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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         5.12, including support for UTF-8 encoded strings and  Unicode  general
30         function  has  some  advantages.  For  a discussion of the two matching         category  properties.  However,  UTF-8  and  Unicode  support has to be
31         algorithms, see the pcrematching page.         explicitly enabled; it is not the default. The  Unicode  tables  corre-
32           spond to Unicode release 5.2.0.
33         PCRE is written in C and released as a C library. A  number  of  people  
34         have  written  wrappers and interfaces of various kinds. In particular,         In  addition to the Perl-compatible matching function, PCRE contains an
35         Google Inc.  have provided a comprehensive C++  wrapper.  This  is  now         alternative function that matches the same compiled patterns in a  dif-
36           ferent way. In certain circumstances, the alternative function has some
37           advantages.  For a discussion of the two matching algorithms,  see  the
38           pcrematching page.
39    
40           PCRE  is  written  in C and released as a C library. A number of people
41           have written wrappers and interfaces of various kinds.  In  particular,
42           Google  Inc.   have  provided  a comprehensive C++ wrapper. This is now
43         included as part of the PCRE distribution. The pcrecpp page has details         included as part of the PCRE distribution. The pcrecpp page has details
44         of this interface. Other people's contributions can  be  found  in  the         of  this  interface.  Other  people's contributions can be found in the
45         Contrib directory at the primary FTP site, which is:         Contrib directory at the primary FTP site, which is:
46    
47         ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre         ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre
48    
49         Details  of  exactly which Perl regular expression features are and are         Details of exactly which Perl regular expression features are  and  are
50         not supported by PCRE are given in separate documents. See the pcrepat-         not supported by PCRE are given in separate documents. See the pcrepat-
51         tern and pcrecompat pages.         tern and pcrecompat pages. There is a syntax summary in the  pcresyntax
52           page.
53    
54         Some  features  of  PCRE can be included, excluded, or changed when the         Some  features  of  PCRE can be included, excluded, or changed when the
55         library is built. The pcre_config() function makes it  possible  for  a         library is built. The pcre_config() function makes it  possible  for  a
56         client  to  discover  which  features are available. The features them-         client  to  discover  which  features are available. The features them-
57         selves are described in the pcrebuild page. Documentation about  build-         selves are described in the pcrebuild page. Documentation about  build-
58         ing  PCRE for various operating systems can be found in the README file         ing  PCRE  for various operating systems can be found in the README and
59         in the source distribution.         NON-UNIX-USE files in the source distribution.
60    
61         The library contains a number of undocumented  internal  functions  and         The library contains a number of undocumented  internal  functions  and
62         data  tables  that  are  used by more than one of the exported external         data  tables  that  are  used by more than one of the exported external
# Line 63  USER DOCUMENTATION Line 72  USER DOCUMENTATION
72         The user documentation for PCRE comprises a number  of  different  sec-         The user documentation for PCRE comprises a number  of  different  sec-
73         tions.  In the "man" format, each of these is a separate "man page". In         tions.  In the "man" format, each of these is a separate "man page". In
74         the HTML format, each is a separate page, linked from the  index  page.         the HTML format, each is a separate page, linked from the  index  page.
75         In  the  plain text format, all the sections are concatenated, for ease         In  the  plain  text format, all the sections, except the pcredemo sec-
76         of searching. The sections are as follows:         tion, are concatenated, for ease of searching. The sections are as fol-
77           lows:
78    
79           pcre              this document           pcre              this document
80             pcre-config       show PCRE installation configuration information
81           pcreapi           details of PCRE's native C API           pcreapi           details of PCRE's native C API
82           pcrebuild         options for building PCRE           pcrebuild         options for building PCRE
83           pcrecallout       details of the callout feature           pcrecallout       details of the callout feature
84           pcrecompat        discussion of Perl compatibility           pcrecompat        discussion of Perl compatibility
85           pcrecpp           details of the C++ wrapper           pcrecpp           details of the C++ wrapper
86             pcredemo          a demonstration C program that uses PCRE
87           pcregrep          description of the pcregrep command           pcregrep          description of the pcregrep command
88           pcrematching      discussion of the two matching algorithms           pcrematching      discussion of the two matching algorithms
89           pcrepartial       details of the partial matching facility           pcrepartial       details of the partial matching facility
# Line 80  USER DOCUMENTATION Line 92  USER DOCUMENTATION
92           pcreperform       discussion of performance issues           pcreperform       discussion of performance issues
93           pcreposix         the POSIX-compatible C API           pcreposix         the POSIX-compatible C API
94           pcreprecompile    details of saving and re-using precompiled patterns           pcreprecompile    details of saving and re-using precompiled patterns
95           pcresample        discussion of the sample program           pcresample        discussion of the pcredemo program
96             pcrestack         discussion of stack usage
97             pcresyntax        quick syntax reference
98           pcretest          description of the pcretest testing command           pcretest          description of the pcretest testing command
99    
100         In  addition,  in the "man" and HTML formats, there is a short page for         In  addition,  in the "man" and HTML formats, there is a short page for
# Line 98  LIMITATIONS Line 112  LIMITATIONS
112         PCRE with an internal linkage size of 3 or 4 (see the  README  file  in         PCRE with an internal linkage size of 3 or 4 (see the  README  file  in
113         the  source  distribution and the pcrebuild documentation for details).         the  source  distribution and the pcrebuild documentation for details).
114         In these cases the limit is substantially larger.  However,  the  speed         In these cases the limit is substantially larger.  However,  the  speed
115         of execution will be slower.         of execution is slower.
116    
117         All values in repeating quantifiers must be less than 65536.  The maxi-         All values in repeating quantifiers must be less than 65536.
        mum number of capturing subpatterns is 65535.  
118    
119         There is no limit to the number of non-capturing subpatterns,  but  the         There is no limit to the number of parenthesized subpatterns, but there
120         maximum  depth  of  nesting  of  all kinds of parenthesized subpattern,         can be no more than 65535 capturing subpatterns.
121         including capturing subpatterns, assertions, and other types of subpat-  
122         tern, is 200.         The maximum length of name for a named subpattern is 32 characters, and
123           the maximum number of named subpatterns is 10000.
124    
125         The  maximum  length of a subject string is the largest positive number         The  maximum  length of a subject string is the largest positive number
126         that an integer variable can hold. However, when using the  traditional         that an integer variable can hold. However, when using the  traditional
127         matching function, PCRE uses recursion to handle subpatterns and indef-         matching function, PCRE uses recursion to handle subpatterns and indef-
128         inite repetition.  This means that the available stack space may  limit         inite repetition.  This means that the available stack space may  limit
129         the size of a subject string that can be processed by certain patterns.         the size of a subject string that can be processed by certain patterns.
130           For a discussion of stack issues, see the pcrestack documentation.
131    
132    
133  UTF-8 AND UNICODE PROPERTY SUPPORT  UTF-8 AND UNICODE PROPERTY SUPPORT
# Line 124  UTF-8 AND UNICODE PROPERTY SUPPORT Line 139  UTF-8 AND UNICODE PROPERTY SUPPORT
139    
140         In  order  process  UTF-8 strings, you must build PCRE to include UTF-8         In  order  process  UTF-8 strings, you must build PCRE to include UTF-8
141         support in the code, and, in addition,  you  must  call  pcre_compile()         support in the code, and, in addition,  you  must  call  pcre_compile()
142         with  the PCRE_UTF8 option flag. When you do this, both the pattern and         with  the  PCRE_UTF8  option  flag,  or the pattern must start with the
143         any subject strings that are matched against it are  treated  as  UTF-8         sequence (*UTF8). When either of these is the case,  both  the  pattern
144         strings instead of just strings of bytes.         and  any  subject  strings  that  are matched against it are treated as
145           UTF-8 strings instead of strings of 1-byte characters.
146         If  you compile PCRE with UTF-8 support, but do not use it at run time,  
147         the library will be a bit bigger, but the additional run time  overhead         If you compile PCRE with UTF-8 support, but do not use it at run  time,
148         is  limited  to testing the PCRE_UTF8 flag in several places, so should         the  library will be a bit bigger, but the additional run time overhead
149         not be very large.         is limited to testing the PCRE_UTF8 flag occasionally, so should not be
150           very big.
151    
152         If PCRE is built with Unicode character property support (which implies         If PCRE is built with Unicode character property support (which implies
153         UTF-8  support),  the  escape sequences \p{..}, \P{..}, and \X are sup-         UTF-8 support), the escape sequences \p{..}, \P{..}, and  \X  are  sup-
154         ported.  The available properties that can be tested are limited to the         ported.  The available properties that can be tested are limited to the
155         general  category  properties such as Lu for an upper case letter or Nd         general category properties such as Lu for an upper case letter  or  Nd
156         for a decimal number. A full list is given in the pcrepattern  documen-         for  a  decimal number, the Unicode script names such as Arabic or Han,
157         tation. The PCRE library is increased in size by about 90K when Unicode         and the derived properties Any and L&. A full  list  is  given  in  the
158         property support is included.         pcrepattern documentation. Only the short names for properties are sup-
159           ported. For example, \p{L} matches a letter. Its Perl synonym,  \p{Let-
160         The following comments apply when PCRE is running in UTF-8 mode:         ter},  is  not  supported.   Furthermore,  in Perl, many properties may
161           optionally be prefixed by "Is", for compatibility with Perl  5.6.  PCRE
162         1. When you set the PCRE_UTF8 flag, the strings passed as patterns  and         does not support this.
163         subjects  are  checked for validity on entry to the relevant functions.  
164         If an invalid UTF-8 string is passed, an error return is given. In some     Validity of UTF-8 strings
165         situations,  you  may  already  know  that  your strings are valid, and  
166         therefore want to skip these checks in order to improve performance. If         When  you  set  the  PCRE_UTF8 flag, the strings passed as patterns and
167         you  set  the  PCRE_NO_UTF8_CHECK  flag at compile time or at run time,         subjects are (by default) checked for validity on entry to the relevant
168         PCRE assumes that the pattern or subject  it  is  given  (respectively)         functions.  From  release 7.3 of PCRE, the check is according the rules
169         contains  only valid UTF-8 codes. In this case, it does not diagnose an         of RFC 3629, which are themselves derived from the  Unicode  specifica-
170         invalid UTF-8 string. If you pass an invalid UTF-8 string to PCRE  when         tion.  Earlier  releases  of PCRE followed the rules of RFC 2279, which
171         PCRE_NO_UTF8_CHECK  is set, the results are undefined. Your program may         allows the full range of 31-bit values (0 to 0x7FFFFFFF).  The  current
172         crash.         check allows only values in the range U+0 to U+10FFFF, excluding U+D800
173           to U+DFFF.
