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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         5.10/5.11, including support for UTF-8 encoded strings and Unicode gen-
30         function  has  some  advantages.  For  a discussion of the two matching         eral  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, by default, the characters that
226         nizes as digits, spaces, or word characters  remain  the  same  set  as         PCRE  recognizes  as digits, spaces, or word characters remain the same
227         before, all with values less than 256. This remains true even when PCRE         set as before, all with values less than 256. This  remains  true  even
228         includes Unicode property support, because to do otherwise  would  slow         when  PCRE  is built to include Unicode property support, because to do
229         down  PCRE in many common cases. If you really want to test for a wider         otherwise would slow down PCRE in many common  cases.  Note  that  this
230         sense of, say, "digit", you must use Unicode  property  tests  such  as         also applies to \b, because it is defined in terms of \w and \W. If you
231         \p{Nd}.         really want to test for a wider sense of, say,  "digit",  you  can  use
232           explicit  Unicode property tests such as \p{Nd}.  Alternatively, if you
233         8.  Similarly,  characters that match the POSIX named character classes         set the PCRE_UCP option, the way that the  character  escapes  work  is
234         are all low-valued characters.         changed  so that Unicode properties are used to determine which charac-
235           ters match. There are more details in the section on generic  character
236           types in the pcrepattern documentation.
237    
238           7.  Similarly,  characters that match the POSIX named character classes
239           are all low-valued characters, unless the PCRE_UCP option is set.
240    
241           8. However, the Perl 5.10 horizontal and vertical  whitespace  matching
242           escapes (\h, \H, \v, and \V) do match all the appropriate Unicode char-
243           acters, whether or not PCRE_UCP is set.
244    
245         9. Case-insensitive matching applies only to  characters  whose  values         9. Case-insensitive matching applies only to  characters  whose  values
246         are  less than 128, unless PCRE is built with Unicode property support.         are  less than 128, unless PCRE is built with Unicode property support.
247         Even when Unicode property support is available, PCRE  still  uses  its         Even when Unicode property support is available, PCRE  still  uses  its
248         own  character  tables when checking the case of low-valued characters,         own  character  tables when checking the case of low-valued characters,
249         so as not to degrade performance.  The Unicode property information  is         so as not to degrade performance.  The Unicode property information  is
250         used only for characters with higher values.         used only for characters with higher values. Even when Unicode property
251           support is available, PCRE supports case-insensitive matching only when
252           there  is  a  one-to-one  mapping between a letter's cases. There are a
253           small number of many-to-one mappings in Unicode;  these  are  not  sup-
254           ported by PCRE.
255    
256    
257  AUTHOR  AUTHOR
258    
259         Philip Hazel         Philip Hazel
260         University Computing Service,         University Computing Service
261         Cambridge CB2 3QG, England.         Cambridge CB2 3QH, England.
262    
263         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,
264         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,
265         name, separated by a dot, at the domain ucs.cam.ac.uk.         followed by the two digits 10, at the domain cam.ac.uk.
266    
 Last updated: 07 March 2005  
 Copyright (c) 1997-2005 University of Cambridge.  
 ------------------------------------------------------------------------------  
267    
268    REVISION
269    
270           Last updated: 12 May 2010
271           Copyright (c) 1997-2010 University of Cambridge.
272    ------------------------------------------------------------------------------
273    
274    
275  PCREBUILD(3)                                                      PCREBUILD(3)  PCREBUILD(3)                                                      PCREBUILD(3)
276    
277    
# Line 220  NAME Line 282  NAME
282  PCRE BUILD-TIME OPTIONS  PCRE BUILD-TIME OPTIONS
283    
284         This  document  describes  the  optional  features  of PCRE that can be         This  document  describes  the  optional  features  of PCRE that can be
285         selected when the library is compiled. They are all selected, or  dese-         selected when the library is compiled. It assumes use of the  configure
286         lected, by providing options to the configure script that is run before         script,  where the optional features are selected or deselected by pro-
287         the make command. The complete list of  options  for  configure  (which         viding options to configure before running the make  command.  However,
288         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
289         directory) can be obtained by running         environments using the GUI facility of cmake-gui if you are using CMake
290           instead of configure to build PCRE.
291    
292           There  is  a  lot more information about building PCRE in non-Unix-like
293           environments in the file called NON_UNIX_USE, which is part of the PCRE
294           distribution.  You  should consult this file as well as the README file
295           if you are building in a non-Unix-like environment.
296    
297           The complete list of options for configure (which includes the standard
298           ones  such  as  the  selection  of  the  installation directory) can be
299           obtained by running
300    
301           ./configure --help           ./configure --help
302    
303         The following sections describe certain options whose names begin  with         The following sections include  descriptions  of  options  whose  names
304         --enable  or  --disable. These settings specify changes to the defaults         begin with --enable or --disable. These settings specify changes to the
305         for the configure command. Because of the  way  that  configure  works,         defaults for the configure command. Because of the way  that  configure
306         --enable  and  --disable  always  come  in  pairs, so the complementary         works,  --enable  and --disable always come in pairs, so the complemen-
307         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
308         not described.         is not described.
309    
310    
311  C++ SUPPORT  C++ SUPPORT
# Line 249  C++ SUPPORT Line 321  C++ SUPPORT
321    
322  UTF-8 SUPPORT  UTF-8 SUPPORT
323    
324         To build PCRE with support for UTF-8 character strings, add         To build PCRE with support for UTF-8 Unicode character strings, add
325    
326           --enable-utf8           --enable-utf8
327    
328         to  the  configure  command.  Of  itself, this does not make PCRE treat         to  the  configure  command.  Of  itself, this does not make PCRE treat
329         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
330         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()
331         function.         or pcre_compile2() functions.
332    
333           If you set --enable-utf8 when compiling in an EBCDIC environment,  PCRE
334           expects its input to be either ASCII or UTF-8 (depending on the runtime
335           option). It is not possible to support both EBCDIC and UTF-8  codes  in
336           the  same  version  of  the  library.  Consequently,  --enable-utf8 and
337           --enable-ebcdic are mutually exclusive.
338    
339    
340  UNICODE CHARACTER PROPERTY SUPPORT  UNICODE CHARACTER PROPERTY SUPPORT
# Line 272  UNICODE CHARACTER PROPERTY SUPPORT Line 350  UNICODE CHARACTER PROPERTY SUPPORT
350         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
351         not explicitly requested it.         not explicitly requested it.
352    
353         Including  Unicode  property  support  adds around 90K of tables to the         Including  Unicode  property  support  adds around 30K of tables to the
354         PCRE library, approximately doubling its size. Only the  general  cate-         PCRE library. Only the general category properties such as  Lu  and  Nd
355         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.  
356    
357    
358  CODE VALUE OF NEWLINE  CODE VALUE OF NEWLINE
359    
360         By default, PCRE treats character 10 (linefeed) as the newline  charac-         By  default,  PCRE interprets the linefeed (LF) character as indicating
361         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
362         compile PCRE to use character 13 (carriage return) instead by adding         systems.  You  can compile PCRE to use carriage return (CR) instead, by
363           adding
364    
365           --enable-newline-is-cr           --enable-newline-is-cr
366    
367         to the configure command. For completeness there is  also  a  --enable-         to the  configure  command.  There  is  also  a  --enable-newline-is-lf
368         newline-is-lf  option,  which explicitly specifies linefeed as the new-         option, which explicitly specifies linefeed as the newline character.
369         line character.  
370           Alternatively, you can specify that line endings are to be indicated by
371           the two character sequence CRLF. If you want this, add
372    
373             --enable-newline-is-crlf
374    
375           to the configure command. There is a fourth option, specified by
376    
377             --enable-newline-is-anycrlf
378    
379           which causes PCRE to recognize any of the three sequences  CR,  LF,  or
380           CRLF as indicating a line ending. Finally, a fifth option, specified by
381    
382             --enable-newline-is-any
383    
384           causes PCRE to recognize any Unicode newline sequence.
385    
386           Whatever  line  ending convention is selected when PCRE is built can be
387           overridden when the library functions are called. At build time  it  is
388           conventional to use the standard for your operating system.
389    
390    
391    WHAT \R MATCHES
392    
393           By  default,  the  sequence \R in a pattern matches any Unicode newline
394           sequence, whatever has been selected as the line  ending  sequence.  If
395           you specify
396    
397             --enable-bsr-anycrlf
398    
399           the  default  is changed so that \R matches only CR, LF, or CRLF. What-
400           ever is selected when PCRE is built can be overridden when the  library
401           functions are called.
402    
403    
404  BUILDING SHARED AND STATIC LIBRARIES  BUILDING SHARED AND STATIC LIBRARIES
405    
406         The PCRE building process uses libtool to build both shared and  static         The  PCRE building process uses libtool to build both shared and static
407         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
408         of         of
409    
410           --disable-shared           --disable-shared
# Line 306  BUILDING SHARED AND STATIC LIBRARIES Line 416  BUILDING SHARED AND STATIC LIBRARIES
416  POSIX MALLOC USAGE  POSIX MALLOC USAGE
417    
418         When PCRE is called through the POSIX interface (see the pcreposix doc-         When PCRE is called through the POSIX interface (see the pcreposix doc-
419         umentation),  additional  working  storage  is required for holding the         umentation), additional working storage is  required  for  holding  the
420         pointers to capturing substrings, because PCRE requires three  integers         pointers  to capturing substrings, because PCRE requires three integers
421         per  substring,  whereas  the POSIX interface provides only two. If the         per substring, whereas the POSIX interface provides only  two.  If  the
422         number of expected substrings is small, the wrapper function uses space         number of expected substrings is small, the wrapper function uses space
423         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.
424         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 429  POSIX MALLOC USAGE
429         to the configure command.         to the configure command.
430    
431    
432    HANDLING VERY LARGE PATTERNS
433    
434           Within a compiled pattern, offset values are used  to  point  from  one
435           part  to another (for example, from an opening parenthesis to an alter-
436           nation metacharacter). By default, two-byte values are used  for  these
437           offsets,  leading  to  a  maximum size for a compiled pattern of around
438           64K. This is sufficient to handle all but the most  gigantic  patterns.
439           Nevertheless,  some  people do want to process truyl enormous patterns,
440           so it is possible to compile PCRE to use three-byte or  four-byte  off-
441           sets by adding a setting such as
442    
443             --with-link-size=3
444    
445           to  the  configure  command.  The value given must be 2, 3, or 4. Using
446           longer offsets slows down the operation of PCRE because it has to  load
447           additional bytes when handling them.
448    
449    
450    AVOIDING EXCESSIVE STACK USAGE
451    
452           When matching with the pcre_exec() function, PCRE implements backtrack-
453           ing by making recursive calls to an internal function  called  match().
454           In  environments  where  the size of the stack is limited, this can se-
455           verely limit PCRE's operation. (The Unix environment does  not  usually
456           suffer from this problem, but it may sometimes be necessary to increase
457           the maximum stack size.  There is a discussion in the  pcrestack  docu-
458           mentation.)  An alternative approach to recursion that uses memory from
459           the heap to remember data, instead of using recursive  function  calls,
460           has  been  implemented to work round the problem of limited stack size.
461           If you want to build a version of PCRE that works this way, add
462    
463             --disable-stack-for-recursion
464    
465           to the configure command. With this configuration, PCRE  will  use  the
466           pcre_stack_malloc  and pcre_stack_free variables to call memory manage-
467           ment functions. By default these point to malloc() and free(), but  you
468           can replace the pointers so that your own functions are used instead.
469    
470           Separate  functions  are  provided  rather  than  using pcre_malloc and
471           pcre_free because the  usage  is  very  predictable:  the  block  sizes
472           requested  are  always  the  same,  and  the blocks are always freed in
473           reverse order. A calling program might be able to  implement  optimized
474           functions  that  perform  better  than  malloc()  and free(). PCRE runs
475           noticeably more slowly when built in this way. This option affects only
476           the pcre_exec() function; it is not relevant for pcre_dfa_exec().
477    
478    
479  LIMITING PCRE RESOURCE USAGE  LIMITING PCRE RESOURCE USAGE
480    
481         Internally,  PCRE has a function called match(), which it calls repeat-         Internally,  PCRE has a function called match(), which it calls repeat-
482         edly  (possibly  recursively)  when  matching  a   pattern   with   the         edly  (sometimes  recursively)  when  matching  a  pattern   with   the
483         pcre_exec()  function.  By controlling the maximum number of times this         pcre_exec()  function.  By controlling the maximum number of times this
484         function may be called during a single matching operation, a limit  can         function may be called during a single matching operation, a limit  can
485         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 492  LIMITING PCRE RESOURCE USAGE
492         to  the  configure  command.  This  setting  has  no  effect   on   the         to  the  configure  command.  This  setting  has  no  effect   on   the
493         pcre_dfa_exec() matching function.         pcre_dfa_exec() matching function.
494    
495           In  some  environments  it is desirable to limit the depth of recursive
496           calls of match() more strictly than the total number of calls, in order
497           to  restrict  the maximum amount of stack (or heap, if --disable-stack-
498           for-recursion is specified) that is used. A second limit controls this;
499           it  defaults  to  the  value  that is set for --with-match-limit, which
500           imposes no additional constraints. However, you can set a  lower  limit
501           by adding, for example,
502    
503             --with-match-limit-recursion=10000
504    
505           to  the  configure  command.  This  value can also be overridden at run
506           time.
507    
508    
509    CREATING CHARACTER TABLES AT BUILD TIME
510    
511           PCRE uses fixed tables for processing characters whose code values  are
512           less  than 256. By default, PCRE is built with a set of tables that are
513           distributed in the file pcre_chartables.c.dist. These  tables  are  for
514           ASCII codes only. If you add
515    
516             --enable-rebuild-chartables
517    
518           to  the  configure  command, the distributed tables are no longer used.
519           Instead, a program called dftables is compiled and  run.  This  outputs
520           the source for new set of tables, created in the default locale of your
521           C runtime system. (This method of replacing the tables does not work if
522           you  are cross compiling, because dftables is run on the local host. If
523           you need to create alternative tables when cross  compiling,  you  will
524           have to do so "by hand".)
525    
 HANDLING VERY LARGE PATTERNS  
526    
527         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  
528    
529           --with-link-size=3         PCRE  assumes  by  default that it will run in an environment where the
530           character code is ASCII (or Unicode, which is  a  superset  of  ASCII).
531           This  is  the  case for most computer operating systems. PCRE can, how-
532           ever, be compiled to run in an EBCDIC environment by adding
533    
534         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.  
535    
536         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-
537         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
538         representation of the compiled pattern, and this changes with the  link         environment (for example,  an  IBM  mainframe  operating  system).  The
539         size.         --enable-ebcdic option is incompatible with --enable-utf8.
540    
541    
542  AVOIDING EXCESSIVE STACK USAGE  PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT
543    
544         When matching with the pcre_exec() function, PCRE implements backtrack-         By default, pcregrep reads all files as plain text. You can build it so
545         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
546         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  
547    
548           --disable-stack-for-recursion           --enable-pcregrep-libz
549             --enable-pcregrep-libbz2
550    
551         to the configure command. With this configuration, PCRE  will  use  the         to the configure command. These options naturally require that the rel-
552         pcre_stack_malloc  and pcre_stack_free variables to call memory manage-         evant libraries are installed on your system. Configuration  will  fail
553         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.  
554    
555    
556  USING EBCDIC CODE  PCRETEST OPTION FOR LIBREADLINE SUPPORT
557    
558         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  
559    
560           --enable-ebcdic           --enable-pcretest-libreadline
561    
562         to the configure command.         to  the  configure  command,  pcretest  is  linked with the libreadline
563           library, and when its input is from a terminal, it reads it  using  the
564           readline() function. This provides line-editing and history facilities.
565           Note that libreadline is GPL-licensed, so if you distribute a binary of
566           pcretest linked in this way, there may be licensing issues.
567    
568           Setting  this  option  causes  the -lreadline option to be added to the
569           pcretest build. In many operating environments with  a  sytem-installed
570           libreadline this is sufficient. However, in some environments (e.g.  if
571           an unmodified distribution version of readline is in use),  some  extra
572           configuration  may  be necessary. The INSTALL file for libreadline says
573           this:
574    
575             "Readline uses the termcap functions, but does not link with the
576             termcap or curses library itself, allowing applications which link
577             with readline the to choose an appropriate library."
578    
579           If your environment has not been set up so that an appropriate  library
580           is automatically included, you may need to add something like
581    
582             LIBS="-ncurses"
583    
584           immediately before the configure command.
585    
586    
587    SEE ALSO
588    
589           pcreapi(3), pcre_config(3).
590    
591    
592    AUTHOR
593    
594           Philip Hazel
595           University Computing Service
596           Cambridge CB2 3QH, England.
597    
 Last updated: 15 August 2005  
 Copyright (c) 1997-2005 University of Cambridge.  
 ------------------------------------------------------------------------------  
598    
599    REVISION
600    
601           Last updated: 29 September 2009
602           Copyright (c) 1997-2009 University of Cambridge.
603    ------------------------------------------------------------------------------
604    
605    
606  PCREMATCHING(3)                                                PCREMATCHING(3)  PCREMATCHING(3)                                                PCREMATCHING(3)
607    
608    
# Line 431  PCRE MATCHING ALGORITHMS Line 635  PCRE MATCHING ALGORITHMS
635           <something> <something else> <something further>           <something> <something else> <something further>
636    
637         there are three possible answers. The standard algorithm finds only one         there are three possible answers. The standard algorithm finds only one
638         of them, whereas the DFA algorithm finds all three.         of them, whereas the alternative algorithm finds all three.
639    
640    
641  REGULAR EXPRESSIONS AS TREES  REGULAR EXPRESSIONS AS TREES
# Line 440  REGULAR EXPRESSIONS AS TREES Line 644  REGULAR EXPRESSIONS AS TREES
644         resented  as  a  tree structure. An unlimited repetition in the pattern         resented  as  a  tree structure. An unlimited repetition in the pattern
645         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
646         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
647         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
648         search  a  tree: depth-first and breadth-first, and these correspond to         tree:  depth-first  and  breadth-first, and these correspond to the two
649         the two matching algorithms provided by PCRE.         matching algorithms provided by PCRE.
650    
651    
652  THE STANDARD MATCHING ALGORITHM  THE STANDARD MATCHING ALGORITHM
653    
654         In the terminology of Jeffrey Friedl's book Mastering  Regular  Expres-         In the terminology of Jeffrey Friedl's book "Mastering Regular  Expres-
655         sions,  the  standard  algorithm  is  an "NFA algorithm". It conducts a         sions",  the  standard  algorithm  is an "NFA algorithm". It conducts a
656         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
657         single path through the tree, checking that the subject matches what is         single path through the tree, checking that the subject matches what is
658         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 676  THE STANDARD MATCHING ALGORITHM
676         This provides support for capturing parentheses and back references.         This provides support for capturing parentheses and back references.
