. By default these point to malloc() and free(), but  you
464           can replace the pointers so that your own functions are used instead.
465    
466           Separate  functions  are  provided  rather  than  using pcre_malloc and
467           pcre_free because the  usage  is  very  predictable:  the  block  sizes
468           requested  are  always  the  same,  and  the blocks are always freed in
469           reverse order. A calling program might be able to  implement  optimized
470           functions  that  perform  better  than  malloc()  and free(). PCRE runs
471           noticeably more slowly when built in this way. This option affects only
472           the pcre_exec() function; it is not relevant for pcre_dfa_exec().
473    
474    
475  LIMITING PCRE RESOURCE USAGE  LIMITING PCRE RESOURCE USAGE
476    
477         Internally,  PCRE has a function called match(), which it calls repeat-         Internally,  PCRE has a function called match(), which it calls repeat-
478         edly  (possibly  recursively)  when  matching  a   pattern   with   the         edly  (sometimes  recursively)  when  matching  a  pattern   with   the
479         pcre_exec()  function.  By controlling the maximum number of times this         pcre_exec()  function.  By controlling the maximum number of times this
480         function may be called during a single matching operation, a limit  can         function may be called during a single matching operation, a limit  can
481         be  placed  on  the resources used by a single call to pcre_exec(). The         be  placed  on  the resources used by a single call to pcre_exec(). The
# Line 335  LIMITING PCRE RESOURCE USAGE Line 488  LIMITING PCRE RESOURCE USAGE
488         to  the  configure  command.  This  setting  has  no  effect   on   the         to  the  configure  command.  This  setting  has  no  effect   on   the
489         pcre_dfa_exec() matching function.         pcre_dfa_exec() matching function.
490    
491           In  some  environments  it is desirable to limit the depth of recursive
492           calls of match() more strictly than the total number of calls, in order
493           to  restrict  the maximum amount of stack (or heap, if --disable-stack-
494           for-recursion is specified) that is used. A second limit controls this;
495           it  defaults  to  the  value  that is set for --with-match-limit, which
496           imposes no additional constraints. However, you can set a  lower  limit
497           by adding, for example,
498    
499             --with-match-limit-recursion=10000
500    
501           to  the  configure  command.  This  value can also be overridden at run
502           time.
503    
504    
505    CREATING CHARACTER TABLES AT BUILD TIME
506    
507           PCRE uses fixed tables for processing characters whose code values  are
508           less  than 256. By default, PCRE is built with a set of tables that are
509           distributed in the file pcre_chartables.c.dist. These  tables  are  for
510           ASCII codes only. If you add
511    
512             --enable-rebuild-chartables
513    
514           to  the  configure  command, the distributed tables are no longer used.
515           Instead, a program called dftables is compiled and  run.  This  outputs
516           the source for new set of tables, created in the default locale of your
517           C runtime system. (This method of replacing the tables does not work if
518           you  are cross compiling, because dftables is run on the local host. If
519           you need to create alternative tables when cross  compiling,  you  will
520           have to do so "by hand".)
521    
 HANDLING VERY LARGE PATTERNS  
522    
523         Within  a  compiled  pattern,  offset values are used to point from one  USING EBCDIC CODE
        part to another (for example, from an opening parenthesis to an  alter-  
        nation  metacharacter).  By default, two-byte values are used for these  
        offsets, leading to a maximum size for a  compiled  pattern  of  around  
        64K.  This  is sufficient to handle all but the most gigantic patterns.  
        Nevertheless, some people do want to process enormous patterns,  so  it  
        is  possible  to compile PCRE to use three-byte or four-byte offsets by  
        adding a setting such as  
524    
525           --with-link-size=3         PCRE  assumes  by  default that it will run in an environment where the
526           character code is ASCII (or Unicode, which is  a  superset  of  ASCII).
527           This  is  the  case for most computer operating systems. PCRE can, how-
528           ever, be compiled to run in an EBCDIC environment by adding
529    
530         to the configure command. The value given must be 2,  3,  or  4.  Using           --enable-ebcdic
        longer  offsets slows down the operation of PCRE because it has to load  
        additional bytes when handling them.  
531    
532         If you build PCRE with an increased link size, test 2 (and  test  5  if         to the configure command. This setting implies --enable-rebuild-charta-
533         you  are using UTF-8) will fail. Part of the output of these tests is a         bles.  You  should  only  use  it if you know that you are in an EBCDIC
534         representation of the compiled pattern, and this changes with the  link         environment (for example,  an  IBM  mainframe  operating  system).  The
535         size.         --enable-ebcdic option is incompatible with --enable-utf8.
536    
537    
538  AVOIDING EXCESSIVE STACK USAGE  PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT
539    
540         When matching with the pcre_exec() function, PCRE implements backtrack-         By default, pcregrep reads all files as plain text. You can build it so
541         ing by making recursive calls to an internal function  called  match().         that it recognizes files whose names end in .gz or .bz2, and reads them
542         In  environments  where  the size of the stack is limited, this can se-         with libz or libbz2, respectively, by adding one or both of
        verely limit PCRE's operation. (The Unix environment does  not  usually  
        suffer  from  this  problem.)  An alternative approach that uses memory  
        from the heap to remember data, instead  of  using  recursive  function  
        calls,  has been implemented to work round this problem. If you want to  
        build a version of PCRE that works this way, add  
543    
544           --disable-stack-for-recursion           --enable-pcregrep-libz
545             --enable-pcregrep-libbz2
546    
547         to the configure command. With this configuration, PCRE  will  use  the         to the configure command. These options naturally require that the rel-
548         pcre_stack_malloc  and pcre_stack_free variables to call memory manage-         evant libraries are installed on your system. Configuration  will  fail
549         ment functions. Separate functions are provided because  the  usage  is         if they are not.
        very  predictable:  the  block sizes requested are always the same, and  
        the blocks are always freed in reverse order. A calling  program  might  
        be  able  to implement optimized functions that perform better than the  
        standard malloc() and  free()  functions.  PCRE  runs  noticeably  more  
        slowly when built in this way. This option affects only the pcre_exec()  
        function; it is not relevant for the the pcre_dfa_exec() function.  
550    
551    
552  USING EBCDIC CODE  PCRETEST OPTION FOR LIBREADLINE SUPPORT
553    
554         PCRE assumes by default that it will run in an  environment  where  the         If you add
        character  code  is  ASCII  (or Unicode, which is a superset of ASCII).  
        PCRE can, however, be compiled to  run  in  an  EBCDIC  environment  by  
        adding  
555    
556           --enable-ebcdic           --enable-pcretest-libreadline
557    
558           to  the  configure  command,  pcretest  is  linked with the libreadline
559           library, and when its input is from a terminal, it reads it  using  the
560           readline() function. This provides line-editing and history facilities.
561           Note that libreadline is GPL-licensed, so if you distribute a binary of
562           pcretest linked in this way, there may be licensing issues.
563    
564           Setting  this  option  causes  the -lreadline option to be added to the
565           pcretest build. In many operating environments with  a  sytem-installed
566           libreadline this is sufficient. However, in some environments (e.g.  if
567           an unmodified distribution version of readline is in use),  some  extra
568           configuration  may  be necessary. The INSTALL file for libreadline says
569           this:
570    
571             "Readline uses the termcap functions, but does not link with the
572             termcap or curses library itself, allowing applications which link
573             with readline the to choose an appropriate library."
574    
575           If your environment has not been set up so that an appropriate  library
576           is automatically included, you may need to add something like
577    
578             LIBS="-ncurses"
579    
580           immediately before the configure command.
581    
582    
583    SEE ALSO
584    
585           pcreapi(3), pcre_config(3).
586    
587    
588    AUTHOR
589    
590           Philip Hazel
591           University Computing Service
592           Cambridge CB2 3QH, England.
593    
        to the configure command.  
594    
595  Last updated: 15 August 2005  REVISION
596  Copyright (c) 1997-2005 University of Cambridge.  
597           Last updated: 29 September 2009
598           Copyright (c) 1997-2009 University of Cambridge.
599  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
600    
601    
# Line 431  PCRE MATCHING ALGORITHMS Line 631  PCRE MATCHING ALGORITHMS
631           <something> <something else> <something further>           <something> <something else> <something further>
632    
633         there are three possible answers. The standard algorithm finds only one         there are three possible answers. The standard algorithm finds only one
634         of them, whereas the DFA algorithm finds all three.         of them, whereas the alternative algorithm finds all three.
635    
636    
637  REGULAR EXPRESSIONS AS TREES  REGULAR EXPRESSIONS AS TREES
# Line 440  REGULAR EXPRESSIONS AS TREES Line 640  REGULAR EXPRESSIONS AS TREES
640         resented  as  a  tree structure. An unlimited repetition in the pattern         resented  as  a  tree structure. An unlimited repetition in the pattern
641         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
642         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
643         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
644         search  a  tree: depth-first and breadth-first, and these correspond to         tree:  depth-first  and  breadth-first, and these correspond to the two
645         the two matching algorithms provided by PCRE.         matching algorithms provided by PCRE.
646    
647    
648  THE STANDARD MATCHING ALGORITHM  THE STANDARD MATCHING ALGORITHM
649    
650         In the terminology of Jeffrey Friedl's book Mastering  Regular  Expres-         In the terminology of Jeffrey Friedl's book "Mastering Regular  Expres-
651         sions,  the  standard  algorithm  is  an "NFA algorithm". It conducts a         sions",  the  standard  algorithm  is an "NFA algorithm". It conducts a
652         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
653         single path through the tree, checking that the subject matches what is         single path through the tree, checking that the subject matches what is
654         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 672  THE STANDARD MATCHING ALGORITHM
672         This provides support for capturing parentheses and back references.         This provides support for capturing parentheses and back references.
673    
674    
675  THE DFA MATCHING ALGORITHM  THE ALTERNATIVE MATCHING ALGORITHM
676    
677         DFA stands for "deterministic finite automaton", but you do not need to         This algorithm conducts a breadth-first search of  the  tree.  Starting
678         understand the origins of that name. This algorithm conducts a breadth-         from  the  first  matching  point  in the subject, it scans the subject
679         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
680         subject,  it scans the subject string from left to right, once, charac-         this,  it remembers all the paths through the tree that represent valid
681         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",
682         through the tree that represent valid matches.         though  it is not implemented as a traditional finite state machine (it
683           keeps multiple states active simultaneously).
684         The  scan  continues until either the end of the subject is reached, or  
685         there are no more unterminated paths. At this point,  terminated  paths         Although the general principle of this matching algorithm  is  that  it
686         represent  the different matching possibilities (if there are none, the         scans  the subject string only once, without backtracking, there is one
687         match has failed).  Thus, if there is more  than  one  possible  match,         exception: when a lookaround assertion is encountered,  the  characters
688           following  or  preceding  the  current  point  have to be independently
689           inspected.
690    
691           The scan continues until either the end of the subject is  reached,  or
692           there  are  no more unterminated paths. At this point, terminated paths
693           represent the different matching possibilities (if there are none,  the
694           match  has  failed).   Thus,  if there is more than one possible match,
695         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-
696         est. In PCRE, there is an option to stop the algorithm after the  first         est.  There  is  an  option to stop the algorithm after the first match
697         match (which is necessarily the shortest) has been found.         (which is necessarily the shortest) is found.
698    
699         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
700         subject. If the pattern         subject. If the pattern
701    
702           cat(er(pillar)?)           cat(er(pillar)?)
703    
704         is matched against the string "the caterpillar catchment",  the  result         is  matched  against the string "the caterpillar catchment", the result
705         will  be the three strings "cat", "cater", and "caterpillar" that start         will be the three strings "cat", "cater", and "caterpillar" that  start
706         at the fourth character of the subject. The algorithm does not automat-         at the fourth character of the subject. The algorithm does not automat-
707         ically move on to find matches that start at later positions.         ically move on to find matches that start at later positions.
708    
709         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
710         supported by the DFA matching algorithm. They are as follows:         supported by the alternative matching algorithm. They are as follows:
711    
712         1. Because the algorithm finds all  possible  matches,  the  greedy  or         1.  Because  the  algorithm  finds  all possible matches, the greedy or
713         ungreedy  nature  of repetition quantifiers is not relevant. Greedy and         ungreedy nature of repetition quantifiers is not relevant.  Greedy  and
714         ungreedy quantifiers are treated in exactly the same way.         ungreedy quantifiers are treated in exactly the same way. However, pos-
715           sessive quantifiers can make a difference when what follows could  also
716           match what is quantified, for example in a pattern like this:
717    
718             ^a++\w!
719    
720           This  pattern matches "aaab!" but not "aaa!", which would be matched by
721           a non-possessive quantifier. Similarly, if an atomic group is  present,
722           it  is matched as if it were a standalone pattern at the current point,
723           and the longest match is then "locked in" for the rest of  the  overall
724           pattern.
725    
726         2. When dealing with multiple paths through the tree simultaneously, it         2. When dealing with multiple paths through the tree simultaneously, it
727         is  not  straightforward  to  keep track of captured substrings for the         is not straightforward to keep track of  captured  substrings  for  the
728         different matching possibilities, and  PCRE's  implementation  of  this         different  matching  possibilities,  and  PCRE's implementation of this
729         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-
730         strings are available.         strings are available.
731    
732         3. Because no substrings are captured, back references within the  pat-         3.  Because no substrings are captured, back references within the pat-
733         tern are not supported, and cause errors if encountered.         tern are not supported, and cause errors if encountered.
734    
735         4.  For  the same reason, conditional expressions that use a backrefer-         4. For the same reason, conditional expressions that use  a  backrefer-
736         ence as the condition are not supported.         ence  as  the  condition or test for a specific group recursion are not
737           supported.
738    
739           5. Because many paths through the tree may be  active,  the  \K  escape
740           sequence, which resets the start of the match when encountered (but may
741           be on some paths and not on others), is not  supported.  It  causes  an
742           error if encountered.
743    
744         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
745         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.
746    
747         6.  The \C escape sequence, which (in the standard algorithm) matches a         7. The \C escape sequence, which (in the standard algorithm) matches  a
748         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-
749         rithm moves through the subject string one character at a time, for all         tive algorithm moves through the subject  string  one  character  at  a
750         active paths through the tree.         time, for all active paths through the tree.
751    
752           8.  Except for (*FAIL), the backtracking control verbs such as (*PRUNE)
753           are not supported. (*FAIL) is supported, and  behaves  like  a  failing
754           negative assertion.
755    
 ADVANTAGES OF THE DFA ALGORITHM  
756    
757         Using the DFA matching algorithm provides the following advantages:  ADVANTAGES OF THE ALTERNATIVE ALGORITHM
758    
759           Using  the alternative matching algorithm provides the following advan-
760           tages:
761    
762         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-
763         ically  found,  and  in particular, the longest match is found. To find         ically  found,  and  in particular, the longest match is found. To find
764         more than one match using the standard algorithm, you have to do kludgy         more than one match using the standard algorithm, you have to do kludgy
765         things with callouts.         things with callouts.
766    
767         2.  There is much better support for partial matching. The restrictions         2.  Because  the  alternative  algorithm  scans the subject string just
768         on the content of the pattern that apply when using the standard  algo-         once, and never needs to backtrack, it is possible to  pass  very  long
769         rithm  for partial matching do not apply to the DFA algorithm. For non-         subject  strings  to  the matching function in several pieces, checking
770         anchored patterns, the starting position of a partial match  is  avail-         for partial matching each time.  The  pcrepartial  documentation  gives
771         able.         details of partial matching.
   
        3.  Because  the  DFA algorithm scans the subject string just once, and  
        never needs to backtrack, it is possible  to  pass  very  long  subject  
        strings  to  the matching function in several pieces, checking for par-  
        tial matching each time.  
772    
773    
774  DISADVANTAGES OF THE DFA ALGORITHM  DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
775    
776         The DFA algorithm suffers from a number of disadvantages:         The alternative algorithm suffers from a number of disadvantages:
777    
778         1. It is substantially slower than  the  standard  algorithm.  This  is         1.  It  is  substantially  slower  than the standard algorithm. This is
779         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
780         because it is less susceptible to optimization.         because it is less susceptible to optimization.
781    
782         2. Capturing parentheses and back references are not supported.         2. Capturing parentheses and back references are not supported.
783    
784         3. The "atomic group" feature of PCRE regular expressions is supported,         3. Although atomic groups are supported, their use does not provide the
785         but  does not provide the advantage that it does for the standard algo-         performance advantage that it does for the standard algorithm.
786         rithm.  
787    
788    AUTHOR
789    
790           Philip Hazel
791           University Computing Service
792           Cambridge CB2 3QH, England.
793    
794    
795  Last updated: 28 February 2005  REVISION
796  Copyright (c) 1997-2005 University of Cambridge.  
797           Last updated: 29 September 2009
798           Copyright (c) 1997-2009 University of Cambridge.
799  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
800    
801    
# Line 616  PCRE NATIVE API Line 848  PCRE NATIVE API
848         int pcre_get_stringnumber(const pcre *code,         int pcre_get_stringnumber(const pcre *code,
849              const char *name);              const char *name);
850    
851           int pcre_get_stringtable_entries(const pcre *code,
852                const char *name, char **first, char **last);
853    
854         int pcre_get_substring(const char *subject, int *ovector,         int pcre_get_substring(const char *subject, int *ovector,
855              int stringcount, int stringnumber,              int stringcount, int stringnumber,
856              const char **stringptr);              const char **stringptr);
# Line 654  PCRE NATIVE API Line 889  PCRE NATIVE API
889  PCRE API OVERVIEW  PCRE API OVERVIEW
890    
891         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
892         is also a set of wrapper functions that correspond to the POSIX regular         are also some wrapper functions that correspond to  the  POSIX  regular
893         expression  API.  These  are  described in the pcreposix documentation.         expression  API.  These  are  described in the pcreposix documentation.
894         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
895         distributed with PCRE. It is documented in the pcrecpp page.         distributed with PCRE. It is documented in the pcrecpp page.
# Line 671  PCRE API OVERVIEW Line 906  PCRE API OVERVIEW
906         pcre_exec() are used for compiling and matching regular expressions  in         pcre_exec() are used for compiling and matching regular expressions  in
907         a  Perl-compatible  manner. A sample program that demonstrates the sim-         a  Perl-compatible  manner. A sample program that demonstrates the sim-
908         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
909         the  source distribution. The pcresample documentation describes how to         the PCRE source distribution. A listing of this program is given in the
910         run it.         pcredemo documentation, and the pcresample documentation describes  how
911           to compile and run it.