174         2. In a pattern, the escape sequence \x{...}, where the contents of the  
175         braces  is  a  string  of hexadecimal digits, is interpreted as a UTF-8         The excluded code points are the "Low Surrogate Area"  of  Unicode,  of
176         character whose code number is the given hexadecimal number, for  exam-         which  the Unicode Standard says this: "The Low Surrogate Area does not
177         ple:  \x{1234}.  If a non-hexadecimal digit appears between the braces,         contain any  character  assignments,  consequently  no  character  code
178         the item is not recognized.  This escape sequence can be used either as         charts or namelists are provided for this area. Surrogates are reserved
179         a literal, or within a character class.         for use with UTF-16 and then must be used in pairs."  The  code  points
180           that  are  encoded  by  UTF-16  pairs are available as independent code
181           points in the UTF-8 encoding. (In  other  words,  the  whole  surrogate
182           thing is a fudge for UTF-16 which unfortunately messes up UTF-8.)
183    
184           If  an  invalid  UTF-8  string  is  passed  to  PCRE,  an  error return
185           (PCRE_ERROR_BADUTF8) is given. In some situations, you may already know
186           that your strings are valid, and therefore want to skip these checks in
187           order to improve performance. If you set the PCRE_NO_UTF8_CHECK flag at
188           compile  time  or at run time, PCRE assumes that the pattern or subject
189           it is given (respectively) contains only valid  UTF-8  codes.  In  this
190           case, it does not diagnose an invalid UTF-8 string.
191    
192           If  you  pass  an  invalid UTF-8 string when PCRE_NO_UTF8_CHECK is set,
193           what happens depends on why the string is invalid. If the  string  con-
194           forms to the "old" definition of UTF-8 (RFC 2279), it is processed as a
195           string of characters in the range 0  to  0x7FFFFFFF.  In  other  words,
196           apart from the initial validity test, PCRE (when in UTF-8 mode) handles
197           strings according to the more liberal rules of RFC  2279.  However,  if
198           the  string does not even conform to RFC 2279, the result is undefined.
199           Your program may crash.
200    
201           If you want to process strings  of  values  in  the  full  range  0  to
202           0x7FFFFFFF,  encoded in a UTF-8-like manner as per the old RFC, you can
203           set PCRE_NO_UTF8_CHECK to bypass the more restrictive test. However, in
204           this situation, you will have to apply your own validity check.
205    
206       General comments about UTF-8 mode
207    
208           1.  An  unbraced  hexadecimal  escape sequence (such as \xb3) matches a
209           two-byte UTF-8 character if the value is greater than 127.
210    
211         3.  The  original hexadecimal escape sequence, \xhh, matches a two-byte         2. Octal numbers up to \777 are recognized, and  match  two-byte  UTF-8
212         UTF-8 character if the value is greater than 127.         characters for values greater than \177.
213    
214         4. Repeat quantifiers apply to complete UTF-8 characters, not to  indi-         3.  Repeat quantifiers apply to complete UTF-8 characters, not to indi-
215         vidual bytes, for example: \x{100}{3}.         vidual bytes, for example: \x{100}{3}.
216    
217         5.  The dot metacharacter matches one UTF-8 character instead of a sin-         4. The dot metacharacter matches one UTF-8 character instead of a  sin-
218         gle byte.         gle byte.
219    
220         6. The escape sequence \C can be used to match a single byte  in  UTF-8         5.  The  escape sequence \C can be used to match a single byte in UTF-8
221         mode,  but  its  use can lead to some strange effects. This facility is         mode, but its use can lead to some strange effects.  This  facility  is
222         not available in the alternative matching function, pcre_dfa_exec().         not available in the alternative matching function, pcre_dfa_exec().
223    
224         7. The character escapes \b, \B, \d, \D, \s, \S, \w, and  \W  correctly         6.  The  character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly
225         test  characters of any code value, but the characters that PCRE recog-         test characters of any code value, but, 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 in particular
230         sense of, say, "digit", you must use Unicode  property  tests  such  as         that this applies to \b and \B, because they are defined in terms of \w
231         \p{Nd}.         and \W. If you really want to test for a wider sense of, say,  "digit",
232           you  can  use  explicit Unicode property tests such as \p{Nd}. Alterna-
233         8.  Similarly,  characters that match the POSIX named character classes         tively, if you set the PCRE_UCP option,  the  way  that  the  character
234         are all low-valued characters.         escapes  work  is changed so that Unicode properties are used to deter-
235           mine which characters match. There are more details in the  section  on
236           generic character 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 horizontal and  vertical  whitespace  matching  escapes
242           (\h,  \H,  \v, and \V) do match all the appropriate Unicode characters,
243           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. Furthermore, PCRE supports
251           case-insensitive matching only  when  there  is  a  one-to-one  mapping
252           between  a letter's cases. There are a small number of many-to-one map-
253           pings in Unicode; these are not supported by PCRE.
254    
255    
256  AUTHOR  AUTHOR
257    
258         Philip Hazel         Philip Hazel
259         University Computing Service,         University Computing Service
260         Cambridge CB2 3QG, England.         Cambridge CB2 3QH, England.
261    
262           Putting an actual email address here seems to have been a spam  magnet,
263           so  I've  taken  it away. If you want to email me, use my two initials,
264           followed by the two digits 10, at the domain cam.ac.uk.
265    
266    
267         Putting  an actual email address here seems to have been a spam magnet,  REVISION
        so I've taken it away. If you want to email me, use my initial and sur-  
        name, separated by a dot, at the domain ucs.cam.ac.uk.  
268    
269  Last updated: 07 March 2005         Last updated: 13 November 2010
270  Copyright (c) 1997-2005 University of Cambridge.         Copyright (c) 1997-2010 University of Cambridge.
271  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
272    
273    
# Line 220  NAME Line 281  NAME
281  PCRE BUILD-TIME OPTIONS  PCRE BUILD-TIME OPTIONS
282    
283         This  document  describes  the  optional  features  of PCRE that can be         This  document  describes  the  optional  features  of PCRE that can be
284         selected when the library is compiled. They are all selected, or  dese-         selected when the library is compiled. It assumes use of the  configure
285         lected, by providing options to the configure script that is run before         script,  where the optional features are selected or deselected by pro-
286         the make command. The complete list of  options  for  configure  (which         viding options to configure before running the make  command.  However,
287         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
288         directory) can be obtained by running         environments using the GUI facility of cmake-gui if you are using CMake
289           instead of configure to build PCRE.
290    
291           There  is  a  lot more information about building PCRE in non-Unix-like
292           environments in the file called NON_UNIX_USE, which is part of the PCRE
293           distribution.  You  should consult this file as well as the README file
294           if you are building in a non-Unix-like environment.
295    
296           The complete list of options for configure (which includes the standard
297           ones  such  as  the  selection  of  the  installation directory) can be
298           obtained by running
299    
300           ./configure --help           ./configure --help
301    
302         The following sections describe certain options whose names begin  with         The following sections include  descriptions  of  options  whose  names
303         --enable  or  --disable. These settings specify changes to the defaults         begin with --enable or --disable. These settings specify changes to the
304         for the configure command. Because of the  way  that  configure  works,         defaults for the configure command. Because of the way  that  configure
305         --enable  and  --disable  always  come  in  pairs, so the complementary         works,  --enable  and --disable always come in pairs, so the complemen-
306         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
307         not described.         is not described.
308    
309    
310  C++ SUPPORT  C++ SUPPORT
# Line 249  C++ SUPPORT Line 320  C++ SUPPORT
320    
321  UTF-8 SUPPORT  UTF-8 SUPPORT
322    
323         To build PCRE with support for UTF-8 character strings, add         To build PCRE with support for UTF-8 Unicode character strings, add
324    
325           --enable-utf8           --enable-utf8
326    
327         to  the  configure  command.  Of  itself, this does not make PCRE treat         to  the  configure  command.  Of  itself, this does not make PCRE treat
328         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
329         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()
330         function.         or pcre_compile2() functions.
331    
332           If you set --enable-utf8 when compiling in an EBCDIC environment,  PCRE
333           expects its input to be either ASCII or UTF-8 (depending on the runtime
334           option). It is not possible to support both EBCDIC and UTF-8  codes  in
335           the  same  version  of  the  library.  Consequently,  --enable-utf8 and
336           --enable-ebcdic are mutually exclusive.
337    
338    
339  UNICODE CHARACTER PROPERTY SUPPORT  UNICODE CHARACTER PROPERTY SUPPORT
# Line 272  UNICODE CHARACTER PROPERTY SUPPORT Line 349  UNICODE CHARACTER PROPERTY SUPPORT
349         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
350         not explicitly requested it.         not explicitly requested it.
351    
352         Including  Unicode  property  support  adds around 90K of tables to the         Including  Unicode  property  support  adds around 30K of tables to the
353         PCRE library, approximately doubling its size. Only the  general  cate-         PCRE library. Only the general category properties such as  Lu  and  Nd
354         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.  
355    
356    
357  CODE VALUE OF NEWLINE  CODE VALUE OF NEWLINE
358    
359         By default, PCRE treats character 10 (linefeed) as the newline  charac-         By  default,  PCRE interprets the linefeed (LF) character as indicating
360         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
361         compile PCRE to use character 13 (carriage return) instead by adding         systems.  You  can compile PCRE to use carriage return (CR) instead, by
362           adding
363    
364           --enable-newline-is-cr           --enable-newline-is-cr
365    
366         to the configure command. For completeness there is  also  a  --enable-         to the  configure  command.  There  is  also  a  --enable-newline-is-lf
367         newline-is-lf  option,  which explicitly specifies linefeed as the new-         option, which explicitly specifies linefeed as the newline character.
368         line character.  
369           Alternatively, you can specify that line endings are to be indicated by
370           the two character sequence CRLF. If you want this, add
371    
372             --enable-newline-is-crlf
373    
374           to the configure command. There is a fourth option, specified by
375    
376             --enable-newline-is-anycrlf
377    
378           which causes PCRE to recognize any of the three sequences  CR,  LF,  or
379           CRLF as indicating a line ending. Finally, a fifth option, specified by
380    
381             --enable-newline-is-any
382    
383           causes PCRE to recognize any Unicode newline sequence.
384    
385           Whatever  line  ending convention is selected when PCRE is built can be
386           overridden when the library functions are called. At build time  it  is
387           conventional to use the standard for your operating system.
388    
389    
390    WHAT \R MATCHES
391    
392           By  default,  the  sequence \R in a pattern matches any Unicode newline
393           sequence, whatever has been selected as the line  ending  sequence.  If
394           you specify
395    
396             --enable-bsr-anycrlf
397    
398           the  default  is changed so that \R matches only CR, LF, or CRLF. What-
399           ever is selected when PCRE is built can be overridden when the  library
400           functions are called.