677    
678    
679  THE DFA MATCHING ALGORITHM  THE ALTERNATIVE MATCHING ALGORITHM
680    
681         DFA stands for "deterministic finite automaton", but you do not need to         This algorithm conducts a breadth-first search of  the  tree.  Starting
682         understand the origins of that name. This algorithm conducts a breadth-         from  the  first  matching  point  in the subject, it scans the subject
683         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
684         subject,  it scans the subject string from left to right, once, charac-         this,  it remembers all the paths through the tree that represent valid
685         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",
686         through the tree that represent valid matches.         though  it is not implemented as a traditional finite state machine (it
687           keeps multiple states active simultaneously).
688         The  scan  continues until either the end of the subject is reached, or  
689         there are no more unterminated paths. At this point,  terminated  paths         Although the general principle of this matching algorithm  is  that  it
690         represent  the different matching possibilities (if there are none, the         scans  the subject string only once, without backtracking, there is one
691         match has failed).  Thus, if there is more  than  one  possible  match,         exception: when a lookaround assertion is encountered,  the  characters
692           following  or  preceding  the  current  point  have to be independently
693           inspected.
694    
695           The scan continues until either the end of the subject is  reached,  or
696           there  are  no more unterminated paths. At this point, terminated paths
697           represent the different matching possibilities (if there are none,  the
698           match  has  failed).   Thus,  if there is more than one possible match,
699         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-
700         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
701         match (which is necessarily the shortest) has been found.         (which is necessarily the shortest) is found.
702    
703         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
704         subject. If the pattern         subject. If the pattern
705    
706           cat(er(pillar)?)           cat(er(pillar)?)
707    
708         is matched against the string "the caterpillar catchment",  the  result         is  matched  against the string "the caterpillar catchment", the result
709         will  be the three strings "cat", "cater", and "caterpillar" that start         will be the three strings "cat", "cater", and "caterpillar" that  start
710         at the fourth character of the subject. The algorithm does not automat-         at the fourth character of the subject. The algorithm does not automat-
711         ically move on to find matches that start at later positions.         ically move on to find matches that start at later positions.
712    
713         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
714         supported by the DFA matching algorithm. They are as follows:         supported by the alternative matching algorithm. They are as follows:
715    
716         1. Because the algorithm finds all  possible  matches,  the  greedy  or         1.  Because  the  algorithm  finds  all possible matches, the greedy or
717         ungreedy  nature  of repetition quantifiers is not relevant. Greedy and         ungreedy nature of repetition quantifiers is not relevant.  Greedy  and
718         ungreedy quantifiers are treated in exactly the same way.         ungreedy quantifiers are treated in exactly the same way. However, pos-
719           sessive quantifiers can make a difference when what follows could  also
720           match what is quantified, for example in a pattern like this:
721    
722             ^a++\w!
723    
724           This  pattern matches "aaab!" but not "aaa!", which would be matched by
725           a non-possessive quantifier. Similarly, if an atomic group is  present,
726           it  is matched as if it were a standalone pattern at the current point,
727           and the longest match is then "locked in" for the rest of  the  overall
728           pattern.
729    
730         2. When dealing with multiple paths through the tree simultaneously, it         2. When dealing with multiple paths through the tree simultaneously, it
731         is  not  straightforward  to  keep track of captured substrings for the         is not straightforward to keep track of  captured  substrings  for  the
732         different matching possibilities, and  PCRE's  implementation  of  this         different  matching  possibilities,  and  PCRE's implementation of this
733         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-
734         strings are available.         strings are available.
735    
736         3. Because no substrings are captured, back references within the  pat-         3.  Because no substrings are captured, back references within the pat-
737         tern are not supported, and cause errors if encountered.         tern are not supported, and cause errors if encountered.
738    
739         4.  For  the same reason, conditional expressions that use a backrefer-         4. For the same reason, conditional expressions that use  a  backrefer-
740         ence as the condition are not supported.         ence  as  the  condition or test for a specific group recursion are not
741           supported.
742    
743           5. Because many paths through the tree may be  active,  the  \K  escape
744           sequence, which resets the start of the match when encountered (but may
745           be on some paths and not on others), is not  supported.  It  causes  an
746           error if encountered.
747    
748         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
749         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.
750    
751         6.  The \C escape sequence, which (in the standard algorithm) matches a         7. The \C escape sequence, which (in the standard algorithm) matches  a
752         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-
753         rithm moves through the subject string one character at a time, for all         tive algorithm moves through the subject  string  one  character  at  a
754         active paths through the tree.         time, for all active paths through the tree.
755    
756           8.  Except for (*FAIL), the backtracking control verbs such as (*PRUNE)
757           are not supported. (*FAIL) is supported, and  behaves  like  a  failing
758           negative assertion.
759    
760    
761  ADVANTAGES OF THE DFA ALGORITHM  ADVANTAGES OF THE ALTERNATIVE ALGORITHM
762    
763         Using the DFA matching algorithm provides the following advantages:         Using  the alternative matching algorithm provides the following advan-
764           tages:
765    
766         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-
767         ically  found,  and  in particular, the longest match is found. To find         ically  found,  and  in particular, the longest match is found. To find
768         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
769         things with callouts.         things with callouts.
770    
771         2.  There is much better support for partial matching. The restrictions         2.  Because  the  alternative  algorithm  scans the subject string just
772         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
773         rithm  for partial matching do not apply to the DFA algorithm. For non-         subject  strings  to  the matching function in several pieces, checking
774         anchored patterns, the starting position of a partial match  is  avail-         for partial matching each time.  The  pcrepartial  documentation  gives
775         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.  
776    
777    
778  DISADVANTAGES OF THE DFA ALGORITHM  DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
779    
780         The DFA algorithm suffers from a number of disadvantages:         The alternative algorithm suffers from a number of disadvantages:
781    
782         1. It is substantially slower than  the  standard  algorithm.  This  is         1.  It  is  substantially  slower  than the standard algorithm. This is
783         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
784         because it is less susceptible to optimization.         because it is less susceptible to optimization.
785    
786         2. Capturing parentheses and back references are not supported.         2. Capturing parentheses and back references are not supported.
787    
788         3. The "atomic group" feature of PCRE regular expressions is supported,         3. Although atomic groups are supported, their use does not provide the
789         but  does not provide the advantage that it does for the standard algo-         performance advantage that it does for the standard algorithm.
        rithm.  
790    
 Last updated: 28 February 2005  
 Copyright (c) 1997-2005 University of Cambridge.  
 ------------------------------------------------------------------------------  
791    
792    AUTHOR
793    
794           Philip Hazel
795           University Computing Service
796           Cambridge CB2 3QH, England.
797    
798    
799    REVISION
800    
801           Last updated: 29 September 2009
802           Copyright (c) 1997-2009 University of Cambridge.
803    ------------------------------------------------------------------------------
804    
805    
806  PCREAPI(3)                                                          PCREAPI(3)  PCREAPI(3)                                                          PCREAPI(3)
807    
808    
# Line 616  PCRE NATIVE API Line 852  PCRE NATIVE API
852         int pcre_get_stringnumber(const pcre *code,         int pcre_get_stringnumber(const pcre *code,
853              const char *name);              const char *name);
854    
855           int pcre_get_stringtable_entries(const pcre *code,
856                const char *name, char **first, char **last);
857    
858         int pcre_get_substring(const char *subject, int *ovector,         int pcre_get_substring(const char *subject, int *ovector,
859              int stringcount, int stringnumber,              int stringcount, int stringnumber,
860              const char **stringptr);              const char **stringptr);
# Line 654  PCRE NATIVE API Line 893  PCRE NATIVE API
893  PCRE API OVERVIEW  PCRE API OVERVIEW
894    
895         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
896         is also a set of wrapper functions that correspond to the POSIX regular         are also some wrapper functions that correspond to  the  POSIX  regular
897         expression  API.  These  are  described in the pcreposix documentation.         expression  API.  These  are  described in the pcreposix documentation.
898         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
899         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 910  PCRE API OVERVIEW
910         pcre_exec() are used for compiling and matching regular expressions  in         pcre_exec() are used for compiling and matching regular expressions  in
911         a  Perl-compatible  manner. A sample program that demonstrates the sim-         a  Perl-compatible  manner. A sample program that demonstrates the sim-
912         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
913         the  source distribution. The pcresample documentation describes how to         the PCRE source distribution. A listing of this program is given in the
914         run it.         pcredemo documentation, and the pcresample documentation describes  how
915           to compile and run it.
916    
917         A second matching function, pcre_dfa_exec(), which is not Perl-compati-         A second matching function, pcre_dfa_exec(), which is not Perl-compati-
918         ble,  is  also provided. This uses a different algorithm for the match-         ble, is also provided. This uses a different algorithm for  the  match-
919         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
920         the  subject),  not  just  one. However, this algorithm does not return         point in the subject), and scans the subject just  once  (unless  there
921           are  lookbehind  assertions).  However,  this algorithm does not return
922         captured substrings. A description of the two matching  algorithms  and         captured substrings. A description of the two matching  algorithms  and
923         their  advantages  and disadvantages is given in the pcrematching docu-         their  advantages  and disadvantages is given in the pcrematching docu-
924         mentation.         mentation.
# Line 692  PCRE API OVERVIEW Line 933  PCRE API OVERVIEW
933           pcre_get_named_substring()           pcre_get_named_substring()
934           pcre_get_substring_list()           pcre_get_substring_list()
935           pcre_get_stringnumber()           pcre_get_stringnumber()
936             pcre_get_stringtable_entries()
937    
938         pcre_free_substring() and pcre_free_substring_list() are also provided,         pcre_free_substring() and pcre_free_substring_list() are also provided,
939         to free the memory used for extracted strings.         to free the memory used for extracted strings.
# Line 723  PCRE API OVERVIEW Line 965  PCRE API OVERVIEW
965         indirections  to  memory  management functions. These special functions         indirections  to  memory  management functions. These special functions
966         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
967         data, instead of recursive function calls, when running the pcre_exec()         data, instead of recursive function calls, when running the pcre_exec()
968         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
969         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-
970         management, it runs more slowly.  Separate functions  are  provided  so         ments that have limited stacks. Because of the greater  use  of  memory
971         that  special-purpose  external  code  can  be used for this case. When         management,  it  runs  more  slowly. Separate functions are provided so
972         used, these functions are always called in a  stack-like  manner  (last         that special-purpose external code can be  used  for  this  case.  When
973         obtained,  first freed), and always for memory blocks of the same size.         used,  these  functions  are always called in a stack-like manner (last
974           obtained, first freed), and always for memory blocks of the same  size.
975           There  is  a discussion about PCRE's stack usage in the pcrestack docu-
976           mentation.
977    
978         The global variable pcre_callout initially contains NULL. It can be set         The global variable pcre_callout initially contains NULL. It can be set
979         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 981  PCRE API OVERVIEW
981         pcrecallout documentation.         pcrecallout documentation.
982    
983    
984    NEWLINES
985    
986           PCRE  supports five different conventions for indicating line breaks in
987           strings: a single CR (carriage return) character, a  single  LF  (line-
988           feed) character, the two-character sequence CRLF, any of the three pre-
989           ceding, or any Unicode newline sequence. The Unicode newline  sequences
990           are  the  three just mentioned, plus the single characters VT (vertical
991           tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS  (line
992           separator, U+2028), and PS (paragraph separator, U+2029).
993    
994           Each  of  the first three conventions is used by at least one operating
995           system as its standard newline sequence. When PCRE is built, a  default
996           can  be  specified.  The default default is LF, which is the Unix stan-
997           dard. When PCRE is run, the default can be overridden,  either  when  a
998           pattern is compiled, or when it is matched.
999    
1000           At compile time, the newline convention can be specified by the options
1001           argument of pcre_compile(), or it can be specified by special  text  at
1002           the start of the pattern itself; this overrides any other settings. See
1003           the pcrepattern page for details of the special character sequences.
1004    
1005           In the PCRE documentation the word "newline" is used to mean "the char-
1006           acter  or pair of characters that indicate a line break". The choice of
1007           newline convention affects the handling of  the  dot,  circumflex,  and
1008           dollar metacharacters, the handling of #-comments in /x mode, and, when
1009           CRLF is a recognized line ending sequence, the match position  advance-
1010           ment for a non-anchored pattern. There is more detail about this in the
1011           section on pcre_exec() options below.
1012    
1013           The choice of newline convention does not affect the interpretation  of
1014           the  \n  or  \r  escape  sequences, nor does it affect what \R matches,
1015           which is controlled in a similar way, but by separate options.
1016    
1017    
1018  MULTITHREADING  MULTITHREADING
1019    
1020         The  PCRE  functions  can be used in multi-threading applications, with         The PCRE functions can be used in  multi-threading  applications,  with
1021         the  proviso  that  the  memory  management  functions  pointed  to  by         the  proviso  that  the  memory  management  functions  pointed  to  by
1022         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
1023         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 1032  SAVING PRECOMPILED PATTERNS FOR LATER US
1032         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
1033         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
1034         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
1035         pcreprecompile documentation.         pcreprecompile documentation. However, compiling a  regular  expression
1036           with  one version of PCRE for use with a different version is not guar-
1037           anteed to work and may cause crashes.
1038    
1039    
1040  CHECKING BUILD-TIME OPTIONS  CHECKING BUILD-TIME OPTIONS
# Line 782  CHECKING BUILD-TIME OPTIONS Line 1063  CHECKING BUILD-TIME OPTIONS
1063    
1064           PCRE_CONFIG_NEWLINE           PCRE_CONFIG_NEWLINE
1065    
1066         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
1067         used  for the newline character. It is either linefeed (10) or carriage         sequence  that is recognized as meaning "newline". The four values that
1068         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,
1069         operating system.         and  -1  for  ANY.  Though they are derived from ASCII, the same values
1070           are returned in EBCDIC environments. The default should normally corre-
1071           spond to the standard sequence for your operating system.
1072    
1073             PCRE_CONFIG_BSR
1074    
1075           The output is an integer whose value indicates what character sequences
1076           the \R escape sequence matches by default. A value of 0 means  that  \R
1077           matches  any  Unicode  line ending sequence; a value of 1 means that \R
1078           matches only CR, LF, or CRLF. The default can be overridden when a pat-
1079           tern is compiled or matched.
1080    
1081           PCRE_CONFIG_LINK_SIZE           PCRE_CONFIG_LINK_SIZE
1082    
# Line 804  CHECKING BUILD-TIME OPTIONS Line 1095  CHECKING BUILD-TIME OPTIONS
1095    
1096           PCRE_CONFIG_MATCH_LIMIT           PCRE_CONFIG_MATCH_LIMIT
1097    
1098         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-
1099         internal  matching  function  calls in a pcre_exec() execution. Further         ber  of  internal  matching  function calls in a pcre_exec() execution.
1100         details are given with pcre_exec() below.         Further details are given with pcre_exec() below.
1101    
1102             PCRE_CONFIG_MATCH_LIMIT_RECURSION
1103    
1104           The output is a long integer that gives the default limit for the depth
1105           of   recursion  when  calling  the  internal  matching  function  in  a
1106           pcre_exec() execution.  Further  details  are  given  with  pcre_exec()
1107           below.
1108    
1109           PCRE_CONFIG_STACKRECURSE           PCRE_CONFIG_STACKRECURSE
1110    
1111         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
1112         running pcre_exec() is implemented by recursive function calls that use         running pcre_exec() is implemented by recursive function calls that use
1113         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
1114         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
1115         on the  heap  instead  of  recursive  function  calls.  In  this  case,         on  the  heap  instead  of  recursive  function  calls.  In  this case,
1116         pcre_stack_malloc  and  pcre_stack_free  are  called  to  manage memory         pcre_stack_malloc and  pcre_stack_free  are  called  to  manage  memory
1117         blocks on the heap, thus avoiding the use of the stack.         blocks on the heap, thus avoiding the use of the stack.
1118    
1119    
# Line 832  COMPILING A PATTERN Line 1130  COMPILING A PATTERN
1130    
1131         Either of the functions pcre_compile() or pcre_compile2() can be called         Either of the functions pcre_compile() or pcre_compile2() can be called
1132         to compile a pattern into an internal form. The only difference between         to compile a pattern into an internal form. The only difference between
1133         the two interfaces is that pcre_compile2() has an additional  argument,         the  two interfaces is that pcre_compile2() has an additional argument,
1134         errorcodeptr, via which a numerical error code can be returned.         errorcodeptr, via which a numerical error  code  can  be  returned.  To
1135           avoid  too  much repetition, we refer just to pcre_compile() below, but
1136           the information applies equally to pcre_compile2().
1137    
1138         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
1139         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
1140         obtained  via  pcre_malloc is returned. This contains the compiled code         obtained via pcre_malloc is returned. This contains the  compiled  code
1141         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
1142         is a typedef for a structure whose contents are not externally defined.         is a typedef for a structure whose contents are not externally defined.
1143         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
1144         required.         longer required.
1145    
1146         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
1147         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
1148         fully  relocatable, because it may contain a copy of the tableptr argu-         fully relocatable, because it may contain a copy of the tableptr  argu-
1149         ment, which is an address (see below).         ment, which is an address (see below).
1150    
1151         The options argument contains independent bits that affect the compila-         The options argument contains various bit settings that affect the com-
1152         tion.  It  should  be  zero  if  no options are required. The available         pilation. It should be zero if no options are required.  The  available
1153         options are described below. Some of them, in  particular,  those  that         options  are  described  below. Some of them (in particular, those that
1154         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
1155         pattern (see the detailed description  in  the  pcrepattern  documenta-         unset  from  within  the  pattern  (see the detailed description in the
1156         tion).  For  these options, the contents of the options argument speci-         pcrepattern documentation). For those options that can be different  in
1157         fies their initial settings at the start of compilation and  execution.         different  parts  of  the pattern, the contents of the options argument
1158         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
1159         at compile time.         PCRE_ANCHORED, PCRE_BSR_xxx, and PCRE_NEWLINE_xxx options can be set at
1160           the time of matching as well as at compile time.
1161    
1162         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
1163         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and
1164         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-
1165         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
1166         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
1167         erroffset,  which  must  not  be  NULL. If it is, an immediate error is         character  that  was  being  processed when the error was discovered is
1168         given.         placed in the variable pointed to by erroffset, which must not be NULL.
1169           If  it  is,  an  immediate error is given. Some errors are not detected
1170         If pcre_compile2() is used instead of pcre_compile(),  and  the  error-         until checks are carried out when the whole pattern has  been  scanned;
1171         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.
1172         via this argument in the event of an error. This is in addition to  the  
1173           If  pcre_compile2()  is  used instead of pcre_compile(), and the error-
1174           codeptr argument is not NULL, a non-zero error code number is  returned
1175           via  this argument in the event of an error. This is in addition to the
1176         textual error message. Error codes and messages are listed below.         textual error message. Error codes and messages are listed below.