912    
913         A second matching function, pcre_dfa_exec(), which is not Perl-compati-         A second matching function, pcre_dfa_exec(), which is not Perl-compati-
914         ble,  is  also provided. This uses a different algorithm for the match-         ble, is also provided. This uses a different algorithm for  the  match-
915         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
916         the  subject),  not  just  one. However, this algorithm does not return         point in the subject), and scans the subject just  once  (unless  there
917           are  lookbehind  assertions).  However,  this algorithm does not return
918         captured substrings. A description of the two matching  algorithms  and         captured substrings. A description of the two matching  algorithms  and
919         their  advantages  and disadvantages is given in the pcrematching docu-         their  advantages  and disadvantages is given in the pcrematching docu-
920         mentation.         mentation.
# Line 692  PCRE API OVERVIEW Line 929  PCRE API OVERVIEW
929           pcre_get_named_substring()           pcre_get_named_substring()
930           pcre_get_substring_list()           pcre_get_substring_list()
931           pcre_get_stringnumber()           pcre_get_stringnumber()
932             pcre_get_stringtable_entries()
933    
934         pcre_free_substring() and pcre_free_substring_list() are also provided,         pcre_free_substring() and pcre_free_substring_list() are also provided,
935         to free the memory used for extracted strings.         to free the memory used for extracted strings.
# Line 723  PCRE API OVERVIEW Line 961  PCRE API OVERVIEW
961         indirections  to  memory  management functions. These special functions         indirections  to  memory  management functions. These special functions
962         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
963         data, instead of recursive function calls, when running the pcre_exec()         data, instead of recursive function calls, when running the pcre_exec()
964         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
965         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-
966         management, it runs more slowly.  Separate functions  are  provided  so         ments that have limited stacks. Because of the greater  use  of  memory
967         that  special-purpose  external  code  can  be used for this case. When         management,  it  runs  more  slowly. Separate functions are provided so
968         used, these functions are always called in a  stack-like  manner  (last         that special-purpose external code can be  used  for  this  case.  When
969         obtained,  first freed), and always for memory blocks of the same size.         used,  these  functions  are always called in a stack-like manner (last
970           obtained, first freed), and always for memory blocks of the same  size.
971           There  is  a discussion about PCRE's stack usage in the pcrestack docu-
972           mentation.
973    
974         The global variable pcre_callout initially contains NULL. It can be set         The global variable pcre_callout initially contains NULL. It can be set
975         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 977  PCRE API OVERVIEW
977         pcrecallout documentation.         pcrecallout documentation.
978    
979    
980    NEWLINES
981    
982           PCRE  supports five different conventions for indicating line breaks in
983           strings: a single CR (carriage return) character, a  single  LF  (line-
984           feed) character, the two-character sequence CRLF, any of the three pre-
985           ceding, or any Unicode newline sequence. The Unicode newline  sequences
986           are  the  three just mentioned, plus the single characters VT (vertical
987           tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS  (line
988           separator, U+2028), and PS (paragraph separator, U+2029).
989    
990           Each  of  the first three conventions is used by at least one operating
991           system as its standard newline sequence. When PCRE is built, a  default
992           can  be  specified.  The default default is LF, which is the Unix stan-
993           dard. When PCRE is run, the default can be overridden,  either  when  a
994           pattern is compiled, or when it is matched.
995    
996           At compile time, the newline convention can be specified by the options
997           argument of pcre_compile(), or it can be specified by special  text  at
998           the start of the pattern itself; this overrides any other settings. See
999           the pcrepattern page for details of the special character sequences.
1000    
1001           In the PCRE documentation the word "newline" is used to mean "the char-
1002           acter  or pair of characters that indicate a line break". The choice of
1003           newline convention affects the handling of  the  dot,  circumflex,  and
1004           dollar metacharacters, the handling of #-comments in /x mode, and, when
1005           CRLF is a recognized line ending sequence, the match position  advance-
1006           ment for a non-anchored pattern. There is more detail about this in the
1007           section on pcre_exec() options below.
1008    
1009           The choice of newline convention does not affect the interpretation  of
1010           the  \n  or  \r  escape  sequences, nor does it affect what \R matches,
1011           which is controlled in a similar way, but by separate options.
1012    
1013    
1014  MULTITHREADING  MULTITHREADING
1015    
1016         The  PCRE  functions  can be used in multi-threading applications, with         The PCRE functions can be used in  multi-threading  applications,  with
1017         the  proviso  that  the  memory  management  functions  pointed  to  by         the  proviso  that  the  memory  management  functions  pointed  to  by
1018         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
1019         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 1028  SAVING PRECOMPILED PATTERNS FOR LATER US
1028         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
1029         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
1030         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
1031         pcreprecompile documentation.         pcreprecompile documentation. However, compiling a  regular  expression
1032           with  one version of PCRE for use with a different version is not guar-
1033           anteed to work and may cause crashes.
1034    
1035    
1036  CHECKING BUILD-TIME OPTIONS  CHECKING BUILD-TIME OPTIONS
# Line 782  CHECKING BUILD-TIME OPTIONS Line 1059  CHECKING BUILD-TIME OPTIONS
1059    
1060           PCRE_CONFIG_NEWLINE           PCRE_CONFIG_NEWLINE
1061    
1062         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
1063         used  for the newline character. It is either linefeed (10) or carriage         sequence  that is recognized as meaning "newline". The four values that
1064         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,
1065         operating system.         and  -1  for  ANY.  Though they are derived from ASCII, the same values
1066           are returned in EBCDIC environments. The default should normally corre-
1067           spond to the standard sequence for your operating system.
1068    
1069             PCRE_CONFIG_BSR
1070    
1071           The output is an integer whose value indicates what character sequences
1072           the \R escape sequence matches by default. A value of 0 means  that  \R
1073           matches  any  Unicode  line ending sequence; a value of 1 means that \R
1074           matches only CR, LF, or CRLF. The default can be overridden when a pat-
1075           tern is compiled or matched.
1076    
1077           PCRE_CONFIG_LINK_SIZE           PCRE_CONFIG_LINK_SIZE
1078    
# Line 804  CHECKING BUILD-TIME OPTIONS Line 1091  CHECKING BUILD-TIME OPTIONS
1091    
1092           PCRE_CONFIG_MATCH_LIMIT           PCRE_CONFIG_MATCH_LIMIT
1093    
1094         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-
1095         internal  matching  function  calls in a pcre_exec() execution. Further         ber  of  internal  matching  function calls in a pcre_exec() execution.
1096         details are given with pcre_exec() below.         Further details are given with pcre_exec() below.
1097    
1098             PCRE_CONFIG_MATCH_LIMIT_RECURSION
1099    
1100           The output is a long integer that gives the default limit for the depth
1101           of   recursion  when  calling  the  internal  matching  function  in  a
1102           pcre_exec() execution.  Further  details  are  given  with  pcre_exec()
1103           below.
1104    
1105           PCRE_CONFIG_STACKRECURSE           PCRE_CONFIG_STACKRECURSE
1106    
1107         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
1108         running pcre_exec() is implemented by recursive function calls that use         running pcre_exec() is implemented by recursive function calls that use
1109         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
1110         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
1111         on the  heap  instead  of  recursive  function  calls.  In  this  case,         on  the  heap  instead  of  recursive  function  calls.  In  this case,
1112         pcre_stack_malloc  and  pcre_stack_free  are  called  to  manage memory         pcre_stack_malloc and  pcre_stack_free  are  called  to  manage  memory
1113         blocks on the heap, thus avoiding the use of the stack.         blocks on the heap, thus avoiding the use of the stack.
1114    
1115    
# Line 832  COMPILING A PATTERN Line 1126  COMPILING A PATTERN
1126    
1127         Either of the functions pcre_compile() or pcre_compile2() can be called         Either of the functions pcre_compile() or pcre_compile2() can be called
1128         to compile a pattern into an internal form. The only difference between         to compile a pattern into an internal form. The only difference between
1129         the two interfaces is that pcre_compile2() has an additional  argument,         the  two interfaces is that pcre_compile2() has an additional argument,
1130         errorcodeptr, via which a numerical error code can be returned.         errorcodeptr, via which a numerical error  code  can  be  returned.  To
1131           avoid  too  much repetition, we refer just to pcre_compile() below, but
1132           the information applies equally to pcre_compile2().
1133    
1134         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
1135         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
1136         obtained  via  pcre_malloc is returned. This contains the compiled code         obtained via pcre_malloc is returned. This contains the  compiled  code
1137         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
1138         is a typedef for a structure whose contents are not externally defined.         is a typedef for a structure whose contents are not externally defined.
1139         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
1140         required.         longer required.
1141    
1142         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
1143         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
1144         fully  relocatable, because it may contain a copy of the tableptr argu-         fully relocatable, because it may contain a copy of the tableptr  argu-
1145         ment, which is an address (see below).         ment, which is an address (see below).
1146    
1147         The options argument contains independent bits that affect the compila-         The options argument contains various bit settings that affect the com-
1148         tion.  It  should  be  zero  if  no options are required. The available         pilation. It should be zero if no options are required.  The  available
1149         options are described below. Some of them, in  particular,  those  that         options  are  described  below. Some of them (in particular, those that
1150         are  compatible  with  Perl,  can also be set and unset from within the         are compatible with Perl, but some others as well) can also be set  and
1151         pattern (see the detailed description  in  the  pcrepattern  documenta-         unset  from  within  the  pattern  (see the detailed description in the
1152         tion).  For  these options, the contents of the options argument speci-         pcrepattern documentation). For those options that can be different  in
1153         fies their initial settings at the start of compilation and  execution.         different  parts  of  the pattern, the contents of the options argument
1154         The  PCRE_ANCHORED option can be set at the time of matching as well as         specifies their settings at the start of compilation and execution. The
1155         at compile time.         PCRE_ANCHORED, PCRE_BSR_xxx, and PCRE_NEWLINE_xxx options can be set at
1156           the time of matching as well as at compile time.
1157    
1158         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
1159         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and
1160         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-
1161         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
1162         the error was discovered is  placed  in  the  variable  pointed  to  by         try to free it. The byte offset from the start of the  pattern  to  the
1163         erroffset,  which  must  not  be  NULL. If it is, an immediate error is         character  that  was  being  processed when the error was discovered is
1164         given.         placed in the variable pointed to by erroffset, which must not be NULL.
1165           If  it  is,  an  immediate error is given. Some errors are not detected
1166         If pcre_compile2() is used instead of pcre_compile(),  and  the  error-         until checks are carried out when the whole pattern has  been  scanned;
1167         codeptr  argument is not NULL, a non-zero error code number is returned         in this case the offset is set to the end of the pattern.
1168         via this argument in the event of an error. This is in addition to  the  
1169           If  pcre_compile2()  is  used instead of pcre_compile(), and the error-
1170           codeptr argument is not NULL, a non-zero error code number is  returned
1171           via  this argument in the event of an error. This is in addition to the
1172         textual error message. Error codes and messages are listed below.         textual error message. Error codes and messages are listed below.
1173    
1174         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
1175         character tables that are  built  when  PCRE  is  compiled,  using  the         character  tables  that  are  built  when  PCRE  is compiled, using the
1176         default  C  locale.  Otherwise, tableptr must be an address that is the         default C locale. Otherwise, tableptr must be an address  that  is  the
1177         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
1178         compiled  pattern,  and used again by pcre_exec(), unless another table         compiled pattern, and used again by pcre_exec(), unless  another  table
1179         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
1180         support below.         support below.
1181    
1182         This  code  fragment  shows a typical straightforward call to pcre_com-         This code fragment shows a typical straightforward  call  to  pcre_com-
1183         pile():         pile():
1184    
1185           pcre *re;           pcre *re;
# Line 892  COMPILING A PATTERN Line 1192  COMPILING A PATTERN
1192             &erroffset,       /* for error offset */             &erroffset,       /* for error offset */
1193             NULL);            /* use default character tables */             NULL);            /* use default character tables */
1194    
1195         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
1196         file:         file:
1197    
1198           PCRE_ANCHORED           PCRE_ANCHORED
1199    
1200         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
1201         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
1202         that  is being searched (the "subject string"). This effect can also be         that is being searched (the "subject string"). This effect can also  be
1203         achieved by appropriate constructs in the pattern itself, which is  the         achieved  by appropriate constructs in the pattern itself, which is the
1204         only way to do it in Perl.         only way to do it in Perl.
1205    
1206           PCRE_AUTO_CALLOUT           PCRE_AUTO_CALLOUT
1207    
1208         If this bit is set, pcre_compile() automatically inserts callout items,         If this bit is set, pcre_compile() automatically inserts callout items,
1209         all with number 255, before each pattern item. For  discussion  of  the         all  with  number  255, before each pattern item. For discussion of the
1210         callout facility, see the pcrecallout documentation.         callout facility, see the pcrecallout documentation.
1211    
1212             PCRE_BSR_ANYCRLF
1213             PCRE_BSR_UNICODE
1214    
1215           These options (which are mutually exclusive) control what the \R escape
1216           sequence  matches.  The choice is either to match only CR, LF, or CRLF,
1217           or to match any Unicode newline sequence. The default is specified when
1218           PCRE is built. It can be overridden from within the pattern, or by set-
1219           ting an option when a compiled pattern is matched.
1220    
1221           PCRE_CASELESS           PCRE_CASELESS
1222    
1223         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
1224         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
1225         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
1226         always understands the concept of case for characters whose values  are         always  understands the concept of case for characters whose values are
1227         less  than 128, so caseless matching is always possible. For characters         less than 128, so caseless matching is always possible. For  characters
1228         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-
1229         piled  with Unicode property support, but not otherwise. If you want to         piled with Unicode property support, but not otherwise. If you want  to
1230         use caseless matching for characters 128 and  above,  you  must  ensure         use  caseless  matching  for  characters 128 and above, you must ensure
1231         that  PCRE  is  compiled  with Unicode property support as well as with         that PCRE is compiled with Unicode property support  as  well  as  with
1232         UTF-8 support.         UTF-8 support.
1233    
1234           PCRE_DOLLAR_ENDONLY           PCRE_DOLLAR_ENDONLY
1235    
1236         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
1237         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
1238         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
1239         not  before  any  other  newlines).  The  PCRE_DOLLAR_ENDONLY option is         before any other newlines). The PCRE_DOLLAR_ENDONLY option  is  ignored
1240         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
1241         in Perl, and no way to set it within a pattern.         Perl, and no way to set it within a pattern.
1242    
1243           PCRE_DOTALL           PCRE_DOTALL
1244    
1245         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-
1246         acters, including newlines. Without it,  newlines  are  excluded.  This         acters,  including  those that indicate newline. Without it, a dot does
1247         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
1248         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
1249         always  matches a newline character, independent of the setting of this         by a (?s) option setting. A negative class such as [^a] always  matches
1250         option.         newline characters, independent of the setting of this option.
1251    
1252             PCRE_DUPNAMES
1253    
1254           If  this  bit is set, names used to identify capturing subpatterns need
1255           not be unique. This can be helpful for certain types of pattern when it
1256           is  known  that  only  one instance of the named subpattern can ever be
1257           matched. There are more details of named subpatterns  below;  see  also
1258           the pcrepattern documentation.
1259    
1260           PCRE_EXTENDED           PCRE_EXTENDED
1261    
1262         If this bit is set, whitespace  data  characters  in  the  pattern  are         If  this  bit  is  set,  whitespace  data characters in the pattern are
1263         totally ignored except when escaped or inside a character class. White-         totally ignored except when escaped or inside a character class. White-
1264         space does not include the VT character (code 11). In addition, charac-         space does not include the VT character (code 11). In addition, charac-
1265         ters between an unescaped # outside a character class and the next new-         ters between an unescaped # outside a character class and the next new-
1266         line character, inclusive, are also  ignored.  This  is  equivalent  to         line,  inclusive,  are  also  ignored.  This is equivalent to Perl's /x
1267         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-
1268         option setting.         ting.
1269    
1270         This option makes it possible to include  comments  inside  complicated         This  option  makes  it possible to include comments inside complicated
1271         patterns.   Note,  however,  that this applies only to data characters.         patterns.  Note, however, that this applies only  to  data  characters.
1272         Whitespace  characters  may  never  appear  within  special   character         Whitespace   characters  may  never  appear  within  special  character
1273         sequences  in  a  pattern,  for  example  within the sequence (?( which         sequences in a pattern, for  example  within  the  sequence  (?(  which
1274         introduces a conditional subpattern.         introduces a conditional subpattern.
1275    
1276           PCRE_EXTRA           PCRE_EXTRA
1277    
1278         This option was invented in order to turn on  additional  functionality         This  option  was invented in order to turn on additional functionality
1279         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
1280         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
1281         letter  that  has  no  special  meaning causes an error, thus reserving         letter that has no special meaning  causes  an  error,  thus  reserving
1282         these combinations for future expansion. By  default,  as  in  Perl,  a         these  combinations  for  future  expansion.  By default, as in Perl, a
1283         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
1284         literal. There are at present no  other  features  controlled  by  this         literal.  (Perl can, however, be persuaded to give a warning for this.)
1285         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
1286           can also be set by a (?X) option setting within a pattern.
1287    
1288           PCRE_FIRSTLINE           PCRE_FIRSTLINE
1289    
1290         If  this  option  is  set,  an  unanchored pattern is required to match         If  this  option  is  set,  an  unanchored pattern is required to match
1291         before or at the first newline character in the subject string,  though         before or at the first  newline  in  the  subject  string,  though  the
1292         the matched text may continue over the newline.         matched text may continue over the newline.
1293    
1294             PCRE_JAVASCRIPT_COMPAT
1295    
1296           If this option is set, PCRE's behaviour is changed in some ways so that
1297           it is compatible with JavaScript rather than Perl. The changes  are  as
1298           follows:
1299    
1300           (1)  A  lone  closing square bracket in a pattern causes a compile-time
1301           error, because this is illegal in JavaScript (by default it is  treated
1302           as a data character). Thus, the pattern AB]CD becomes illegal when this
1303           option is set.