401    
402    
403  BUILDING SHARED AND STATIC LIBRARIES  BUILDING SHARED AND STATIC LIBRARIES
404    
405         The PCRE building process uses libtool to build both shared and  static         The  PCRE building process uses libtool to build both shared and static
406         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
407         of         of
408    
409           --disable-shared           --disable-shared
# Line 306  BUILDING SHARED AND STATIC LIBRARIES Line 415  BUILDING SHARED AND STATIC LIBRARIES
415  POSIX MALLOC USAGE  POSIX MALLOC USAGE
416    
417         When PCRE is called through the POSIX interface (see the pcreposix doc-         When PCRE is called through the POSIX interface (see the pcreposix doc-
418         umentation),  additional  working  storage  is required for holding the         umentation), additional working storage is  required  for  holding  the
419         pointers to capturing substrings, because PCRE requires three  integers         pointers  to capturing substrings, because PCRE requires three integers
420         per  substring,  whereas  the POSIX interface provides only two. If the         per substring, whereas the POSIX interface provides only  two.  If  the
421         number of expected substrings is small, the wrapper function uses space         number of expected substrings is small, the wrapper function uses space
422         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.
423         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 428  POSIX MALLOC USAGE
428         to the configure command.         to the configure command.
429    
430    
431    HANDLING VERY LARGE PATTERNS
432    
433           Within a compiled pattern, offset values are used  to  point  from  one
434           part  to another (for example, from an opening parenthesis to an alter-
435           nation metacharacter). By default, two-byte values are used  for  these
436           offsets,  leading  to  a  maximum size for a compiled pattern of around
437           64K. This is sufficient to handle all but the most  gigantic  patterns.
438           Nevertheless,  some  people do want to process truyl enormous patterns,
439           so it is possible to compile PCRE to use three-byte or  four-byte  off-
440           sets by adding a setting such as
441    
442             --with-link-size=3
443    
444           to  the  configure  command.  The value given must be 2, 3, or 4. Using
445           longer offsets slows down the operation of PCRE because it has to  load
446           additional bytes when handling them.
447    
448    
449    AVOIDING EXCESSIVE STACK USAGE
450    
451           When matching with the pcre_exec() function, PCRE implements backtrack-
452           ing by making recursive calls to an internal function  called  match().
453           In  environments  where  the size of the stack is limited, this can se-
454           verely limit PCRE's operation. (The Unix environment does  not  usually
455           suffer from this problem, but it may sometimes be necessary to increase
456           the maximum stack size.  There is a discussion in the  pcrestack  docu-
457           mentation.)  An alternative approach to recursion that uses memory from
458           the heap to remember data, instead of using recursive  function  calls,
459           has  been  implemented to work round the problem of limited stack size.
460           If you want to build a version of PCRE that works this way, add
461    
462             --disable-stack-for-recursion
463    
464           to the configure command. With this configuration, PCRE  will  use  the
465           pcre_stack_malloc  and pcre_stack_free variables to call memory manage-
466           ment functions. By default these point to malloc() and free(), but  you
467           can replace the pointers so that your own functions are used instead.
468    
469           Separate  functions  are  provided  rather  than  using pcre_malloc and
470           pcre_free because the  usage  is  very  predictable:  the  block  sizes
471           requested  are  always  the  same,  and  the blocks are always freed in
472           reverse order. A calling program might be able to  implement  optimized
473           functions  that  perform  better  than  malloc()  and free(). PCRE runs
474           noticeably more slowly when built in this way. This option affects only
475           the pcre_exec() function; it is not relevant for pcre_dfa_exec().
476    
477    
478  LIMITING PCRE RESOURCE USAGE  LIMITING PCRE RESOURCE USAGE
479    
480         Internally,  PCRE has a function called match(), which it calls repeat-         Internally,  PCRE has a function called match(), which it calls repeat-
481         edly  (possibly  recursively)  when  matching  a   pattern   with   the         edly  (sometimes  recursively)  when  matching  a  pattern   with   the
482         pcre_exec()  function.  By controlling the maximum number of times this         pcre_exec()  function.  By controlling the maximum number of times this
483         function may be called during a single matching operation, a limit  can         function may be called during a single matching operation, a limit  can
484         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 491  LIMITING PCRE RESOURCE USAGE
491         to  the  configure  command.  This  setting  has  no  effect   on   the         to  the  configure  command.  This  setting  has  no  effect   on   the
492         pcre_dfa_exec() matching function.         pcre_dfa_exec() matching function.
493    
494           In  some  environments  it is desirable to limit the depth of recursive
495           calls of match() more strictly than the total number of calls, in order
496           to  restrict  the maximum amount of stack (or heap, if --disable-stack-
497           for-recursion is specified) that is used. A second limit controls this;
498           it  defaults  to  the  value  that is set for --with-match-limit, which
499           imposes no additional constraints. However, you can set a  lower  limit
500           by adding, for example,
501    
502             --with-match-limit-recursion=10000
503    
504           to  the  configure  command.  This  value can also be overridden at run
505           time.
506    
507    
508    CREATING CHARACTER TABLES AT BUILD TIME
509    
510           PCRE uses fixed tables for processing characters whose code values  are
511           less  than 256. By default, PCRE is built with a set of tables that are
512           distributed in the file pcre_chartables.c.dist. These  tables  are  for
513           ASCII codes only. If you add
514    
515             --enable-rebuild-chartables
516    
517           to  the  configure  command, the distributed tables are no longer used.
518           Instead, a program called dftables is compiled and  run.  This  outputs
519           the source for new set of tables, created in the default locale of your
520           C runtime system. (This method of replacing the tables does not work if
521           you  are cross compiling, because dftables is run on the local host. If
522           you need to create alternative tables when cross  compiling,  you  will
523           have to do so "by hand".)
524    
 HANDLING VERY LARGE PATTERNS  
525    
526         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  
527    
528           --with-link-size=3         PCRE  assumes  by  default that it will run in an environment where the
529           character code is ASCII (or Unicode, which is  a  superset  of  ASCII).
530           This  is  the  case for most computer operating systems. PCRE can, how-
531           ever, be compiled to run in an EBCDIC environment by adding
532    
533         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.  
534    
535         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-
536         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
537         representation of the compiled pattern, and this changes with the  link         environment (for example,  an  IBM  mainframe  operating  system).  The
538         size.         --enable-ebcdic option is incompatible with --enable-utf8.
539    
540    
541  AVOIDING EXCESSIVE STACK USAGE  PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT
542    
543         When matching with the pcre_exec() function, PCRE implements backtrack-         By default, pcregrep reads all files as plain text. You can build it so
544         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
545         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  
546    
547           --disable-stack-for-recursion           --enable-pcregrep-libz
548             --enable-pcregrep-libbz2
549    
550         to the configure command. With this configuration, PCRE  will  use  the         to the configure command. These options naturally require that the rel-
551         pcre_stack_malloc  and pcre_stack_free variables to call memory manage-         evant libraries are installed on your system. Configuration  will  fail
552         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.  
553    
554    
555  USING EBCDIC CODE  PCRETEST OPTION FOR LIBREADLINE SUPPORT
556    
557         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  
558    
559           --enable-ebcdic           --enable-pcretest-libreadline
560    
561         to the configure command.         to  the  configure  command,  pcretest  is  linked with the libreadline
562           library, and when its input is from a terminal, it reads it  using  the
563           readline() function. This provides line-editing and history facilities.
564           Note that libreadline is GPL-licensed, so if you distribute a binary of
565           pcretest linked in this way, there may be licensing issues.
566    
567           Setting  this  option  causes  the -lreadline option to be added to the
568           pcretest build. In many operating environments with  a  sytem-installed
569           libreadline this is sufficient. However, in some environments (e.g.  if
570           an unmodified distribution version of readline is in use),  some  extra
571           configuration  may  be necessary. The INSTALL file for libreadline says
572           this:
573    
574             "Readline uses the termcap functions, but does not link with the
575             termcap or curses library itself, allowing applications which link
576             with readline the to choose an appropriate library."
577    
578           If your environment has not been set up so that an appropriate  library
579           is automatically included, you may need to add something like
580    
581  Last updated: 15 August 2005           LIBS="-ncurses"
582  Copyright (c) 1997-2005 University of Cambridge.  
583           immediately before the configure command.
584    
585    
586    SEE ALSO
587    
588           pcreapi(3), pcre_config(3).
589    
590    
591    AUTHOR
592    
593           Philip Hazel
594           University Computing Service
595           Cambridge CB2 3QH, England.
596    
597    
598    REVISION
599    
600           Last updated: 29 September 2009
601           Copyright (c) 1997-2009 University of Cambridge.
602  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
603    
604    
# Line 431  PCRE MATCHING ALGORITHMS Line 634  PCRE MATCHING ALGORITHMS
634           <something> <something else> <something further>           <something> <something else> <something further>
635    
636         there are three possible answers. The standard algorithm finds only one         there are three possible answers. The standard algorithm finds only one
637         of them, whereas the DFA algorithm finds all three.         of them, whereas the alternative algorithm finds all three.
638    
639    
640  REGULAR EXPRESSIONS AS TREES  REGULAR EXPRESSIONS AS TREES
# Line 440  REGULAR EXPRESSIONS AS TREES Line 643  REGULAR EXPRESSIONS AS TREES
643         resented  as  a  tree structure. An unlimited repetition in the pattern         resented  as  a  tree structure. An unlimited repetition in the pattern
644         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
645         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
646         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
647         search  a  tree: depth-first and breadth-first, and these correspond to         tree:  depth-first  and  breadth-first, and these correspond to the two
648         the two matching algorithms provided by PCRE.         matching algorithms provided by PCRE.
649    
650    
651  THE STANDARD MATCHING ALGORITHM  THE STANDARD MATCHING ALGORITHM
652    
653         In the terminology of Jeffrey Friedl's book Mastering  Regular  Expres-         In the terminology of Jeffrey Friedl's book "Mastering Regular  Expres-
654         sions,  the  standard  algorithm  is  an "NFA algorithm". It conducts a         sions",  the  standard  algorithm  is an "NFA algorithm". It conducts a
655         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
656         single path through the tree, checking that the subject matches what is         single path through the tree, checking that the subject matches what is
657         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 675  THE STANDARD MATCHING ALGORITHM
675         This provides support for capturing parentheses and back references.         This provides support for capturing parentheses and back references.
676    
677    
678  THE DFA MATCHING ALGORITHM  THE ALTERNATIVE MATCHING ALGORITHM
679    
680         DFA stands for "deterministic finite automaton", but you do not need to         This algorithm conducts a breadth-first search of  the  tree.  Starting
681         understand the origins of that name. This algorithm conducts a breadth-         from  the  first  matching  point  in the subject, it scans the subject
682         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
683         subject,  it scans the subject string from left to right, once, charac-         this,  it remembers all the paths through the tree that represent valid
684         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",
685         through the tree that represent valid matches.         though  it is not implemented as a traditional finite state machine (it
686           keeps multiple states active simultaneously).
687         The  scan  continues until either the end of the subject is reached, or  
688         there are no more unterminated paths. At this point,  terminated  paths         Although the general principle of this matching algorithm  is  that  it
689         represent  the different matching possibilities (if there are none, the         scans  the subject string only once, without backtracking, there is one
690         match has failed).  Thus, if there is more  than  one  possible  match,         exception: when a lookaround assertion is encountered,  the  characters
691           following  or  preceding  the  current  point  have to be independently
692           inspected.