1177    
1178         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
1179         character tables that are  built  when  PCRE  is  compiled,  using  the         character  tables  that  are  built  when  PCRE  is compiled, using the
1180         default  C  locale.  Otherwise, tableptr must be an address that is the         default C locale. Otherwise, tableptr must be an address  that  is  the
1181         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
1182         compiled  pattern,  and used again by pcre_exec(), unless another table         compiled pattern, and used again by pcre_exec(), unless  another  table
1183         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
1184         support below.         support below.
1185    
1186         This  code  fragment  shows a typical straightforward call to pcre_com-         This code fragment shows a typical straightforward  call  to  pcre_com-
1187         pile():         pile():
1188    
1189           pcre *re;           pcre *re;
# Line 892  COMPILING A PATTERN Line 1196  COMPILING A PATTERN
1196             &erroffset,       /* for error offset */             &erroffset,       /* for error offset */
1197             NULL);            /* use default character tables */             NULL);            /* use default character tables */
1198    
1199         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
1200         file:         file:
1201    
1202           PCRE_ANCHORED           PCRE_ANCHORED
1203    
1204         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
1205         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
1206         that  is being searched (the "subject string"). This effect can also be         that is being searched (the "subject string"). This effect can also  be
1207         achieved by appropriate constructs in the pattern itself, which is  the         achieved  by appropriate constructs in the pattern itself, which is the
1208         only way to do it in Perl.         only way to do it in Perl.
1209    
1210           PCRE_AUTO_CALLOUT           PCRE_AUTO_CALLOUT
1211    
1212         If this bit is set, pcre_compile() automatically inserts callout items,         If this bit is set, pcre_compile() automatically inserts callout items,
1213         all with number 255, before each pattern item. For  discussion  of  the         all  with  number  255, before each pattern item. For discussion of the
1214         callout facility, see the pcrecallout documentation.         callout facility, see the pcrecallout documentation.
1215    
1216             PCRE_BSR_ANYCRLF
1217             PCRE_BSR_UNICODE
1218    
1219           These options (which are mutually exclusive) control what the \R escape
1220           sequence  matches.  The choice is either to match only CR, LF, or CRLF,
1221           or to match any Unicode newline sequence. The default is specified when
1222           PCRE is built. It can be overridden from within the pattern, or by set-
1223           ting an option when a compiled pattern is matched.
1224    
1225           PCRE_CASELESS           PCRE_CASELESS
1226    
1227         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
1228         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
1229         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
1230         always understands the concept of case for characters whose values  are         always  understands the concept of case for characters whose values are
1231         less  than 128, so caseless matching is always possible. For characters         less than 128, so caseless matching is always possible. For  characters
1232         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-
1233         piled  with Unicode property support, but not otherwise. If you want to         piled with Unicode property support, but not otherwise. If you want  to
1234         use caseless matching for characters 128 and  above,  you  must  ensure         use  caseless  matching  for  characters 128 and above, you must ensure
1235         that  PCRE  is  compiled  with Unicode property support as well as with         that PCRE is compiled with Unicode property support  as  well  as  with
1236         UTF-8 support.         UTF-8 support.
1237    
1238           PCRE_DOLLAR_ENDONLY           PCRE_DOLLAR_ENDONLY
1239    
1240         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
1241         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
1242         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
1243         not  before  any  other  newlines).  The  PCRE_DOLLAR_ENDONLY option is         before any other newlines). The PCRE_DOLLAR_ENDONLY option  is  ignored
1244         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
1245         in Perl, and no way to set it within a pattern.         Perl, and no way to set it within a pattern.
1246    
1247           PCRE_DOTALL           PCRE_DOTALL
1248    
1249         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-
1250         acters, including newlines. Without it,  newlines  are  excluded.  This         acters,  including  those that indicate newline. Without it, a dot does
1251         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
1252         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
1253         always  matches a newline character, independent of the setting of this         by a (?s) option setting. A negative class such as [^a] always  matches
1254         option.         newline characters, independent of the setting of this option.
1255    
1256             PCRE_DUPNAMES
1257    
1258           If  this  bit is set, names used to identify capturing subpatterns need
1259           not be unique. This can be helpful for certain types of pattern when it
1260           is  known  that  only  one instance of the named subpattern can ever be
1261           matched. There are more details of named subpatterns  below;  see  also
1262           the pcrepattern documentation.
1263    
1264           PCRE_EXTENDED           PCRE_EXTENDED
1265    
1266         If this bit is set, whitespace  data  characters  in  the  pattern  are         If  this  bit  is  set,  whitespace  data characters in the pattern are
1267         totally ignored except when escaped or inside a character class. White-         totally ignored except when escaped or inside a character class. White-
1268         space does not include the VT character (code 11). In addition, charac-         space does not include the VT character (code 11). In addition, charac-
1269         ters between an unescaped # outside a character class and the next new-         ters between an unescaped # outside a character class and the next new-
1270         line character, inclusive, are also  ignored.  This  is  equivalent  to         line,  inclusive,  are  also  ignored.  This is equivalent to Perl's /x
1271         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-
1272         option setting.         ting.
1273    
1274         This option makes it possible to include  comments  inside  complicated         This  option  makes  it possible to include comments inside complicated
1275         patterns.   Note,  however,  that this applies only to data characters.         patterns.  Note, however, that this applies only  to  data  characters.
1276         Whitespace  characters  may  never  appear  within  special   character         Whitespace   characters  may  never  appear  within  special  character
1277         sequences  in  a  pattern,  for  example  within the sequence (?( which         sequences in a pattern, for  example  within  the  sequence  (?(  which
1278         introduces a conditional subpattern.         introduces a conditional subpattern.
1279    
1280           PCRE_EXTRA           PCRE_EXTRA
1281    
1282         This option was invented in order to turn on  additional  functionality         This  option  was invented in order to turn on additional functionality
1283         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
1284         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
1285         letter  that  has  no  special  meaning causes an error, thus reserving         letter that has no special meaning  causes  an  error,  thus  reserving
1286         these combinations for future expansion. By  default,  as  in  Perl,  a         these  combinations  for  future  expansion.  By default, as in Perl, a
1287         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
1288         literal. There are at present no  other  features  controlled  by  this         literal. (Perl can, however, be persuaded to give an error for this, by
1289         option. It can also be set by a (?X) option setting within a pattern.         running it with the -w option.) There are at present no other  features
1290           controlled  by this option. It can also be set by a (?X) option setting
1291           within a pattern.
1292    
1293           PCRE_FIRSTLINE           PCRE_FIRSTLINE
1294    
1295         If  this  option  is  set,  an  unanchored pattern is required to match         If this option is set, an  unanchored  pattern  is  required  to  match
1296         before or at the first newline character in the subject string,  though         before  or  at  the  first  newline  in  the subject string, though the
1297         the matched text may continue over the newline.         matched text may continue over the newline.
1298    
1299             PCRE_JAVASCRIPT_COMPAT
1300    
1301           If this option is set, PCRE's behaviour is changed in some ways so that
1302           it  is  compatible with JavaScript rather than Perl. The changes are as
1303           follows:
1304    
1305           (1) A lone closing square bracket in a pattern  causes  a  compile-time
1306           error,  because this is illegal in JavaScript (by default it is treated
1307           as a data character). Thus, the pattern AB]CD becomes illegal when this
1308           option is set.
1309    
1310           (2)  At run time, a back reference to an unset subpattern group matches
1311           an empty string (by default this causes the current  matching  alterna-
1312           tive  to  fail). A pattern such as (\1)(a) succeeds when this option is
1313           set (assuming it can find an "a" in the subject), whereas it  fails  by
1314           default, for Perl compatibility.
1315    
1316           PCRE_MULTILINE           PCRE_MULTILINE
1317    
# Line 983  COMPILING A PATTERN Line 1323  COMPILING A PATTERN
1323         is set). This is the same as Perl.         is set). This is the same as Perl.
1324    
1325         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"
1326         constructs  match  immediately following or immediately before any new-         constructs  match  immediately following or immediately before internal
1327         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
1328         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
1329         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-
1330         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,
1331         setting PCRE_MULTILINE has no effect.         setting PCRE_MULTILINE has no effect.
1332    
1333             PCRE_NEWLINE_CR
1334             PCRE_NEWLINE_LF
1335             PCRE_NEWLINE_CRLF
1336             PCRE_NEWLINE_ANYCRLF
1337             PCRE_NEWLINE_ANY
1338    
1339           These options override the default newline definition that  was  chosen
1340           when  PCRE  was built. Setting the first or the second specifies that a
1341           newline is indicated by a single character (CR  or  LF,  respectively).
1342           Setting  PCRE_NEWLINE_CRLF specifies that a newline is indicated by the
1343           two-character CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF  specifies
1344           that any of the three preceding sequences should be recognized. Setting
1345           PCRE_NEWLINE_ANY specifies that any Unicode newline sequence should  be
1346           recognized. The Unicode newline sequences are the three just mentioned,
1347           plus the single characters VT (vertical  tab,  U+000B),  FF  (formfeed,
1348           U+000C),  NEL  (next line, U+0085), LS (line separator, U+2028), and PS
1349           (paragraph separator, U+2029). The last  two  are  recognized  only  in
1350           UTF-8 mode.
1351    
1352           The  newline  setting  in  the  options  word  uses three bits that are
1353           treated as a number, giving eight possibilities. Currently only six are
1354           used  (default  plus the five values above). This means that if you set
1355           more than one newline option, the combination may or may not be  sensi-
1356           ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
1357           PCRE_NEWLINE_CRLF, but other combinations may yield unused numbers  and
1358           cause an error.
1359    
1360           The  only time that a line break is specially recognized when compiling
1361           a pattern is if PCRE_EXTENDED is set, and  an  unescaped  #  outside  a
1362           character  class  is  encountered.  This indicates a comment that lasts
1363           until after the next line break sequence. In other circumstances,  line
1364           break   sequences   are   treated  as  literal  data,  except  that  in
1365           PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters
1366           and are therefore ignored.
1367    
1368           The newline option that is set at compile time becomes the default that
1369           is used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
1370    
1371           PCRE_NO_AUTO_CAPTURE           PCRE_NO_AUTO_CAPTURE
1372    
1373         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-
# Line 1017  COMPILING A PATTERN Line 1395  COMPILING A PATTERN
1395           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
1396    
1397         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
1398         automatically  checked. If an invalid UTF-8 sequence of bytes is found,         automatically  checked.  There  is  a  discussion about the validity of
1399         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
1400         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
1401         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-
1402         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
1403         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
1404         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
1405         ing of subject strings.         can also be passed to pcre_exec() and pcre_dfa_exec(), to suppress  the
1406           UTF-8 validity checking of subject strings.
1407    
1408    
1409  COMPILATION ERROR CODES  COMPILATION ERROR CODES
1410    
1411         The following table lists the error  codes  than  may  be  returned  by         The  following  table  lists  the  error  codes than may be returned by
1412         pcre_compile2(),  along with the error messages that may be returned by         pcre_compile2(), along with the error messages that may be returned  by
1413         both compiling functions.         both  compiling functions. As PCRE has developed, some error codes have
1414           fallen out of use. To avoid confusion, they have not been re-used.
1415    
1416            0  no error            0  no error
1417            1  \ at end of pattern            1  \ at end of pattern
# Line 1043  COMPILATION ERROR CODES Line 1423  COMPILATION ERROR CODES
1423            7  invalid escape sequence in character class            7  invalid escape sequence in character class
1424            8  range out of order in character class            8  range out of order in character class
1425            9  nothing to repeat            9  nothing to repeat
1426           10  operand of unlimited repeat could match the empty string           10  [this code is not in use]
1427           11  internal error: unexpected repeat           11  internal error: unexpected repeat
1428           12  unrecognized character after (?           12  unrecognized character after (? or (?-
1429           13  POSIX named classes are supported only within a class           13  POSIX named classes are supported only within a class
1430           14  missing )           14  missing )
1431           15  reference to non-existent subpattern           15  reference to non-existent subpattern
1432           16  erroffset passed as NULL           16  erroffset passed as NULL
1433           17  unknown option bit(s) set           17  unknown option bit(s) set
1434           18  missing ) after comment           18  missing ) after comment
1435           19  parentheses nested too deeply           19  [this code is not in use]
1436           20  regular expression too large           20  regular expression is too large
1437           21  failed to get memory           21  failed to get memory
1438           22  unmatched parentheses           22  unmatched parentheses
1439           23  internal error: code overflow           23  internal error: code overflow
1440           24  unrecognized character after (?<           24  unrecognized character after (?<
1441           25  lookbehind assertion is not fixed length           25  lookbehind assertion is not fixed length
1442           26  malformed number after (?(           26  malformed number or name after (?(
1443           27  conditional group contains more than two branches           27  conditional group contains more than two branches
1444           28  assertion expected after (?(           28  assertion expected after (?(
1445           29  (?R or (?digits must be followed by )           29  (?R or (?[+-]digits must be followed by )
1446           30  unknown POSIX class name           30  unknown POSIX class name
1447           31  POSIX collating elements are not supported           31  POSIX collating elements are not supported
1448           32  this version of PCRE is not compiled with PCRE_UTF8 support           32  this version of PCRE is not compiled with PCRE_UTF8 support
1449           33  spare error           33  [this code is not in use]
1450           34  character value in \x{...} sequence is too large           34  character value in \x{...} sequence is too large
1451           35  invalid condition (?(0)           35  invalid condition (?(0)
1452           36  \C not allowed in lookbehind assertion           36  \C not allowed in lookbehind assertion
# Line 1075  COMPILATION ERROR CODES Line 1455  COMPILATION ERROR CODES
1455           39  closing ) for (?C expected           39  closing ) for (?C expected
1456           40  recursive call could loop indefinitely           40  recursive call could loop indefinitely
1457           41  unrecognized character after (?P           41  unrecognized character after (?P
1458           42  syntax error after (?P           42  syntax error in subpattern name (missing terminator)
1459           43  two named groups have the same name           43  two named subpatterns have the same name
1460           44  invalid UTF-8 string           44  invalid UTF-8 string
1461           45  support for \P, \p, and \X has not been compiled           45  support for \P, \p, and \X has not been compiled
1462           46  malformed \P or \p sequence           46  malformed \P or \p sequence
1463           47  unknown property name after \P or \p           47  unknown property name after \P or \p
1464             48  subpattern name is too long (maximum 32 characters)
1465             49  too many named subpatterns (maximum 10000)
1466             50  [this code is not in use]
1467             51  octal value is greater than \377 (not in UTF-8 mode)
1468             52  internal error: overran compiling workspace
1469             53  internal  error:  previously-checked  referenced  subpattern  not
1470           found
1471             54  DEFINE group contains more than one branch
1472             55  repeating a DEFINE group is not allowed
1473             56  inconsistent NEWLINE options
1474             57  \g is not followed by a braced, angle-bracketed, or quoted
1475                   name/number or by a plain number
1476             58  a numbered reference must not be zero
1477             59  an argument is not allowed for (*ACCEPT), (*FAIL), or (*COMMIT)
1478             60  (*VERB) not recognized
1479             61  number is too big
1480             62  subpattern name expected
1481             63  digit expected after (?+
1482             64  ] is an invalid data character in JavaScript compatibility mode
1483             65   different  names  for  subpatterns  of  the  same number are not
1484           allowed
1485             66  (*MARK) must have an argument
1486    
1487           The numbers 32 and 10000 in errors 48 and 49  are  defaults;  different
1488           values may be used if the limits were changed when PCRE was built.
1489    
1490    
1491  STUDYING A PATTERN  STUDYING A PATTERN
# Line 1088  STUDYING A PATTERN Line 1493  STUDYING A PATTERN
1493         pcre_extra *pcre_study(const pcre *code, int options         pcre_extra *pcre_study(const pcre *code, int options
1494              const char **errptr);              const char **errptr);
1495    
1496         If a compiled pattern is going to be used several times,  it  is  worth         If  a  compiled  pattern is going to be used several times, it is worth
1497         spending more time analyzing it in order to speed up the time taken for         spending more time analyzing it in order to speed up the time taken for
1498         matching. The function pcre_study() takes a pointer to a compiled  pat-         matching.  The function pcre_study() takes a pointer to a compiled pat-
1499         tern as its first argument. If studying the pattern produces additional         tern as its first argument. If studying the pattern produces additional
1500         information that will help speed up matching,  pcre_study()  returns  a         information  that  will  help speed up matching, pcre_study() returns a
1501         pointer  to a pcre_extra block, in which the study_data field points to         pointer to a pcre_extra block, in which the study_data field points  to
1502         the results of the study.         the results of the study.
1503    
1504         The  returned  value  from  pcre_study()  can  be  passed  directly  to         The  returned  value  from  pcre_study()  can  be  passed  directly  to
1505         pcre_exec().  However,  a  pcre_extra  block also contains other fields         pcre_exec() or pcre_dfa_exec(). However, a pcre_extra block  also  con-
1506         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
1507         described below in the section on matching a pattern.         passed; these are described below in the section on matching a pattern.
1508    
1509         If  studying  the  pattern  does not produce any additional information         If studying the  pattern  does  not  produce  any  useful  information,
1510         pcre_study() returns NULL. In that circumstance, if the calling program         pcre_study() returns NULL. In that circumstance, if the calling program
1511         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
1512         its own pcre_extra block.         pcre_dfa_exec(), it must set up its own pcre_extra block.
1513    
1514         The second argument of pcre_study() contains option bits.  At  present,         The  second  argument of pcre_study() contains option bits. At present,
1515         no options are defined, and this argument should always be zero.         no options are defined, and this argument should always be zero.
1516    
1517         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.
1518         If studying succeeds (even if no data is  returned),  the  variable  it         If  studying  succeeds  (even  if no data is returned), the variable it
1519         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
1520         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
1521         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
1522           after calling pcre_study(), to be sure that it has run successfully.
1523    
1524         This is a typical call to pcre_study():         This is a typical call to pcre_study():
1525    
# Line 1123  STUDYING A PATTERN Line 1529  STUDYING A PATTERN
1529             0,              /* no options exist */             0,              /* no options exist */
1530             &error);        /* set to NULL or points to a message */             &error);        /* set to NULL or points to a message */
1531    
1532         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
1533         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
1534         ble starting bytes is created.         does not mean that there are any strings of that length that match, but
1535           it does guarantee that no shorter strings match. The value is  used  by
1536           pcre_exec()  and  pcre_dfa_exec()  to  avoid  wasting time by trying to
1537           match strings that are shorter than the lower bound. You can  find  out
1538           the value in a calling program via the pcre_fullinfo() function.
1539    
1540           Studying a pattern is also useful for non-anchored patterns that do not
1541           have a single fixed starting character. A bitmap of  possible  starting
1542           bytes  is  created. This speeds up finding a position in the subject at
1543           which to start matching.