1304    
1305           (2) At run time, a back reference to an unset subpattern group  matches
1306           an  empty  string (by default this causes the current matching alterna-
1307           tive to fail). A pattern such as (\1)(a) succeeds when this  option  is
1308           set  (assuming  it can find an "a" in the subject), whereas it fails by
1309           default, for Perl compatibility.
1310    
1311           PCRE_MULTILINE           PCRE_MULTILINE
1312    
1313         By  default,  PCRE  treats the subject string as consisting of a single         By default, PCRE treats the subject string as consisting  of  a  single
1314         line of characters (even if it actually contains newlines). The  "start         line  of characters (even if it actually contains newlines). The "start
1315         of  line"  metacharacter  (^)  matches only at the start of the string,         of line" metacharacter (^) matches only at the  start  of  the  string,
1316         while the "end of line" metacharacter ($) matches only at  the  end  of         while  the  "end  of line" metacharacter ($) matches only at the end of
1317         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY
1318         is set). This is the same as Perl.         is set). This is the same as Perl.
1319    
1320         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"
1321         constructs  match  immediately following or immediately before any new-         constructs match immediately following or immediately  before  internal
1322         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
1323         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
1324         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-
1325         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,
1326         setting PCRE_MULTILINE has no effect.         setting PCRE_MULTILINE has no effect.
1327    
1328             PCRE_NEWLINE_CR
1329             PCRE_NEWLINE_LF
1330             PCRE_NEWLINE_CRLF
1331             PCRE_NEWLINE_ANYCRLF
1332             PCRE_NEWLINE_ANY
1333    
1334           These  options  override the default newline definition that was chosen
1335           when PCRE was built. Setting the first or the second specifies  that  a
1336           newline  is  indicated  by a single character (CR or LF, respectively).
1337           Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by  the
1338           two-character  CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF specifies
1339           that any of the three preceding sequences should be recognized. Setting
1340           PCRE_NEWLINE_ANY  specifies that any Unicode newline sequence should be
1341           recognized. The Unicode newline sequences are the three just mentioned,
1342           plus  the  single  characters  VT (vertical tab, U+000B), FF (formfeed,
1343           U+000C), NEL (next line, U+0085), LS (line separator, U+2028),  and  PS
1344           (paragraph  separator,  U+2029).  The  last  two are recognized only in
1345           UTF-8 mode.
1346    
1347           The newline setting in the  options  word  uses  three  bits  that  are
1348           treated as a number, giving eight possibilities. Currently only six are
1349           used (default plus the five values above). This means that if  you  set
1350           more  than one newline option, the combination may or may not be sensi-
1351           ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
1352           PCRE_NEWLINE_CRLF,  but other combinations may yield unused numbers and
1353           cause an error.
1354    
1355           The only time that a line break is specially recognized when  compiling
1356           a  pattern  is  if  PCRE_EXTENDED  is set, and an unescaped # outside a
1357           character class is encountered. This indicates  a  comment  that  lasts
1358           until  after the next line break sequence. In other circumstances, line
1359           break  sequences  are  treated  as  literal  data,   except   that   in
1360           PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters
1361           and are therefore ignored.
1362    
1363           The newline option that is set at compile time becomes the default that
1364           is used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
1365    
1366           PCRE_NO_AUTO_CAPTURE           PCRE_NO_AUTO_CAPTURE
1367    
1368         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-
1369         theses  in the pattern. Any opening parenthesis that is not followed by         theses in the pattern. Any opening parenthesis that is not followed  by
1370         ? behaves as if it were followed by ?: but named parentheses can  still         ?  behaves as if it were followed by ?: but named parentheses can still
1371         be  used  for  capturing  (and  they acquire numbers in the usual way).         be used for capturing (and they acquire  numbers  in  the  usual  way).
1372         There is no equivalent of this option in Perl.         There is no equivalent of this option in Perl.
1373    
1374           PCRE_UNGREEDY           PCRE_UNGREEDY
1375    
1376         This option inverts the "greediness" of the quantifiers  so  that  they         This  option  inverts  the "greediness" of the quantifiers so that they
1377         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
1378         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
1379         within the pattern.         within the pattern.
1380    
1381           PCRE_UTF8           PCRE_UTF8
1382    
1383         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
1384         strings of UTF-8 characters instead of single-byte  character  strings.         strings  of  UTF-8 characters instead of single-byte character strings.
1385         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-
1386         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
1387         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
1388         UTF-8 support in the main pcre page.         UTF-8 support in the main pcre page.
1389    
1390           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
1391    
1392         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
1393         automatically  checked. If an invalid UTF-8 sequence of bytes is found,         automatically checked. There is a  discussion  about  the  validity  of
1394         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
1395         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
1396         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-
1397         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
1398         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
1399         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
1400         ing of subject strings.         can  also be passed to pcre_exec() and pcre_dfa_exec(), to suppress the
1401           UTF-8 validity checking of subject strings.
1402    
1403    
1404  COMPILATION ERROR CODES  COMPILATION ERROR CODES
1405    
1406         The following table lists the error  codes  than  may  be  returned  by         The following table lists the error  codes  than  may  be  returned  by
1407         pcre_compile2(),  along with the error messages that may be returned by         pcre_compile2(),  along with the error messages that may be returned by
1408         both compiling functions.         both compiling functions. As PCRE has developed, some error codes  have
1409           fallen out of use. To avoid confusion, they have not been re-used.
1410    
1411            0  no error            0  no error
1412            1  \ at end of pattern            1  \ at end of pattern
# Line 1043  COMPILATION ERROR CODES Line 1418  COMPILATION ERROR CODES
1418            7  invalid escape sequence in character class            7  invalid escape sequence in character class
1419            8  range out of order in character class            8  range out of order in character class
1420            9  nothing to repeat            9  nothing to repeat
1421           10  operand of unlimited repeat could match the empty string           10  [this code is not in use]
1422           11  internal error: unexpected repeat           11  internal error: unexpected repeat
1423           12  unrecognized character after (?           12  unrecognized character after (? or (?-
1424           13  POSIX named classes are supported only within a class           13  POSIX named classes are supported only within a class
1425           14  missing )           14  missing )
1426           15  reference to non-existent subpattern           15  reference to non-existent subpattern
1427           16  erroffset passed as NULL           16  erroffset passed as NULL
1428           17  unknown option bit(s) set           17  unknown option bit(s) set
1429           18  missing ) after comment           18  missing ) after comment
1430           19  parentheses nested too deeply           19  [this code is not in use]
1431           20  regular expression too large           20  regular expression is too large
1432           21  failed to get memory           21  failed to get memory
1433           22  unmatched parentheses           22  unmatched parentheses
1434           23  internal error: code overflow           23  internal error: code overflow
1435           24  unrecognized character after (?<           24  unrecognized character after (?<
1436           25  lookbehind assertion is not fixed length           25  lookbehind assertion is not fixed length
1437           26  malformed number after (?(           26  malformed number or name after (?(
1438           27  conditional group contains more than two branches           27  conditional group contains more than two branches
1439           28  assertion expected after (?(           28  assertion expected after (?(
1440           29  (?R or (?digits must be followed by )           29  (?R or (?[+-]digits must be followed by )
1441           30  unknown POSIX class name           30  unknown POSIX class name
1442           31  POSIX collating elements are not supported           31  POSIX collating elements are not supported
1443           32  this version of PCRE is not compiled with PCRE_UTF8 support           32  this version of PCRE is not compiled with PCRE_UTF8 support
1444           33  spare error           33  [this code is not in use]
1445           34  character value in \x{...} sequence is too large           34  character value in \x{...} sequence is too large
1446           35  invalid condition (?(0)           35  invalid condition (?(0)
1447           36  \C not allowed in lookbehind assertion           36  \C not allowed in lookbehind assertion
# Line 1075  COMPILATION ERROR CODES Line 1450  COMPILATION ERROR CODES
1450           39  closing ) for (?C expected           39  closing ) for (?C expected
1451           40  recursive call could loop indefinitely           40  recursive call could loop indefinitely
1452           41  unrecognized character after (?P           41  unrecognized character after (?P
1453           42  syntax error after (?P           42  syntax error in subpattern name (missing terminator)
1454           43  two named groups have the same name           43  two named subpatterns have the same name
1455           44  invalid UTF-8 string           44  invalid UTF-8 string
1456           45  support for \P, \p, and \X has not been compiled           45  support for \P, \p, and \X has not been compiled
1457           46  malformed \P or \p sequence           46  malformed \P or \p sequence
1458           47  unknown property name after \P or \p           47  unknown property name after \P or \p
1459             48  subpattern name is too long (maximum 32 characters)
1460             49  too many named subpatterns (maximum 10000)
1461             50  [this code is not in use]
1462             51  octal value is greater than \377 (not in UTF-8 mode)
1463             52  internal error: overran compiling workspace
1464             53   internal  error:  previously-checked  referenced  subpattern not
1465           found
1466             54  DEFINE group contains more than one branch
1467             55  repeating a DEFINE group is not allowed
1468             56  inconsistent NEWLINE options
1469             57  \g is not followed by a braced, angle-bracketed, or quoted
1470                   name/number or by a plain number
1471             58  a numbered reference must not be zero
1472             59  an argument is not allowed for (*ACCEPT), (*FAIL), or (*COMMIT)
1473             60  (*VERB) not recognized
1474             61  number is too big
1475             62  subpattern name expected
1476             63  digit expected after (?+
1477             64  ] is an invalid data character in JavaScript compatibility mode
1478             65  different names for  subpatterns  of  the  same  number  are  not
1479           allowed
1480             66  (*MARK) must have an argument
1481    
1482           The  numbers  32  and 10000 in errors 48 and 49 are defaults; different
1483           values may be used if the limits were changed when PCRE was built.
1484    
1485    
1486  STUDYING A PATTERN  STUDYING A PATTERN
# Line 1097  STUDYING A PATTERN Line 1497  STUDYING A PATTERN
1497         the results of the study.         the results of the study.
1498    
1499         The  returned  value  from  pcre_study()  can  be  passed  directly  to         The  returned  value  from  pcre_study()  can  be  passed  directly  to
1500         pcre_exec().  However,  a  pcre_extra  block also contains other fields         pcre_exec()  or  pcre_dfa_exec(). However, a pcre_extra block also con-
1501         that can be set by the caller before the block  is  passed;  these  are         tains other fields that can be set by the caller before  the  block  is
1502         described below in the section on matching a pattern.         passed; these are described below in the section on matching a pattern.
1503    
1504         If  studying  the  pattern  does not produce any additional information         If  studying  the  pattern  does  not  produce  any useful information,
1505         pcre_study() returns NULL. In that circumstance, if the calling program         pcre_study() returns NULL. In that circumstance, if the calling program
1506         wants  to  pass  any of the other fields to pcre_exec(), it must set up         wants   to   pass   any   of   the   other  fields  to  pcre_exec()  or
1507         its own pcre_extra block.         pcre_dfa_exec(), it must set up its own pcre_extra block.
1508    
1509         The second argument of pcre_study() contains option bits.  At  present,         The second argument of pcre_study() contains option bits.  At  present,
1510         no options are defined, and this argument should always be zero.         no options are defined, and this argument should always be zero.
1511    
1512         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.
1513         If studying succeeds (even if no data is  returned),  the  variable  it         If studying succeeds (even if no data is  returned),  the  variable  it
1514         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
1515         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
1516         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
1517           after calling pcre_study(), to be sure that it has run successfully.
1518    
1519         This is a typical call to pcre_study():         This is a typical call to pcre_study():
1520    
# Line 1123  STUDYING A PATTERN Line 1524  STUDYING A PATTERN
1524             0,              /* no options exist */             0,              /* no options exist */
1525             &error);        /* set to NULL or points to a message */             &error);        /* set to NULL or points to a message */
1526    
1527         At present, studying a pattern is useful only for non-anchored patterns         Studying a pattern does two things: first, a lower bound for the length
1528         that do not have a single fixed starting character. A bitmap of  possi-         of subject string that is needed to match the pattern is computed. This
1529         ble starting bytes is created.         does not mean that there are any strings of that length that match, but
1530           it  does  guarantee that no shorter strings match. The value is used by
1531           pcre_exec() and pcre_dfa_exec() to avoid  wasting  time  by  trying  to
1532           match  strings  that are shorter than the lower bound. You can find out
1533           the value in a calling program via the pcre_fullinfo() function.
1534    
1535           Studying a pattern is also useful for non-anchored patterns that do not
1536           have  a  single fixed starting character. A bitmap of possible starting
1537           bytes is created. This speeds up finding a position in the  subject  at
1538           which to start matching.
1539    
1540    
1541  LOCALE SUPPORT  LOCALE SUPPORT
1542    
1543         PCRE  handles  caseless matching, and determines whether characters are         PCRE  handles  caseless matching, and determines whether characters are
1544         letters digits, or whatever, by reference to a set of  tables,  indexed         letters, digits, or whatever, by reference to a set of tables,  indexed
1545         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
1546         characters with codes less than 128. Higher-valued  codes  never  match         characters with codes less than 128. Higher-valued  codes  never  match
1547         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
1548         with Unicode character property support.         with Unicode character property support. The use of locales  with  Uni-
1549           code  is discouraged. If you are handling characters with codes greater
1550         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
1551         is  built.  This  is  used when the final argument of pcre_compile() is         not try to mix the two.
1552         NULL, and is sufficient for many applications. An  alternative  set  of  
1553         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
1554         locale from the default. As more and more applications change to  using         argument of pcre_compile() is  NULL.  These  are  sufficient  for  many
1555         Unicode, the need for this locale support is expected to die away.         applications.  Normally, the internal tables recognize only ASCII char-
1556           acters. However, when PCRE is built, it is possible to cause the inter-
1557           nal tables to be rebuilt in the default "C" locale of the local system,
1558           which may cause them to be different.
1559    
1560           The internal tables can always be overridden by tables supplied by  the
1561           application that calls PCRE. These may be created in a different locale
1562           from the default. As more and more applications change  to  using  Uni-
1563           code, the need for this locale support is expected to die away.
1564    
1565         External  tables  are  built by calling the pcre_maketables() function,         External  tables  are  built by calling the pcre_maketables() function,
1566         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 1573  LOCALE SUPPORT
1573           tables = pcre_maketables();           tables = pcre_maketables();
1574           re = pcre_compile(..., tables);           re = pcre_compile(..., tables);
1575    
1576         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;
1577         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".
1578         that the memory containing the tables remains available for as long  as  
1579           When  pcre_maketables()  runs,  the  tables are built in memory that is
1580           obtained via pcre_malloc. It is the caller's responsibility  to  ensure
1581           that  the memory containing the tables remains available for as long as
1582         it is needed.         it is needed.
1583    
1584         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
1585         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()
1586         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-
1587         tern, compilation, studying and matching all happen in the same locale,         tern, compilation, studying and matching all happen in the same locale,
1588         but different patterns can be compiled in different locales.         but different patterns can be compiled in different locales.
1589    
1590         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
1591         the internal tables) to pcre_exec(). Although  not  intended  for  this         the  internal  tables)  to  pcre_exec(). Although not intended for this
1592         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
1593         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
1594         run time is discussed below in the section on matching a pattern.         run time is discussed below in the section on matching a pattern.
1595    
# Line 1178  INFORMATION ABOUT A PATTERN Line 1599  INFORMATION ABOUT A PATTERN
1599         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
1600              int what, void *where);              int what, void *where);
1601    
1602         The  pcre_fullinfo() function returns information about a compiled pat-         The pcre_fullinfo() function returns information about a compiled  pat-
1603         tern. It replaces the obsolete pcre_info() function, which is neverthe-         tern. It replaces the obsolete pcre_info() function, which is neverthe-
1604         less retained for backwards compability (and is documented below).         less retained for backwards compability (and is documented below).
1605    
1606         The  first  argument  for  pcre_fullinfo() is a pointer to the compiled         The first argument for pcre_fullinfo() is a  pointer  to  the  compiled
1607         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
1608         the  pattern  was not studied. The third argument specifies which piece         the pattern was not studied. The third argument specifies  which  piece
1609         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
1610         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
1611         success, or one of the following negative numbers:         success, or one of the following negative numbers:
1612    
1613           PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_NULL       the argument code was NULL
# Line 1194  INFORMATION ABOUT A PATTERN Line 1615  INFORMATION ABOUT A PATTERN
1615           PCRE_ERROR_BADMAGIC   the "magic number" was not found           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1616           PCRE_ERROR_BADOPTION  the value of what was invalid           PCRE_ERROR_BADOPTION  the value of what was invalid
1617    
1618         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
1619         an  simple check against passing an arbitrary memory pointer. Here is a         an simple check against passing an arbitrary memory pointer. Here is  a
1620         typical call of pcre_fullinfo(), to obtain the length of  the  compiled         typical  call  of pcre_fullinfo(), to obtain the length of the compiled
1621         pattern:         pattern:
1622    
1623           int rc;           int rc;
1624           unsigned long int length;           size_t length;
1625           rc = pcre_fullinfo(           rc = pcre_fullinfo(
1626             re,               /* result of pcre_compile() */             re,               /* result of pcre_compile() */
1627             pe,               /* result of pcre_study(), or NULL */             pe,               /* result of pcre_study(), or NULL */
1628             PCRE_INFO_SIZE,   /* what is required */             PCRE_INFO_SIZE,   /* what is required */
1629             &length);         /* where to put the data */             &length);         /* where to put the data */
1630    
1631         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
1632         are as follows:         are as follows:
1633    
1634           PCRE_INFO_BACKREFMAX           PCRE_INFO_BACKREFMAX
1635    
1636         Return the number of the highest back reference  in  the  pattern.  The         Return  the  number  of  the highest back reference in the pattern. The
1637         fourth  argument  should  point to an int variable. Zero is returned if         fourth argument should point to an int variable. Zero  is  returned  if
1638         there are no back references.         there are no back references.
1639    
1640           PCRE_INFO_CAPTURECOUNT           PCRE_INFO_CAPTURECOUNT
1641    
1642         Return the number of capturing subpatterns in the pattern.  The  fourth         Return  the  number of capturing subpatterns in the pattern. The fourth
1643         argument should point to an int variable.         argument should point to an int variable.