693    
694           The scan continues until either the end of the subject is  reached,  or
695           there  are  no more unterminated paths. At this point, terminated paths
696           represent the different matching possibilities (if there are none,  the
697           match  has  failed).   Thus,  if there is more than one possible match,
698         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-
699         est. In PCRE, there is an option to stop the algorithm after the  first         est.  The  matches are returned in decreasing order of length. There is
700         match (which is necessarily the shortest) has been found.         an option to stop the algorithm after the first match (which is  neces-
701           sarily 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 "caterpillar", "cater", and "cat" that start
710         at the fourth character of the subject. The algorithm does not automat-         at the fifth character of the subject. The algorithm does not automati-
711         ically move on to find matches that start at later positions.         cally 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
# Line 516  THE DFA MATCHING ALGORITHM Line 737  THE DFA MATCHING ALGORITHM
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    
 ADVANTAGES OF THE DFA ALGORITHM  
760    
761         Using the DFA matching algorithm provides the following advantages:  ADVANTAGES OF THE ALTERNATIVE ALGORITHM
762    
763           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. Although it is possible to do multi-
775         able.         segment matching using the standard algorithm (pcre_exec()), by retain-
776           ing  partially matched substrings, it is more complicated. The pcrepar-
777           tial documentation gives details  of  partial  matching  and  discusses
778           multi-segment matching.
779    
        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.  
780    
781    DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
782    
783  DISADVANTAGES OF THE DFA ALGORITHM         The alternative algorithm suffers from a number of disadvantages:
784    
785         The DFA algorithm suffers from a number of disadvantages:         1.  It  is  substantially  slower  than the standard algorithm. This is
786           partly because it has to search for all possible matches, but  is  also
        1. It is substantially slower than  the  standard  algorithm.  This  is  
        partly  because  it has to search for all possible matches, but is also  
787         because it is less susceptible to optimization.         because it is less susceptible to optimization.
788    
789         2. Capturing parentheses and back references are not supported.         2. Capturing parentheses and back references are not supported.
790    
791         3. The "atomic group" feature of PCRE regular expressions is supported,         3. Although atomic groups are supported, their use does not provide the
792         but  does not provide the advantage that it does for the standard algo-         performance advantage that it does for the standard algorithm.
793         rithm.  
794    
795  Last updated: 28 February 2005  AUTHOR
796  Copyright (c) 1997-2005 University of Cambridge.  
797           Philip Hazel
798           University Computing Service
799           Cambridge CB2 3QH, England.
800    
801    
802    REVISION
803    
804           Last updated: 17 November 2010
805           Copyright (c) 1997-2010 University of Cambridge.
806  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
807    
808    
# Line 616  PCRE NATIVE API Line 855  PCRE NATIVE API
855         int pcre_get_stringnumber(const pcre *code,         int pcre_get_stringnumber(const pcre *code,
856              const char *name);              const char *name);
857    
858           int pcre_get_stringtable_entries(const pcre *code,
859                const char *name, char **first, char **last);
860    
861         int pcre_get_substring(const char *subject, int *ovector,         int pcre_get_substring(const char *subject, int *ovector,
862              int stringcount, int stringnumber,              int stringcount, int stringnumber,
863              const char **stringptr);              const char **stringptr);
# Line 654  PCRE NATIVE API Line 896  PCRE NATIVE API
896  PCRE API OVERVIEW  PCRE API OVERVIEW
897    
898         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
899         is also a set of wrapper functions that correspond to the POSIX regular         are also some wrapper functions that correspond to  the  POSIX  regular
900         expression  API.  These  are  described in the pcreposix documentation.         expression  API.  These  are  described in the pcreposix documentation.
901         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
902         distributed with PCRE. It is documented in the pcrecpp page.         distributed with PCRE. It is documented in the pcrecpp page.
# Line 667  PCRE API OVERVIEW Line 909  PCRE API OVERVIEW
909         bers for the library.  Applications can use these  to  include  support         bers for the library.  Applications can use these  to  include  support
910         for different releases of PCRE.         for different releases of PCRE.
911    
912           In a Windows environment, if you want to statically link an application
913           program against a non-dll pcre.a  file,  you  must  define  PCRE_STATIC
914           before  including  pcre.h or pcrecpp.h, because otherwise the pcre_mal-
915           loc()   and   pcre_free()   exported   functions   will   be   declared
916           __declspec(dllimport), with unwanted results.
917    
918         The   functions   pcre_compile(),  pcre_compile2(),  pcre_study(),  and         The   functions   pcre_compile(),  pcre_compile2(),  pcre_study(),  and
919         pcre_exec() are used for compiling and matching regular expressions  in         pcre_exec() are used for compiling and matching regular expressions  in
920         a  Perl-compatible  manner. A sample program that demonstrates the sim-         a  Perl-compatible  manner. A sample program that demonstrates the sim-
921         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
922         the  source distribution. The pcresample documentation describes how to         the PCRE source distribution. A listing of this program is given in the
923         run it.         pcredemo documentation, and the pcresample documentation describes  how
924           to compile and run it.
925    
926         A second matching function, pcre_dfa_exec(), which is not Perl-compati-         A second matching function, pcre_dfa_exec(), which is not Perl-compati-
927         ble,  is  also provided. This uses a different algorithm for the match-         ble, is also provided. This uses a different algorithm for  the  match-
928         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
929         the  subject),  not  just  one. However, this algorithm does not return         point in the subject), and scans the subject just  once  (unless  there
930           are  lookbehind  assertions).  However,  this algorithm does not return
931         captured substrings. A description of the two matching  algorithms  and         captured substrings. A description of the two matching  algorithms  and
932         their  advantages  and disadvantages is given in the pcrematching docu-         their  advantages  and disadvantages is given in the pcrematching docu-
933         mentation.         mentation.
# Line 692  PCRE API OVERVIEW Line 942  PCRE API OVERVIEW
942           pcre_get_named_substring()           pcre_get_named_substring()
943           pcre_get_substring_list()           pcre_get_substring_list()
944           pcre_get_stringnumber()           pcre_get_stringnumber()
945             pcre_get_stringtable_entries()
946    
947         pcre_free_substring() and pcre_free_substring_list() are also provided,         pcre_free_substring() and pcre_free_substring_list() are also provided,
948         to free the memory used for extracted strings.         to free the memory used for extracted strings.
# Line 723  PCRE API OVERVIEW Line 974  PCRE API OVERVIEW
974         indirections  to  memory  management functions. These special functions         indirections  to  memory  management functions. These special functions
975         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
976         data, instead of recursive function calls, when running the pcre_exec()         data, instead of recursive function calls, when running the pcre_exec()
977         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
978         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-
979         management, it runs more slowly.  Separate functions  are  provided  so         ments that have limited stacks. Because of the greater  use  of  memory
980         that  special-purpose  external  code  can  be used for this case. When         management,  it  runs  more  slowly. Separate functions are provided so
981         used, these functions are always called in a  stack-like  manner  (last         that special-purpose external code can be  used  for  this  case.  When
982         obtained,  first freed), and always for memory blocks of the same size.         used,  these  functions  are always called in a stack-like manner (last
983           obtained, first freed), and always for memory blocks of the same  size.
984           There  is  a discussion about PCRE's stack usage in the pcrestack docu-
985           mentation.
986    
987         The global variable pcre_callout initially contains NULL. It can be set         The global variable pcre_callout initially contains NULL. It can be set
988         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 990  PCRE API OVERVIEW
990         pcrecallout documentation.         pcrecallout documentation.
991    
992    
993    NEWLINES
994    
995           PCRE  supports five different conventions for indicating line breaks in
996           strings: a single CR (carriage return) character, a  single  LF  (line-
997           feed) character, the two-character sequence CRLF, any of the three pre-
998           ceding, or any Unicode newline sequence. The Unicode newline  sequences
999           are  the  three just mentioned, plus the single characters VT (vertical
1000           tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS  (line
1001           separator, U+2028), and PS (paragraph separator, U+2029).
1002    
1003           Each  of  the first three conventions is used by at least one operating
1004           system as its standard newline sequence. When PCRE is built, a  default
1005           can  be  specified.  The default default is LF, which is the Unix stan-
1006           dard. When PCRE is run, the default can be overridden,  either  when  a
1007           pattern is compiled, or when it is matched.
1008    
1009           At compile time, the newline convention can be specified by the options
1010           argument of pcre_compile(), or it can be specified by special  text  at
1011           the start of the pattern itself; this overrides any other settings. See
1012           the pcrepattern page for details of the special character sequences.
1013    
1014           In the PCRE documentation the word "newline" is used to mean "the char-
1015           acter  or pair of characters that indicate a line break". The choice of
1016           newline convention affects the handling of  the  dot,  circumflex,  and
1017           dollar metacharacters, the handling of #-comments in /x mode, and, when
1018           CRLF is a recognized line ending sequence, the match position  advance-
1019           ment for a non-anchored pattern. There is more detail about this in the
1020           section on pcre_exec() options below.
1021    
1022           The choice of newline convention does not affect the interpretation  of
1023           the  \n  or  \r  escape  sequences, nor does it affect what \R matches,
1024           which is controlled in a similar way, but by separate options.
1025    
1026    
1027  MULTITHREADING  MULTITHREADING
1028    
1029         The  PCRE  functions  can be used in multi-threading applications, with         The PCRE functions can be used in  multi-threading  applications,  with
1030         the  proviso  that  the  memory  management  functions  pointed  to  by         the  proviso  that  the  memory  management  functions  pointed  to  by
1031         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
1032         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 1041  SAVING PRECOMPILED PATTERNS FOR LATER US
1041         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
1042         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
1043         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
1044         pcreprecompile documentation.         pcreprecompile documentation. However, compiling a  regular  expression
1045           with  one version of PCRE for use with a different version is not guar-
1046           anteed to work and may cause crashes.
1047    
1048    
1049  CHECKING BUILD-TIME OPTIONS  CHECKING BUILD-TIME OPTIONS
# Line 782  CHECKING BUILD-TIME OPTIONS Line 1072  CHECKING BUILD-TIME OPTIONS
1072    
1073           PCRE_CONFIG_NEWLINE           PCRE_CONFIG_NEWLINE
1074    
1075         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
1076         used  for the newline character. It is either linefeed (10) or carriage         sequence  that is recognized as meaning "newline". The four values that
1077         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,
1078         operating system.         and  -1  for  ANY.  Though they are derived from ASCII, the same values
1079           are returned in EBCDIC environments. The default should normally corre-
1080           spond to the standard sequence for your operating system.
1081    
1082             PCRE_CONFIG_BSR
1083    
1084           The output is an integer whose value indicates what character sequences
1085           the \R escape sequence matches by default. A value of 0 means  that  \R
1086           matches  any  Unicode  line ending sequence; a value of 1 means that \R
1087           matches only CR, LF, or CRLF. The default can be overridden when a pat-
1088           tern is compiled or matched.