1544    
1545    
1546  LOCALE SUPPORT  LOCALE SUPPORT
1547    
1548         PCRE  handles  caseless matching, and determines whether characters are         PCRE handles caseless matching, and determines whether  characters  are
1549         letters digits, or whatever, by reference to a set of  tables,  indexed         letters,  digits, or whatever, by reference to a set of tables, indexed
1550         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
1551         characters with codes less than 128. Higher-valued  codes  never  match         characters  with  codes  less than 128. Higher-valued codes never match
1552         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
1553         with Unicode character property support.         with  Unicode  character property support. The use of locales with Uni-
1554           code is discouraged. If you are handling characters with codes  greater
1555         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
1556         is  built.  This  is  used when the final argument of pcre_compile() is         not try to mix the two.
1557         NULL, and is sufficient for many applications. An  alternative  set  of  
1558         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
1559         locale from the default. As more and more applications change to  using         argument  of  pcre_compile()  is  NULL.  These  are sufficient for many
1560         Unicode, the need for this locale support is expected to die away.         applications.  Normally, the internal tables recognize only ASCII char-
1561           acters. However, when PCRE is built, it is possible to cause the inter-
1562         External  tables  are  built by calling the pcre_maketables() function,         nal tables to be rebuilt in the default "C" locale of the local system,
1563         which has no arguments, in the relevant locale. The result can then  be         which may cause them to be different.
1564         passed  to  pcre_compile()  or  pcre_exec()  as often as necessary. For  
1565         example, to build and use tables that are appropriate  for  the  French         The  internal tables can always be overridden by tables supplied by the
1566         locale  (where  accented  characters  with  values greater than 128 are         application that calls PCRE. These may be created in a different locale
1567           from  the  default.  As more and more applications change to using Uni-
1568           code, the need for this locale support is expected to die away.
1569    
1570           External tables are built by calling  the  pcre_maketables()  function,
1571           which  has no arguments, in the relevant locale. The result can then be
1572           passed to pcre_compile() or pcre_exec()  as  often  as  necessary.  For
1573           example,  to  build  and use tables that are appropriate for the French
1574           locale (where accented characters with  values  greater  than  128  are
1575         treated as letters), the following code could be used:         treated as letters), the following code could be used:
1576    
1577           setlocale(LC_CTYPE, "fr_FR");           setlocale(LC_CTYPE, "fr_FR");
1578           tables = pcre_maketables();           tables = pcre_maketables();
1579           re = pcre_compile(..., tables);           re = pcre_compile(..., tables);
1580    
1581           The  locale  name "fr_FR" is used on Linux and other Unix-like systems;
1582           if you are using Windows, the name for the French locale is "french".
1583    
1584         When pcre_maketables() runs, the tables are built  in  memory  that  is         When pcre_maketables() runs, the tables are built  in  memory  that  is
1585         obtained  via  pcre_malloc. It is the caller's responsibility to ensure         obtained  via  pcre_malloc. It is the caller's responsibility to ensure
1586         that the memory containing the tables remains available for as long  as         that the memory containing the tables remains available for as long  as
# Line 1200  INFORMATION ABOUT A PATTERN Line 1626  INFORMATION ABOUT A PATTERN
1626         pattern:         pattern:
1627    
1628           int rc;           int rc;
1629           unsigned long int length;           size_t length;
1630           rc = pcre_fullinfo(           rc = pcre_fullinfo(
1631             re,               /* result of pcre_compile() */             re,               /* result of pcre_compile() */
1632             pe,               /* result of pcre_study(), or NULL */             pe,               /* result of pcre_study(), or NULL */
# Line 1232  INFORMATION ABOUT A PATTERN Line 1658  INFORMATION ABOUT A PATTERN
1658           PCRE_INFO_FIRSTBYTE           PCRE_INFO_FIRSTBYTE
1659    
1660         Return  information  about  the first byte of any matched string, for a         Return  information  about  the first byte of any matched string, for a
1661         non-anchored   pattern.   (This    option    used    to    be    called         non-anchored pattern. The fourth argument should point to an int  vari-
1662         PCRE_INFO_FIRSTCHAR;  the  old  name  is still recognized for backwards         able.  (This option used to be called PCRE_INFO_FIRSTCHAR; the old name
1663         compatibility.)         is still recognized for backwards compatibility.)
1664    
1665         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
1666         (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  
1667    
1668         (a) the pattern was compiled with the PCRE_MULTILINE option, and  every         (a)  the pattern was compiled with the PCRE_MULTILINE option, and every
1669         branch starts with "^", or         branch starts with "^", or
1670    
1671         (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not         (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
1672         set (if it were set, the pattern would be anchored),         set (if it were set, the pattern would be anchored),
1673    
1674         -1 is returned, indicating that the pattern matches only at  the  start         -1  is  returned, indicating that the pattern matches only at the start
1675         of  a  subject string or after any newline within the string. Otherwise         of a subject string or after any newline within the  string.  Otherwise
1676         -2 is returned. For anchored patterns, -2 is returned.         -2 is returned. For anchored patterns, -2 is returned.
1677    
1678           PCRE_INFO_FIRSTTABLE           PCRE_INFO_FIRSTTABLE
1679    
1680         If the pattern was studied, and this resulted in the construction of  a         If  the pattern was studied, and this resulted in the construction of a
1681         256-bit table indicating a fixed set of bytes for the first byte in any         256-bit table indicating a fixed set of bytes for the first byte in any
1682         matching string, a pointer to the table is returned. Otherwise NULL  is         matching  string, a pointer to the table is returned. Otherwise NULL is
1683         returned.  The fourth argument should point to an unsigned char * vari-         returned. The fourth argument should point to an unsigned char *  vari-
1684         able.         able.
1685    
1686             PCRE_INFO_HASCRORLF
1687    
1688           Return  1  if  the  pattern  contains any explicit matches for CR or LF
1689           characters, otherwise 0. The fourth argument should  point  to  an  int
1690           variable.  An explicit match is either a literal CR or LF character, or
1691           \r or \n.
1692    
1693             PCRE_INFO_JCHANGED
1694    
1695           Return 1 if the (?J) or (?-J) option setting is used  in  the  pattern,
1696           otherwise  0. The fourth argument should point to an int variable. (?J)
1697           and (?-J) set and unset the local PCRE_DUPNAMES option, respectively.
1698    
1699           PCRE_INFO_LASTLITERAL           PCRE_INFO_LASTLITERAL
1700    
1701         Return the value of the rightmost literal byte that must exist  in  any         Return the value of the rightmost literal byte that must exist  in  any
# Line 1268  INFORMATION ABOUT A PATTERN Line 1706  INFORMATION ABOUT A PATTERN
1706         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
1707         /^a\dz\d/ the returned value is -1.         /^a\dz\d/ the returned value is -1.
1708    
1709             PCRE_INFO_MINLENGTH
1710    
1711           If the pattern was studied and a minimum length  for  matching  subject
1712           strings  was  computed,  its  value is returned. Otherwise the returned
1713           value is -1. The value is a number of characters, not bytes  (this  may
1714           be  relevant in UTF-8 mode). The fourth argument should point to an int
1715           variable. A non-negative value is a lower bound to the  length  of  any
1716           matching  string.  There  may not be any strings of that length that do
1717           actually match, but every string that does match is at least that long.
1718    
1719           PCRE_INFO_NAMECOUNT           PCRE_INFO_NAMECOUNT
1720           PCRE_INFO_NAMEENTRYSIZE           PCRE_INFO_NAMEENTRYSIZE
1721           PCRE_INFO_NAMETABLE           PCRE_INFO_NAMETABLE
1722    
1723         PCRE supports the use of named as well as numbered capturing  parenthe-         PCRE supports the use of named as well as numbered capturing  parenthe-
1724         ses.  The names are just an additional way of identifying the parenthe-         ses.  The names are just an additional way of identifying the parenthe-
1725         ses,  which  still  acquire  numbers.  A  convenience  function  called         ses, which still acquire numbers. Several convenience functions such as
1726         pcre_get_named_substring()  is  provided  for  extracting an individual         pcre_get_named_substring()  are  provided  for extracting captured sub-
1727         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
1728         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
1729         the correct pointers in the output vector (described  with  pcre_exec()         pointers in the output vector (described with pcre_exec() below). To do
1730         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
1731         which is described by these three values.         described by these three values.
1732    
1733         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
1734         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
# Line 1289  INFORMATION ABOUT A PATTERN Line 1737  INFORMATION ABOUT A PATTERN
1737         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
1738         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-
1739         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-
1740         sponding  name,  zero  terminated. The names are in alphabetical order.         sponding name, zero terminated.
        For example, consider the following pattern  (assume  PCRE_EXTENDED  is  
        set, so white space - including newlines - is ignored):  
1741    
1742           (?P<date> (?P<year>(\d\d)?\d\d) -         The  names are in alphabetical order. Duplicate names may appear if (?|
1743           (?P<month>\d\d) - (?P<day>\d\d) )         is used to create multiple groups with the same number, as described in
1744           the  section  on  duplicate subpattern numbers in the pcrepattern page.
1745           Duplicate names for subpatterns with different  numbers  are  permitted
1746           only  if  PCRE_DUPNAMES  is  set. In all cases of duplicate names, they
1747           appear in the table in the order in which they were found in  the  pat-
1748           tern.  In  the  absence  of (?| this is the order of increasing number;
1749           when (?| is used this is not necessarily the case because later subpat-
1750           terns may have lower numbers.
1751    
1752           As  a  simple  example of the name/number table, consider the following
1753           pattern (assume PCRE_EXTENDED is set, so white space -  including  new-
1754           lines - is ignored):
1755    
1756             (?<date> (?<year>(\d\d)?\d\d) -
1757             (?<month>\d\d) - (?<day>\d\d) )
1758    
1759         There  are  four  named subpatterns, so the table has four entries, and         There  are  four  named subpatterns, so the table has four entries, and
1760         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,
# Line 1307  INFORMATION ABOUT A PATTERN Line 1767  INFORMATION ABOUT A PATTERN
1767           00 02 y  e  a  r  00 ??           00 02 y  e  a  r  00 ??
1768    
1769         When writing code to extract data  from  named  subpatterns  using  the         When writing code to extract data  from  named  subpatterns  using  the
1770         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
1771         be different for each compiled pattern.         to be different for each compiled pattern.
1772    
1773             PCRE_INFO_OKPARTIAL
1774    
1775           Return 1  if  the  pattern  can  be  used  for  partial  matching  with
1776           pcre_exec(),  otherwise  0.  The fourth argument should point to an int
1777           variable. From  release  8.00,  this  always  returns  1,  because  the
1778           restrictions  that  previously  applied  to  partial matching have been
1779           lifted. The pcrepartial documentation gives details of  partial  match-
1780           ing.
1781    
1782           PCRE_INFO_OPTIONS           PCRE_INFO_OPTIONS
1783    
1784         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
1785         fourth  argument  should  point to an unsigned long int variable. These         fourth argument should point to an unsigned long  int  variable.  These
1786         option bits are those specified in the call to pcre_compile(), modified         option bits are those specified in the call to pcre_compile(), modified
1787         by any top-level option settings within the pattern itself.         by any top-level option settings at the start of the pattern itself. In
1788           other  words,  they are the options that will be in force when matching
1789           starts. For example, if the pattern /(?im)abc(?-i)d/ is  compiled  with
1790           the  PCRE_EXTENDED option, the result is PCRE_CASELESS, PCRE_MULTILINE,
1791           and PCRE_EXTENDED.
1792    
1793         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
1794         alternatives begin with one of the following:         alternatives begin with one of the following:
1795    
1796           ^     unless PCRE_MULTILINE is set           ^     unless PCRE_MULTILINE is set
# Line 1331  INFORMATION ABOUT A PATTERN Line 1804  INFORMATION ABOUT A PATTERN
1804    
1805           PCRE_INFO_SIZE           PCRE_INFO_SIZE
1806    
1807         Return  the  size  of the compiled pattern, that is, the value that was         Return the size of the compiled pattern, that is, the  value  that  was
1808         passed as the argument to pcre_malloc() when PCRE was getting memory in         passed as the argument to pcre_malloc() when PCRE was getting memory in
1809         which to place the compiled data. The fourth argument should point to a         which to place the compiled data. The fourth argument should point to a
1810         size_t variable.         size_t variable.
# Line 1339  INFORMATION ABOUT A PATTERN Line 1812  INFORMATION ABOUT A PATTERN
1812           PCRE_INFO_STUDYSIZE           PCRE_INFO_STUDYSIZE
1813    
1814         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
1815         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
1816         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
1817         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
1818           data,  zero  is  returned. The fourth argument should point to a size_t
1819         variable.         variable.
1820    
1821    
# Line 1395  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1869  MATCHING A PATTERN: THE TRADITIONAL FUNC
1869              const char *subject, int length, int startoffset,              const char *subject, int length, int startoffset,
1870              int options, int *ovector, int ovecsize);              int options, int *ovector, int ovecsize);
1871    
1872         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
1873         compiled  pattern, which is passed in the code argument. If the pattern         compiled pattern, which is passed in the code argument. If the  pattern
1874         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
1875         argument.  This  function is the main matching facility of the library,         argument. This function is the main matching facility of  the  library,
1876         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
1877         an  alternative matching function, which is described below in the sec-         an alternative matching function, which is described below in the  sec-
1878         tion about the pcre_dfa_exec() function.         tion about the pcre_dfa_exec() function.
1879    
1880         In most applications, the pattern will have been compiled (and  option-         In  most applications, the pattern will have been compiled (and option-
1881         ally  studied)  in the same process that calls pcre_exec(). However, it         ally studied) in the same process that calls pcre_exec().  However,  it
1882         is possible to save compiled patterns and study data, and then use them         is possible to save compiled patterns and study data, and then use them
1883         later  in  different processes, possibly even on different hosts. For a         later in different processes, possibly even on different hosts.  For  a
1884         discussion about this, see the pcreprecompile documentation.         discussion about this, see the pcreprecompile documentation.
1885    
1886         Here is an example of a simple call to pcre_exec():         Here is an example of a simple call to pcre_exec():
# Line 1425  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1899  MATCHING A PATTERN: THE TRADITIONAL FUNC
1899    
1900     Extra data for pcre_exec()     Extra data for pcre_exec()
1901    
1902         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
1903         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
1904         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-
1905         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
1906         lows:         fields (not necessarily in this order):
1907    
1908           unsigned long int flags;           unsigned long int flags;
1909           void *study_data;           void *study_data;
1910           unsigned long int match_limit;           unsigned long int match_limit;
1911             unsigned long int match_limit_recursion;
1912           void *callout_data;           void *callout_data;
1913           const unsigned char *tables;           const unsigned char *tables;
1914             unsigned char **mark;
1915    
1916         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
1917         are set. The flag bits are:         are set. The flag bits are:
1918    
1919           PCRE_EXTRA_STUDY_DATA           PCRE_EXTRA_STUDY_DATA
1920           PCRE_EXTRA_MATCH_LIMIT           PCRE_EXTRA_MATCH_LIMIT
1921             PCRE_EXTRA_MATCH_LIMIT_RECURSION
1922           PCRE_EXTRA_CALLOUT_DATA           PCRE_EXTRA_CALLOUT_DATA
1923           PCRE_EXTRA_TABLES           PCRE_EXTRA_TABLES
1924             PCRE_EXTRA_MARK
1925    
1926         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
1927         the pcre_extra block that is returned by  pcre_study(),  together  with         the  pcre_extra  block  that is returned by pcre_study(), together with
1928         the appropriate flag bit. You should not set this yourself, but you may         the appropriate flag bit. You should not set this yourself, but you may
1929         add to the block by setting the other fields  and  their  corresponding         add  to  the  block by setting the other fields and their corresponding
1930         flag bits.         flag bits.
1931    
1932         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
1933         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
1934         match,  but  which  have  a very large number of possibilities in their         match, but which have a very large number  of  possibilities  in  their
1935         search trees. The classic  example  is  the  use  of  nested  unlimited         search  trees. The classic example is a pattern that uses nested unlim-
1936         repeats.         ited repeats.
1937    
1938         Internally,  PCRE uses a function called match() which it calls repeat-         Internally, PCRE uses a function called match() which it calls  repeat-
1939         edly (sometimes recursively). The limit is imposed  on  the  number  of         edly  (sometimes  recursively). The limit set by match_limit is imposed
1940         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
1941         limiting the amount of recursion and backtracking that can take  place.         has  the  effect  of  limiting the amount of backtracking that can take
1942         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
1943         position in the subject string.         for each position in the subject string.
1944    
1945         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
1946         default  default  is 10 million, which handles all but the most extreme         default default is 10 million, which handles all but the  most  extreme
1947         cases. You can reduce  the  default  by  suppling  pcre_exec()  with  a         cases.  You  can  override  the  default by suppling pcre_exec() with a
1948         pcre_extra  block  in  which match_limit is set to a smaller value, and         pcre_extra    block    in    which    match_limit    is    set,     and
1949         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
1950         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1951    
1952         The  pcre_callout  field is used in conjunction with the "callout" fea-         The match_limit_recursion field is similar to match_limit, but  instead
1953         ture, which is described in the pcrecallout documentation.         of limiting the total number of times that match() is called, it limits
1954           the depth of recursion. The recursion depth is a  smaller  number  than
1955           the  total number of calls, because not all calls to match() are recur-
1956           sive.  This limit is of use only if it is set smaller than match_limit.
1957    
1958           Limiting the recursion depth limits the amount of  stack  that  can  be
1959           used, or, when PCRE has been compiled to use memory on the heap instead
1960           of the stack, the amount of heap memory that can be used.
1961    
1962           The default value for match_limit_recursion can be  set  when  PCRE  is
1963           built;  the  default  default  is  the  same  value  as the default for
1964           match_limit. You can override the default by suppling pcre_exec()  with
1965           a   pcre_extra   block  in  which  match_limit_recursion  is  set,  and
1966           PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in  the  flags  field.  If  the
1967           limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1968    
1969           The  callout_data  field is used in conjunction with the "callout" fea-
1970           ture, and is described in the pcrecallout documentation.
1971    
1972         The tables field  is  used  to  pass  a  character  tables  pointer  to         The tables field  is  used  to  pass  a  character  tables  pointer  to
1973         pcre_exec();  this overrides the value that is stored with the compiled         pcre_exec();  this overrides the value that is stored with the compiled
# Line 1485  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1980  MATCHING A PATTERN: THE TRADITIONAL FUNC
1980         address when pcre_exec() is called. See the  pcreprecompile  documenta-         address when pcre_exec() is called. See the  pcreprecompile  documenta-
1981         tion for a discussion of saving compiled patterns for later use.         tion for a discussion of saving compiled patterns for later use.
1982    
1983           If  PCRE_EXTRA_MARK  is  set in the flags field, the mark field must be
1984           set to point to a char * variable. If the pattern  contains  any  back-
1985           tracking  control verbs such as (*MARK:NAME), and the execution ends up
1986           with a name to pass back, a pointer to the  name  string  (zero  termi-
1987           nated)  is  placed  in  the  variable pointed to by the mark field. The
1988           names are within the compiled pattern; if you wish  to  retain  such  a
1989           name  you must copy it before freeing the memory of a compiled pattern.