1644    
1645           PCRE_INFO_DEFAULT_TABLES           PCRE_INFO_DEFAULT_TABLES
1646    
1647         Return  a pointer to the internal default character tables within PCRE.         Return a pointer to the internal default character tables within  PCRE.
1648         The fourth argument should point to an unsigned char *  variable.  This         The  fourth  argument should point to an unsigned char * variable. This
1649         information call is provided for internal use by the pcre_study() func-         information call is provided for internal use by the pcre_study() func-
1650         tion. External callers can cause PCRE to use  its  internal  tables  by         tion.  External  callers  can  cause PCRE to use its internal tables by
1651         passing a NULL table pointer.         passing a NULL table pointer.
1652    
1653           PCRE_INFO_FIRSTBYTE           PCRE_INFO_FIRSTBYTE
1654    
1655         Return  information  about  the first byte of any matched string, for a         Return information about the first byte of any matched  string,  for  a
1656         non-anchored   pattern.   (This    option    used    to    be    called         non-anchored  pattern. The fourth argument should point to an int vari-
1657         PCRE_INFO_FIRSTCHAR;  the  old  name  is still recognized for backwards         able. (This option used to be called PCRE_INFO_FIRSTCHAR; the old  name
1658         compatibility.)         is still recognized for backwards compatibility.)
1659    
1660         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
1661         (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  
1662    
1663         (a) the pattern was compiled with the PCRE_MULTILINE option, and  every         (a) the pattern was compiled with the PCRE_MULTILINE option, and  every
1664         branch starts with "^", or         branch starts with "^", or
# Line 1258  INFORMATION ABOUT A PATTERN Line 1678  INFORMATION ABOUT A PATTERN
1678         returned.  The fourth argument should point to an unsigned char * vari-         returned.  The fourth argument should point to an unsigned char * vari-
1679         able.         able.
1680    
1681             PCRE_INFO_HASCRORLF
1682    
1683           Return 1 if the pattern contains any explicit  matches  for  CR  or  LF
1684           characters,  otherwise  0.  The  fourth argument should point to an int
1685           variable. An explicit match is either a literal CR or LF character,  or
1686           \r or \n.
1687    
1688             PCRE_INFO_JCHANGED
1689    
1690           Return  1  if  the (?J) or (?-J) option setting is used in the pattern,
1691           otherwise 0. The fourth argument should point to an int variable.  (?J)
1692           and (?-J) set and unset the local PCRE_DUPNAMES option, respectively.
1693    
1694           PCRE_INFO_LASTLITERAL           PCRE_INFO_LASTLITERAL
1695    
1696         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
1697         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
1698         recorded. The fourth argument should point to an int variable. If there         recorded. The fourth argument should point to an int variable. If there
1699         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
1700         byte is recorded only if it follows something of variable  length.  For         byte  is  recorded only if it follows something of variable length. For
1701         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
1702         /^a\dz\d/ the returned value is -1.         /^a\dz\d/ the returned value is -1.
1703    
1704             PCRE_INFO_MINLENGTH
1705    
1706           If  the  pattern  was studied and a minimum length for matching subject
1707           strings was computed, its value is  returned.  Otherwise  the  returned
1708           value  is  -1. The value is a number of characters, not bytes (this may
1709           be relevant in UTF-8 mode). The fourth argument should point to an  int
1710           variable.  A  non-negative  value is a lower bound to the length of any
1711           matching string. There may not be any strings of that  length  that  do
1712           actually match, but every string that does match is at least that long.
1713    
1714           PCRE_INFO_NAMECOUNT           PCRE_INFO_NAMECOUNT
1715           PCRE_INFO_NAMEENTRYSIZE           PCRE_INFO_NAMEENTRYSIZE
1716           PCRE_INFO_NAMETABLE           PCRE_INFO_NAMETABLE
1717    
1718         PCRE supports the use of named as well as numbered capturing  parenthe-         PCRE  supports the use of named as well as numbered capturing parenthe-
1719         ses.  The names are just an additional way of identifying the parenthe-         ses. The names are just an additional way of identifying the  parenthe-
1720         ses,  which  still  acquire  numbers.  A  convenience  function  called         ses, which still acquire numbers. Several convenience functions such as
1721         pcre_get_named_substring()  is  provided  for  extracting an individual         pcre_get_named_substring() are provided for  extracting  captured  sub-
1722         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
1723         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
1724         the correct pointers in the output vector (described  with  pcre_exec()         pointers in the output vector (described with pcre_exec() below). To do
1725         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
1726         which is described by these three values.         described by these three values.
1727    
1728         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
1729         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
1730         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
1731         depends  on the length of the longest name. PCRE_INFO_NAMETABLE returns         depends on the length of the longest name. PCRE_INFO_NAMETABLE  returns
1732         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
1733         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-
1734         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-
1735         sponding  name,  zero  terminated. The names are in alphabetical order.         sponding name, zero terminated.
1736         For example, consider the following pattern  (assume  PCRE_EXTENDED  is  
1737         set, so white space - including newlines - is ignored):         The names are in alphabetical order. Duplicate names may appear if  (?|
1738           is used to create multiple groups with the same number, as described in
1739           the section on duplicate subpattern numbers in  the  pcrepattern  page.
1740           Duplicate  names  for  subpatterns with different numbers are permitted
1741           only if PCRE_DUPNAMES is set. In all cases  of  duplicate  names,  they
1742           appear  in  the table in the order in which they were found in the pat-
1743           tern. In the absence of (?| this is the  order  of  increasing  number;
1744           when (?| is used this is not necessarily the case because later subpat-
1745           terns may have lower numbers.
1746    
1747           As a simple example of the name/number table,  consider  the  following
1748           pattern  (assume  PCRE_EXTENDED is set, so white space - including new-
1749           lines - is ignored):
1750    
1751           (?P<date> (?P<year>(\d\d)?\d\d) -           (?<date> (?<year>(\d\d)?\d\d) -
1752           (?P<month>\d\d) - (?P<day>\d\d) )           (?<month>\d\d) - (?<day>\d\d) )
1753    
1754         There  are  four  named subpatterns, so the table has four entries, and         There are four named subpatterns, so the table has  four  entries,  and
1755         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,
1756         with non-printing bytes shows in hexadecimal, and undefined bytes shown         with non-printing bytes shows in hexadecimal, and undefined bytes shown
1757         as ??:         as ??:
1758    
# Line 1306  INFORMATION ABOUT A PATTERN Line 1761  INFORMATION ABOUT A PATTERN
1761           00 04 m  o  n  t  h  00           00 04 m  o  n  t  h  00
1762           00 02 y  e  a  r  00 ??           00 02 y  e  a  r  00 ??
1763    
1764         When writing code to extract data  from  named  subpatterns  using  the         When  writing  code  to  extract  data from named subpatterns using the
1765         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
1766         be different for each compiled pattern.         to be different for each compiled pattern.
1767    
1768             PCRE_INFO_OKPARTIAL
1769    
1770           Return  1  if  the  pattern  can  be  used  for  partial  matching with
1771           pcre_exec(), otherwise 0. The fourth argument should point  to  an  int
1772           variable.  From  release  8.00,  this  always  returns  1,  because the
1773           restrictions that previously applied  to  partial  matching  have  been
1774           lifted.  The  pcrepartial documentation gives details of partial match-
1775           ing.
1776    
1777           PCRE_INFO_OPTIONS           PCRE_INFO_OPTIONS
1778    
1779         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
1780         fourth  argument  should  point to an unsigned long int variable. These         fourth  argument  should  point to an unsigned long int variable. These
1781         option bits are those specified in the call to pcre_compile(), modified         option bits are those specified in the call to pcre_compile(), modified
1782         by any top-level option settings within the pattern itself.         by any top-level option settings at the start of the pattern itself. In
1783           other words, they are the options that will be in force  when  matching
1784           starts.  For  example, if the pattern /(?im)abc(?-i)d/ is compiled with
1785           the PCRE_EXTENDED option, the result is PCRE_CASELESS,  PCRE_MULTILINE,
1786           and PCRE_EXTENDED.
1787    
1788         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
1789         alternatives begin with one of the following:         alternatives begin with one of the following:
# Line 1341  INFORMATION ABOUT A PATTERN Line 1809  INFORMATION ABOUT A PATTERN
1809         Return the size of the data block pointed to by the study_data field in         Return the size of the data block pointed to by the study_data field in
1810         a  pcre_extra  block.  That  is,  it  is  the  value that was passed to         a  pcre_extra  block.  That  is,  it  is  the  value that was passed to
1811         pcre_malloc() when PCRE was getting memory into which to place the data         pcre_malloc() when PCRE was getting memory into which to place the data
1812         created  by  pcre_study(). The fourth argument should point to a size_t         created  by  pcre_study().  If pcre_extra is NULL, or there is no study
1813           data, zero is returned. The fourth argument should point  to  a  size_t
1814         variable.         variable.
1815    
1816    
# Line 1349  OBSOLETE INFO FUNCTION Line 1818  OBSOLETE INFO FUNCTION
1818    
1819         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
1820    
1821         The pcre_info() function is now obsolete because its interface  is  too         The  pcre_info()  function is now obsolete because its interface is too
1822         restrictive  to return all the available data about a compiled pattern.         restrictive to return all the available data about a compiled  pattern.
1823         New  programs  should  use  pcre_fullinfo()  instead.  The   yield   of         New   programs   should  use  pcre_fullinfo()  instead.  The  yield  of
1824         pcre_info()  is the number of capturing subpatterns, or one of the fol-         pcre_info() is the number of capturing subpatterns, or one of the  fol-
1825         lowing negative numbers:         lowing negative numbers:
1826    
1827           PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_NULL       the argument code was NULL
1828           PCRE_ERROR_BADMAGIC   the "magic number" was not found           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1829    
1830         If the optptr argument is not NULL, a copy of the  options  with  which         If  the  optptr  argument is not NULL, a copy of the options with which
1831         the  pattern  was  compiled  is placed in the integer it points to (see         the pattern was compiled is placed in the integer  it  points  to  (see
1832         PCRE_INFO_OPTIONS above).         PCRE_INFO_OPTIONS above).
1833    
1834         If the pattern is not anchored and the  firstcharptr  argument  is  not         If  the  pattern  is  not anchored and the firstcharptr argument is not
1835         NULL,  it is used to pass back information about the first character of         NULL, it is used to pass back information about the first character  of
1836         any matched string (see PCRE_INFO_FIRSTBYTE above).         any matched string (see PCRE_INFO_FIRSTBYTE above).
1837    
1838    
# Line 1371  REFERENCE COUNTS Line 1840  REFERENCE COUNTS
1840    
1841         int pcre_refcount(pcre *code, int adjust);         int pcre_refcount(pcre *code, int adjust);
1842    
1843         The pcre_refcount() function is used to maintain a reference  count  in         The  pcre_refcount()  function is used to maintain a reference count in
1844         the data block that contains a compiled pattern. It is provided for the         the data block that contains a compiled pattern. It is provided for the
1845         benefit of applications that  operate  in  an  object-oriented  manner,         benefit  of  applications  that  operate  in an object-oriented manner,
1846         where different parts of the application may be using the same compiled         where different parts of the application may be using the same compiled
1847         pattern, but you want to free the block when they are all done.         pattern, but you want to free the block when they are all done.
1848    
1849         When a pattern is compiled, the reference count field is initialized to         When a pattern is compiled, the reference count field is initialized to
1850         zero.   It is changed only by calling this function, whose action is to         zero.  It is changed only by calling this function, whose action is  to
1851         add the adjust value (which may be positive or  negative)  to  it.  The         add  the  adjust  value  (which may be positive or negative) to it. The
1852         yield of the function is the new value. However, the value of the count         yield of the function is the new value. However, the value of the count
1853         is constrained to lie between 0 and 65535, inclusive. If the new  value         is  constrained to lie between 0 and 65535, inclusive. If the new value
1854         is outside these limits, it is forced to the appropriate limit value.         is outside these limits, it is forced to the appropriate limit value.
1855    
1856         Except  when it is zero, the reference count is not correctly preserved         Except when it is zero, the reference count is not correctly  preserved
1857         if a pattern is compiled on one host and then  transferred  to  a  host         if  a  pattern  is  compiled on one host and then transferred to a host
1858         whose byte-order is different. (This seems a highly unlikely scenario.)         whose byte-order is different. (This seems a highly unlikely scenario.)
1859    
1860    
# Line 1397  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1866  MATCHING A PATTERN: THE TRADITIONAL FUNC
1866    
1867         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
1868         compiled  pattern, which is passed in the code argument. If the pattern         compiled  pattern, which is passed in the code argument. If the pattern
1869         has been studied, the result of the study should be passed in the extra         was studied, the result of the study should  be  passed  in  the  extra
1870         argument.  This  function is the main matching facility of the library,         argument.  This  function is the main matching facility of the library,
1871         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
1872         an  alternative matching function, which is described below in the sec-         an  alternative matching function, which is described below in the sec-
# Line 1428  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1897  MATCHING A PATTERN: THE TRADITIONAL FUNC
1897         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
1898         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
1899         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-
1900         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
1901         lows:         fields (not necessarily in this order):
1902    
1903           unsigned long int flags;           unsigned long int flags;
1904           void *study_data;           void *study_data;
1905           unsigned long int match_limit;           unsigned long int match_limit;
1906             unsigned long int match_limit_recursion;
1907           void *callout_data;           void *callout_data;
1908           const unsigned char *tables;           const unsigned char *tables;
1909             unsigned char **mark;
1910    
1911         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
1912         are set. The flag bits are:         are set. The flag bits are:
1913    
1914           PCRE_EXTRA_STUDY_DATA           PCRE_EXTRA_STUDY_DATA
1915           PCRE_EXTRA_MATCH_LIMIT           PCRE_EXTRA_MATCH_LIMIT
1916             PCRE_EXTRA_MATCH_LIMIT_RECURSION
1917           PCRE_EXTRA_CALLOUT_DATA           PCRE_EXTRA_CALLOUT_DATA
1918           PCRE_EXTRA_TABLES           PCRE_EXTRA_TABLES
1919             PCRE_EXTRA_MARK
1920    
1921         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
1922         the pcre_extra block that is returned by  pcre_study(),  together  with         the pcre_extra block that is returned by  pcre_study(),  together  with
# Line 1454  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1927  MATCHING A PATTERN: THE TRADITIONAL FUNC
1927         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
1928         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
1929         match,  but  which  have  a very large number of possibilities in their         match,  but  which  have  a very large number of possibilities in their
1930         search trees. The classic  example  is  the  use  of  nested  unlimited         search trees. The classic example is a pattern that uses nested  unlim-
1931         repeats.         ited repeats.
1932    
1933         Internally,  PCRE uses a function called match() which it calls repeat-         Internally,  PCRE uses a function called match() which it calls repeat-
1934         edly (sometimes recursively). The limit is imposed  on  the  number  of         edly (sometimes recursively). The limit set by match_limit  is  imposed
1935         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
1936         limiting the amount of recursion and backtracking that can take  place.         has the effect of limiting the amount of  backtracking  that  can  take
1937         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
1938         position in the subject string.         for each position in the subject string.
1939    
1940         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
1941         default  default  is 10 million, which handles all but the most extreme         default  default  is 10 million, which handles all but the most extreme
1942         cases. You can reduce  the  default  by  suppling  pcre_exec()  with  a         cases. You can override the default  by  suppling  pcre_exec()  with  a
1943         pcre_extra  block  in  which match_limit is set to a smaller value, and         pcre_extra     block    in    which    match_limit    is    set,    and
1944         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
1945         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1946    
1947         The  pcre_callout  field is used in conjunction with the "callout" fea-         The  match_limit_recursion field is similar to match_limit, but instead
1948         ture, which is described in the pcrecallout documentation.         of limiting the total number of times that match() is called, it limits
1949           the  depth  of  recursion. The recursion depth is a smaller number than
1950         The tables field  is  used  to  pass  a  character  tables  pointer  to         the total number of calls, because not all calls to match() are  recur-
1951         pcre_exec();  this overrides the value that is stored with the compiled         sive.  This limit is of use only if it is set smaller than match_limit.
1952         pattern. A non-NULL value is stored with the compiled pattern  only  if  
1953         custom  tables  were  supplied to pcre_compile() via its tableptr argu-         Limiting  the  recursion  depth  limits the amount of stack that can be
1954           used, or, when PCRE has been compiled to use memory on the heap instead
1955           of the stack, the amount of heap memory that can be used.
1956    
1957           The  default  value  for  match_limit_recursion can be set when PCRE is
1958           built; the default default  is  the  same  value  as  the  default  for
1959           match_limit.  You can override the default by suppling pcre_exec() with
1960           a  pcre_extra  block  in  which  match_limit_recursion  is   set,   and
1961           PCRE_EXTRA_MATCH_LIMIT_RECURSION  is  set  in  the  flags field. If the
1962           limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1963    
1964           The callout_data field is used in conjunction with the  "callout"  fea-
1965           ture, and is described in the pcrecallout documentation.
1966    
1967           The  tables  field  is  used  to  pass  a  character  tables pointer to
1968           pcre_exec(); this overrides the value that is stored with the  compiled
1969           pattern.  A  non-NULL value is stored with the compiled pattern only if
1970           custom tables were supplied to pcre_compile() via  its  tableptr  argu-
1971         ment.  If NULL is passed to pcre_exec() using this mechanism, it forces         ment.  If NULL is passed to pcre_exec() using this mechanism, it forces
1972         PCRE's  internal  tables  to be used. This facility is helpful when re-         PCRE's internal tables to be used. This facility is  helpful  when  re-
1973         using patterns that have been saved after compiling  with  an  external         using  patterns  that  have been saved after compiling with an external
1974         set  of  tables,  because  the  external tables might be at a different         set of tables, because the external tables  might  be  at  a  different
1975         address when pcre_exec() is called. See the  pcreprecompile  documenta-         address  when  pcre_exec() is called. See the pcreprecompile documenta-
1976         tion for a discussion of saving compiled patterns for later use.         tion for a discussion of saving compiled patterns for later use.