1089    
1090           PCRE_CONFIG_LINK_SIZE           PCRE_CONFIG_LINK_SIZE
1091    
# Line 804  CHECKING BUILD-TIME OPTIONS Line 1104  CHECKING BUILD-TIME OPTIONS
1104    
1105           PCRE_CONFIG_MATCH_LIMIT           PCRE_CONFIG_MATCH_LIMIT
1106    
1107         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-
1108         internal  matching  function  calls in a pcre_exec() execution. Further         ber  of  internal  matching  function calls in a pcre_exec() execution.
1109         details are given with pcre_exec() below.         Further details are given with pcre_exec() below.
1110    
1111             PCRE_CONFIG_MATCH_LIMIT_RECURSION
1112    
1113           The output is a long integer that gives the default limit for the depth
1114           of   recursion  when  calling  the  internal  matching  function  in  a
1115           pcre_exec() execution.  Further  details  are  given  with  pcre_exec()
1116           below.
1117    
1118           PCRE_CONFIG_STACKRECURSE           PCRE_CONFIG_STACKRECURSE
1119    
1120         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
1121         running pcre_exec() is implemented by recursive function calls that use         running pcre_exec() is implemented by recursive function calls that use
1122         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
1123         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
1124         on the  heap  instead  of  recursive  function  calls.  In  this  case,         on  the  heap  instead  of  recursive  function  calls.  In  this case,
1125         pcre_stack_malloc  and  pcre_stack_free  are  called  to  manage memory         pcre_stack_malloc and  pcre_stack_free  are  called  to  manage  memory
1126         blocks on the heap, thus avoiding the use of the stack.         blocks on the heap, thus avoiding the use of the stack.
1127    
1128    
# Line 832  COMPILING A PATTERN Line 1139  COMPILING A PATTERN
1139    
1140         Either of the functions pcre_compile() or pcre_compile2() can be called         Either of the functions pcre_compile() or pcre_compile2() can be called
1141         to compile a pattern into an internal form. The only difference between         to compile a pattern into an internal form. The only difference between
1142         the two interfaces is that pcre_compile2() has an additional  argument,         the  two interfaces is that pcre_compile2() has an additional argument,
1143         errorcodeptr, via which a numerical error code can be returned.         errorcodeptr, via which a numerical error  code  can  be  returned.  To
1144           avoid  too  much repetition, we refer just to pcre_compile() below, but
1145           the information applies equally to pcre_compile2().
1146    
1147         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
1148         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
1149         obtained  via  pcre_malloc is returned. This contains the compiled code         obtained via pcre_malloc is returned. This contains the  compiled  code
1150         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
1151         is a typedef for a structure whose contents are not externally defined.         is a typedef for a structure whose contents are not externally defined.
1152         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
1153         required.         longer required.
1154    
1155         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
1156         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
1157         fully  relocatable, because it may contain a copy of the tableptr argu-         fully relocatable, because it may contain a copy of the tableptr  argu-
1158         ment, which is an address (see below).         ment, which is an address (see below).
1159    
1160         The options argument contains independent bits that affect the compila-         The options argument contains various bit settings that affect the com-
1161         tion.  It  should  be  zero  if  no options are required. The available         pilation. It should be zero if no options are required.  The  available
1162         options are described below. Some of them, in  particular,  those  that         options  are  described  below. Some of them (in particular, those that
1163         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
1164         pattern (see the detailed description  in  the  pcrepattern  documenta-         unset  from  within  the  pattern  (see the detailed description in the
1165         tion).  For  these options, the contents of the options argument speci-         pcrepattern documentation). For those options that can be different  in
1166         fies their initial settings at the start of compilation and  execution.         different  parts  of  the pattern, the contents of the options argument
1167         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
1168           PCRE_ANCHORED,  PCRE_BSR_xxx, PCRE_NEWLINE_xxx, PCRE_NO_UTF8_CHECK, and
1169           PCRE_NO_START_OPT options can be set at the time of matching as well as
1170         at compile time.         at compile time.
1171    
1172         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
1173         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and         if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and
1174         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-
1175         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
1176         the error was discovered is  placed  in  the  variable  pointed  to  by         try  to  free  it. The offset from the start of the pattern to the byte
1177         erroffset,  which  must  not  be  NULL. If it is, an immediate error is         that was being processed when the error was discovered is placed in the
1178         given.         variable  pointed to by erroffset, which must not be NULL. If it is, an
1179           immediate error is given. Some errors are not detected until checks are
1180           carried  out  when the whole pattern has been scanned; in this case the
1181           offset is set to the end of the pattern.
1182    
1183           Note that the offset is in bytes, not characters, even in  UTF-8  mode.
1184           It  may  point  into the middle of a UTF-8 character (for example, when
1185           PCRE_ERROR_BADUTF8 is returned for an invalid UTF-8 string).
1186    
1187         If pcre_compile2() is used instead of pcre_compile(),  and  the  error-         If pcre_compile2() is used instead of pcre_compile(),  and  the  error-
1188         codeptr  argument is not NULL, a non-zero error code number is returned         codeptr  argument is not NULL, a non-zero error code number is returned
# Line 909  COMPILING A PATTERN Line 1227  COMPILING A PATTERN
1227         all with number 255, before each pattern item. For  discussion  of  the         all with number 255, before each pattern item. For  discussion  of  the
1228         callout facility, see the pcrecallout documentation.         callout facility, see the pcrecallout documentation.
1229    
1230             PCRE_BSR_ANYCRLF
1231             PCRE_BSR_UNICODE
1232    
1233           These options (which are mutually exclusive) control what the \R escape
1234           sequence matches. The choice is either to match only CR, LF,  or  CRLF,
1235           or to match any Unicode newline sequence. The default is specified when
1236           PCRE is built. It can be overridden from within the pattern, or by set-
1237           ting an option when a compiled pattern is matched.
1238    
1239           PCRE_CASELESS           PCRE_CASELESS
1240    
1241         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
# Line 926  COMPILING A PATTERN Line 1253  COMPILING A PATTERN
1253    
1254         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
1255         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
1256         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
1257         not  before  any  other  newlines).  The  PCRE_DOLLAR_ENDONLY option is         before  any  other newlines). The PCRE_DOLLAR_ENDONLY option is ignored
1258         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
1259         in Perl, and no way to set it within a pattern.         Perl, and no way to set it within a pattern.
1260    
1261           PCRE_DOTALL           PCRE_DOTALL
1262    
1263         If this bit is set, a dot metacharater in the pattern matches all char-         If  this bit is set, a dot metacharacter in the pattern matches a char-
1264         acters, including newlines. Without it,  newlines  are  excluded.  This         acter of any value, including one that indicates a newline. However, it
1265         option  is equivalent to Perl's /s option, and it can be changed within         only  ever  matches  one character, even if newlines are coded as CRLF.
1266         a pattern by a (?s) option setting.  A  negative  class  such  as  [^a]         Without this option, a dot does not match when the current position  is
1267         always  matches a newline character, independent of the setting of this         at a newline. This option is equivalent to Perl's /s option, and it can
1268         option.         be changed within a pattern by a (?s) option setting. A negative  class
1269           such as [^a] always matches newline characters, independent of the set-
1270           ting of this option.
1271    
1272             PCRE_DUPNAMES
1273    
1274           If this bit is set, names used to identify capturing  subpatterns  need
1275           not be unique. This can be helpful for certain types of pattern when it
1276           is known that only one instance of the named  subpattern  can  ever  be
1277           matched.  There  are  more details of named subpatterns below; see also
1278           the pcrepattern documentation.
1279    
1280           PCRE_EXTENDED           PCRE_EXTENDED
1281    
# Line 946  COMPILING A PATTERN Line 1283  COMPILING A PATTERN
1283         totally ignored except when escaped or inside a character class. White-         totally ignored except when escaped or inside a character class. White-
1284         space does not include the VT character (code 11). In addition, charac-         space does not include the VT character (code 11). In addition, charac-
1285         ters between an unescaped # outside a character class and the next new-         ters between an unescaped # outside a character class and the next new-
1286         line character, inclusive, are also  ignored.  This  is  equivalent  to         line, inclusive, are also ignored. This  is  equivalent  to  Perl's  /x
1287         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-
1288         option setting.         ting.
1289    
1290         This option makes it possible to include  comments  inside  complicated         Which characters are interpreted  as  newlines  is  controlled  by  the
1291         patterns.   Note,  however,  that this applies only to data characters.         options  passed to pcre_compile() or by a special sequence at the start
1292         Whitespace  characters  may  never  appear  within  special   character         of the pattern, as described in the section entitled  "Newline  conven-
1293         sequences  in  a  pattern,  for  example  within the sequence (?( which         tions" in the pcrepattern documentation. Note that the end of this type
1294         introduces a conditional subpattern.         of comment is  a  literal  newline  sequence  in  the  pattern;  escape
1295           sequences that happen to represent a newline do not count.
1296    
1297           This  option  makes  it possible to include comments inside complicated
1298           patterns.  Note, however, that this applies only  to  data  characters.
1299           Whitespace   characters  may  never  appear  within  special  character
1300           sequences in a pattern, for example within the sequence (?( that intro-
1301           duces a conditional subpattern.
1302    
1303           PCRE_EXTRA           PCRE_EXTRA
1304    
1305         This option was invented in order to turn on  additional  functionality         This  option  was invented in order to turn on additional functionality
1306         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
1307         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
1308         letter  that  has  no  special  meaning causes an error, thus reserving         letter that has no special meaning  causes  an  error,  thus  reserving
1309         these combinations for future expansion. By  default,  as  in  Perl,  a         these  combinations  for  future  expansion.  By default, as in Perl, a
1310         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
1311         literal. There are at present no  other  features  controlled  by  this         literal. (Perl can, however, be persuaded to give an error for this, by
1312         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
1313           controlled  by this option. It can also be set by a (?X) option setting
1314           within a pattern.
1315    
1316           PCRE_FIRSTLINE           PCRE_FIRSTLINE
1317    
1318         If  this  option  is  set,  an  unanchored pattern is required to match         If this option is set, an  unanchored  pattern  is  required  to  match
1319         before or at the first newline character in the subject string,  though         before  or  at  the  first  newline  in  the subject string, though the
1320         the matched text may continue over the newline.         matched text may continue over the newline.
1321    
1322             PCRE_JAVASCRIPT_COMPAT
1323    
1324           If this option is set, PCRE's behaviour is changed in some ways so that
1325           it  is  compatible with JavaScript rather than Perl. The changes are as
1326           follows:
1327    
1328           (1) A lone closing square bracket in a pattern  causes  a  compile-time
1329           error,  because this is illegal in JavaScript (by default it is treated
1330           as a data character). Thus, the pattern AB]CD becomes illegal when this
1331           option is set.