1990           If there is no name to pass back, the variable pointed to by  the  mark
1991           field  set  to NULL. For details of the backtracking control verbs, see
1992           the section entitled "Backtracking control" in the pcrepattern documen-
1993           tation.
1994    
1995     Option bits for pcre_exec()     Option bits for pcre_exec()
1996    
1997         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.
1998         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,
1999         PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK and PCRE_PARTIAL.         PCRE_NOTBOL,    PCRE_NOTEOL,    PCRE_NOTEMPTY,   PCRE_NOTEMPTY_ATSTART,
2000           PCRE_NO_START_OPTIMIZE,  PCRE_NO_UTF8_CHECK,   PCRE_PARTIAL_SOFT,   and
2001           PCRE_PARTIAL_HARD.
2002    
2003           PCRE_ANCHORED           PCRE_ANCHORED
2004    
# Line 1498  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2007  MATCHING A PATTERN: THE TRADITIONAL FUNC
2007         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
2008         unachored at matching time.         unachored at matching time.
2009    
2010             PCRE_BSR_ANYCRLF
2011             PCRE_BSR_UNICODE
2012    
2013           These options (which are mutually exclusive) control what the \R escape
2014           sequence  matches.  The choice is either to match only CR, LF, or CRLF,
2015           or to match any Unicode newline sequence. These  options  override  the
2016           choice that was made or defaulted when the pattern was compiled.
2017    
2018             PCRE_NEWLINE_CR
2019             PCRE_NEWLINE_LF
2020             PCRE_NEWLINE_CRLF
2021             PCRE_NEWLINE_ANYCRLF
2022             PCRE_NEWLINE_ANY
2023    
2024           These  options  override  the  newline  definition  that  was chosen or
2025           defaulted when the pattern was compiled. For details, see the  descrip-
2026           tion  of  pcre_compile()  above.  During  matching,  the newline choice
2027           affects the behaviour of the dot, circumflex,  and  dollar  metacharac-
2028           ters.  It may also alter the way the match position is advanced after a
2029           match failure for an unanchored pattern.
2030    
2031           When PCRE_NEWLINE_CRLF, PCRE_NEWLINE_ANYCRLF,  or  PCRE_NEWLINE_ANY  is
2032           set,  and a match attempt for an unanchored pattern fails when the cur-
2033           rent position is at a  CRLF  sequence,  and  the  pattern  contains  no
2034           explicit  matches  for  CR  or  LF  characters,  the  match position is
2035           advanced by two characters instead of one, in other words, to after the
2036           CRLF.
2037    
2038           The above rule is a compromise that makes the most common cases work as
2039           expected. For example, if the  pattern  is  .+A  (and  the  PCRE_DOTALL
2040           option is not set), it does not match the string "\r\nA" because, after
2041           failing at the start, it skips both the CR and the LF before  retrying.
2042           However,  the  pattern  [\r\n]A does match that string, because it con-
2043           tains an explicit CR or LF reference, and so advances only by one char-
2044           acter after the first failure.
2045    
2046           An explicit match for CR of LF is either a literal appearance of one of
2047           those characters, or one of the \r or  \n  escape  sequences.  Implicit
2048           matches  such  as [^X] do not count, nor does \s (which includes CR and
2049           LF in the characters that it matches).
2050    
2051           Notwithstanding the above, anomalous effects may still occur when  CRLF
2052           is a valid newline sequence and explicit \r or \n escapes appear in the
2053           pattern.
2054    
2055           PCRE_NOTBOL           PCRE_NOTBOL
2056    
2057         This option specifies that first character of the subject string is not         This option specifies that first character of the subject string is not
# Line 1524  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2078  MATCHING A PATTERN: THE TRADITIONAL FUNC
2078    
2079           a?b?           a?b?
2080    
2081         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
2082         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
2083         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-
2084         rences of "a" or "b".         rences of "a" or "b".
2085    
2086         Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a spe-           PCRE_NOTEMPTY_ATSTART
2087         cial case of a pattern match of the empty  string  within  its  split()  
2088         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
2089         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
2090         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.
2091         if that fails by advancing the starting offset (see below)  and  trying  
2092         an ordinary match again. There is some code that demonstrates how to do         Perl     has    no    direct    equivalent    of    PCRE_NOTEMPTY    or
2093         this in the pcredemo.c sample program.         PCRE_NOTEMPTY_ATSTART, but it does make a special  case  of  a  pattern
2094           match  of  the empty string within its split() function, and when using
2095           the /g modifier. It is  possible  to  emulate  Perl's  behaviour  after
2096           matching a null string by first trying the match again at the same off-
2097           set with PCRE_NOTEMPTY_ATSTART and  PCRE_ANCHORED,  and  then  if  that
2098           fails, by advancing the starting offset (see below) and trying an ordi-
2099           nary match again. There is some code that demonstrates how to  do  this
2100           in the pcredemo sample program.
2101    
2102             PCRE_NO_START_OPTIMIZE
2103    
2104           There  are a number of optimizations that pcre_exec() uses at the start
2105           of a match, in order to speed up the process. For  example,  if  it  is
2106           known  that  a  match must start with a specific character, it searches
2107           the subject for that character, and fails immediately if it cannot find
2108           it,  without actually running the main matching function. When callouts
2109           are in use, these optimizations can cause  them  to  be  skipped.  This
2110           option  disables  the  "start-up" optimizations, causing performance to
2111           suffer, but ensuring that the callouts do occur.
2112    
2113           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
2114    
2115         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
2116         UTF-8  string is automatically checked when pcre_exec() is subsequently         UTF-8  string is automatically checked when pcre_exec() is subsequently
2117         called.  The value of startoffset is also checked  to  ensure  that  it         called.  The value of startoffset is also checked  to  ensure  that  it
2118         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
2119         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
2120         startoffset  contains  an  invalid  value, PCRE_ERROR_BADUTF8_OFFSET is         main  pcre  page.  If  an  invalid  UTF-8  sequence  of bytes is found,
2121         returned.         pcre_exec() returns the error PCRE_ERROR_BADUTF8. If  startoffset  con-
2122           tains an invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.
2123         If you already know that your subject is valid, and you  want  to  skip  
2124         these    checks    for   performance   reasons,   you   can   set   the         If  you  already  know that your subject is valid, and you want to skip
2125         PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might  want  to         these   checks   for   performance   reasons,   you   can    set    the
2126         do  this  for the second and subsequent calls to pcre_exec() if you are         PCRE_NO_UTF8_CHECK  option  when calling pcre_exec(). You might want to
2127         making repeated calls to find all  the  matches  in  a  single  subject         do this for the second and subsequent calls to pcre_exec() if  you  are
2128         string.  However,  you  should  be  sure  that the value of startoffset         making  repeated  calls  to  find  all  the matches in a single subject
2129         points to the start of a UTF-8 character.  When  PCRE_NO_UTF8_CHECK  is         string. However, you should be  sure  that  the  value  of  startoffset
2130         set,  the  effect of passing an invalid UTF-8 string as a subject, or a         points  to  the  start of a UTF-8 character. When PCRE_NO_UTF8_CHECK is
2131         value of startoffset that does not point to the start of a UTF-8  char-         set, the effect of passing an invalid UTF-8 string as a subject,  or  a
2132           value  of startoffset that does not point to the start of a UTF-8 char-
2133         acter, is undefined. Your program may crash.         acter, is undefined. Your program may crash.
2134    
2135           PCRE_PARTIAL           PCRE_PARTIAL_HARD
2136             PCRE_PARTIAL_SOFT
2137    
2138         This  option  turns  on  the  partial  matching feature. If the subject         These options turn on the partial matching feature. For backwards  com-
2139         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
2140         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,
2141         partially matches the pattern and the failure to  match  occurred  only         but  there  are not enough subject characters to complete the match. If
2142         because  there were not enough subject characters), pcre_exec() returns         this happens when PCRE_PARTIAL_HARD  is  set,  pcre_exec()  immediately
2143         PCRE_ERROR_PARTIAL instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL  is         returns  PCRE_ERROR_PARTIAL.  Otherwise,  if  PCRE_PARTIAL_SOFT is set,
2144         used,  there  are restrictions on what may appear in the pattern. These         matching continues by testing any other alternatives. Only if they  all
2145         are discussed in the pcrepartial documentation.         fail  is  PCRE_ERROR_PARTIAL  returned (instead of PCRE_ERROR_NOMATCH).
2146           The portion of the string that was inspected when the partial match was
2147           found  is  set  as  the first matching string. There is a more detailed
2148           discussion in the pcrepartial documentation.
2149    
2150     The string to be matched by pcre_exec()     The string to be matched by pcre_exec()
2151    
2152         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
2153         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.
2154         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-
2155         Unlike  the  pattern string, the subject may contain binary zero bytes.         acter.  Unlike  the pattern string, the subject may contain binary zero
2156         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
2157         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
2158           case.
2159         A  non-zero  starting offset is useful when searching for another match  
2160         in the same subject by calling pcre_exec() again after a previous  suc-         A non-zero starting offset is useful when searching for  another  match
2161         cess.   Setting  startoffset differs from just passing over a shortened         in  the same subject by calling pcre_exec() again after a previous suc-
2162         string and setting PCRE_NOTBOL in the case of  a  pattern  that  begins         cess.  Setting startoffset differs from just passing over  a  shortened
2163           string  and  setting  PCRE_NOTBOL  in the case of a pattern that begins
2164         with any kind of lookbehind. For example, consider the pattern         with any kind of lookbehind. For example, consider the pattern
2165    
2166           \Biss\B           \Biss\B
2167    
2168         which  finds  occurrences  of "iss" in the middle of words. (\B matches         which finds occurrences of "iss" in the middle of  words.  (\B  matches
2169         only if the current position in the subject is not  a  word  boundary.)         only  if  the  current position in the subject is not a word boundary.)
2170         When  applied  to the string "Mississipi" the first call to pcre_exec()         When applied to the string "Mississipi" the first call  to  pcre_exec()
2171         finds the first occurrence. If pcre_exec() is called  again  with  just         finds  the  first  occurrence. If pcre_exec() is called again with just
2172         the  remainder  of  the  subject,  namely  "issipi", it does not match,         the remainder of the subject,  namely  "issipi",  it  does  not  match,
2173         because \B is always false at the start of the subject, which is deemed         because \B is always false at the start of the subject, which is deemed
2174         to  be  a  word  boundary. However, if pcre_exec() is passed the entire         to be a word boundary. However, if pcre_exec()  is  passed  the  entire
2175         string again, but with startoffset set to 4, it finds the second occur-         string again, but with startoffset set to 4, it finds the second occur-
2176         rence  of "iss" because it is able to look behind the starting point to         rence of "iss" because it is able to look behind the starting point  to
2177         discover that it is preceded by a letter.         discover that it is preceded by a letter.
2178    
2179         If a non-zero starting offset is passed when the pattern  is  anchored,         If  a  non-zero starting offset is passed when the pattern is anchored,
2180         one attempt to match at the given offset is made. This can only succeed         one attempt to match at the given offset is made. This can only succeed
2181         if the pattern does not require the match to be at  the  start  of  the         if  the  pattern  does  not require the match to be at the start of the
2182         subject.         subject.
2183    
2184     How pcre_exec() returns captured substrings     How pcre_exec() returns captured substrings
2185    
2186         In  general, a pattern matches a certain portion of the subject, and in         In general, a pattern matches a certain portion of the subject, and  in
2187         addition, further substrings from the subject  may  be  picked  out  by         addition,  further  substrings  from  the  subject may be picked out by
2188         parts  of  the  pattern.  Following the usage in Jeffrey Friedl's book,         parts of the pattern. Following the usage  in  Jeffrey  Friedl's  book,
2189         this is called "capturing" in what follows, and the  phrase  "capturing         this  is  called "capturing" in what follows, and the phrase "capturing
2190         subpattern"  is  used for a fragment of a pattern that picks out a sub-         subpattern" is used for a fragment of a pattern that picks out  a  sub-
2191         string. PCRE supports several other kinds of  parenthesized  subpattern         string.  PCRE  supports several other kinds of parenthesized subpattern
2192         that do not cause substrings to be captured.         that do not cause substrings to be captured.
2193    
2194         Captured  substrings are returned to the caller via a vector of integer         Captured substrings are returned to the caller via a vector of integers
2195         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-
2196         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:
2197         Note: this argument is NOT the size of ovector in bytes.         this argument is NOT the size of ovector in bytes.
2198    
2199         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-
2200         strings,  each  substring using a pair of integers. The remaining third         strings, each substring using a pair of integers. The  remaining  third
2201         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-
2202         turing  subpatterns, and is not available for passing back information.         turing subpatterns, and is not available for passing back  information.
2203         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
2204         it is not, it is rounded down.         it is not, it is rounded down.
2205    
2206         When  a  match  is successful, information about captured substrings is         When a match is successful, information about  captured  substrings  is
2207         returned in pairs of integers, starting at the  beginning  of  ovector,         returned  in  pairs  of integers, starting at the beginning of ovector,
2208         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
2209         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
2210         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
2211         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
2212         tor[1],  identify  the  portion  of  the  subject string matched by the         byte offsets, even in UTF-8 mode. They are not character counts.
2213         entire pattern. The next pair is used for the first  capturing  subpat-  
2214         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
2215         pairs that have been set. If there are no  capturing  subpatterns,  the         portion  of  the subject string matched by the entire pattern. The next
2216         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
2217         first pair of offsets has been set.         returned by pcre_exec() is one more than the highest numbered pair that
2218           has been set.  For example, if two substrings have been  captured,  the
2219         Some convenience functions are provided  for  extracting  the  captured         returned  value is 3. If there are no capturing subpatterns, the return
2220         substrings  as  separate  strings. These are described in the following         value from a successful match is 1, indicating that just the first pair
2221         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.  
2222    
2223         If a capturing subpattern is matched repeatedly, it is the last portion         If a capturing subpattern is matched repeatedly, it is the last portion
2224         of the string that it matched that is returned.         of the string that it matched that is returned.
2225    
2226         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,
2227         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
2228         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
2229         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
2230         as  NULL  and  ovecsize  as zero. However, if the pattern contains back         ovecsize as zero. However, if the pattern contains back references  and
2231         references and the ovector is not big enough to  remember  the  related         the  ovector is not big enough to remember the related substrings, PCRE
2232         substrings,  PCRE has to get additional memory for use during matching.         has to get additional memory for use during matching. Thus it  is  usu-
2233         Thus it is usually advisable to supply an ovector.         ally advisable to supply an ovector.
2234    
2235         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
2236         patterns there are in a compiled pattern. The smallest size for ovector         subpatterns there are in a compiled  pattern.  The  smallest  size  for
2237         that will allow for n captured substrings, in addition to  the  offsets         ovector  that  will allow for n captured substrings, in addition to the
2238         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.
2239    
2240           It is possible for capturing subpattern number n+1 to match  some  part
2241           of the subject when subpattern n has not been used at all. For example,
2242           if the string "abc" is matched  against  the  pattern  (a|(z))(bc)  the
2243           return from the function is 4, and subpatterns 1 and 3 are matched, but
2244           2 is not. When this happens, both values in  the  offset  pairs  corre-
2245           sponding to unused subpatterns are set to -1.
2246    
2247           Offset  values  that correspond to unused subpatterns at the end of the
2248           expression are also set to -1. For example,  if  the  string  "abc"  is
2249           matched  against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not
2250           matched. The return from the function is 2, because  the  highest  used
2251           capturing subpattern number is 1. However, you can refer to the offsets
2252           for the second and third capturing subpatterns if  you  wish  (assuming
2253           the vector is large enough, of course).
2254    
2255           Some  convenience  functions  are  provided for extracting the captured
2256           substrings as separate strings. These are described below.
2257    
2258     Return values from pcre_exec()     Error return values from pcre_exec()
2259    
2260         If  pcre_exec()  fails, it returns a negative number. The following are         If pcre_exec() fails, it returns a negative number. The  following  are
2261         defined in the header file:         defined in the header file:
2262    
2263           PCRE_ERROR_NOMATCH        (-1)           PCRE_ERROR_NOMATCH        (-1)
# Line 1676  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2266  MATCHING A PATTERN: THE TRADITIONAL FUNC
2266    
2267           PCRE_ERROR_NULL           (-2)           PCRE_ERROR_NULL           (-2)
2268    
2269         Either code or subject was passed as NULL,  or  ovector  was  NULL  and         Either  code  or  subject  was  passed as NULL, or ovector was NULL and
2270         ovecsize was not zero.         ovecsize was not zero.
2271    
2272           PCRE_ERROR_BADOPTION      (-3)           PCRE_ERROR_BADOPTION      (-3)
# Line 1685  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2275  MATCHING A PATTERN: THE TRADITIONAL FUNC
2275    
2276           PCRE_ERROR_BADMAGIC       (-4)           PCRE_ERROR_BADMAGIC       (-4)
2277    
2278         PCRE  stores a 4-byte "magic number" at the start of the compiled code,         PCRE stores a 4-byte "magic number" at the start of the compiled  code,
2279         to catch the case when it is passed a junk pointer and to detect when a         to catch the case when it is passed a junk pointer and to detect when a
2280         pattern that was compiled in an environment of one endianness is run in         pattern that was compiled in an environment of one endianness is run in
2281         an environment with the other endianness. This is the error  that  PCRE         an  environment  with the other endianness. This is the error that PCRE
2282         gives when the magic number is not present.         gives when the magic number is not present.
2283    
2284           PCRE_ERROR_UNKNOWN_NODE   (-5)           PCRE_ERROR_UNKNOWN_OPCODE (-5)
2285    
2286         While running the pattern match, an unknown item was encountered in the         While running the pattern match, an unknown item was encountered in the
2287         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
2288         overwriting of the compiled pattern.         overwriting of the compiled pattern.
2289    
2290           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2291    
2292         If  a  pattern contains back references, but the ovector that is passed         If a pattern contains back references, but the ovector that  is  passed
2293         to pcre_exec() is not big enough to remember the referenced substrings,         to pcre_exec() is not big enough to remember the referenced substrings,
2294         PCRE  gets  a  block of memory at the start of matching to use for this         PCRE gets a block of memory at the start of matching to  use  for  this
2295         purpose. If the call via pcre_malloc() fails, this error is given.  The         purpose.  If the call via pcre_malloc() fails, this error is given. The
2296         memory is automatically freed at the end of matching.         memory is automatically freed at the end of matching.
2297    
2298           PCRE_ERROR_NOSUBSTRING    (-7)           PCRE_ERROR_NOSUBSTRING    (-7)
2299    
2300         This  error is used by the pcre_copy_substring(), pcre_get_substring(),         This error is used by the pcre_copy_substring(),  pcre_get_substring(),
2301         and  pcre_get_substring_list()  functions  (see  below).  It  is  never         and  pcre_get_substring_list()  functions  (see  below).  It  is  never
2302         returned by pcre_exec().         returned by pcre_exec().