1977    
1978           If PCRE_EXTRA_MARK is set in the flags field, the mark  field  must  be
1979           set  to  point  to a char * variable. If the pattern contains any back-
1980           tracking control verbs such as (*MARK:NAME), and the execution ends  up
1981           with  a  name  to  pass back, a pointer to the name string (zero termi-
1982           nated) is placed in the variable pointed to  by  the  mark  field.  The
1983           names  are  within  the  compiled pattern; if you wish to retain such a
1984           name you must copy it before freeing the memory of a compiled  pattern.
1985           If  there  is no name to pass back, the variable pointed to by the mark
1986           field set to NULL. For details of the backtracking control  verbs,  see
1987           the section entitled "Backtracking control" in the pcrepattern documen-
1988           tation.
1989    
1990     Option bits for pcre_exec()     Option bits for pcre_exec()
1991    
1992         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.
1993         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,
1994         PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK and PCRE_PARTIAL.         PCRE_NOTBOL,   PCRE_NOTEOL,    PCRE_NOTEMPTY,    PCRE_NOTEMPTY_ATSTART,
1995           PCRE_NO_START_OPTIMIZE,   PCRE_NO_UTF8_CHECK,   PCRE_PARTIAL_SOFT,  and
1996           PCRE_PARTIAL_HARD.
1997    
1998           PCRE_ANCHORED           PCRE_ANCHORED
1999    
2000         The  PCRE_ANCHORED  option  limits pcre_exec() to matching at the first         The PCRE_ANCHORED option limits pcre_exec() to matching  at  the  first
2001         matching position. If a pattern was  compiled  with  PCRE_ANCHORED,  or         matching  position.  If  a  pattern was compiled with PCRE_ANCHORED, or
2002         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
2003         unachored at matching time.         unachored at matching time.
2004    
2005             PCRE_BSR_ANYCRLF
2006             PCRE_BSR_UNICODE
2007    
2008           These options (which are mutually exclusive) control what the \R escape
2009           sequence matches. The choice is either to match only CR, LF,  or  CRLF,
2010           or  to  match  any Unicode newline sequence. These options override the
2011           choice that was made or defaulted when the pattern was compiled.
2012    
2013             PCRE_NEWLINE_CR
2014             PCRE_NEWLINE_LF
2015             PCRE_NEWLINE_CRLF
2016             PCRE_NEWLINE_ANYCRLF
2017             PCRE_NEWLINE_ANY
2018    
2019           These options override  the  newline  definition  that  was  chosen  or
2020           defaulted  when the pattern was compiled. For details, see the descrip-
2021           tion of pcre_compile()  above.  During  matching,  the  newline  choice
2022           affects  the  behaviour  of the dot, circumflex, and dollar metacharac-
2023           ters. It may also alter the way the match position is advanced after  a
2024           match failure for an unanchored pattern.
2025    
2026           When  PCRE_NEWLINE_CRLF,  PCRE_NEWLINE_ANYCRLF,  or PCRE_NEWLINE_ANY is
2027           set, and a match attempt for an unanchored pattern fails when the  cur-
2028           rent  position  is  at  a  CRLF  sequence,  and the pattern contains no
2029           explicit matches for  CR  or  LF  characters,  the  match  position  is
2030           advanced by two characters instead of one, in other words, to after the
2031           CRLF.
2032    
2033           The above rule is a compromise that makes the most common cases work as
2034           expected.  For  example,  if  the  pattern  is .+A (and the PCRE_DOTALL
2035           option is not set), it does not match the string "\r\nA" because, after
2036           failing  at the start, it skips both the CR and the LF before retrying.
2037           However, the pattern [\r\n]A does match that string,  because  it  con-
2038           tains an explicit CR or LF reference, and so advances only by one char-
2039           acter after the first failure.
2040    
2041           An explicit match for CR of LF is either a literal appearance of one of
2042           those  characters,  or  one  of the \r or \n escape sequences. Implicit
2043           matches such as [^X] do not count, nor does \s (which includes  CR  and
2044           LF in the characters that it matches).
2045    
2046           Notwithstanding  the above, anomalous effects may still occur when CRLF
2047           is a valid newline sequence and explicit \r or \n escapes appear in the
2048           pattern.
2049    
2050           PCRE_NOTBOL           PCRE_NOTBOL
2051    
2052         This option specifies that first character of the subject string is not         This option specifies that first character of the subject string is not
2053         the  beginning  of  a  line, so the circumflex metacharacter should not         the beginning of a line, so the  circumflex  metacharacter  should  not
2054         match before it. Setting this without PCRE_MULTILINE (at compile  time)         match  before it. Setting this without PCRE_MULTILINE (at compile time)
2055         causes  circumflex  never to match. This option affects only the behav-         causes circumflex never to match. This option affects only  the  behav-
2056         iour of the circumflex metacharacter. It does not affect \A.         iour of the circumflex metacharacter. It does not affect \A.
2057    
2058           PCRE_NOTEOL           PCRE_NOTEOL
2059    
2060         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
2061         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
2062         in multiline mode) a newline immediately before it. Setting this  with-         in  multiline mode) a newline immediately before it. Setting this with-
2063         out PCRE_MULTILINE (at compile time) causes dollar never to match. This         out PCRE_MULTILINE (at compile time) causes dollar never to match. This
2064         option affects only the behaviour of the dollar metacharacter. It  does         option  affects only the behaviour of the dollar metacharacter. It does
2065         not affect \Z or \z.         not affect \Z or \z.
2066    
2067           PCRE_NOTEMPTY           PCRE_NOTEMPTY
2068    
2069         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
2070         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
2071         the  alternatives  match  the empty string, the entire match fails. For         the alternatives match the empty string, the entire  match  fails.  For
2072         example, if the pattern         example, if the pattern
2073    
2074           a?b?           a?b?
2075    
2076         is applied to a string not beginning with "a" or "b",  it  matches  the         is  applied  to  a  string not beginning with "a" or "b", it matches an
2077         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
2078         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-
2079         rences of "a" or "b".         rences of "a" or "b".
2080    
2081         Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a spe-           PCRE_NOTEMPTY_ATSTART
2082         cial case of a pattern match of the empty  string  within  its  split()  
2083         function,  and  when  using  the /g modifier. It is possible to emulate         This is like PCRE_NOTEMPTY, except that an empty string match  that  is
2084         Perl's behaviour after matching a null string by first trying the match         not  at  the  start  of  the  subject  is  permitted. If the pattern is
2085         again at the same offset with PCRE_NOTEMPTY and PCRE_ANCHORED, and then         anchored, such a match can occur only if the pattern contains \K.
2086         if that fails by advancing the starting offset (see below)  and  trying  
2087         an ordinary match again. There is some code that demonstrates how to do         Perl    has    no    direct    equivalent    of    PCRE_NOTEMPTY     or
2088         this in the pcredemo.c sample program.         PCRE_NOTEMPTY_ATSTART,  but  it  does  make a special case of a pattern
2089           match of the empty string within its split() function, and  when  using
2090           the  /g  modifier.  It  is  possible  to emulate Perl's behaviour after
2091           matching a null string by first trying the match again at the same off-
2092           set  with  PCRE_NOTEMPTY_ATSTART  and  PCRE_ANCHORED,  and then if that
2093           fails, by advancing the starting offset (see below) and trying an ordi-
2094           nary  match  again. There is some code that demonstrates how to do this
2095           in the pcredemo sample program.
2096    
2097             PCRE_NO_START_OPTIMIZE
2098    
2099           There are a number of optimizations that pcre_exec() uses at the  start
2100           of  a  match,  in  order to speed up the process. For example, if it is
2101           known that a match must start with a specific  character,  it  searches
2102           the subject for that character, and fails immediately if it cannot find
2103           it, without actually running the main matching function. When  callouts
2104           are  in  use,  these  optimizations  can cause them to be skipped. This
2105           option disables the "start-up" optimizations,  causing  performance  to
2106           suffer, but ensuring that the callouts do occur.
2107    
2108           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
2109    
2110         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
2111         UTF-8  string is automatically checked when pcre_exec() is subsequently         UTF-8 string is automatically checked when pcre_exec() is  subsequently
2112         called.  The value of startoffset is also checked  to  ensure  that  it         called.   The  value  of  startoffset is also checked to ensure that it
2113         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
2114         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
2115         startoffset  contains  an  invalid  value, PCRE_ERROR_BADUTF8_OFFSET is         main pcre page. If  an  invalid  UTF-8  sequence  of  bytes  is  found,
2116         returned.         pcre_exec()  returns  the error PCRE_ERROR_BADUTF8. If startoffset con-
2117           tains an invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.
2118    
2119         If you already know that your subject is valid, and you  want  to  skip         If you already know that your subject is valid, and you  want  to  skip
2120         these    checks    for   performance   reasons,   you   can   set   the         these    checks    for   performance   reasons,   you   can   set   the
# Line 1559  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2127  MATCHING A PATTERN: THE TRADITIONAL FUNC
2127         value of startoffset that does not point to the start of a UTF-8  char-         value of startoffset that does not point to the start of a UTF-8  char-
2128         acter, is undefined. Your program may crash.         acter, is undefined. Your program may crash.
2129    
2130           PCRE_PARTIAL           PCRE_PARTIAL_HARD
2131             PCRE_PARTIAL_SOFT
2132    
2133         This  option  turns  on  the  partial  matching feature. If the subject         These  options turn on the partial matching feature. For backwards com-
2134         string fails to match the pattern, but at some point during the  match-         patibility, PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A  partial
2135         ing  process  the  end of the subject was reached (that is, the subject         match  occurs if the end of the subject string is reached successfully,
2136         partially matches the pattern and the failure to  match  occurred  only         but there are not enough subject characters to complete the  match.  If
2137         because  there were not enough subject characters), pcre_exec() returns         this  happens  when  PCRE_PARTIAL_HARD  is set, pcre_exec() immediately
2138         PCRE_ERROR_PARTIAL instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL  is         returns PCRE_ERROR_PARTIAL. Otherwise,  if  PCRE_PARTIAL_SOFT  is  set,
2139         used,  there  are restrictions on what may appear in the pattern. These         matching  continues by testing any other alternatives. Only if they all
2140         are discussed in the pcrepartial documentation.         fail is PCRE_ERROR_PARTIAL returned  (instead  of  PCRE_ERROR_NOMATCH).
2141           The portion of the string that was inspected when the partial match was
2142           found is set as the first matching string. There  is  a  more  detailed
2143           discussion in the pcrepartial documentation.
2144    
2145     The string to be matched by pcre_exec()     The string to be matched by pcre_exec()
2146    
2147         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
2148         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.
2149         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-
2150         Unlike  the  pattern string, the subject may contain binary zero bytes.         acter. Unlike the pattern string, the subject may contain  binary  zero
2151         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
2152         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
2153           case.
2154    
2155         A  non-zero  starting offset is useful when searching for another match         A  non-zero  starting offset is useful when searching for another match
2156         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 2186  MATCHING A PATTERN: THE TRADITIONAL FUNC
2186         string. PCRE supports several other kinds of  parenthesized  subpattern         string. PCRE supports several other kinds of  parenthesized  subpattern
2187         that do not cause substrings to be captured.         that do not cause substrings to be captured.
2188    
2189         Captured  substrings are returned to the caller via a vector of integer         Captured substrings are returned to the caller via a vector of integers
2190         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-
2191         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:
2192         Note: this argument is NOT the size of ovector in bytes.         this argument is NOT the size of ovector in bytes.
2193    
2194         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-
2195         strings,  each  substring using a pair of integers. The remaining third         strings,  each  substring using a pair of integers. The remaining third
2196         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-
2197         turing  subpatterns, and is not available for passing back information.         turing  subpatterns, and is not available for passing back information.
2198         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
2199         it is not, it is rounded down.         it is not, it is rounded down.
2200    
2201         When  a  match  is successful, information about captured substrings is         When  a  match  is successful, information about captured substrings is
2202         returned in pairs of integers, starting at the  beginning  of  ovector,         returned in pairs of integers, starting at the  beginning  of  ovector,
2203         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
2204         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
2205         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
2206         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
2207         tor[1],  identify  the  portion  of  the  subject string matched by the         byte offsets, even in UTF-8 mode. They are not character counts.
2208         entire pattern. The next pair is used for the first  capturing  subpat-  
2209         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
2210         pairs that have been set. If there are no  capturing  subpatterns,  the         portion of the subject string matched by the entire pattern.  The  next
2211         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
2212         first pair of offsets has been set.         returned by pcre_exec() is one more than the highest numbered pair that
2213           has  been  set.  For example, if two substrings have been captured, the
2214         Some convenience functions are provided  for  extracting  the  captured         returned value is 3. If there are no capturing subpatterns, the  return
2215         substrings  as  separate  strings. These are described in the following         value from a successful match is 1, indicating that just the first pair
2216         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.  
2217    
2218         If a capturing subpattern is matched repeatedly, it is the last portion         If a capturing subpattern is matched repeatedly, it is the last portion
2219         of the string that it matched that is returned.         of the string that it matched that is returned.
2220    
2221         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,
2222         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
2223         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
2224         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
2225         as  NULL  and  ovecsize  as zero. However, if the pattern contains back         ovecsize  as zero. However, if the pattern contains back references and
2226         references and the ovector is not big enough to  remember  the  related         the ovector is not big enough to remember the related substrings,  PCRE
2227         substrings,  PCRE has to get additional memory for use during matching.         has  to  get additional memory for use during matching. Thus it is usu-
2228         Thus it is usually advisable to supply an ovector.         ally advisable to supply an ovector.
2229    
2230         Note that pcre_info() can be used to find out how many  capturing  sub-         The pcre_fullinfo() function can be used to find out how many capturing
2231         patterns there are in a compiled pattern. The smallest size for ovector         subpatterns  there  are  in  a  compiled pattern. The smallest size for
2232         that will allow for n captured substrings, in addition to  the  offsets         ovector that will allow for n captured substrings, in addition  to  the
2233         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.
2234    
2235           It  is  possible for capturing subpattern number n+1 to match some part
2236           of the subject when subpattern n has not been used at all. For example,
2237           if  the  string  "abc"  is  matched against the pattern (a|(z))(bc) the
2238           return from the function is 4, and subpatterns 1 and 3 are matched, but
2239           2  is  not.  When  this happens, both values in the offset pairs corre-
2240           sponding to unused subpatterns are set to -1.
2241    
2242           Offset values that correspond to unused subpatterns at the end  of  the
2243           expression  are  also  set  to  -1. For example, if the string "abc" is
2244           matched against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are  not
2245           matched.  The  return  from the function is 2, because the highest used
2246           capturing subpattern number is 1. However, you can refer to the offsets
2247           for  the  second  and third capturing subpatterns if you wish (assuming
2248           the vector is large enough, of course).
2249    
2250           Some convenience functions are provided  for  extracting  the  captured
2251           substrings as separate strings. These are described below.
2252    
2253     Return values from pcre_exec()     Error return values from pcre_exec()
2254    
2255         If  pcre_exec()  fails, it returns a negative number. The following are         If  pcre_exec()  fails, it returns a negative number. The following are
2256         defined in the header file:         defined in the header file:
# Line 1691  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2276  MATCHING A PATTERN: THE TRADITIONAL FUNC
2276         an environment with the other endianness. This is the error  that  PCRE         an environment with the other endianness. This is the error  that  PCRE
2277         gives when the magic number is not present.         gives when the magic number is not present.
2278    
2279           PCRE_ERROR_UNKNOWN_NODE   (-5)           PCRE_ERROR_UNKNOWN_OPCODE (-5)
2280    
2281         While running the pattern match, an unknown item was encountered in the         While running the pattern match, an unknown item was encountered in the
2282         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 2298  MATCHING A PATTERN: THE TRADITIONAL FUNC
2298    
2299           PCRE_ERROR_MATCHLIMIT     (-8)           PCRE_ERROR_MATCHLIMIT     (-8)
2300    
2301         The  recursion  and backtracking limit, as specified by the match_limit         The  backtracking  limit,  as  specified  by the match_limit field in a
2302         field in a pcre_extra structure (or defaulted)  was  reached.  See  the         pcre_extra structure (or defaulted) was reached.  See  the  description
2303         description above.         above.
2304    
2305           PCRE_ERROR_CALLOUT        (-9)           PCRE_ERROR_CALLOUT        (-9)
2306    
# Line 1741  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2326  MATCHING A PATTERN: THE TRADITIONAL FUNC
2326    
2327           PCRE_ERROR_BADPARTIAL     (-13)           PCRE_ERROR_BADPARTIAL     (-13)
2328    
2329         The  PCRE_PARTIAL  option  was  used with a compiled pattern containing         This  code  is  no  longer  in  use.  It was formerly returned when the
2330         items that are not supported for partial matching. See the  pcrepartial         PCRE_PARTIAL option was used with a compiled pattern  containing  items
2331         documentation for details of partial matching.         that  were  not  supported  for  partial  matching.  From  release 8.00
2332           onwards, there are no restrictions on partial matching.
2333    
2334           PCRE_ERROR_INTERNAL       (-14)           PCRE_ERROR_INTERNAL       (-14)
2335    
2336         An  unexpected  internal error has occurred. This error could be caused         An unexpected internal error has occurred. This error could  be  caused
2337         by a bug in PCRE or by overwriting of the compiled pattern.         by a bug in PCRE or by overwriting of the compiled pattern.
2338    
2339           PCRE_ERROR_BADCOUNT       (-15)           PCRE_ERROR_BADCOUNT       (-15)
2340    
2341         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.
2342    
2343             PCRE_ERROR_RECURSIONLIMIT (-21)
2344    
2345           The internal recursion limit, as specified by the match_limit_recursion
2346           field in a pcre_extra structure (or defaulted)  was  reached.  See  the
2347           description above.
2348    
2349             PCRE_ERROR_BADNEWLINE     (-23)
2350    
2351           An invalid combination of PCRE_NEWLINE_xxx options was given.
2352    
2353           Error numbers -16 to -20 and -22 are not used by pcre_exec().
2354    
2355    
2356  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
# Line 1774  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2372  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2372         string_list() are provided for extracting captured substrings  as  new,         string_list() are provided for extracting captured substrings  as  new,
2373         separate,  zero-terminated strings. These functions identify substrings         separate,  zero-terminated strings. These functions identify substrings
2374         by number. The next section describes functions  for  extracting  named         by number. The next section describes functions  for  extracting  named
2375         substrings.  A  substring  that  contains  a  binary  zero is correctly         substrings.