1332    
1333           (2)  At run time, a back reference to an unset subpattern group matches
1334           an empty string (by default this causes the current  matching  alterna-
1335           tive  to  fail). A pattern such as (\1)(a) succeeds when this option is
1336           set (assuming it can find an "a" in the subject), whereas it  fails  by
1337           default, for Perl compatibility.
1338    
1339           PCRE_MULTILINE           PCRE_MULTILINE
1340    
# Line 983  COMPILING A PATTERN Line 1346  COMPILING A PATTERN
1346         is set). This is the same as Perl.         is set). This is the same as Perl.
1347    
1348         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"
1349         constructs  match  immediately following or immediately before any new-         constructs  match  immediately following or immediately before internal
1350         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
1351         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
1352         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-
1353         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,
1354         setting PCRE_MULTILINE has no effect.         setting PCRE_MULTILINE has no effect.
1355    
1356             PCRE_NEWLINE_CR
1357             PCRE_NEWLINE_LF
1358             PCRE_NEWLINE_CRLF
1359             PCRE_NEWLINE_ANYCRLF
1360             PCRE_NEWLINE_ANY
1361    
1362           These options override the default newline definition that  was  chosen
1363           when  PCRE  was built. Setting the first or the second specifies that a
1364           newline is indicated by a single character (CR  or  LF,  respectively).
1365           Setting  PCRE_NEWLINE_CRLF specifies that a newline is indicated by the
1366           two-character CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF  specifies
1367           that any of the three preceding sequences should be recognized. Setting
1368           PCRE_NEWLINE_ANY specifies that any Unicode newline sequence should  be
1369           recognized. The Unicode newline sequences are the three just mentioned,
1370           plus the single characters VT (vertical  tab,  U+000B),  FF  (formfeed,
1371           U+000C),  NEL  (next line, U+0085), LS (line separator, U+2028), and PS
1372           (paragraph separator, U+2029). The last  two  are  recognized  only  in
1373           UTF-8 mode.
1374    
1375           The  newline  setting  in  the  options  word  uses three bits that are
1376           treated as a number, giving eight possibilities. Currently only six are
1377           used  (default  plus the five values above). This means that if you set
1378           more than one newline option, the combination may or may not be  sensi-
1379           ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
1380           PCRE_NEWLINE_CRLF, but other combinations may yield unused numbers  and
1381           cause an error.
1382    
1383           The  only  time  that a line break in a pattern is specially recognized
1384           when compiling is when PCRE_EXTENDED is set. CR and LF  are  whitespace
1385           characters,  and so are ignored in this mode. Also, an unescaped # out-
1386           side a character class indicates a comment that lasts until  after  the
1387           next  line break sequence. In other circumstances, line break sequences
1388           in patterns are treated as literal data.
1389    
1390           The newline option that is set at compile time becomes the default that
1391           is used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
1392    
1393           PCRE_NO_AUTO_CAPTURE           PCRE_NO_AUTO_CAPTURE
1394    
1395         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-
1396         theses  in the pattern. Any opening parenthesis that is not followed by         theses in the pattern. Any opening parenthesis that is not followed  by
1397         ? behaves as if it were followed by ?: but named parentheses can  still         ?  behaves as if it were followed by ?: but named parentheses can still
1398         be  used  for  capturing  (and  they acquire numbers in the usual way).         be used for capturing (and they acquire  numbers  in  the  usual  way).
1399         There is no equivalent of this option in Perl.         There is no equivalent of this option in Perl.
1400    
1401             NO_START_OPTIMIZE
1402    
1403           This  is an option that acts at matching time; that is, it is really an
1404           option for pcre_exec() or pcre_dfa_exec(). If  it  is  set  at  compile
1405           time,  it is remembered with the compiled pattern and assumed at match-
1406           ing time. For details  see  the  discussion  of  PCRE_NO_START_OPTIMIZE
1407           below.
1408    
1409             PCRE_UCP
1410    
1411           This  option changes the way PCRE processes \B, \b, \D, \d, \S, \s, \W,
1412           \w, and some of the POSIX character classes.  By  default,  only  ASCII
1413           characters  are  recognized, but if PCRE_UCP is set, Unicode properties
1414           are used instead to classify characters. More details are given in  the
1415           section  on generic character types in the pcrepattern page. If you set
1416           PCRE_UCP, matching one of the items it affects takes much  longer.  The
1417           option  is  available only if PCRE has been compiled with Unicode prop-
1418           erty support.
1419    
1420           PCRE_UNGREEDY           PCRE_UNGREEDY
1421    
1422         This option inverts the "greediness" of the quantifiers  so  that  they         This option inverts the "greediness" of the quantifiers  so  that  they
# Line 1017  COMPILING A PATTERN Line 1436  COMPILING A PATTERN
1436           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
1437    
1438         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
1439         automatically  checked. If an invalid UTF-8 sequence of bytes is found,         automatically  checked.  There  is  a  discussion about the validity of
1440         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
1441         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
1442         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-
1443         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
1444         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
1445         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
1446         ing of subject strings.         can also be passed to pcre_exec() and pcre_dfa_exec(), to suppress  the
1447           UTF-8 validity checking of subject strings.
1448    
1449    
1450  COMPILATION ERROR CODES  COMPILATION ERROR CODES
1451    
1452         The following table lists the error  codes  than  may  be  returned  by         The  following  table  lists  the  error  codes than may be returned by
1453         pcre_compile2(),  along with the error messages that may be returned by         pcre_compile2(), along with the error messages that may be returned  by
1454         both compiling functions.         both  compiling functions. As PCRE has developed, some error codes have
1455           fallen out of use. To avoid confusion, they have not been re-used.
1456    
1457            0  no error            0  no error
1458            1  \ at end of pattern            1  \ at end of pattern
# Line 1043  COMPILATION ERROR CODES Line 1464  COMPILATION ERROR CODES
1464            7  invalid escape sequence in character class            7  invalid escape sequence in character class
1465            8  range out of order in character class            8  range out of order in character class
1466            9  nothing to repeat            9  nothing to repeat
1467           10  operand of unlimited repeat could match the empty string           10  [this code is not in use]
1468           11  internal error: unexpected repeat           11  internal error: unexpected repeat
1469           12  unrecognized character after (?           12  unrecognized character after (? or (?-
1470           13  POSIX named classes are supported only within a class           13  POSIX named classes are supported only within a class
1471           14  missing )           14  missing )
1472           15  reference to non-existent subpattern           15  reference to non-existent subpattern
1473           16  erroffset passed as NULL           16  erroffset passed as NULL
1474           17  unknown option bit(s) set           17  unknown option bit(s) set
1475           18  missing ) after comment           18  missing ) after comment
1476           19  parentheses nested too deeply           19  [this code is not in use]
1477           20  regular expression too large           20  regular expression is too large
1478           21  failed to get memory           21  failed to get memory
1479           22  unmatched parentheses           22  unmatched parentheses
1480           23  internal error: code overflow           23  internal error: code overflow
1481           24  unrecognized character after (?<           24  unrecognized character after (?<
1482           25  lookbehind assertion is not fixed length           25  lookbehind assertion is not fixed length
1483           26  malformed number after (?(           26  malformed number or name after (?(
1484           27  conditional group contains more than two branches           27  conditional group contains more than two branches
1485           28  assertion expected after (?(           28  assertion expected after (?(
1486           29  (?R or (?digits must be followed by )           29  (?R or (?[+-]digits must be followed by )
1487           30  unknown POSIX class name           30  unknown POSIX class name
1488           31  POSIX collating elements are not supported           31  POSIX collating elements are not supported
1489           32  this version of PCRE is not compiled with PCRE_UTF8 support           32  this version of PCRE is not compiled with PCRE_UTF8 support
1490           33  spare error           33  [this code is not in use]
1491           34  character value in \x{...} sequence is too large           34  character value in \x{...} sequence is too large
1492           35  invalid condition (?(0)           35  invalid condition (?(0)
1493           36  \C not allowed in lookbehind assertion           36  \C not allowed in lookbehind assertion
# Line 1075  COMPILATION ERROR CODES Line 1496  COMPILATION ERROR CODES
1496           39  closing ) for (?C expected           39  closing ) for (?C expected
1497           40  recursive call could loop indefinitely           40  recursive call could loop indefinitely
1498           41  unrecognized character after (?P           41  unrecognized character after (?P
1499           42  syntax error after (?P           42  syntax error in subpattern name (missing terminator)
1500           43  two named groups have the same name           43  two named subpatterns have the same name
1501           44  invalid UTF-8 string           44  invalid UTF-8 string
1502           45  support for \P, \p, and \X has not been compiled           45  support for \P, \p, and \X has not been compiled
1503           46  malformed \P or \p sequence           46  malformed \P or \p sequence
1504           47  unknown property name after \P or \p           47  unknown property name after \P or \p
1505             48  subpattern name is too long (maximum 32 characters)
1506             49  too many named subpatterns (maximum 10000)
1507             50  [this code is not in use]
1508             51  octal value is greater than \377 (not in UTF-8 mode)
1509             52  internal error: overran compiling workspace
1510             53  internal error: previously-checked referenced subpattern
1511                   not found
1512             54  DEFINE group contains more than one branch
1513             55  repeating a DEFINE group is not allowed
1514             56  inconsistent NEWLINE options
1515             57  \g is not followed by a braced, angle-bracketed, or quoted
1516                   name/number or by a plain number
1517             58  a numbered reference must not be zero
1518             59  an argument is not allowed for (*ACCEPT), (*FAIL), or (*COMMIT)
1519             60  (*VERB) not recognized
1520             61  number is too big
1521             62  subpattern name expected
1522             63  digit expected after (?+
1523             64  ] is an invalid data character in JavaScript compatibility mode
1524             65  different names for subpatterns of the same number are
1525                   not allowed
1526             66  (*MARK) must have an argument
1527             67  this version of PCRE is not compiled with PCRE_UCP support
1528    
1529           The numbers 32 and 10000 in errors 48 and 49  are  defaults;  different
1530           values may be used if the limits were changed when PCRE was built.
1531    
1532    
1533  STUDYING A PATTERN  STUDYING A PATTERN
# Line 1088  STUDYING A PATTERN Line 1535  STUDYING A PATTERN
1535         pcre_extra *pcre_study(const pcre *code, int options         pcre_extra *pcre_study(const pcre *code, int options
1536              const char **errptr);              const char **errptr);
1537    
1538         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
1539         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
1540         matching. The function pcre_study() takes a pointer to a compiled  pat-         matching.  The function pcre_study() takes a pointer to a compiled pat-
1541         tern as its first argument. If studying the pattern produces additional         tern as its first argument. If studying the pattern produces additional
1542         information that will help speed up matching,  pcre_study()  returns  a         information  that  will  help speed up matching, pcre_study() returns a
1543         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
1544         the results of the study.         the results of the study.