2303    
2304           PCRE_ERROR_MATCHLIMIT     (-8)           PCRE_ERROR_MATCHLIMIT     (-8)
2305    
2306         The  recursion  and backtracking limit, as specified by the match_limit         The backtracking limit, as specified by  the  match_limit  field  in  a
2307         field in a pcre_extra structure (or defaulted)  was  reached.  See  the         pcre_extra  structure  (or  defaulted) was reached. See the description
2308         description above.         above.
2309    
2310           PCRE_ERROR_CALLOUT        (-9)           PCRE_ERROR_CALLOUT        (-9)
2311    
2312         This error is never generated by pcre_exec() itself. It is provided for         This error is never generated by pcre_exec() itself. It is provided for
2313         use by callout functions that want to yield a distinctive  error  code.         use  by  callout functions that want to yield a distinctive error code.
2314         See the pcrecallout documentation for details.         See the pcrecallout documentation for details.
2315    
2316           PCRE_ERROR_BADUTF8        (-10)           PCRE_ERROR_BADUTF8        (-10)
2317    
2318         A  string  that contains an invalid UTF-8 byte sequence was passed as a         A string that contains an invalid UTF-8 byte sequence was passed  as  a
2319         subject.         subject.
2320    
2321           PCRE_ERROR_BADUTF8_OFFSET (-11)           PCRE_ERROR_BADUTF8_OFFSET (-11)
2322    
2323         The UTF-8 byte sequence that was passed as a subject was valid, but the         The UTF-8 byte sequence that was passed as a subject was valid, but the
2324         value  of startoffset did not point to the beginning of a UTF-8 charac-         value of startoffset did not point to the beginning of a UTF-8  charac-
2325         ter.         ter.
2326    
2327           PCRE_ERROR_PARTIAL        (-12)           PCRE_ERROR_PARTIAL        (-12)
2328    
2329         The subject string did not match, but it did match partially.  See  the         The  subject  string did not match, but it did match partially. See the
2330         pcrepartial documentation for details of partial matching.         pcrepartial documentation for details of partial matching.
2331    
2332           PCRE_ERROR_BADPARTIAL     (-13)           PCRE_ERROR_BADPARTIAL     (-13)
2333    
2334         The  PCRE_PARTIAL  option  was  used with a compiled pattern containing         This code is no longer in  use.  It  was  formerly  returned  when  the
2335         items that are not supported for partial matching. See the  pcrepartial         PCRE_PARTIAL  option  was used with a compiled pattern containing items
2336         documentation for details of partial matching.         that were  not  supported  for  partial  matching.  From  release  8.00
2337           onwards, there are no restrictions on partial matching.
2338    
2339           PCRE_ERROR_INTERNAL       (-14)           PCRE_ERROR_INTERNAL       (-14)
2340    
# Line 1752  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2343  MATCHING A PATTERN: THE TRADITIONAL FUNC
2343    
2344           PCRE_ERROR_BADCOUNT       (-15)           PCRE_ERROR_BADCOUNT       (-15)
2345    
2346         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.
2347    
2348             PCRE_ERROR_RECURSIONLIMIT (-21)
2349    
2350           The internal recursion limit, as specified by the match_limit_recursion
2351           field  in  a  pcre_extra  structure (or defaulted) was reached. See the
2352           description above.
2353    
2354             PCRE_ERROR_BADNEWLINE     (-23)
2355    
2356           An invalid combination of PCRE_NEWLINE_xxx options was given.
2357    
2358           Error numbers -16 to -20 and -22 are not used by pcre_exec().
2359    
2360    
2361  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
# Line 1768  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2371  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2371         int pcre_get_substring_list(const char *subject,         int pcre_get_substring_list(const char *subject,
2372              int *ovector, int stringcount, const char ***listptr);              int *ovector, int stringcount, const char ***listptr);
2373    
2374         Captured  substrings  can  be  accessed  directly  by using the offsets         Captured substrings can be  accessed  directly  by  using  the  offsets
2375         returned by pcre_exec() in  ovector.  For  convenience,  the  functions         returned  by  pcre_exec()  in  ovector.  For convenience, the functions
2376         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-
2377         string_list() are provided for extracting captured substrings  as  new,         string_list()  are  provided for extracting captured substrings as new,
2378         separate,  zero-terminated strings. These functions identify substrings         separate, zero-terminated strings. These functions identify  substrings
2379         by number. The next section describes functions  for  extracting  named         by  number.  The  next section describes functions for extracting named
2380         substrings.  A  substring  that  contains  a  binary  zero is correctly         substrings.
2381         extracted and has a further zero added on the end, but  the  result  is  
2382         not, of course, a C string.         A substring that contains a binary zero is correctly extracted and  has
2383           a  further zero added on the end, but the result is not, of course, a C
2384           string.  However, you can process such a string  by  referring  to  the
2385           length  that  is  returned  by  pcre_copy_substring() and pcre_get_sub-
2386           string().  Unfortunately, the interface to pcre_get_substring_list() is
2387           not  adequate for handling strings containing binary zeros, because the
2388           end of the final string is not independently indicated.
2389    
2390         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-
2391         tions: subject is the subject string that has  just  been  successfully         tions:  subject  is  the subject string that has just been successfully
2392         matched, ovector is a pointer to the vector of integer offsets that was         matched, ovector is a pointer to the vector of integer offsets that was
2393         passed to pcre_exec(), and stringcount is the number of substrings that         passed to pcre_exec(), and stringcount is the number of substrings that
2394         were  captured  by  the match, including the substring that matched the         were captured by the match, including the substring  that  matched  the
2395         entire regular expression. This is the value returned by pcre_exec() if         entire regular expression. This is the value returned by pcre_exec() if
2396         it  is greater than zero. If pcre_exec() returned zero, indicating that         it is greater than zero. If pcre_exec() returned zero, indicating  that
2397         it ran out of space in ovector, the value passed as stringcount  should         it  ran out of space in ovector, the value passed as stringcount should
2398         be the number of elements in the vector divided by three.         be the number of elements in the vector divided by three.
2399    
2400         The  functions pcre_copy_substring() and pcre_get_substring() extract a         The functions pcre_copy_substring() and pcre_get_substring() extract  a
2401         single substring, whose number is given as  stringnumber.  A  value  of         single  substring,  whose  number  is given as stringnumber. A value of
2402         zero  extracts  the  substring that matched the entire pattern, whereas         zero extracts the substring that matched the  entire  pattern,  whereas
2403         higher values  extract  the  captured  substrings.  For  pcre_copy_sub-         higher  values  extract  the  captured  substrings.  For pcre_copy_sub-
2404         string(),  the  string  is  placed  in buffer, whose length is given by         string(), the string is placed in buffer,  whose  length  is  given  by
2405         buffersize, while for pcre_get_substring() a new  block  of  memory  is         buffersize,  while  for  pcre_get_substring()  a new block of memory is
2406         obtained  via  pcre_malloc,  and its address is returned via stringptr.         obtained via pcre_malloc, and its address is  returned  via  stringptr.
2407         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
2408         the terminating zero, or one of         the terminating zero, or one of these error codes:
2409    
2410           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2411    
2412         The  buffer  was too small for pcre_copy_substring(), or the attempt to         The buffer was too small for pcre_copy_substring(), or the  attempt  to
2413         get memory failed for pcre_get_substring().         get memory failed for pcre_get_substring().
2414    
2415           PCRE_ERROR_NOSUBSTRING    (-7)           PCRE_ERROR_NOSUBSTRING    (-7)
2416    
2417         There is no substring whose number is stringnumber.         There is no substring whose number is stringnumber.
2418    
2419         The pcre_get_substring_list()  function  extracts  all  available  sub-         The  pcre_get_substring_list()  function  extracts  all  available sub-
2420         strings  and  builds  a list of pointers to them. All this is done in a         strings and builds a list of pointers to them. All this is  done  in  a
2421         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
2422         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
2423         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
2424         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
2425           error code
2426    
2427           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2428    
# Line 1831  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2441  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2441         tively.  They  do  nothing  more  than  call the function pointed to by         tively.  They  do  nothing  more  than  call the function pointed to by
2442         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.
2443         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-
2444         cial  interface  to  another  programming  language  which  cannot  use         cial  interface  to  another  programming  language  that  cannot   use
2445         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-
2446         vided.         vided.
2447    
# Line 1854  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2464  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2464         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-
2465         ber.  For example, for this pattern         ber.  For example, for this pattern
2466    
2467           (a+)b(?P<xxx>\d+)...           (a+)b(?<xxx>\d+)...
2468    
2469         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
2470         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
2471         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-
2472         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
2473         there is no subpattern of that name.         the  subpattern  number,  or PCRE_ERROR_NOSUBSTRING (-7) if there is no
2474           subpattern of that name.
2475    
2476         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
2477         the functions described in the previous section. For convenience, there         the functions described in the previous section. For convenience, there
2478         are also two functions that do the whole job.         are also two functions that do the whole job.
2479    
2480         Most    of    the    arguments   of   pcre_copy_named_substring()   and         Most   of   the   arguments    of    pcre_copy_named_substring()    and
2481         pcre_get_named_substring() are the same  as  those  for  the  similarly         pcre_get_named_substring()  are  the  same  as  those for the similarly
2482         named  functions  that extract by number. As these are described in the         named functions that extract by number. As these are described  in  the
2483         previous section, they are not re-described here. There  are  just  two         previous  section,  they  are not re-described here. There are just two
2484         differences:         differences:
2485    
2486         First,  instead  of a substring number, a substring name is given. Sec-         First, instead of a substring number, a substring name is  given.  Sec-
2487         ond, there is an extra argument, given at the start, which is a pointer         ond, there is an extra argument, given at the start, which is a pointer
2488         to  the compiled pattern. This is needed in order to gain access to the         to the compiled pattern. This is needed in order to gain access to  the
2489         name-to-number translation table.         name-to-number translation table.
2490    
2491         These functions call pcre_get_stringnumber(), and if it succeeds,  they         These  functions call pcre_get_stringnumber(), and if it succeeds, they
2492         then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-         then call pcre_copy_substring() or pcre_get_substring(),  as  appropri-
2493         ate.         ate.  NOTE:  If PCRE_DUPNAMES is set and there are duplicate names, the
2494           behaviour may not be what you want (see the next section).
2495    
2496           Warning: If the pattern uses the (?| feature to set up multiple subpat-
2497           terns  with  the  same number, as described in the section on duplicate
2498           subpattern numbers in the pcrepattern page, you  cannot  use  names  to
2499           distinguish  the  different subpatterns, because names are not included
2500           in the compiled code. The matching process uses only numbers. For  this
2501           reason,  the  use of different names for subpatterns of the same number
2502           causes an error at compile time.
2503    
2504    
2505    DUPLICATE SUBPATTERN NAMES
2506    
2507           int pcre_get_stringtable_entries(const pcre *code,
2508                const char *name, char **first, char **last);
2509    
2510           When a pattern is compiled with the  PCRE_DUPNAMES  option,  names  for
2511           subpatterns  are not required to be unique. (Duplicate names are always
2512           allowed for subpatterns with the same number, created by using the  (?|
2513           feature.  Indeed,  if  such subpatterns are named, they are required to
2514           use the same names.)
2515    
2516           Normally, patterns with duplicate names are such that in any one match,
2517           only  one of the named subpatterns participates. An example is shown in
2518           the pcrepattern documentation.
2519    
2520           When   duplicates   are   present,   pcre_copy_named_substring()    and
2521           pcre_get_named_substring()  return the first substring corresponding to
2522           the given name that is set. If  none  are  set,  PCRE_ERROR_NOSUBSTRING
2523           (-7)  is  returned;  no  data  is returned. The pcre_get_stringnumber()
2524           function returns one of the numbers that are associated with the  name,
2525           but it is not defined which it is.
2526    
2527           If  you want to get full details of all captured substrings for a given
2528           name, you must use  the  pcre_get_stringtable_entries()  function.  The
2529           first argument is the compiled pattern, and the second is the name. The
2530           third and fourth are pointers to variables which  are  updated  by  the
2531           function. After it has run, they point to the first and last entries in
2532           the name-to-number table  for  the  given  name.  The  function  itself
2533           returns  the  length  of  each entry, or PCRE_ERROR_NOSUBSTRING (-7) if
2534           there are none. The format of the table is described above in the  sec-
2535           tion  entitled  Information  about  a  pattern.  Given all the relevant
2536           entries for the name, you can extract each of their numbers, and  hence
2537           the captured data, if any.
2538    
2539    
2540  FINDING ALL POSSIBLE MATCHES  FINDING ALL POSSIBLE MATCHES
2541    
2542         The traditional matching function uses a  similar  algorithm  to  Perl,         The  traditional  matching  function  uses a similar algorithm to Perl,
2543         which stops when it finds the first match, starting at a given point in         which stops when it finds the first match, starting at a given point in
2544         the subject. If you want to find all possible matches, or  the  longest         the  subject.  If you want to find all possible matches, or the longest
2545         possible  match,  consider using the alternative matching function (see         possible match, consider using the alternative matching  function  (see
2546         below) instead. If you cannot use the alternative function,  but  still         below)  instead.  If you cannot use the alternative function, but still
2547         need  to  find all possible matches, you can kludge it up by making use         need to find all possible matches, you can kludge it up by  making  use
2548         of the callout facility, which is described in the pcrecallout documen-         of the callout facility, which is described in the pcrecallout documen-
2549         tation.         tation.
2550    
2551         What you have to do is to insert a callout right at the end of the pat-         What you have to do is to insert a callout right at the end of the pat-
2552         tern.  When your callout function is called, extract and save the  cur-         tern.   When your callout function is called, extract and save the cur-
2553         rent  matched  substring.  Then  return  1, which forces pcre_exec() to         rent matched substring. Then return  1,  which  forces  pcre_exec()  to
2554         backtrack and try other alternatives. Ultimately, when it runs  out  of         backtrack  and  try other alternatives. Ultimately, when it runs out of
2555         matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.         matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
2556    
2557    
# Line 1907  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2562  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2562              int options, int *ovector, int ovecsize,              int options, int *ovector, int ovecsize,
2563              int *workspace, int wscount);              int *workspace, int wscount);
2564    
2565         The  function  pcre_dfa_exec()  is  called  to  match  a subject string         The function pcre_dfa_exec()  is  called  to  match  a  subject  string
2566         against a compiled pattern, using a "DFA" matching algorithm. This  has         against  a  compiled pattern, using a matching algorithm that scans the
2567         different  characteristics to the normal algorithm, and is not compati-         subject string just once, and does not backtrack.  This  has  different
2568         ble with Perl. Some of the features of PCRE patterns are not supported.         characteristics  to  the  normal  algorithm, and is not compatible with
2569         Nevertheless, there are times when this kind of matching can be useful.         Perl. Some of the features of PCRE patterns are not  supported.  Never-
2570         For a discussion of the two matching algorithms, see  the  pcrematching         theless,  there are times when this kind of matching can be useful. For
2571         documentation.         a discussion of the two matching algorithms, and  a  list  of  features
2572           that  pcre_dfa_exec() does not support, see the pcrematching documenta-
2573           tion.
2574    
2575         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
2576         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-
2577         ent  way,  and  this is described below. The other common arguments are         ent way, and this is described below. The other  common  arguments  are
2578         used in the same way as for pcre_exec(), so their  description  is  not         used  in  the  same way as for pcre_exec(), so their description is not
2579         repeated here.         repeated here.
2580    
2581         The  two  additional  arguments provide workspace for the function. The         The two additional arguments provide workspace for  the  function.  The
2582         workspace vector should contain at least 20 elements. It  is  used  for         workspace  vector  should  contain at least 20 elements. It is used for
2583         keeping  track  of  multiple  paths  through  the  pattern  tree.  More         keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2584         workspace will be needed for patterns and subjects where  there  are  a         workspace  will  be  needed for patterns and subjects where there are a
2585         lot of possible matches.         lot of potential matches.
2586    
2587         Here is an example of a simple call to pcre_exec():         Here is an example of a simple call to pcre_dfa_exec():
2588    
2589           int rc;           int rc;
2590           int ovector[10];           int ovector[10];
2591           int wspace[20];           int wspace[20];
2592           rc = pcre_exec(           rc = pcre_dfa_exec(
2593             re,             /* result of pcre_compile() */             re,             /* result of pcre_compile() */
2594             NULL,           /* we didn't study the pattern */             NULL,           /* we didn't study the pattern */
2595             "some string",  /* the subject string */             "some string",  /* the subject string */
# Line 1946  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2603  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2603    
2604     Option bits for pcre_dfa_exec()     Option bits for pcre_dfa_exec()
2605    
2606         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
2607         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-
2608         PCRE_NOTEOL,     PCRE_NOTEMPTY,    PCRE_NO_UTF8_CHECK,    PCRE_PARTIAL,         LINE_xxx,        PCRE_NOTBOL,        PCRE_NOTEOL,        PCRE_NOTEMPTY,
2609         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-
2610         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
2611         repeated here.         four  of  these  are  exactly  the  same  as  for pcre_exec(), so their
2612           description is not repeated here.
2613           PCRE_PARTIAL  
2614             PCRE_PARTIAL_HARD
2615         This has the same general effect as it does for  pcre_exec(),  but  the           PCRE_PARTIAL_SOFT
2616         details   are   slightly   different.  When  PCRE_PARTIAL  is  set  for  
2617         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
2618         PCRE_ERROR_PARTIAL  if  the  end  of the subject is reached, there have         details  are  slightly  different.  When  PCRE_PARTIAL_HARD  is set for
2619         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-
2620         sibility.  The portion of the string that provided the partial match is         ject  is  reached  and there is still at least one matching possibility
2621         set as the first matching string.         that requires additional characters. This happens even if some complete
2622           matches have also been found. When PCRE_PARTIAL_SOFT is set, the return
2623           code PCRE_ERROR_NOMATCH is converted into PCRE_ERROR_PARTIAL if the end
2624           of  the  subject  is  reached, there have been no complete matches, but
2625           there is still at least one matching possibility. The  portion  of  the
2626           string  that  was inspected when the longest partial match was found is
2627           set as the first matching string in both cases.
2628    
2629           PCRE_DFA_SHORTEST           PCRE_DFA_SHORTEST
2630    
2631         Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to         Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to
2632         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-
2633         algorithm works, this is necessarily the shortest possible match at the         tive algorithm works, this is necessarily the shortest  possible  match
2634         first possible matching point in the subject string.         at the first possible matching point in the subject string.
2635    
2636           PCRE_DFA_RESTART           PCRE_DFA_RESTART
2637    
2638         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
2639         returns a partial match, it is possible to call it  again,  with  addi-         again, with additional subject characters, and have  it  continue  with
2640         tional  subject  characters,  and have it continue with the same match.         the  same match. The PCRE_DFA_RESTART option requests this action; when
2641         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
2642         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
2643         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
2644         match.  There  is  more  discussion of this facility in the pcrepartial         pcrepartial documentation.
        documentation.  