2376         extracted and has a further zero added on the end, but  the  result  is  
2377         not, of course, a C string.         A  substring that contains a binary zero is correctly extracted and has
2378           a further zero added on the end, but the result is not, of course, a  C
2379           string.   However,  you  can  process such a string by referring to the
2380           length that is  returned  by  pcre_copy_substring()  and  pcre_get_sub-
2381           string().  Unfortunately, the interface to pcre_get_substring_list() is
2382           not adequate for handling strings containing binary zeros, because  the
2383           end of the final string is not independently indicated.
2384    
2385         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-
2386         tions: subject is the subject string that has  just  been  successfully         tions: subject is the subject string that has  just  been  successfully
# Line 1796  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2400  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2400         buffersize, while for pcre_get_substring() a new  block  of  memory  is         buffersize, while for pcre_get_substring() a new  block  of  memory  is
2401         obtained  via  pcre_malloc,  and its address is returned via stringptr.         obtained  via  pcre_malloc,  and its address is returned via stringptr.
2402         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
2403         the terminating zero, or one of         the terminating zero, or one of these error codes:
2404    
2405           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2406    
# Line 1812  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2416  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2416         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
2417         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
2418         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
2419         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
2420           error code
2421    
2422           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2423    
2424         if the attempt to get the memory block failed.         if the attempt to get the memory block failed.
2425    
2426         When  any of these functions encounter a substring that is unset, which         When any of these functions encounter a substring that is unset,  which
2427         can happen when capturing subpattern number n+1 matches  some  part  of         can  happen  when  capturing subpattern number n+1 matches some part of
2428         the  subject, but subpattern n has not been used at all, they return an         the subject, but subpattern n has not been used at all, they return  an
2429         empty string. This can be distinguished from a genuine zero-length sub-         empty string. This can be distinguished from a genuine zero-length sub-
2430         string  by inspecting the appropriate offset in ovector, which is nega-         string by inspecting the appropriate offset in ovector, which is  nega-
2431         tive for unset substrings.         tive for unset substrings.
2432    
2433         The two convenience functions pcre_free_substring() and  pcre_free_sub-         The  two convenience functions pcre_free_substring() and pcre_free_sub-
2434         string_list()  can  be  used  to free the memory returned by a previous         string_list() can be used to free the memory  returned  by  a  previous
2435         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-
2436         tively.  They  do  nothing  more  than  call the function pointed to by         tively. They do nothing more than  call  the  function  pointed  to  by
2437         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.
2438         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-
2439         cial  interface  to  another  programming  language  which  cannot  use         cial   interface  to  another  programming  language  that  cannot  use
2440         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-
2441         vided.         vided.
2442    
2443    
# Line 1851  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2456  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2456              int stringcount, const char *stringname,              int stringcount, const char *stringname,
2457              const char **stringptr);              const char **stringptr);
2458    
2459         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-
2460         ber.  For example, for this pattern         ber.  For example, for this pattern
2461    
2462           (a+)b(?P<xxx>\d+)...           (a+)b(?<xxx>\d+)...
2463    
2464         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
2465         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
2466         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-
2467         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
2468         there is no subpattern of that name.         the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if  there  is  no
2469           subpattern of that name.
2470    
2471         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
2472         the functions described in the previous section. For convenience, there         the functions described in the previous section. For convenience, there
# Line 1879  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2485  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2485    
2486         These functions call pcre_get_stringnumber(), and if it succeeds,  they         These functions call pcre_get_stringnumber(), and if it succeeds,  they
2487         then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-         then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-
2488         ate.         ate. NOTE: If PCRE_DUPNAMES is set and there are duplicate  names,  the
2489           behaviour may not be what you want (see the next section).
2490    
2491           Warning: If the pattern uses the (?| feature to set up multiple subpat-
2492           terns with the same number, as described in the  section  on  duplicate
2493           subpattern  numbers  in  the  pcrepattern page, you cannot use names to
2494           distinguish the different subpatterns, because names are  not  included
2495           in  the compiled code. The matching process uses only numbers. For this
2496           reason, the use of different names for subpatterns of the  same  number
2497           causes an error at compile time.
2498    
2499    
2500    DUPLICATE SUBPATTERN NAMES
2501    
2502           int pcre_get_stringtable_entries(const pcre *code,
2503                const char *name, char **first, char **last);
2504    
2505           When  a  pattern  is  compiled with the PCRE_DUPNAMES option, names for
2506           subpatterns are not required to be unique. (Duplicate names are  always
2507           allowed  for subpatterns with the same number, created by using the (?|
2508           feature. Indeed, if such subpatterns are named, they  are  required  to
2509           use the same names.)
2510    
2511           Normally, patterns with duplicate names are such that in any one match,
2512           only one of the named subpatterns participates. An example is shown  in
2513           the pcrepattern documentation.
2514    
2515           When    duplicates   are   present,   pcre_copy_named_substring()   and
2516           pcre_get_named_substring() return the first substring corresponding  to
2517           the  given  name  that  is set. If none are set, PCRE_ERROR_NOSUBSTRING
2518           (-7) is returned; no  data  is  returned.  The  pcre_get_stringnumber()
2519           function  returns one of the numbers that are associated with the name,
2520           but it is not defined which it is.
2521    
2522           If you want to get full details of all captured substrings for a  given
2523           name,  you  must  use  the pcre_get_stringtable_entries() function. The
2524           first argument is the compiled pattern, and the second is the name. The
2525           third  and  fourth  are  pointers to variables which are updated by the
2526           function. After it has run, they point to the first and last entries in
2527           the  name-to-number  table  for  the  given  name.  The function itself
2528           returns the length of each entry,  or  PCRE_ERROR_NOSUBSTRING  (-7)  if
2529           there  are none. The format of the table is described above in the sec-
2530           tion entitled Information about a  pattern.   Given  all  the  relevant
2531           entries  for the name, you can extract each of their numbers, and hence
2532           the captured data, if any.
2533    
2534    
2535  FINDING ALL POSSIBLE MATCHES  FINDING ALL POSSIBLE MATCHES
# Line 1908  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2558  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2558              int *workspace, int wscount);              int *workspace, int wscount);
2559    
2560         The  function  pcre_dfa_exec()  is  called  to  match  a subject string         The  function  pcre_dfa_exec()  is  called  to  match  a subject string
2561         against a compiled pattern, using a "DFA" matching algorithm. This  has         against a compiled pattern, using a matching algorithm that  scans  the
2562         different  characteristics to the normal algorithm, and is not compati-         subject  string  just  once, and does not backtrack. This has different
2563         ble with Perl. Some of the features of PCRE patterns are not supported.         characteristics to the normal algorithm, and  is  not  compatible  with
2564         Nevertheless, there are times when this kind of matching can be useful.         Perl.  Some  of the features of PCRE patterns are not supported. Never-
2565         For a discussion of the two matching algorithms, see  the  pcrematching         theless, there are times when this kind of matching can be useful.  For
2566         documentation.         a  discussion  of  the  two matching algorithms, and a list of features
2567           that pcre_dfa_exec() does not support, see the pcrematching  documenta-
2568           tion.
2569    
2570         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
2571         pcre_exec(), plus two extras. The ovector argument is used in a differ-         pcre_exec(), plus two extras. The ovector argument is used in a differ-
# Line 1925  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2577  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2577         workspace vector should contain at least 20 elements. It  is  used  for         workspace vector should contain at least 20 elements. It  is  used  for
2578         keeping  track  of  multiple  paths  through  the  pattern  tree.  More         keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2579         workspace will be needed for patterns and subjects where  there  are  a         workspace will be needed for patterns and subjects where  there  are  a
2580         lot of possible matches.         lot of potential matches.
2581    
2582         Here is an example of a simple call to pcre_exec():         Here is an example of a simple call to pcre_dfa_exec():
2583    
2584           int rc;           int rc;
2585           int ovector[10];           int ovector[10];
2586           int wspace[20];           int wspace[20];
2587           rc = pcre_exec(           rc = pcre_dfa_exec(
2588             re,             /* result of pcre_compile() */             re,             /* result of pcre_compile() */
2589             NULL,           /* we didn't study the pattern */             NULL,           /* we didn't study the pattern */
2590             "some string",  /* the subject string */             "some string",  /* the subject string */
# Line 1947  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2599  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2599     Option bits for pcre_dfa_exec()     Option bits for pcre_dfa_exec()
2600    
2601         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
2602         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-
2603         PCRE_NOTEOL,     PCRE_NOTEMPTY,    PCRE_NO_UTF8_CHECK,    PCRE_PARTIAL,         LINE_xxx,        PCRE_NOTBOL,        PCRE_NOTEOL,        PCRE_NOTEMPTY,
2604         PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All  but  the  last  three  of         PCRE_NOTEMPTY_ATSTART, PCRE_NO_UTF8_CHECK, PCRE_PARTIAL_HARD, PCRE_PAR-
2605         these  are  the  same  as  for pcre_exec(), so their description is not         TIAL_SOFT,  PCRE_DFA_SHORTEST,  and  PCRE_DFA_RESTART. All but the last
2606         repeated here.         four of these are  exactly  the  same  as  for  pcre_exec(),  so  their
2607           description is not repeated here.
2608           PCRE_PARTIAL  
2609             PCRE_PARTIAL_HARD
2610         This has the same general effect as it does for  pcre_exec(),  but  the           PCRE_PARTIAL_SOFT
2611         details   are   slightly   different.  When  PCRE_PARTIAL  is  set  for  
2612         pcre_dfa_exec(), the return code PCRE_ERROR_NOMATCH is  converted  into         These  have the same general effect as they do for pcre_exec(), but the
2613         PCRE_ERROR_PARTIAL  if  the  end  of the subject is reached, there have         details are slightly  different.  When  PCRE_PARTIAL_HARD  is  set  for
2614         been no complete matches, but there is still at least one matching pos-         pcre_dfa_exec(),  it  returns PCRE_ERROR_PARTIAL if the end of the sub-
2615         sibility.  The portion of the string that provided the partial match is         ject is reached and there is still at least  one  matching  possibility
2616         set as the first matching string.         that requires additional characters. This happens even if some complete
2617           matches have also been found. When PCRE_PARTIAL_SOFT is set, the return
2618           code PCRE_ERROR_NOMATCH is converted into PCRE_ERROR_PARTIAL if the end
2619           of the subject is reached, there have been  no  complete  matches,  but
2620           there  is  still  at least one matching possibility. The portion of the
2621           string that was inspected when the longest partial match was  found  is
2622           set as the first matching string in both cases.
2623    
2624           PCRE_DFA_SHORTEST           PCRE_DFA_SHORTEST
2625    
2626         Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to         Setting  the  PCRE_DFA_SHORTEST option causes the matching algorithm to
2627         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-
2628         algorithm works, this is necessarily the shortest possible match at the         tive  algorithm  works, this is necessarily the shortest possible match
2629         first possible matching point in the subject string.         at the first possible matching point in the subject string.
2630    
2631           PCRE_DFA_RESTART           PCRE_DFA_RESTART
2632    
2633         When  pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option, and         When pcre_dfa_exec() returns a partial match, it is possible to call it
2634         returns a partial match, it is possible to call it  again,  with  addi-         again,  with  additional  subject characters, and have it continue with
2635         tional  subject  characters,  and have it continue with the same match.         the same match. The PCRE_DFA_RESTART option requests this action;  when
2636         The PCRE_DFA_RESTART option requests this action; when it is  set,  the         it  is  set,  the workspace and wscount options must reference the same
2637         workspace  and wscount options must reference the same vector as before         vector as before because data about the match so far is  left  in  them
2638         because data about the match so far is left in  them  after  a  partial         after a partial match. There is more discussion of this facility in the
2639         match.  There  is  more  discussion of this facility in the pcrepartial         pcrepartial documentation.
        documentation.  
2640    
2641     Successful returns from pcre_dfa_exec()     Successful returns from pcre_dfa_exec()
2642    
# Line 2004  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2661  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2661         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,
2662         which  is  the  number of matched substrings. The substrings themselves         which  is  the  number of matched substrings. The substrings themselves
2663         are returned in ovector. Each string uses two elements;  the  first  is         are returned in ovector. Each string uses two elements;  the  first  is
2664         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
2665         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
2666         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
2667         with the way pcre_exec() returns data, even though the meaning  of  the         compatibility with the way pcre_exec() returns data,  even  though  the
2668         strings is different.)         meaning of the strings is different.)
2669    
2670         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-
2671         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
# Line 2030  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2687  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2687    
2688           PCRE_ERROR_DFA_UCOND      (-17)           PCRE_ERROR_DFA_UCOND      (-17)
2689    
2690         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
2691         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
2692         supported.         in a specific group. These are not supported.
2693    
2694           PCRE_ERROR_DFA_UMLIMIT    (-18)           PCRE_ERROR_DFA_UMLIMIT    (-18)
2695    
# Line 2052  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2709  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2709         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
2710         should be extremely rare, as a vector of size 1000 is used.         should be extremely rare, as a vector of size 1000 is used.
2711    
2712  Last updated: 16 May 2005  
2713  Copyright (c) 1997-2005 University of Cambridge.  SEE ALSO
2714    
2715           pcrebuild(3),  pcrecallout(3), pcrecpp(3)(3), pcrematching(3), pcrepar-
2716           tial(3), pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
2717    
2718    
2719    AUTHOR
2720    
2721           Philip Hazel
2722           University Computing Service
2723           Cambridge CB2 3QH, England.
2724    
2725    
2726    REVISION
2727    
2728           Last updated: 26 March 2010
2729           Copyright (c) 1997-2010 University of Cambridge.
2730  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2731    
2732    
# Line 2080  PCRE CALLOUTS Line 2753  PCRE CALLOUTS
2753         default value is zero.  For  example,  this  pattern  has  two  callout         default value is zero.  For  example,  this  pattern  has  two  callout
2754         points:         points:
2755    
2756           (?C1)eabc(?C2)def           (?C1)abc(?C2)def
2757    
2758         If  the  PCRE_AUTO_CALLOUT  option  bit  is  set when pcre_compile() is         If  the  PCRE_AUTO_CALLOUT  option  bit  is  set when pcre_compile() or
2759         called, PCRE automatically  inserts  callouts,  all  with  number  255,         pcre_compile2() is called, PCRE  automatically  inserts  callouts,  all
2760         before  each  item in the pattern. For example, if PCRE_AUTO_CALLOUT is         with  number  255,  before  each  item  in the pattern. For example, if
2761         used with the pattern         PCRE_AUTO_CALLOUT is used with the pattern
2762    
2763           A(\d{2}|--)           A(\d{2}|--)
2764    
# Line 2104  PCRE CALLOUTS Line 2777  PCRE CALLOUTS
2777  MISSING CALLOUTS  MISSING CALLOUTS
2778    
2779         You  should  be  aware  that,  because of optimizations in the way PCRE         You  should  be  aware  that,  because of optimizations in the way PCRE
2780         matches patterns, callouts sometimes do not happen. For example, if the         matches patterns by default, callouts  sometimes  do  not  happen.  For
2781         pattern is         example, if the pattern is
2782    
2783           ab(?C4)cd           ab(?C4)cd
2784    
# Line 2114  MISSING CALLOUTS Line 2787  MISSING CALLOUTS
2787         ever  start,  and  the  callout is never reached. However, with "abyd",         ever  start,  and  the  callout is never reached. However, with "abyd",
2788         though the result is still no match, the callout is obeyed.         though the result is still no match, the callout is obeyed.
2789    
2790           If the pattern is studied, PCRE knows the minimum length of a  matching
2791           string,  and will immediately give a "no match" return without actually
2792           running a match if the subject is not long enough, or,  for  unanchored
2793           patterns, if it has been scanned far enough.
2794    
2795           You  can disable these optimizations by passing the PCRE_NO_START_OPTI-
2796           MIZE option to pcre_exec() or  pcre_dfa_exec().  This  slows  down  the
2797           matching  process,  but  does  ensure that callouts such as the example
2798           above are obeyed.
2799    
2800    
2801  THE CALLOUT INTERFACE  THE CALLOUT INTERFACE
2802    
# Line 2141  THE CALLOUT INTERFACE Line 2824  THE CALLOUT INTERFACE
2824         version number will change again in future  if  additional  fields  are         version number will change again in future  if  additional  fields  are
2825         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.
2826    
2827         The callout_number field contains the number of the  callout,  as  com-         The  callout_number  field  contains the number of the callout, as com-
2828         piled  into  the pattern (that is, the number after ?C for manual call-         piled into the pattern (that is, the number after ?C for  manual  call-
2829         outs, and 255 for automatically generated callouts).         outs, and 255 for automatically generated callouts).
2830    
2831         The offset_vector field is a pointer to the vector of offsets that  was         The  offset_vector field is a pointer to the vector of offsets that was
2832         passed   by   the   caller  to  pcre_exec()  or  pcre_dfa_exec().  When         passed  by  the  caller  to  pcre_exec()   or   pcre_dfa_exec().   When
2833         pcre_exec() is used, the contents can be inspected in order to  extract         pcre_exec()  is used, the contents can be inspected in order to extract
2834         substrings  that  have  been  matched  so  far,  in the same way as for         substrings that have been matched so  far,  in  the  same  way  as  for
2835         extracting substrings after a match has completed. For  pcre_dfa_exec()         extracting  substrings after a match has completed. For pcre_dfa_exec()
2836         this field is not useful.         this field is not useful.
2837    
2838         The subject and subject_length fields contain copies of the values that         The subject and subject_length fields contain copies of the values that
2839         were passed to pcre_exec().         were passed to pcre_exec().
2840    
2841         The start_match field contains the offset within the subject  at  which         The  start_match  field normally contains the offset within the subject
2842         the  current match attempt started. If the pattern is not anchored, the         at which the current match attempt  started.  However,  if  the  escape
2843         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
2844         pattern for different starting points in the subject.         modified starting point. If the pattern is not  anchored,  the  callout
2845           function may be called several times from the same point in the pattern
2846           for different starting points in the subject.
2847    
2848         The  current_position  field  contains the offset within the subject of         The current_position field contains the offset within  the  subject  of
2849         the current match pointer.         the current match pointer.