1545    
1546         The  returned  value  from  pcre_study()  can  be  passed  directly  to         The  returned  value  from  pcre_study()  can  be  passed  directly  to
1547         pcre_exec().  However,  a  pcre_extra  block also contains other fields         pcre_exec() or pcre_dfa_exec(). However, a pcre_extra block  also  con-
1548         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
1549         described below in the section on matching a pattern.         passed; these are described below in the section on matching a pattern.
1550    
1551         If  studying  the  pattern  does not produce any additional information         If studying the  pattern  does  not  produce  any  useful  information,
1552         pcre_study() returns NULL. In that circumstance, if the calling program         pcre_study() returns NULL. In that circumstance, if the calling program
1553         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
1554         its own pcre_extra block.         pcre_dfa_exec(), it must set up its own pcre_extra block.
1555    
1556         The second argument of pcre_study() contains option bits.  At  present,         The  second  argument of pcre_study() contains option bits. At present,
1557         no options are defined, and this argument should always be zero.         no options are defined, and this argument should always be zero.
1558    
1559         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.
1560         If studying succeeds (even if no data is  returned),  the  variable  it         If  studying  succeeds  (even  if no data is returned), the variable it
1561         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
1562         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
1563         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
1564           after calling pcre_study(), to be sure that it has run successfully.
1565    
1566         This is a typical call to pcre_study():         This is a typical call to pcre_study():
1567    
# Line 1123  STUDYING A PATTERN Line 1571  STUDYING A PATTERN
1571             0,              /* no options exist */             0,              /* no options exist */
1572             &error);        /* set to NULL or points to a message */             &error);        /* set to NULL or points to a message */
1573    
1574         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
1575         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
1576         ble starting bytes is created.         does not mean that there are any strings of that length that match, but
1577           it does guarantee that no shorter strings match. The value is  used  by
1578           pcre_exec()  and  pcre_dfa_exec()  to  avoid  wasting time by trying to
1579           match strings that are shorter than the lower bound. You can  find  out
1580           the value in a calling program via the pcre_fullinfo() function.
1581    
1582           Studying a pattern is also useful for non-anchored patterns that do not
1583           have a single fixed starting character. A bitmap of  possible  starting
1584           bytes  is  created. This speeds up finding a position in the subject at
1585           which to start matching.
1586    
1587           The two optimizations just described can be  disabled  by  setting  the
1588           PCRE_NO_START_OPTIMIZE    option    when    calling    pcre_exec()   or
1589           pcre_dfa_exec(). You might want to do this  if  your  pattern  contains
1590           callouts  or  (*MARK),  and you want to make use of these facilities in
1591           cases where matching fails. See the discussion  of  PCRE_NO_START_OPTI-
1592           MIZE below.
1593    
1594    
1595  LOCALE SUPPORT  LOCALE SUPPORT
1596    
1597         PCRE  handles  caseless matching, and determines whether characters are         PCRE  handles  caseless matching, and determines whether characters are
1598         letters digits, or whatever, by reference to a set of  tables,  indexed         letters, digits, or whatever, by reference to a set of tables,  indexed
1599         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
1600         characters with codes less than 128. Higher-valued  codes  never  match         characters with codes less than 128. By  default,  higher-valued  codes
1601         escapes  such  as  \w or \d, but can be tested with \p if PCRE is built         never match escapes such as \w or \d, but they can be tested with \p if
1602         with Unicode character property support.         PCRE is built with Unicode character property  support.  Alternatively,
1603           the  PCRE_UCP  option  can  be  set at compile time; this causes \w and
1604         An internal set of tables is created in the default C locale when  PCRE         friends to use Unicode property support instead of built-in tables. The
1605         is  built.  This  is  used when the final argument of pcre_compile() is         use of locales with Unicode is discouraged. If you are handling charac-
1606         NULL, and is sufficient for many applications. An  alternative  set  of         ters with codes greater than 128, you should either use UTF-8 and  Uni-
1607         tables  can,  however, be supplied. These may be created in a different         code, or use locales, but not try to mix the two.
1608         locale from the default. As more and more applications change to  using  
1609         Unicode, the need for this locale support is expected to die away.         PCRE  contains  an  internal set of tables that are used when the final
1610           argument of pcre_compile() is  NULL.  These  are  sufficient  for  many
1611           applications.  Normally, the internal tables recognize only ASCII char-
1612           acters. However, when PCRE is built, it is possible to cause the inter-
1613           nal tables to be rebuilt in the default "C" locale of the local system,
1614           which may cause them to be different.
1615    
1616           The internal tables can always be overridden by tables supplied by  the
1617           application that calls PCRE. These may be created in a different locale
1618           from the default. As more and more applications change  to  using  Uni-
1619           code, the need for this locale support is expected to die away.
1620    
1621         External  tables  are  built by calling the pcre_maketables() function,         External  tables  are  built by calling the pcre_maketables() function,
1622         which has no arguments, in the relevant locale. The result can then  be         which has no arguments, in the relevant locale. The result can then  be
# Line 1155  LOCALE SUPPORT Line 1629  LOCALE SUPPORT
1629           tables = pcre_maketables();           tables = pcre_maketables();
1630           re = pcre_compile(..., tables);           re = pcre_compile(..., tables);
1631    
1632         When pcre_maketables() runs, the tables are built  in  memory  that  is         The locale name "fr_FR" is used on Linux and other  Unix-like  systems;
1633         obtained  via  pcre_malloc. It is the caller's responsibility to ensure         if you are using Windows, the name for the French locale is "french".
1634         that the memory containing the tables remains available for as long  as  
1635           When  pcre_maketables()  runs,  the  tables are built in memory that is
1636           obtained via pcre_malloc. It is the caller's responsibility  to  ensure
1637           that  the memory containing the tables remains available for as long as
1638         it is needed.         it is needed.
1639    
1640         The pointer that is passed to pcre_compile() is saved with the compiled         The pointer that is passed to pcre_compile() is saved with the compiled
1641         pattern, and the same tables are used via this pointer by  pcre_study()         pattern,  and the same tables are used via this pointer by pcre_study()
1642         and normally also by pcre_exec(). Thus, by default, for any single pat-         and normally also by pcre_exec(). Thus, by default, for any single pat-
1643         tern, compilation, studying and matching all happen in the same locale,         tern, compilation, studying and matching all happen in the same locale,
1644         but different patterns can be compiled in different locales.         but different patterns can be compiled in different locales.
1645    
1646         It  is  possible to pass a table pointer or NULL (indicating the use of         It is possible to pass a table pointer or NULL (indicating the  use  of
1647         the internal tables) to pcre_exec(). Although  not  intended  for  this         the  internal  tables)  to  pcre_exec(). Although not intended for this
1648         purpose,  this facility could be used to match a pattern in a different         purpose, this facility could be used to match a pattern in a  different
1649         locale from the one in which it was compiled. Passing table pointers at         locale from the one in which it was compiled. Passing table pointers at
1650         run time is discussed below in the section on matching a pattern.         run time is discussed below in the section on matching a pattern.
1651    
# Line 1178  INFORMATION ABOUT A PATTERN Line 1655  INFORMATION ABOUT A PATTERN
1655         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
1656              int what, void *where);              int what, void *where);
1657    
1658         The  pcre_fullinfo() function returns information about a compiled pat-         The pcre_fullinfo() function returns information about a compiled  pat-
1659         tern. It replaces the obsolete pcre_info() function, which is neverthe-         tern. It replaces the obsolete pcre_info() function, which is neverthe-
1660         less retained for backwards compability (and is documented below).         less retained for backwards compability (and is documented below).
1661    
1662         The  first  argument  for  pcre_fullinfo() is a pointer to the compiled         The first argument for pcre_fullinfo() is a  pointer  to  the  compiled
1663         pattern. The second argument is the result of pcre_study(), or NULL  if         pattern.  The second argument is the result of pcre_study(), or NULL if
1664         the  pattern  was not studied. The third argument specifies which piece         the pattern was not studied. The third argument specifies  which  piece
1665         of information is required, and the fourth argument is a pointer  to  a         of  information  is required, and the fourth argument is a pointer to a
1666         variable  to  receive  the  data. The yield of the function is zero for         variable to receive the data. The yield of the  function  is  zero  for
1667         success, or one of the following negative numbers:         success, or one of the following negative numbers:
1668    
1669           PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_NULL       the argument code was NULL
# Line 1194  INFORMATION ABOUT A PATTERN Line 1671  INFORMATION ABOUT A PATTERN
1671           PCRE_ERROR_BADMAGIC   the "magic number" was not found           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1672           PCRE_ERROR_BADOPTION  the value of what was invalid           PCRE_ERROR_BADOPTION  the value of what was invalid
1673    
1674         The "magic number" is placed at the start of each compiled  pattern  as         The  "magic  number" is placed at the start of each compiled pattern as
1675         an  simple check against passing an arbitrary memory pointer. Here is a         an simple check against passing an arbitrary memory pointer. Here is  a
1676         typical call of pcre_fullinfo(), to obtain the length of  the  compiled         typical  call  of pcre_fullinfo(), to obtain the length of the compiled
1677         pattern:         pattern:
1678    
1679           int rc;           int rc;
1680           unsigned long int length;           size_t length;
1681           rc = pcre_fullinfo(           rc = pcre_fullinfo(
1682             re,               /* result of pcre_compile() */             re,               /* result of pcre_compile() */
1683             pe,               /* result of pcre_study(), or NULL */             pe,               /* result of pcre_study(), or NULL */
1684             PCRE_INFO_SIZE,   /* what is required */             PCRE_INFO_SIZE,   /* what is required */
1685             &length);         /* where to put the data */             &length);         /* where to put the data */
1686    
1687         The  possible  values for the third argument are defined in pcre.h, and         The possible values for the third argument are defined in  pcre.h,  and
1688         are as follows:         are as follows:
1689    
1690           PCRE_INFO_BACKREFMAX           PCRE_INFO_BACKREFMAX
1691    
1692         Return the number of the highest back reference  in  the  pattern.  The         Return  the  number  of  the highest back reference in the pattern. The
1693         fourth  argument  should  point to an int variable. Zero is returned if         fourth argument should point to an int variable. Zero  is  returned  if
1694         there are no back references.         there are no back references.
1695    
1696           PCRE_INFO_CAPTURECOUNT           PCRE_INFO_CAPTURECOUNT
1697    
1698         Return the number of capturing subpatterns in the pattern.  The  fourth         Return  the  number of capturing subpatterns in the pattern. The fourth
1699         argument should point to an int variable.         argument should point to an int variable.
1700    
1701           PCRE_INFO_DEFAULT_TABLES           PCRE_INFO_DEFAULT_TABLES
1702    
1703         Return  a pointer to the internal default character tables within PCRE.         Return a pointer to the internal default character tables within  PCRE.
1704         The fourth argument should point to an unsigned char *  variable.  This         The  fourth  argument should point to an unsigned char * variable. This
1705         information call is provided for internal use by the pcre_study() func-         information call is provided for internal use by the pcre_study() func-
1706         tion. External callers can cause PCRE to use  its  internal  tables  by         tion.  External  callers  can  cause PCRE to use its internal tables by
1707         passing a NULL table pointer.         passing a NULL table pointer.