2645    
2646     Successful returns from pcre_dfa_exec()     Successful returns from pcre_dfa_exec()
2647    
2648         When pcre_dfa_exec() succeeds, it may have matched more than  one  sub-         When  pcre_dfa_exec()  succeeds, it may have matched more than one sub-
2649         string in the subject. Note, however, that all the matches from one run         string in the subject. Note, however, that all the matches from one run
2650         of the function start at the same point in  the  subject.  The  shorter         of  the  function  start  at the same point in the subject. The shorter
2651         matches  are all initial substrings of the longer matches. For example,         matches are all initial substrings of the longer matches. For  example,
2652         if the pattern         if the pattern
2653    
2654           <.*>           <.*>
# Line 2001  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2663  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2663           <something> <something else>           <something> <something else>
2664           <something> <something else> <something further>           <something> <something else> <something further>
2665    
2666         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,
2667         which  is  the  number of matched substrings. The substrings themselves         which is the number of matched substrings.  The  substrings  themselves
2668         are returned in ovector. Each string uses two elements;  the  first  is         are  returned  in  ovector. Each string uses two elements; the first is
2669         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
2670         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
2671         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
2672         with the way pcre_exec() returns data, even though the meaning  of  the         compatibility  with  the  way pcre_exec() returns data, even though the
2673         strings is different.)         meaning of the strings is different.)
2674    
2675         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-
2676         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
2677         fit  into ovector, the yield of the function is zero, and the vector is         fit into ovector, the yield of the function is zero, and the vector  is
2678         filled with the longest matches.         filled with the longest matches.
2679    
2680     Error returns from pcre_dfa_exec()     Error returns from pcre_dfa_exec()
2681    
2682         The pcre_dfa_exec() function returns a negative number when  it  fails.         The  pcre_dfa_exec()  function returns a negative number when it fails.
2683         Many  of  the  errors  are  the  same as for pcre_exec(), and these are         Many of the errors are the same  as  for  pcre_exec(),  and  these  are
2684         described above.  There are in addition the following errors  that  are         described  above.   There are in addition the following errors that are
2685         specific to pcre_dfa_exec():         specific to pcre_dfa_exec():
2686    
2687           PCRE_ERROR_DFA_UITEM      (-16)           PCRE_ERROR_DFA_UITEM      (-16)
2688    
2689         This  return is given if pcre_dfa_exec() encounters an item in the pat-         This return is given if pcre_dfa_exec() encounters an item in the  pat-
2690         tern that it does not support, for instance, the use of \C  or  a  back         tern  that  it  does not support, for instance, the use of \C or a back
2691         reference.         reference.
2692    
2693           PCRE_ERROR_DFA_UCOND      (-17)           PCRE_ERROR_DFA_UCOND      (-17)
2694    
2695         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
2696         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
2697         supported.         in a specific group. These are not supported.
2698    
2699           PCRE_ERROR_DFA_UMLIMIT    (-18)           PCRE_ERROR_DFA_UMLIMIT    (-18)
2700    
2701         This  return  is given if pcre_dfa_exec() is called with an extra block         This return is given if pcre_dfa_exec() is called with an  extra  block
2702         that contains a setting of the match_limit field. This is not supported         that contains a setting of the match_limit field. This is not supported
2703         (it is meaningless).         (it is meaningless).
2704    
2705           PCRE_ERROR_DFA_WSSIZE     (-19)           PCRE_ERROR_DFA_WSSIZE     (-19)
2706    
2707         This  return  is  given  if  pcre_dfa_exec()  runs  out of space in the         This return is given if  pcre_dfa_exec()  runs  out  of  space  in  the
2708         workspace vector.         workspace vector.
2709    
2710           PCRE_ERROR_DFA_RECURSE    (-20)           PCRE_ERROR_DFA_RECURSE    (-20)
2711    
2712         When a recursive subpattern is processed, the matching  function  calls         When  a  recursive subpattern is processed, the matching function calls
2713         itself  recursively,  using  private vectors for ovector and workspace.         itself recursively, using private vectors for  ovector  and  workspace.
2714         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
2715         should be extremely rare, as a vector of size 1000 is used.         should be extremely rare, as a vector of size 1000 is used.
2716    
2717  Last updated: 16 May 2005  
2718  Copyright (c) 1997-2005 University of Cambridge.  SEE ALSO
2719  ------------------------------------------------------------------------------  
2720           pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3),  pcrepar-
2721           tial(3), pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
2722    
2723    
2724    AUTHOR
2725    
2726           Philip Hazel
2727           University Computing Service
2728           Cambridge CB2 3QH, England.
2729    
2730    
2731    REVISION
2732    
2733           Last updated: 03 May 2010
2734           Copyright (c) 1997-2010 University of Cambridge.
2735    ------------------------------------------------------------------------------
2736    
2737    
2738  PCRECALLOUT(3)                                                  PCRECALLOUT(3)  PCRECALLOUT(3)                                                  PCRECALLOUT(3)
2739    
2740    
# Line 2080  PCRE CALLOUTS Line 2758  PCRE CALLOUTS
2758         default value is zero.  For  example,  this  pattern  has  two  callout         default value is zero.  For  example,  this  pattern  has  two  callout
2759         points:         points:
2760    
2761           (?C1)eabc(?C2)def           (?C1)abc(?C2)def
2762    
2763         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
2764         called, PCRE automatically  inserts  callouts,  all  with  number  255,         pcre_compile2() is called, PCRE  automatically  inserts  callouts,  all
2765         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
2766         used with the pattern         PCRE_AUTO_CALLOUT is used with the pattern
2767    
2768           A(\d{2}|--)           A(\d{2}|--)
2769    
# Line 2104  PCRE CALLOUTS Line 2782  PCRE CALLOUTS
2782  MISSING CALLOUTS  MISSING CALLOUTS
2783    
2784         You  should  be  aware  that,  because of optimizations in the way PCRE         You  should  be  aware  that,  because of optimizations in the way PCRE
2785         matches patterns, callouts sometimes do not happen. For example, if the         matches patterns by default, callouts  sometimes  do  not  happen.  For
2786         pattern is         example, if the pattern is
2787    
2788           ab(?C4)cd           ab(?C4)cd
2789    
# Line 2114  MISSING CALLOUTS Line 2792  MISSING CALLOUTS
2792         ever  start,  and  the  callout is never reached. However, with "abyd",         ever  start,  and  the  callout is never reached. However, with "abyd",
2793         though the result is still no match, the callout is obeyed.         though the result is still no match, the callout is obeyed.
2794    
2795           If the pattern is studied, PCRE knows the minimum length of a  matching
2796           string,  and will immediately give a "no match" return without actually
2797           running a match if the subject is not long enough, or,  for  unanchored
2798           patterns, if it has been scanned far enough.
2799    
2800           You  can disable these optimizations by passing the PCRE_NO_START_OPTI-
2801           MIZE option to pcre_exec() or  pcre_dfa_exec().  This  slows  down  the
2802           matching  process,  but  does  ensure that callouts such as the example
2803           above are obeyed.
2804    
2805    
2806  THE CALLOUT INTERFACE  THE CALLOUT INTERFACE
2807    
# Line 2141  THE CALLOUT INTERFACE Line 2829  THE CALLOUT INTERFACE
2829         version number will change again in future  if  additional  fields  are         version number will change again in future  if  additional  fields  are
2830         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.
2831    
2832         The callout_number field contains the number of the  callout,  as  com-         The  callout_number  field  contains the number of the callout, as com-
2833         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-
2834         outs, and 255 for automatically generated callouts).         outs, and 255 for automatically generated callouts).
2835    
2836         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
2837         passed   by   the   caller  to  pcre_exec()  or  pcre_dfa_exec().  When         passed  by  the  caller  to  pcre_exec()   or   pcre_dfa_exec().   When
2838         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
2839         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
2840         extracting substrings after a match has completed. For  pcre_dfa_exec()         extracting  substrings after a match has completed. For pcre_dfa_exec()
2841         this field is not useful.         this field is not useful.
2842    
2843         The subject and subject_length fields contain copies of the values that         The subject and subject_length fields contain copies of the values that
2844         were passed to pcre_exec().         were passed to pcre_exec().
2845    
2846         The start_match field contains the offset within the subject  at  which         The  start_match  field normally contains the offset within the subject
2847         the  current match attempt started. If the pattern is not anchored, the         at which the current match attempt  started.  However,  if  the  escape
2848         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
2849         pattern for different starting points in the subject.         modified starting point. If the pattern is not  anchored,  the  callout
2850           function may be called several times from the same point in the pattern
2851           for different starting points in the subject.
2852    
2853         The  current_position  field  contains the offset within the subject of         The current_position field contains the offset within  the  subject  of
2854         the current match pointer.         the current match pointer.
2855    
2856         When the pcre_exec() function is used, the capture_top  field  contains         When  the  pcre_exec() function is used, the capture_top field contains
2857         one  more than the number of the highest numbered captured substring so         one more than the number of the highest numbered captured substring  so
2858         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
2859         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
2860         does not support captured substrings.         does not support captured substrings.
2861    
2862         The capture_last field contains the number of the  most  recently  cap-         The  capture_last  field  contains the number of the most recently cap-
2863         tured  substring. If no substrings have been captured, its value is -1.         tured substring. If no substrings have been captured, its value is  -1.
2864         This is always the case when pcre_dfa_exec() is used.         This is always the case when pcre_dfa_exec() is used.
2865    
2866         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()
2867         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-
2868         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
2869         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
2870         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
2871         structure in the pcreapi documentation.         structure in the pcreapi documentation.
2872    
2873         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-
2874         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
2875         the pattern string.         the pattern string.
2876    
2877         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-
2878         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
2879         the  pattern  string. When the callout immediately precedes an alterna-         the pattern string. When the callout immediately precedes  an  alterna-
2880         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
2881         is  zero.  When the callout precedes an opening parenthesis, the length         is zero. When the callout precedes an opening parenthesis,  the  length
2882         is that of the entire subpattern.         is that of the entire subpattern.
2883    
2884         The pattern_position and next_item_length fields are intended  to  help         The  pattern_position  and next_item_length fields are intended to help
2885         in  distinguishing between different automatic callouts, which all have         in distinguishing between different automatic callouts, which all  have
2886         the same callout number. However, they are set for all callouts.         the same callout number. However, they are set for all callouts.
2887    
2888    
2889  RETURN VALUES  RETURN VALUES
2890    
2891         The external callout function returns an integer to PCRE. If the  value         The  external callout function returns an integer to PCRE. If the value
2892         is  zero,  matching  proceeds  as  normal. If the value is greater than         is zero, matching proceeds as normal. If  the  value  is  greater  than
2893         zero, matching fails at the current point, but  the  testing  of  other         zero,  matching  fails  at  the current point, but the testing of other
2894         matching possibilities goes ahead, just as if a lookahead assertion had         matching possibilities goes ahead, just as if a lookahead assertion had
2895         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
2896         pcre_exec() (or pcre_dfa_exec()) returns the negative value.         pcre_exec() or pcre_dfa_exec() returns the negative value.
2897    
2898         Negative   values   should   normally   be   chosen  from  the  set  of         Negative  values  should  normally  be   chosen   from   the   set   of
2899         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-
2900         dard  "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT is         dard "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT  is
2901         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
2902         itself.         itself.
2903    
 Last updated: 28 February 2005  
 Copyright (c) 1997-2005 University of Cambridge.  
 ------------------------------------------------------------------------------  
2904    
2905    AUTHOR
2906    
2907           Philip Hazel
2908           University Computing Service
2909           Cambridge CB2 3QH, England.
2910    
2911    
2912    REVISION
2913    
2914           Last updated: 29 September 2009
2915           Copyright (c) 1997-2009 University of Cambridge.
2916    ------------------------------------------------------------------------------
2917    
2918    
2919  PCRECOMPAT(3)                                                    PCRECOMPAT(3)  PCRECOMPAT(3)                                                    PCRECOMPAT(3)
2920    
2921    
# Line 2227  DIFFERENCES BETWEEN PCRE AND PERL Line 2927  DIFFERENCES BETWEEN PCRE AND PERL
2927    
2928         This  document describes the differences in the ways that PCRE and Perl         This  document describes the differences in the ways that PCRE and Perl
2929         handle regular expressions. The differences  described  here  are  with         handle regular expressions. The differences  described  here  are  with
2930         respect to Perl 5.8.         respect to Perl 5.10.
2931    
2932         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
2933         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
2934           main pcre page.
2935    
2936         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl
2937         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,
2938         (?!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
2939         just asserts that the next character is not "a" three times.         just asserts that the next character is not "a" three times.
2940    
2941         3.  Capturing  subpatterns  that occur inside negative lookahead asser-         3. Capturing subpatterns that occur inside  negative  lookahead  asser-
2942         tions are counted, but their entries in the offsets  vector  are  never         tions  are  counted,  but their entries in the offsets vector are never
2943         set.  Perl sets its numerical variables from any such patterns that are         set. Perl sets its numerical variables from any such patterns that  are
2944         matched before the assertion fails to match something (thereby succeed-         matched before the assertion fails to match something (thereby succeed-
2945         ing),  but  only  if the negative lookahead assertion contains just one         ing), but only if the negative lookahead assertion  contains  just  one
2946         branch.         branch.
2947    
2948         4. Though binary zero characters are supported in the  subject  string,         4.  Though  binary zero characters are supported in the subject string,
2949         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-
2950         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
2951         the pattern to represent a binary zero.         the pattern to represent a binary zero.
2952    
2953         5.  The  following Perl escape sequences are not supported: \l, \u, \L,         5. The following Perl escape sequences are not supported: \l,  \u,  \L,
2954         \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-
2955         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
2956         are encountered by PCRE, an error is generated.         are encountered by PCRE, an error is generated.
2957    
2958         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
2959         is  built  with Unicode character property support. The properties that         is built with Unicode character property support. The  properties  that
2960         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-
2961         erties such as Lu and Nd.         erties such as Lu and Nd, script names such as Greek or  Han,  and  the
2962           derived  properties  Any  and  L&. PCRE does support the Cs (surrogate)
2963           property, which Perl does not; the  Perl  documentation  says  "Because
2964           Perl hides the need for the user to understand the internal representa-
2965           tion of Unicode characters, there is no need to implement the  somewhat
2966           messy concept of surrogates."
2967    
2968         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
2969         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 2981  DIFFERENCES BETWEEN PCRE AND PERL
2981         The  \Q...\E  sequence  is recognized both inside and outside character         The  \Q...\E  sequence  is recognized both inside and outside character
2982         classes.         classes.
2983    
2984         8. Fairly obviously, PCRE does not support the (?{code}) and (?p{code})         8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
2985         constructions.  However,  there is support for recursive patterns using         constructions.  However,  there is support for recursive patterns. This
2986         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
2987         "callout"  feature allows an external function to be called during pat-         "callout"  feature allows an external function to be called during pat-
2988         tern matching. See the pcrecallout documentation for details.         tern matching. See the pcrecallout documentation for details.
2989    
2990         9. There are some differences that are concerned with the  settings  of         9. Subpatterns that are called  recursively  or  as  "subroutines"  are
2991           always  treated  as  atomic  groups  in  PCRE. This is like Python, but
2992           unlike Perl. There is a discussion of an example that explains this  in
2993           more  detail  in  the section on recursion differences from Perl in the
2994           pcrepattern page.
2995    
2996           10. There are some differences that are concerned with the settings  of
2997         captured  strings  when  part  of  a  pattern is repeated. For example,         captured  strings  when  part  of  a  pattern is repeated. For example,
2998         matching "aba" against the  pattern  /^(a(b)?)+$/  in  Perl  leaves  $2         matching "aba" against the  pattern  /^(a(b)?)+$/  in  Perl  leaves  $2
2999         unset, but in PCRE it is set to "b".         unset, but in PCRE it is set to "b".
3000    
3001         10. PCRE provides some extensions to the Perl regular expression facil-         11.  PCRE  does  support  Perl  5.10's  backtracking  verbs  (*ACCEPT),
3002         ities:         (*FAIL), (*F), (*COMMIT), (*PRUNE), (*SKIP), and (*THEN), but  only  in
3003           the forms without an argument. PCRE does not support (*MARK).
3004         (a) Although lookbehind assertions must  match  fixed  length  strings,  
3005         each alternative branch of a lookbehind assertion can match a different         12.  PCRE's handling of duplicate subpattern numbers and duplicate sub-
3006         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
3007           fact the PCRE works internally just with numbers, using an external ta-
3008           ble to translate between numbers and names. In  particular,  a  pattern
3009           such  as  (?|(?<a>A)|(?<b)B),  where the two capturing parentheses have
3010           the same number but different names, is not supported,  and  causes  an
3011           error  at compile time. If it were allowed, it would not be possible to
3012           distinguish which parentheses matched, because both names map  to  cap-
3013           turing subpattern number 1. To avoid this confusing situation, an error
3014           is given at compile time.
3015    
3016           13. PCRE provides some extensions to the Perl regular expression facil-
3017           ities.   Perl  5.10  includes new features that are not in earlier ver-
3018           sions of Perl, some of which (such as named parentheses) have  been  in
3019           PCRE for some time. This list is with respect to Perl 5.10:
3020    
3021           (a)  Although  lookbehind  assertions  in  PCRE must match fixed length
3022           strings, each alternative branch of a lookbehind assertion can match  a
3023           different  length  of  string.  Perl requires them all to have the same
3024           length.
3025    
3026         (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  $
3027         meta-character matches only at the very end of the string.         meta-character matches only at the very end of the string.
3028    
3029         (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-
3030         cial meaning is faulted.         cial meaning is faulted. Otherwise, like Perl, the backslash is quietly
3031           ignored.  (Perl can be made to issue a warning.)
3032    
3033         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-         (d)  If  PCRE_UNGREEDY is set, the greediness of the repetition quanti-
3034         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-
3035         lowed by a question mark they are.         lowed by a question mark they are.
3036    
3037         (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
3038         tried only at the first matching position in the subject string.         tried only at the first matching position in the subject string.
3039    
3040         (f)  The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAP-         (f) The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART,
3041         TURE options for pcre_exec() have no Perl equivalents.         and  PCRE_NO_AUTO_CAPTURE  options for pcre_exec() have no Perl equiva-
3042           lents.
3043    
3044         (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
3045         pattern  matching  (Perl  can  do  this using the (?p{code}) construct,         CRLF by the PCRE_BSR_ANYCRLF option.
        which PCRE cannot support.)  
3046    
3047         (h) PCRE supports named capturing substrings, using the Python  syntax.         (h) The callout facility is PCRE-specific.
3048    
3049         (i)  PCRE  supports  the  possessive quantifier "++" syntax, taken from         (i) The partial matching facility is PCRE-specific.
        Sun's Java package.  
3050    
3051         (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,
3052           even on different hosts that have the other endianness.
3053    
3054         (k) The callout facility is PCRE-specific.         (k) The alternative matching function (pcre_dfa_exec())  matches  in  a
3055           different way and is not Perl-compatible.