2850    
2851         When the pcre_exec() function is used, the capture_top  field  contains         When  the  pcre_exec() function is used, the capture_top field contains
2852         one  more than the number of the highest numbered captured substring so         one more than the number of the highest numbered captured substring  so
2853         far. If no substrings have been captured, the value of  capture_top  is         far.  If  no substrings have been captured, the value of capture_top is
2854         one.  This  is always the case when pcre_dfa_exec() is used, because it         one. This is always the case when pcre_dfa_exec() is used,  because  it
2855         does not support captured substrings.         does not support captured substrings.
2856    
2857         The capture_last field contains the number of the  most  recently  cap-         The  capture_last  field  contains the number of the most recently cap-
2858         tured  substring. If no substrings have been captured, its value is -1.         tured substring. If no substrings have been captured, its value is  -1.
2859         This is always the case when pcre_dfa_exec() is used.         This is always the case when pcre_dfa_exec() is used.
2860    
2861         The callout_data field contains a value that is passed  to  pcre_exec()         The  callout_data  field contains a value that is passed to pcre_exec()
2862         or  pcre_dfa_exec() specifically so that it can be passed back in call-         or pcre_dfa_exec() specifically so that it can be passed back in  call-
2863         outs. It is passed in the pcre_callout field  of  the  pcre_extra  data         outs.  It  is  passed  in the pcre_callout field of the pcre_extra data
2864         structure.  If  no such data was passed, the value of callout_data in a         structure. If no such data was passed, the value of callout_data  in  a
2865         pcre_callout block is NULL. There is a description  of  the  pcre_extra         pcre_callout  block  is  NULL. There is a description of the pcre_extra
2866         structure in the pcreapi documentation.         structure in the pcreapi documentation.
2867    
2868         The  pattern_position field is present from version 1 of the pcre_call-         The pattern_position field is present from version 1 of the  pcre_call-
2869         out structure. It contains the offset to the next item to be matched in         out structure. It contains the offset to the next item to be matched in
2870         the pattern string.         the pattern string.
2871    
2872         The  next_item_length field is present from version 1 of the pcre_call-         The next_item_length field is present from version 1 of the  pcre_call-
2873         out structure. It contains the length of the next item to be matched in         out structure. It contains the length of the next item to be matched in
2874         the  pattern  string. When the callout immediately precedes an alterna-         the pattern string. When the callout immediately precedes  an  alterna-
2875         tion bar, a closing parenthesis, or the end of the pattern, the  length         tion  bar, a closing parenthesis, or the end of the pattern, the length
2876         is  zero.  When the callout precedes an opening parenthesis, the length         is zero. When the callout precedes an opening parenthesis,  the  length
2877         is that of the entire subpattern.         is that of the entire subpattern.
2878    
2879         The pattern_position and next_item_length fields are intended  to  help         The  pattern_position  and next_item_length fields are intended to help
2880         in  distinguishing between different automatic callouts, which all have         in distinguishing between different automatic callouts, which all  have
2881         the same callout number. However, they are set for all callouts.         the same callout number. However, they are set for all callouts.
2882    
2883    
2884  RETURN VALUES  RETURN VALUES
2885    
2886         The external callout function returns an integer to PCRE. If the  value         The  external callout function returns an integer to PCRE. If the value
2887         is  zero,  matching  proceeds  as  normal. If the value is greater than         is zero, matching proceeds as normal. If  the  value  is  greater  than
2888         zero, matching fails at the current point, but  the  testing  of  other         zero,  matching  fails  at  the current point, but the testing of other
2889         matching possibilities goes ahead, just as if a lookahead assertion had         matching possibilities goes ahead, just as if a lookahead assertion had
2890         failed. If the value is less than zero, the  match  is  abandoned,  and         failed.  If  the  value  is less than zero, the match is abandoned, and
2891         pcre_exec() (or pcre_dfa_exec()) returns the negative value.         pcre_exec() or pcre_dfa_exec() returns the negative value.
2892    
2893         Negative   values   should   normally   be   chosen  from  the  set  of         Negative  values  should  normally  be   chosen   from   the   set   of
2894         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-
2895         dard  "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT is         dard "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT  is
2896         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
2897         itself.         itself.
2898    
2899  Last updated: 28 February 2005  
2900  Copyright (c) 1997-2005 University of Cambridge.  AUTHOR
2901    
2902           Philip Hazel
2903           University Computing Service
2904           Cambridge CB2 3QH, England.
2905    
2906    
2907    REVISION
2908    
2909           Last updated: 29 September 2009
2910           Copyright (c) 1997-2009 University of Cambridge.
2911  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2912    
2913    
# Line 2227  DIFFERENCES BETWEEN PCRE AND PERL Line 2922  DIFFERENCES BETWEEN PCRE AND PERL
2922    
2923         This  document describes the differences in the ways that PCRE and Perl         This  document describes the differences in the ways that PCRE and Perl
2924         handle regular expressions. The differences  described  here  are  with         handle regular expressions. The differences  described  here  are  with
2925         respect to Perl 5.8.         respect to Perl 5.10.
2926    
2927         1.  PCRE does not have full UTF-8 support. Details of what it does have         1.  PCRE has only a subset of Perl's UTF-8 and Unicode support. Details
2928         are given in the section on UTF-8 support in the main pcre page.         of what it does have are given in the section on UTF-8 support  in  the
2929           main pcre page.
2930    
2931         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl
2932         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,
2933         (?!a){3} does not assert that the next three characters are not "a". It         (?!a){3} does not assert that the next three characters are not "a". It
2934         just asserts that the next character is not "a" three times.         just asserts that the next character is not "a" three times.
2935    
2936         3.  Capturing  subpatterns  that occur inside negative lookahead asser-         3. Capturing subpatterns that occur inside  negative  lookahead  asser-
2937         tions are counted, but their entries in the offsets  vector  are  never         tions  are  counted,  but their entries in the offsets vector are never
2938         set.  Perl sets its numerical variables from any such patterns that are         set. Perl sets its numerical variables from any such patterns that  are
2939         matched before the assertion fails to match something (thereby succeed-         matched before the assertion fails to match something (thereby succeed-
2940         ing),  but  only  if the negative lookahead assertion contains just one         ing), but only if the negative lookahead assertion  contains  just  one
2941         branch.         branch.
2942    
2943         4. Though binary zero characters are supported in the  subject  string,         4.  Though  binary zero characters are supported in the subject string,
2944         they are not allowed in a pattern string because it is passed as a nor-         they are not allowed in a pattern string because it is passed as a nor-
2945         mal C string, terminated by zero. The escape sequence \0 can be used in         mal C string, terminated by zero. The escape sequence \0 can be used in
2946         the pattern to represent a binary zero.         the pattern to represent a binary zero.
2947    
2948         5.  The  following Perl escape sequences are not supported: \l, \u, \L,         5. The following Perl escape sequences are not supported: \l,  \u,  \L,
2949         \U, and \N. In fact these are implemented by Perl's general string-han-         \U, and \N. In fact these are implemented by Perl's general string-han-
2950         dling  and are not part of its pattern matching engine. If any of these         dling and are not part of its pattern matching engine. If any of  these
2951         are encountered by PCRE, an error is generated.         are encountered by PCRE, an error is generated.
2952    
2953         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
2954         is  built  with Unicode character property support. The properties that         is built with Unicode character property support. The  properties  that
2955         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-
2956         erties such as Lu and Nd.         erties such as Lu and Nd, script names such as Greek or  Han,  and  the
2957           derived  properties  Any  and  L&. PCRE does support the Cs (surrogate)
2958           property, which Perl does not; the  Perl  documentation  says  "Because
2959           Perl hides the need for the user to understand the internal representa-
2960           tion of Unicode characters, there is no need to implement the  somewhat
2961           messy concept of surrogates."
2962    
2963         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
2964         ters in between are treated as literals.  This  is  slightly  different         ters in between are treated as literals.  This  is  slightly  different
# Line 2275  DIFFERENCES BETWEEN PCRE AND PERL Line 2976  DIFFERENCES BETWEEN PCRE AND PERL
2976         The  \Q...\E  sequence  is recognized both inside and outside character         The  \Q...\E  sequence  is recognized both inside and outside character
2977         classes.         classes.
2978    
2979         8. Fairly obviously, PCRE does not support the (?{code}) and (?p{code})         8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
2980         constructions.  However,  there is support for recursive patterns using         constructions.  However,  there is support for recursive patterns. This
2981         the non-Perl items (?R),  (?number),  and  (?P>name).  Also,  the  PCRE         is not available in Perl 5.8, but it is in Perl 5.10.  Also,  the  PCRE
2982         "callout"  feature allows an external function to be called during pat-         "callout"  feature allows an external function to be called during pat-
2983         tern matching. See the pcrecallout documentation for details.         tern matching. See the pcrecallout documentation for details.
2984    
2985         9. There are some differences that are concerned with the  settings  of         9. Subpatterns that are called  recursively  or  as  "subroutines"  are
2986           always  treated  as  atomic  groups  in  PCRE. This is like Python, but
2987           unlike Perl. There is a discussion of an example that explains this  in
2988           more  detail  in  the section on recursion differences from Perl in the
2989           pcrepattern page.
2990    
2991           10. There are some differences that are concerned with the settings  of
2992         captured  strings  when  part  of  a  pattern is repeated. For example,         captured  strings  when  part  of  a  pattern is repeated. For example,
2993         matching "aba" against the  pattern  /^(a(b)?)+$/  in  Perl  leaves  $2         matching "aba" against the  pattern  /^(a(b)?)+$/  in  Perl  leaves  $2
2994         unset, but in PCRE it is set to "b".         unset, but in PCRE it is set to "b".
2995    
2996         10. PCRE provides some extensions to the Perl regular expression facil-         11.  PCRE  does  support  Perl  5.10's  backtracking  verbs  (*ACCEPT),
2997         ities:         (*FAIL), (*F), (*COMMIT), (*PRUNE), (*SKIP), and (*THEN), but  only  in
2998           the forms without an argument. PCRE does not support (*MARK).
2999         (a) Although lookbehind assertions must  match  fixed  length  strings,  
3000         each alternative branch of a lookbehind assertion can match a different         12.  PCRE's handling of duplicate subpattern numbers and duplicate sub-
3001         length of string. Perl requires them all to have the same length.         pattern names is not as general as Perl's. This is a consequence of the
3002           fact the PCRE works internally just with numbers, using an external ta-
3003           ble to translate between numbers and names. In  particular,  a  pattern
3004           such  as  (?|(?<a>A)|(?<b)B),  where the two capturing parentheses have
3005           the same number but different names, is not supported,  and  causes  an
3006           error  at compile time. If it were allowed, it would not be possible to
3007           distinguish which parentheses matched, because both names map  to  cap-
3008           turing subpattern number 1. To avoid this confusing situation, an error
3009           is given at compile time.
3010    
3011           13. PCRE provides some extensions to the Perl regular expression facil-
3012           ities.   Perl  5.10  includes new features that are not in earlier ver-
3013           sions of Perl, some of which (such as named parentheses) have  been  in
3014           PCRE for some time. This list is with respect to Perl 5.10:
3015    
3016           (a)  Although  lookbehind  assertions  in  PCRE must match fixed length
3017           strings, each alternative branch of a lookbehind assertion can match  a
3018           different  length  of  string.  Perl requires them all to have the same
3019           length.
3020    
3021         (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  $
3022         meta-character matches only at the very end of the string.         meta-character matches only at the very end of the string.
3023    
3024         (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-
3025         cial meaning is faulted.         cial meaning is faulted. Otherwise, like Perl, the backslash is quietly
3026           ignored.  (Perl can be made to issue a warning.)
3027    
3028         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-         (d)  If  PCRE_UNGREEDY is set, the greediness of the repetition quanti-
3029         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-
3030         lowed by a question mark they are.         lowed by a question mark they are.
3031    
3032         (e) PCRE_ANCHORED can be used at matching time to force a pattern to be         (e) PCRE_ANCHORED can be used at matching time to force a pattern to be
3033         tried only at the first matching position in the subject string.         tried only at the first matching position in the subject string.
3034    
3035         (f)  The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAP-         (f) The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART,
3036         TURE options for pcre_exec() have no Perl equivalents.         and  PCRE_NO_AUTO_CAPTURE  options for pcre_exec() have no Perl equiva-
3037           lents.
3038    
3039         (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
3040         pattern  matching  (Perl  can  do  this using the (?p{code}) construct,         CRLF by the PCRE_BSR_ANYCRLF option.
        which PCRE cannot support.)  
3041    
3042         (h) PCRE supports named capturing substrings, using the Python  syntax.         (h) The callout facility is PCRE-specific.
3043    
3044         (i)  PCRE  supports  the  possessive quantifier "++" syntax, taken from         (i) The partial matching facility is PCRE-specific.
        Sun's Java package.  
3045    
3046         (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,
3047           even on different hosts that have the other endianness.
3048    
3049         (k) The callout facility is PCRE-specific.         (k) The alternative matching function (pcre_dfa_exec())  matches  in  a
3050           different way and is not Perl-compatible.
3051    
3052         (l) The partial matching facility is PCRE-specific.         (l)  PCRE  recognizes some special sequences such as (*CR) at the start
3053           of a pattern that set overall options that cannot be changed within the
3054           pattern.
3055    
        (m) Patterns compiled by PCRE can be saved and re-used at a later time,  
        even on different hosts that have the other endianness.  
3056    
3057         (n)  The  alternative  matching function (pcre_dfa_exec()) matches in a  AUTHOR
        different way and is not Perl-compatible.  
3058    
3059  Last updated: 28 February 2005         Philip Hazel
3060  Copyright (c) 1997-2005 University of Cambridge.         University Computing Service
3061           Cambridge CB2 3QH, England.
3062    
3063    
3064    REVISION
3065    
3066           Last updated: 04 October 2009
3067           Copyright (c) 1997-2009 University of Cambridge.
3068  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
3069    
3070    
# Line 2344  NAME Line 3077  NAME
3077    
3078  PCRE REGULAR EXPRESSION DETAILS  PCRE REGULAR EXPRESSION DETAILS
3079    
3080         The  syntax  and semantics of the regular expressions supported by PCRE         The  syntax and semantics of the regular expressions that are supported
3081         are described below. Regular expressions are also described in the Perl         by PCRE are described in detail below. There is a quick-reference  syn-
3082         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
3083         examples.  Jeffrey Friedl's "Mastering Regular Expressions",  published         semantics as closely as it can. PCRE  also  supports  some  alternative
3084         by  O'Reilly, covers regular expressions in great detail. This descrip-         regular  expression  syntax (which does not conflict with the Perl syn-
3085         tion of PCRE's regular expressions is intended as reference material.         tax) in order to provide some compatibility with regular expressions in
3086           Python, .NET, and Oniguruma.
3087    
3088           Perl's  regular expressions are described in its own documentation, and
3089           regular expressions in general are covered in a number of  books,  some
3090           of  which  have  copious  examples. Jeffrey Friedl's "Mastering Regular
3091           Expressions", published by  O'Reilly,  covers  regular  expressions  in
3092           great  detail.  This  description  of  PCRE's  regular  expressions  is
3093           intended as reference material.
3094    
3095         The original operation of PCRE was on strings of  one-byte  characters.         The original operation of PCRE was on strings of  one-byte  characters.
3096         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
3097         this, you must build PCRE to  include  UTF-8  support,  and  then  call         this, PCRE must be built to include UTF-8 support, and  you  must  call
3098         pcre_compile()  with  the  PCRE_UTF8  option.  How this affects pattern         pcre_compile()  or  pcre_compile2() with the PCRE_UTF8 option. There is
3099         matching is mentioned in several places below. There is also a  summary         also a special sequence that can be given at the start of a pattern:
3100         of  UTF-8  features  in  the  section on UTF-8 support in the main pcre  
3101         page.           (*UTF8)
3102    
3103           Starting a pattern with this sequence  is  equivalent  to  setting  the
3104           PCRE_UTF8  option.  This  feature  is  not Perl-compatible. How setting
3105           UTF-8 mode affects pattern matching  is  mentioned  in  several  places
3106           below.  There  is  also  a  summary of UTF-8 features in the section on
3107           UTF-8 support in the main pcre page.
3108    
3109         The remainder of this document discusses the  patterns  that  are  sup-         The remainder of this document discusses the  patterns  that  are  sup-
3110         ported  by  PCRE when its main matching function, pcre_exec(), is used.         ported  by  PCRE when its main matching function, pcre_exec(), is used.
3111         From  release  6.0,   PCRE   offers   a   second   matching   function,         From  release  6.0,   PCRE   offers   a   second   matching   function,
3112         pcre_dfa_exec(),  which matches using a different algorithm that is not         pcre_dfa_exec(),  which matches using a different algorithm that is not
3113         Perl-compatible. The advantages and disadvantages  of  the  alternative         Perl-compatible. Some of the features discussed below are not available
3114         function, and how it differs from the normal function, are discussed in         when  pcre_dfa_exec()  is used. The advantages and disadvantages of the
3115         the pcrematching page.         alternative function, and how it differs from the normal function,  are
3116           discussed in the pcrematching page.
3117         A regular expression is a pattern that is  matched  against  a  subject  
3118         string  from  left  to right. Most characters stand for themselves in a  
3119         pattern, and match the corresponding characters in the  subject.  As  a  NEWLINE CONVENTIONS
3120    
3121           PCRE  supports five different conventions for indicating line breaks in
3122           strings: a single CR (carriage return) character, a  single  LF  (line-
3123           feed) character, the two-character sequence CRLF, any of the three pre-
3124           ceding, or any Unicode newline sequence. The pcreapi page  has  further
3125           discussion  about newlines, and shows how to set the newline convention
3126           in the options arguments for the compiling and matching functions.
3127    
3128           It is also possible to specify a newline convention by starting a  pat-
3129           tern string with one of the following five sequences:
3130    
3131             (*CR)        carriage return
3132             (*LF)        linefeed
3133             (*CRLF)      carriage return, followed by linefeed
3134             (*ANYCRLF)   any of the three above
3135             (*ANY)       all Unicode newline sequences
3136    
3137           These  override  the default and the options given to pcre_compile() or
3138           pcre_compile2(). For example, on a Unix system where LF is the  default
3139           newline sequence, the pattern
3140    
3141             (*CR)a.b
3142    
3143           changes the convention to CR. That pattern matches "a\nb" because LF is
3144           no longer a newline. Note that these special settings,  which  are  not
3145           Perl-compatible,  are  recognized  only at the very start of a pattern,
3146           and that they must be in upper case.  If  more  than  one  of  them  is
3147           present, the last one is used.