3056    
3057         (l) The partial matching facility is PCRE-specific.         (l)  PCRE  recognizes some special sequences such as (*CR) at the start
3058           of a pattern that set overall options that cannot be changed within the
3059           pattern.
3060    
        (m) Patterns compiled by PCRE can be saved and re-used at a later time,  
        even on different hosts that have the other endianness.  
3061    
3062         (n)  The  alternative  matching function (pcre_dfa_exec()) matches in a  AUTHOR
3063         different way and is not Perl-compatible.  
3064           Philip Hazel
3065           University Computing Service
3066           Cambridge CB2 3QH, England.
3067    
 Last updated: 28 February 2005  
 Copyright (c) 1997-2005 University of Cambridge.  
 ------------------------------------------------------------------------------  
3068    
3069    REVISION
3070    
3071           Last updated: 04 October 2009
3072           Copyright (c) 1997-2009 University of Cambridge.
3073    ------------------------------------------------------------------------------
3074    
3075    
3076  PCREPATTERN(3)                                                  PCREPATTERN(3)  PCREPATTERN(3)                                                  PCREPATTERN(3)
3077    
3078    
# Line 2344  NAME Line 3082  NAME
3082    
3083  PCRE REGULAR EXPRESSION DETAILS  PCRE REGULAR EXPRESSION DETAILS
3084    
3085         The  syntax  and semantics of the regular expressions supported by PCRE         The  syntax and semantics of the regular expressions that are supported
3086         are described below. Regular expressions are also described in the Perl         by PCRE are described in detail below. There is a quick-reference  syn-
3087         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
3088         examples.  Jeffrey Friedl's "Mastering Regular Expressions",  published         semantics as closely as it can. PCRE  also  supports  some  alternative
3089         by  O'Reilly, covers regular expressions in great detail. This descrip-         regular  expression  syntax (which does not conflict with the Perl syn-
3090         tion of PCRE's regular expressions is intended as reference material.         tax) in order to provide some compatibility with regular expressions in
3091           Python, .NET, and Oniguruma.
3092    
3093           Perl's  regular expressions are described in its own documentation, and
3094           regular expressions in general are covered in a number of  books,  some
3095           of  which  have  copious  examples. Jeffrey Friedl's "Mastering Regular
3096           Expressions", published by  O'Reilly,  covers  regular  expressions  in
3097           great  detail.  This  description  of  PCRE's  regular  expressions  is
3098           intended as reference material.
3099    
3100         The original operation of PCRE was on strings of  one-byte  characters.         The original operation of PCRE was on strings of  one-byte  characters.
3101         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
3102         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
3103         pcre_compile()  with  the  PCRE_UTF8  option.  How this affects pattern         pcre_compile()  or  pcre_compile2() with the PCRE_UTF8 option. There is
3104         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:
3105         of  UTF-8  features  in  the  section on UTF-8 support in the main pcre  
3106         page.           (*UTF8)
3107    
3108           Starting a pattern with this sequence  is  equivalent  to  setting  the
3109           PCRE_UTF8  option.  This  feature  is  not Perl-compatible. How setting
3110           UTF-8 mode affects pattern matching  is  mentioned  in  several  places
3111           below.  There  is  also  a  summary of UTF-8 features in the section on
3112           UTF-8 support in the main pcre page.
3113    
3114         The remainder of this document discusses the  patterns  that  are  sup-         The remainder of this document discusses the  patterns  that  are  sup-
3115         ported  by  PCRE when its main matching function, pcre_exec(), is used.         ported  by  PCRE when its main matching function, pcre_exec(), is used.
3116         From  release  6.0,   PCRE   offers   a   second   matching   function,         From  release  6.0,   PCRE   offers   a   second   matching   function,
3117         pcre_dfa_exec(),  which matches using a different algorithm that is not         pcre_dfa_exec(),  which matches using a different algorithm that is not
3118         Perl-compatible. The advantages and disadvantages  of  the  alternative         Perl-compatible. Some of the features discussed below are not available
3119         function, and how it differs from the normal function, are discussed in         when  pcre_dfa_exec()  is used. The advantages and disadvantages of the
3120         the pcrematching page.         alternative function, and how it differs from the normal function,  are
3121           discussed in the pcrematching page.
3122         A regular expression is a pattern that is  matched  against  a  subject  
3123         string  from  left  to right. Most characters stand for themselves in a  
3124         pattern, and match the corresponding characters in the  subject.  As  a  NEWLINE CONVENTIONS
3125    
3126           PCRE  supports five different conventions for indicating line breaks in
3127           strings: a single CR (carriage return) character, a  single  LF  (line-
3128           feed) character, the two-character sequence CRLF, any of the three pre-
3129           ceding, or any Unicode newline sequence. The pcreapi page  has  further
3130           discussion  about newlines, and shows how to set the newline convention
3131           in the options arguments for the compiling and matching functions.
3132    
3133           It is also possible to specify a newline convention by starting a  pat-
3134           tern string with one of the following five sequences:
3135    
3136             (*CR)        carriage return
3137             (*LF)        linefeed
3138             (*CRLF)      carriage return, followed by linefeed
3139             (*ANYCRLF)   any of the three above
3140             (*ANY)       all Unicode newline sequences
3141    
3142           These  override  the default and the options given to pcre_compile() or
3143           pcre_compile2(). For example, on a Unix system where LF is the  default
3144           newline sequence, the pattern
3145    
3146             (*CR)a.b
3147    
3148           changes the convention to CR. That pattern matches "a\nb" because LF is
3149           no longer a newline. Note that these special settings,  which  are  not
3150           Perl-compatible,  are  recognized  only at the very start of a pattern,
3151           and that they must be in upper case.  If  more  than  one  of  them  is
3152           present, the last one is used.
3153    
3154           The  newline convention affects the interpretation of the dot metachar-
3155           acter when PCRE_DOTALL is not set, and also the behaviour of  \N.  How-
3156           ever,  it  does  not  affect  what  the  \R escape sequence matches. By
3157           default, this is any Unicode newline sequence, for Perl  compatibility.
3158           However,  this can be changed; see the description of \R in the section
3159           entitled "Newline sequences" below. A change of \R setting can be  com-
3160           bined with a change of newline convention.
3161    
3162    
3163    CHARACTERS AND METACHARACTERS
3164    
3165           A  regular  expression  is  a pattern that is matched against a subject
3166           string from left to right. Most characters stand for  themselves  in  a
3167           pattern,  and  match  the corresponding characters in the subject. As a
3168         trivial example, the pattern         trivial example, the pattern
3169    
3170           The quick brown fox           The quick brown fox
3171    
3172         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
3173         caseless matching is specified (the PCRE_CASELESS option), letters  are         caseless  matching is specified (the PCRE_CASELESS option), letters are
3174         matched  independently  of case. In UTF-8 mode, PCRE always understands         matched independently of case. In UTF-8 mode, PCRE  always  understands
3175         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
3176         caseless  matching  is always possible. For characters with higher val-         caseless matching is always possible. For characters with  higher  val-
3177         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
3178         property  support,  but  not  otherwise.   If  you want to use caseless         property support, but not otherwise.   If  you  want  to  use  caseless
3179         matching for characters 128 and above, you must  ensure  that  PCRE  is         matching  for  characters  128  and above, you must ensure that PCRE is
3180         compiled with Unicode property support as well as with UTF-8 support.         compiled with Unicode property support as well as with UTF-8 support.
3181    
3182         The  power  of  regular  expressions  comes from the ability to include         The power of regular expressions comes  from  the  ability  to  include
3183         alternatives and repetitions in the pattern. These are encoded  in  the         alternatives  and  repetitions in the pattern. These are encoded in the
3184         pattern by the use of metacharacters, which do not stand for themselves         pattern by the use of metacharacters, which do not stand for themselves
3185         but instead are interpreted in some special way.         but instead are interpreted in some special way.
3186    
3187         There are two different sets of metacharacters: those that  are  recog-         There  are  two different sets of metacharacters: those that are recog-
3188         nized  anywhere in the pattern except within square brackets, and those         nized anywhere in the pattern except within square brackets, and  those
3189         that are recognized in square brackets. Outside  square  brackets,  the         that  are  recognized  within square brackets. Outside square brackets,
3190         metacharacters are as follows:         the metacharacters are as follows:
3191    
3192           \      general escape character with several uses           \      general escape character with several uses
3193           ^      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 3205  PCRE REGULAR EXPRESSION DETAILS
3205                  also "possessive quantifier"                  also "possessive quantifier"
3206           {      start min/max quantifier           {      start min/max quantifier
3207    
3208         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
3209         class". In a character class the only metacharacters are:         class". In a character class the only metacharacters are:
3210    
3211           \      general escape character           \      general escape character
# Line 2420  PCRE REGULAR EXPRESSION DETAILS Line 3215  PCRE REGULAR EXPRESSION DETAILS
3215                    syntax)                    syntax)
3216           ]      terminates the character class           ]      terminates the character class
3217    
3218         The following sections describe the use of each of the  metacharacters.         The following sections describe the use of each of the metacharacters.
3219    
3220    
3221  BACKSLASH  BACKSLASH
# Line 2439  BACKSLASH Line 3234  BACKSLASH
3234    
3235         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in
3236         the pattern (other than in a character class) and characters between  a         the pattern (other than in a character class) and characters between  a
3237         # outside a character class and the next newline character are ignored.         # outside a character class and the next newline are ignored. An escap-
3238         An escaping backslash can be used to include a whitespace or #  charac-         ing backslash can be used to include a whitespace  or  #  character  as
3239         ter as part of the pattern.         part of the pattern.
3240    
3241         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-
3242         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 3260  BACKSLASH
3260         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
3261         appearance of non-printing characters, apart from the binary zero  that         appearance of non-printing characters, apart from the binary zero  that
3262         terminates  a  pattern,  but  when  a pattern is being prepared by text         terminates  a  pattern,  but  when  a pattern is being prepared by text
3263         editing, it is usually easier  to  use  one  of  the  following  escape         editing, it is  often  easier  to  use  one  of  the  following  escape
3264         sequences than the binary character it represents:         sequences than the binary character it represents:
3265    
3266           \a        alarm, that is, the BEL character (hex 07)           \a        alarm, that is, the BEL character (hex 07)
3267           \cx       "control-x", where x is any character           \cx       "control-x", where x is any character
3268           \e        escape (hex 1B)           \e        escape (hex 1B)
3269           \f        formfeed (hex 0C)           \f        formfeed (hex 0C)
3270           \n        newline (hex 0A)           \n        linefeed (hex 0A)
3271           \r        carriage return (hex 0D)           \r        carriage return (hex 0D)
3272           \t        tab (hex 09)           \t        tab (hex 09)
3273           \ddd      character with octal code ddd, or backreference           \ddd      character with octal code ddd, or back reference
3274           \xhh      character with hex code hh           \xhh      character with hex code hh
3275           \x{hhh..} character with hex code hhh... (UTF-8 mode only)           \x{hhh..} character with hex code hhh..
3276    
3277         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,
3278         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 3280  BACKSLASH
3280         becomes hex 7B.         becomes hex 7B.
3281    
3282         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
3283         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
3284         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
3285         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,
3286         7FFFFFFF). If characters other than hexadecimal digits  appear  between         the maximum value in hexadecimal is 7FFFFFFF. Note that this is  bigger
3287         \x{  and }, or if there is no terminating }, this form of escape is not         than the largest Unicode code point, which is 10FFFF.
3288         recognized. Instead, the initial \x will  be  interpreted  as  a  basic  
3289         hexadecimal  escape, with no following digits, giving a character whose         If  characters  other than hexadecimal digits appear between \x{ and },
3290         value is zero.         or if there is no terminating }, this form of escape is not recognized.
3291           Instead,  the  initial  \x  will  be interpreted as a basic hexadecimal
3292           escape, with no following digits, giving a  character  whose  value  is
3293           zero.
3294    
3295         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
3296         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-
3297         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}.
3298         \x{dc}.  
3299           After  \0  up  to two further octal digits are read. If there are fewer
3300         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
3301         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
3302         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
3303         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.  
3304    
3305         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-
3306         cated.  Outside a character class, PCRE reads it and any following dig-         cated.  Outside a character class, PCRE reads it and any following dig-
3307         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
3308         have been at least that many previous capturing left parentheses in the         have been at least that many previous capturing left parentheses in the
3309         expression, the entire  sequence  is  taken  as  a  back  reference.  A         expression,  the  entire  sequence  is  taken  as  a  back reference. A
3310         description  of how this works is given later, following the discussion         description of how this works is given later, following the  discussion
3311         of parenthesized subpatterns.         of parenthesized subpatterns.
3312    
3313         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
3314         and  there have not been that many capturing subpatterns, PCRE re-reads         and there have not been that many capturing subpatterns, PCRE  re-reads
3315         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-
3316         gle byte from the least significant 8 bits of the value. Any subsequent         erate a data character. Any subsequent digits stand for themselves.  In
3317         digits stand for themselves.  For example:         non-UTF-8  mode,  the  value  of a character specified in octal must be
3318           less than \400. In UTF-8 mode, values up to  \777  are  permitted.  For
3319           example:
3320    
3321           \040   is another way of writing a space           \040   is another way of writing a space
3322           \40    is the same, provided there are fewer than 40           \40    is the same, provided there are fewer than 40
# Line 2535  BACKSLASH Line 3333  BACKSLASH
3333           \81    is either a back reference, or a binary zero           \81    is either a back reference, or a binary zero
3334                     followed by the two characters "8" and "1"                     followed by the two characters "8" and "1"
3335    
3336         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
3337         leading zero, because no more than three octal digits are ever read.         leading zero, because no more than three octal digits are ever read.
3338    
3339         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
3340         character (in UTF-8 mode) can be used both inside and outside character         inside  and  outside character classes. In addition, inside a character
3341         classes.  In  addition,  inside  a  character class, the sequence \b is         class, the sequence \b is interpreted as the backspace  character  (hex
3342         interpreted as the backspace character (hex 08), and the sequence \X is         08).  The sequences \B, \N, \R, and \X are not special inside a charac-
3343         interpreted  as  the  character  "X".  Outside a character class, these         ter class. Like any  other  unrecognized  escape  sequences,  they  are
3344         sequences have different meanings (see below).         treated  as  the  literal characters "B", "N", "R", and "X" by default,
3345           but cause an error if the PCRE_EXTRA option is set. Outside a character
3346           class, these sequences have different meanings.
3347    
3348       Absolute and relative back references
3349    
3350           The  sequence  \g followed by an unsigned or a negative number, option-
3351           ally enclosed in braces, is an absolute or relative back  reference.  A
3352           named back reference can be coded as \g{name}. Back references are dis-
3353           cussed later, following the discussion of parenthesized subpatterns.
3354    
3355       Absolute and relative subroutine calls
3356    
3357           For compatibility with Oniguruma, the non-Perl syntax \g followed by  a
3358           name or a number enclosed either in angle brackets or single quotes, is
3359           an alternative syntax for referencing a subpattern as  a  "subroutine".
3360           Details  are  discussed  later.   Note  that  \g{...} (Perl syntax) and
3361           \g<...> (Oniguruma syntax) are not synonymous. The  former  is  a  back
3362           reference; the latter is a subroutine call.
3363    
3364     Generic character types     Generic character types
3365    
3366         The third use of backslash is for specifying generic  character  types.         Another use of backslash is for specifying generic character types:
        The following are always recognized:  
3367    
3368           \d     any decimal digit           \d     any decimal digit
3369           \D     any character that is not a decimal digit           \D     any character that is not a decimal digit
3370             \h     any horizontal whitespace character
3371             \H     any character that is not a horizontal whitespace character
3372           \s     any whitespace character           \s     any whitespace character
3373           \S     any character that is not a whitespace character           \S     any character that is not a whitespace character
3374             \v     any vertical whitespace character
3375             \V     any character that is not a vertical whitespace character
3376           \w     any "word" character           \w     any "word" character
3377           \W     any "non-word" character           \W     any "non-word" character
3378    
3379         Each pair of escape sequences partitions the complete set of characters         There is also the single sequence \N, which matches a non-newline char-
3380         into two disjoint sets. Any given character matches one, and only  one,         acter.  This is the same as the "." metacharacter when  PCRE_DOTALL  is
3381         of each pair.         not set.
3382    
3383           Each  pair of lower and upper case escape sequences partitions the com-
3384           plete set of characters into two disjoint  sets.  Any  given  character
3385           matches one, and only one, of each pair.
3386    
3387         These character type sequences can appear both inside and outside char-         These character type sequences can appear both inside and outside char-
3388         acter classes. They each match one character of the  appropriate  type.         acter classes. They each match one character of the  appropriate  type.
# Line 2568  BACKSLASH Line 3391  BACKSLASH
3391    
3392         For compatibility with Perl, \s does not match the VT  character  (code         For compatibility with Perl, \s does not match the VT  character  (code
3393         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
3394         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
3395           "use locale;" is included in a Perl script, \s may match the VT charac-
3396         A "word" character is an underscore or any character less than 256 that         ter. In PCRE, it never does.
        is  a  letter  or  digit.  The definition of letters and digits is con-  
        trolled by PCRE's low-valued character tables, and may vary if  locale-  
        specific  matching is taking place (see "Locale support" in the pcreapi  
        page). For example, in the  "fr_FR"  (French)  locale,  some  character  
        codes  greater  than  128  are used for accented letters, and these are  
        matched by \w.  
3397    
3398         In UTF-8 mode, characters with values greater than 128 never match  \d,         In UTF-8 mode, characters with values greater than 128 never match  \d,
3399         \s, or \w, and always match \D, \S, and \W. This is true even when Uni-         \s, or \w, and always match \D, \S, and \W. This is true even when Uni-
3400         code character property support is available.         code character property support is available.  These  sequences  retain
3401           their original meanings from before UTF-8 support was available, mainly
3402           for efficiency reasons. Note that this also affects \b, because  it  is
3403           defined in terms of \w and \W.
3404    
3405           The sequences \h, \H, \v, and \V are Perl 5.10 features. In contrast to
3406           the other sequences, these do match certain high-valued  codepoints  in
3407           UTF-8 mode.  The horizontal space characters are:
3408    
3409             U+0009     Horizontal tab
3410             U+0020     Space
3411             U+00A0     Non-break space
3412             U+1680     Ogham space mark
3413             U+180E     Mongolian vowel separator
3414             U+2000     En quad
3415             U+2001     Em quad
3416             U+2002     En space
3417             U+2003     Em space
3418             U+2004     Three-per-em space
3419             U+2005     Four-per-em space
3420             U+2006     Six-per-em space
3421             U+2007     Figure space
3422             U+2008     Punctuation space
3423             U+2009     Thin space
3424             U+200A     Hair space
3425             U+202F     Narrow no-break space
3426             U+205F     Medium mathematical space
3427             U+3000     Ideographic space
3428    
3429           The vertical space characters are:
3430    
3431             U+000A     Linefeed