3148    
3149           The  newline  convention  does  not  affect what the \R escape sequence
3150           matches. By default, this is any Unicode  newline  sequence,  for  Perl
3151           compatibility.  However, this can be changed; see the description of \R
3152           in the section entitled "Newline sequences" below. A change of \R  set-
3153           ting can be combined with a change of newline convention.
3154    
3155    
3156    CHARACTERS AND METACHARACTERS
3157    
3158           A  regular  expression  is  a pattern that is matched against a subject
3159           string from left to right. Most characters stand for  themselves  in  a
3160           pattern,  and  match  the corresponding characters in the subject. As a
3161         trivial example, the pattern         trivial example, the pattern
3162    
3163           The quick brown fox           The quick brown fox
3164    
3165         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
3166         caseless matching is specified (the PCRE_CASELESS option), letters  are         caseless  matching is specified (the PCRE_CASELESS option), letters are
3167         matched  independently  of case. In UTF-8 mode, PCRE always understands         matched independently of case. In UTF-8 mode, PCRE  always  understands
3168         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
3169         caseless  matching  is always possible. For characters with higher val-         caseless matching is always possible. For characters with  higher  val-
3170         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
3171         property  support,  but  not  otherwise.   If  you want to use caseless         property support, but not otherwise.   If  you  want  to  use  caseless
3172         matching for characters 128 and above, you must  ensure  that  PCRE  is         matching  for  characters  128  and above, you must ensure that PCRE is
3173         compiled with Unicode property support as well as with UTF-8 support.         compiled with Unicode property support as well as with UTF-8 support.
3174    
3175         The  power  of  regular  expressions  comes from the ability to include         The power of regular expressions comes  from  the  ability  to  include
3176         alternatives and repetitions in the pattern. These are encoded  in  the         alternatives  and  repetitions in the pattern. These are encoded in the
3177         pattern by the use of metacharacters, which do not stand for themselves         pattern by the use of metacharacters, which do not stand for themselves
3178         but instead are interpreted in some special way.         but instead are interpreted in some special way.
3179    
3180         There are two different sets of metacharacters: those that  are  recog-         There  are  two different sets of metacharacters: those that are recog-
3181         nized  anywhere in the pattern except within square brackets, and those         nized anywhere in the pattern except within square brackets, and  those
3182         that are recognized in square brackets. Outside  square  brackets,  the         that  are  recognized  within square brackets. Outside square brackets,
3183         metacharacters are as follows:         the metacharacters are as follows:
3184    
3185           \      general escape character with several uses           \      general escape character with several uses
3186           ^      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 3198  PCRE REGULAR EXPRESSION DETAILS
3198                  also "possessive quantifier"                  also "possessive quantifier"
3199           {      start min/max quantifier           {      start min/max quantifier
3200    
3201         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
3202         class". In a character class the only metacharacters are:         class". In a character class the only metacharacters are:
3203    
3204           \      general escape character           \      general escape character
# Line 2420  PCRE REGULAR EXPRESSION DETAILS Line 3208  PCRE REGULAR EXPRESSION DETAILS
3208                    syntax)                    syntax)
3209           ]      terminates the character class           ]      terminates the character class
3210    
3211         The following sections describe the use of each of the  metacharacters.         The following sections describe the use of each of the metacharacters.
3212    
3213    
3214  BACKSLASH  BACKSLASH
# Line 2439  BACKSLASH Line 3227  BACKSLASH
3227    
3228         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in
3229         the pattern (other than in a character class) and characters between  a         the pattern (other than in a character class) and characters between  a
3230         # outside a character class and the next newline character are ignored.         # outside a character class and the next newline are ignored. An escap-
3231         An escaping backslash can be used to include a whitespace or #  charac-         ing backslash can be used to include a whitespace  or  #  character  as
3232         ter as part of the pattern.         part of the pattern.
3233    
3234         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-
3235         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 2465  BACKSLASH Line 3253  BACKSLASH
3253         acters  in patterns in a visible manner. There is no restriction on the         acters  in patterns in a visible manner. There is no restriction on the
3254         appearance of non-printing characters, apart from the binary zero  that         appearance of non-printing characters, apart from the binary zero  that
3255         terminates  a  pattern,  but  when  a pattern is being prepared by text         terminates  a  pattern,  but  when  a pattern is being prepared by text
3256         editing, it is usually easier  to  use  one  of  the  following  escape         editing, it is  often  easier  to  use  one  of  the  following  escape
3257         sequences than the binary character it represents:         sequences than the binary character it represents:
3258    
3259           \a        alarm, that is, the BEL character (hex 07)           \a        alarm, that is, the BEL character (hex 07)
3260           \cx       "control-x", where x is any character           \cx       "control-x", where x is any character
3261           \e        escape (hex 1B)           \e        escape (hex 1B)
3262           \f        formfeed (hex 0C)           \f        formfeed (hex 0C)
3263           \n        newline (hex 0A)           \n        linefeed (hex 0A)
3264           \r        carriage return (hex 0D)           \r        carriage return (hex 0D)
3265           \t        tab (hex 09)           \t        tab (hex 09)
3266           \ddd      character with octal code ddd, or backreference           \ddd      character with octal code ddd, or back reference
3267           \xhh      character with hex code hh           \xhh      character with hex code hh
3268           \x{hhh..} character with hex code hhh... (UTF-8 mode only)           \x{hhh..} character with hex code hhh..
3269    
3270         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,
3271         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 3273  BACKSLASH
3273         becomes hex 7B.         becomes hex 7B.
3274    
3275         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
3276         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
3277         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
3278         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,
3279         7FFFFFFF). If characters other than hexadecimal digits  appear  between         the maximum value in hexadecimal is 7FFFFFFF. Note that this is  bigger
3280         \x{  and }, or if there is no terminating }, this form of escape is not         than the largest Unicode code point, which is 10FFFF.
3281         recognized. Instead, the initial \x will  be  interpreted  as  a  basic  
3282         hexadecimal  escape, with no following digits, giving a character whose         If  characters  other than hexadecimal digits appear between \x{ and },
3283         value is zero.         or if there is no terminating }, this form of escape is not recognized.
3284           Instead,  the  initial  \x  will  be interpreted as a basic hexadecimal
3285           escape, with no following digits, giving a  character  whose  value  is
3286           zero.
3287    
3288         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
3289         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-
3290         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}.
3291         \x{dc}.  
3292           After  \0  up  to two further octal digits are read. If there are fewer
3293         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
3294         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
3295         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
3296         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.  
3297    
3298         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-
3299         cated.  Outside a character class, PCRE reads it and any following dig-         cated.  Outside a character class, PCRE reads it and any following dig-
3300         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
3301         have been at least that many previous capturing left parentheses in the         have been at least that many previous capturing left parentheses in the
3302         expression, the entire  sequence  is  taken  as  a  back  reference.  A         expression,  the  entire  sequence  is  taken  as  a  back reference. A
3303         description  of how this works is given later, following the discussion         description of how this works is given later, following the  discussion
3304         of parenthesized subpatterns.         of parenthesized subpatterns.
3305    
3306         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
3307         and  there have not been that many capturing subpatterns, PCRE re-reads         and there have not been that many capturing subpatterns, PCRE  re-reads
3308         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-
3309         gle byte from the least significant 8 bits of the value. Any subsequent         erate a data character. Any subsequent digits stand for themselves.  In
3310         digits stand for themselves.  For example:         non-UTF-8  mode,  the  value  of a character specified in octal must be
3311           less than \400. In UTF-8 mode, values up to  \777  are  permitted.  For
3312           example:
3313    
3314           \040   is another way of writing a space           \040   is another way of writing a space
3315           \40    is the same, provided there are fewer than 40           \40    is the same, provided there are fewer than 40
# Line 2535  BACKSLASH Line 3326  BACKSLASH
3326           \81    is either a back reference, or a binary zero           \81    is either a back reference, or a binary zero
3327                     followed by the two characters "8" and "1"                     followed by the two characters "8" and "1"
3328    
3329         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
3330         leading zero, because no more than three octal digits are ever read.         leading zero, because no more than three octal digits are ever read.
3331    
3332         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
3333         character (in UTF-8 mode) can be used both inside and outside character         inside  and  outside character classes. In addition, inside a character
3334         classes.  In  addition,  inside  a  character class, the sequence \b is         class, the sequence \b is interpreted as the backspace  character  (hex
3335         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"
3336         interpreted  as  the  character  "X".  Outside a character class, these         and "X", respectively. Outside a character class, these sequences  have
3337         sequences have different meanings (see below).         different meanings (see below).
3338    
3339       Absolute and relative back references
3340    
3341           The  sequence  \g followed by an unsigned or a negative number, option-
3342           ally enclosed in braces, is an absolute or relative back  reference.  A
3343           named back reference can be coded as \g{name}. Back references are dis-
3344           cussed later, following the discussion of parenthesized subpatterns.
3345    
3346       Absolute and relative subroutine calls
3347    
3348           For compatibility with Oniguruma, the non-Perl syntax \g followed by  a
3349           name or a number enclosed either in angle brackets or single quotes, is
3350           an alternative syntax for referencing a subpattern as  a  "subroutine".
3351           Details  are  discussed  later.   Note  that  \g{...} (Perl syntax) and
3352           \g<...> (Oniguruma syntax) are not synonymous. The  former  is  a  back
3353           reference; the latter is a subroutine call.
3354    
3355     Generic character types     Generic character types
3356    
3357         The third use of backslash is for specifying generic  character  types.         Another use of backslash is for specifying generic character types. The
3358         The following are always recognized:         following are always recognized:
3359    
3360           \d     any decimal digit           \d     any decimal digit
3361           \D     any character that is not a decimal digit           \D     any character that is not a decimal digit
3362             \h     any horizontal whitespace character
3363             \H     any character that is not a horizontal whitespace character
3364           \s     any whitespace character           \s     any whitespace character
3365           \S     any character that is not a whitespace character           \S     any character that is not a whitespace character
3366             \v     any vertical whitespace character
3367             \V     any character that is not a vertical whitespace character
3368           \w     any "word" character           \w     any "word" character
3369           \W     any "non-word" character           \W     any "non-word" character
3370    
3371         Each pair of escape sequences partitions the complete set of characters         Each pair of escape sequences partitions the complete set of characters
3372         into two disjoint sets. Any given character matches one, and only  one,         into  two disjoint sets. Any given character matches one, and only one,
3373         of each pair.         of each pair.
3374    
3375         These character type sequences can appear both inside and outside char-         These character type sequences can appear both inside and outside char-
3376         acter classes. They each match one character of the  appropriate  type.         acter  classes.  They each match one character of the appropriate type.
3377         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
3378         of them fail, since there is no character to match.         of them fail, since there is no character to match.
3379    
3380         For compatibility with Perl, \s does not match the VT  character  (code         For  compatibility  with Perl, \s does not match the VT character (code
3381         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
3382         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
3383           "use locale;" is included in a Perl script, \s may match the VT charac-
3384           ter. In PCRE, it never does.
3385    
3386           In  UTF-8 mode, characters with values greater than 128 never match \d,
3387           \s, or \w, and always match \D, \S, and \W. This is true even when Uni-
3388           code  character  property  support is available. These sequences retain
3389           their original meanings from before UTF-8 support was available, mainly
3390           for  efficiency  reasons. Note that this also affects \b, because it is
3391           defined in terms of \w and \W.
3392    
3393           The sequences \h, \H, \v, and \V are Perl 5.10 features. In contrast to
3394           the  other  sequences, these do match certain high-valued codepoints in
3395           UTF-8 mode.  The horizontal space characters are:
3396    
3397             U+0009     Horizontal tab
3398             U+0020     Space
3399             U+00A0     Non-break space
3400             U+1680     Ogham space mark
3401             U+180E     Mongolian vowel separator
3402             U+2000     En quad
3403             U+2001     Em quad
3404             U+2002     En space
3405             U+2003     Em space
3406             U+2004     Three-per-em space
3407             U+2005     Four-per-em space
3408             U+2006     Six-per-em space
3409             U+2007     Figure space
3410             U+2008     Punctuation space
3411             U+2009     Thin space
3412             U+200A     Hair space
3413             U+202F     Narrow no-break space
3414             U+205F     Medium mathematical space
3415             U+3000     Ideographic space
3416    
3417           The vertical space characters are:
3418    
3419             U+000A     Linefeed
3420             U+000B     Vertical tab
3421             U+000C     Formfeed
3422             U+000D     Carriage return
3423             U+0085     Next line
3424             U+2028     Line separator
3425             U+2029     Paragraph separator
3426    
3427         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
3428         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-
3429         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-
3430         specific  matching is taking place (see "Locale support" in the pcreapi         specific  matching is taking place (see "Locale support" in the pcreapi
3431         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
3432         codes  greater  than  128  are used for accented letters, and these are         systems,  or "french" in Windows, some character codes greater than 128
3433         matched by \w.         are used for accented letters, and these are matched by \w. The use  of
3434           locales with Unicode is discouraged.
3435    
3436       Newline sequences
3437    
3438           Outside  a  character class, by default, the escape sequence \R matches
3439           any Unicode newline sequence. This is a Perl 5.10 feature. In non-UTF-8
3440           mode \R is equivalent to the following:
3441    
3442             (?>\r\n|\n|\x0b|\f|\r|\x85)
3443    
3444           This  is  an  example  of an "atomic group", details of which are given
3445           below.  This particular group matches either the two-character sequence
3446           CR  followed  by  LF,  or  one  of  the single characters LF (linefeed,
3447           U+000A), VT (vertical tab, U+000B), FF (formfeed, U+000C), CR (carriage
3448           return, U+000D), or NEL (next line, U+0085). The two-character sequence
3449           is treated as a single unit that cannot be split.
3450    
3451           In UTF-8 mode, two additional characters whose codepoints  are  greater
3452           than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa-
3453           rator, U+2029).  Unicode character property support is not  needed  for
3454           these characters to be recognized.
3455    
3456           It is possible to restrict \R to match only CR, LF, or CRLF (instead of
3457           the complete set  of  Unicode  line  endings)  by  setting  the  option
3458           PCRE_BSR_ANYCRLF either at compile time or when the pattern is matched.
3459           (BSR is an abbrevation for "backslash R".) This can be made the default
3460           when  PCRE  is  built;  if this is the case, the other behaviour can be
3461           requested via the PCRE_BSR_UNICODE option.   It  is  also  possible  to
3462           specify  these  settings  by  starting a pattern string with one of the
3463           following sequences:
3464    
3465             (*BSR_ANYCRLF)   CR, LF, or CRLF only
3466             (*BSR_UNICODE)   any Unicode newline sequence
3467    
3468           These override the default and the options given to  pcre_compile()  or
3469           pcre_compile2(),  but  they  can  be  overridden  by  options  given to
3470           pcre_exec() or pcre_dfa_exec(). Note that these special settings, which
3471           are  not  Perl-compatible,  are  recognized only at the very start of a
3472           pattern, and that they must be in upper case. If more than one of  them
3473           is present, the last one is used. They can be combined with a change of
3474           newline convention, for example, a pattern can start with:
3475    
3476         In UTF-8 mode, characters with values greater than 128 never match  \d,           (*ANY)(*BSR_ANYCRLF)
3477         \s, or \w, and always match \D, \S, and \W. This is true even when Uni-  
3478         code character property support is available.         Inside a character class, \R matches the letter "R".
3479    
3480     Unicode character properties     Unicode character properties
3481    
3482         When PCRE is built with Unicode character property support, three addi-         When PCRE is built with Unicode character property support, three addi-
3483         tional  escape sequences to match generic character types are available         tional  escape sequences that match characters with specific properties
3484         when UTF-8 mode is selected. They are:         are available.  When not in UTF-8 mode, these sequences are  of  course
3485           limited  to  testing characters whose codepoints are less than 256, but
3486          \p{xx}   a character with the xx property         they do work in this mode.  The extra escape sequences are:
3487          \P{xx}   a character without the xx property  
3488          \X       an extended Unicode sequence           \p{xx}   a character with the xx property
3489             \P{xx}   a character without the xx property
3490             \X       an extended Unicode sequence
3491    
3492         The property names represented by xx above are limited to  the  Unicode         The property names represented by xx above are limited to  the  Unicode
3493         general  category properties. Each character has exactly one such prop-         script names, the general category properties, and "Any", which matches
3494         erty, specified by a two-letter abbreviation.  For  compatibility  with         any character (including newline). Other properties such as "InMusical-
3495         Perl,  negation  can be specified by including a circumflex between the         Symbols"  are  not  currently supported by PCRE. Note that \P{Any} does
3496         opening brace and the property name. For example, \p{^Lu} is  the  same         not match any characters, so always causes a match failure.
3497         as \P{Lu}.  
3498           Sets of Unicode characters are defined as belonging to certain scripts.
3499         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.
3500         properties that start with that letter. In this case, in the absence of         For example:
3501         negation, the curly brackets in the escape sequence are optional; these  
3502         two examples have the same effect:           \p{Greek}
3503             \P{Han}
3504    
3505           Those that are not part of an identified script are lumped together  as
3506           "Common". The current list of scripts is:
3507    
3508           Arabic, Armenian, Avestan, Balinese, Bamum, Bengali, Bopomofo, Braille,
3509           Buginese, Buhid, Canadian_Aboriginal, Carian, Cham,  Cherokee,  Common,
3510           Coptic,   Cuneiform,  Cypriot,  Cyrillic,  Deseret,  Devanagari,  Egyp-
3511           tian_Hieroglyphs,  Ethiopic,  Georgian,  Glagolitic,   Gothic,   Greek,
3512           Gujarati,  Gurmukhi,  Han,  Hangul,  Hanunoo,  Hebrew,  Hiragana, Impe-
3513           rial_Aramaic, Inherited, Inscriptional_Pahlavi, Inscriptional_Parthian,
3514           Javanese,  Kaithi, Kannada, Katakana, Kayah_Li, Kharoshthi, Khmer, Lao,