1708    
1709           PCRE_INFO_FIRSTBYTE           PCRE_INFO_FIRSTBYTE
1710    
1711         Return  information  about  the first byte of any matched string, for a         Return information about the first byte of any matched  string,  for  a
1712         non-anchored   pattern.   (This    option    used    to    be    called         non-anchored  pattern. The fourth argument should point to an int vari-
1713         PCRE_INFO_FIRSTCHAR;  the  old  name  is still recognized for backwards         able. (This option used to be called PCRE_INFO_FIRSTCHAR; the old  name
1714         compatibility.)         is still recognized for backwards compatibility.)
1715    
1716         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
1717         (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  
1718    
1719         (a) the pattern was compiled with the PCRE_MULTILINE option, and  every         (a) the pattern was compiled with the PCRE_MULTILINE option, and  every
1720         branch starts with "^", or         branch starts with "^", or
# Line 1258  INFORMATION ABOUT A PATTERN Line 1734  INFORMATION ABOUT A PATTERN
1734         returned.  The fourth argument should point to an unsigned char * vari-         returned.  The fourth argument should point to an unsigned char * vari-
1735         able.         able.
1736    
1737             PCRE_INFO_HASCRORLF
1738    
1739           Return 1 if the pattern contains any explicit  matches  for  CR  or  LF
1740           characters,  otherwise  0.  The  fourth argument should point to an int
1741           variable. An explicit match is either a literal CR or LF character,  or
1742           \r or \n.
1743    
1744             PCRE_INFO_JCHANGED
1745    
1746           Return  1  if  the (?J) or (?-J) option setting is used in the pattern,
1747           otherwise 0. The fourth argument should point to an int variable.  (?J)
1748           and (?-J) set and unset the local PCRE_DUPNAMES option, respectively.
1749    
1750           PCRE_INFO_LASTLITERAL           PCRE_INFO_LASTLITERAL
1751    
1752         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
1753         matched  string,  other  than  at  its  start,  if such a byte has been         matched string, other than at its  start,  if  such  a  byte  has  been
1754         recorded. The fourth argument should point to an int variable. If there         recorded. The fourth argument should point to an int variable. If there
1755         is  no such byte, -1 is returned. For anchored patterns, a last literal         is no such byte, -1 is returned. For anchored patterns, a last  literal
1756         byte is recorded only if it follows something of variable  length.  For         byte  is  recorded only if it follows something of variable length. For
1757         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
1758         /^a\dz\d/ the returned value is -1.         /^a\dz\d/ the returned value is -1.
1759    
1760             PCRE_INFO_MINLENGTH
1761    
1762           If  the  pattern  was studied and a minimum length for matching subject
1763           strings was computed, its value is  returned.  Otherwise  the  returned
1764           value  is  -1. The value is a number of characters, not bytes (this may
1765           be relevant in UTF-8 mode). The fourth argument should point to an  int
1766           variable.  A  non-negative  value is a lower bound to the length of any
1767           matching string. There may not be any strings of that  length  that  do
1768           actually match, but every string that does match is at least that long.
1769    
1770           PCRE_INFO_NAMECOUNT           PCRE_INFO_NAMECOUNT
1771           PCRE_INFO_NAMEENTRYSIZE           PCRE_INFO_NAMEENTRYSIZE
1772           PCRE_INFO_NAMETABLE           PCRE_INFO_NAMETABLE
1773    
1774         PCRE supports the use of named as well as numbered capturing  parenthe-         PCRE  supports the use of named as well as numbered capturing parenthe-
1775         ses.  The names are just an additional way of identifying the parenthe-         ses. The names are just an additional way of identifying the  parenthe-
1776         ses,  which  still  acquire  numbers.  A  convenience  function  called         ses, which still acquire numbers. Several convenience functions such as
1777         pcre_get_named_substring()  is  provided  for  extracting an individual         pcre_get_named_substring() are provided for  extracting  captured  sub-
1778         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
1779         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
1780         the correct pointers in the output vector (described  with  pcre_exec()         pointers in the output vector (described with pcre_exec() below). To do
1781         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
1782         which is described by these three values.         described by these three values.
1783    
1784         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
1785         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
1786         of each entry; both of these  return  an  int  value.  The  entry  size         of  each  entry;  both  of  these  return  an int value. The entry size
1787         depends  on the length of the longest name. PCRE_INFO_NAMETABLE returns         depends on the length of the longest name. PCRE_INFO_NAMETABLE  returns
1788         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
1789         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-
1790         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-
1791         sponding  name,  zero  terminated. The names are in alphabetical order.         sponding name, zero terminated.
1792         For example, consider the following pattern  (assume  PCRE_EXTENDED  is  
1793         set, so white space - including newlines - is ignored):         The names are in alphabetical order. Duplicate names may appear if  (?|
1794           is used to create multiple groups with the same number, as described in
1795           the section on duplicate subpattern numbers in  the  pcrepattern  page.
1796           Duplicate  names  for  subpatterns with different numbers are permitted
1797           only if PCRE_DUPNAMES is set. In all cases  of  duplicate  names,  they
1798           appear  in  the table in the order in which they were found in the pat-
1799           tern. In the absence of (?| this is the  order  of  increasing  number;
1800           when (?| is used this is not necessarily the case because later subpat-
1801           terns may have lower numbers.
1802    
1803           As a simple example of the name/number table,  consider  the  following
1804           pattern  (assume  PCRE_EXTENDED is set, so white space - including new-
1805           lines - is ignored):
1806    
1807           (?P<date> (?P<year>(\d\d)?\d\d) -           (?<date> (?<year>(\d\d)?\d\d) -
1808           (?P<month>\d\d) - (?P<day>\d\d) )           (?<month>\d\d) - (?<day>\d\d) )
1809    
1810         There  are  four  named subpatterns, so the table has four entries, and         There are four named subpatterns, so the table has  four  entries,  and
1811         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,
1812         with non-printing bytes shows in hexadecimal, and undefined bytes shown         with non-printing bytes shows in hexadecimal, and undefined bytes shown
1813         as ??:         as ??:
1814    
# Line 1306  INFORMATION ABOUT A PATTERN Line 1817  INFORMATION ABOUT A PATTERN
1817           00 04 m  o  n  t  h  00           00 04 m  o  n  t  h  00
1818           00 02 y  e  a  r  00 ??           00 02 y  e  a  r  00 ??
1819    
1820         When writing code to extract data  from  named  subpatterns  using  the         When  writing  code  to  extract  data from named subpatterns using the
1821         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
1822         be different for each compiled pattern.         to be different for each compiled pattern.
1823    
1824             PCRE_INFO_OKPARTIAL
1825    
1826           Return  1  if  the  pattern  can  be  used  for  partial  matching with
1827           pcre_exec(), otherwise 0. The fourth argument should point  to  an  int
1828           variable.  From  release  8.00,  this  always  returns  1,  because the
1829           restrictions that previously applied  to  partial  matching  have  been
1830           lifted.  The  pcrepartial documentation gives details of partial match-
1831           ing.
1832    
1833           PCRE_INFO_OPTIONS           PCRE_INFO_OPTIONS
1834    
1835         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
1836         fourth  argument  should  point to an unsigned long int variable. These         fourth  argument  should  point to an unsigned long int variable. These
1837         option bits are those specified in the call to pcre_compile(), modified         option bits are those specified in the call to pcre_compile(), modified
1838         by any top-level option settings within the pattern itself.         by any top-level option settings at the start of the pattern itself. In
1839           other words, they are the options that will be in force  when  matching
1840           starts.  For  example, if the pattern /(?im)abc(?-i)d/ is compiled with
1841           the PCRE_EXTENDED option, the result is PCRE_CASELESS,  PCRE_MULTILINE,
1842           and PCRE_EXTENDED.
1843    
1844         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
1845         alternatives begin with one of the following:         alternatives begin with one of the following:
# Line 1341  INFORMATION ABOUT A PATTERN Line 1865  INFORMATION ABOUT A PATTERN
1865         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
1866         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
1867         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
1868         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
1869           data, zero is returned. The fourth argument should point  to  a  size_t
1870         variable.         variable.
1871    
1872    
# Line 1349  OBSOLETE INFO FUNCTION Line 1874  OBSOLETE INFO FUNCTION
1874    
1875         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
1876    
1877         The pcre_info() function is now obsolete because its interface  is  too         The  pcre_info()  function is now obsolete because its interface is too
1878         restrictive  to return all the available data about a compiled pattern.         restrictive to return all the available data about a compiled  pattern.
1879         New  programs  should  use  pcre_fullinfo()  instead.  The   yield   of         New   programs   should  use  pcre_fullinfo()  instead.  The  yield  of
1880         pcre_info()  is the number of capturing subpatterns, or one of the fol-         pcre_info() is the number of capturing subpatterns, or one of the  fol-
1881         lowing negative numbers:         lowing negative numbers:
1882    
1883           PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_NULL       the argument code was NULL
1884           PCRE_ERROR_BADMAGIC   the "magic number" was not found           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1885    
1886         If the optptr argument is not NULL, a copy of the  options  with  which         If  the  optptr  argument is not NULL, a copy of the options with which
1887         the  pattern  was  compiled  is placed in the integer it points to (see         the pattern was compiled is placed in the integer  it  points  to  (see
1888         PCRE_INFO_OPTIONS above).         PCRE_INFO_OPTIONS above).
1889    
1890         If the pattern is not anchored and the  firstcharptr  argument  is  not         If  the  pattern  is  not anchored and the firstcharptr argument is not
1891         NULL,  it is used to pass back information about the first character of         NULL, it is used to pass back information about the first character  of
1892         any matched string (see PCRE_INFO_FIRSTBYTE above).         any matched string (see PCRE_INFO_FIRSTBYTE above).
1893    
1894    
# Line 1371  REFERENCE COUNTS Line 1896  REFERENCE COUNTS
1896    
1897         int pcre_refcount(pcre *code, int adjust);         int pcre_refcount(pcre *code, int adjust);
1898    
1899         The pcre_refcount() function is used to maintain a reference  count  in         The  pcre_refcount()  function is used to maintain a reference count in
1900         the data block that contains a compiled pattern. It is provided for the         the data block that contains a compiled pattern. It is provided for the
1901         benefit of applications that  operate  in  an  object-oriented  manner,         benefit  of  applications  that  operate  in an object-oriented manner,
1902         where different parts of the application may be using the same compiled         where different parts of the application may be using the same compiled
1903         pattern, but you want to free the block when they are all done.         pattern, but you want to free the block when they are all done.
1904    
1905         When a pattern is compiled, the reference count field is initialized to         When a pattern is compiled, the reference count field is initialized to
1906         zero.   It is changed only by calling this function, whose action is to         zero.  It is changed only by calling this function, whose action is  to
1907         add the adjust value (which may be positive or  negative)  to  it.  The         add  the  adjust  value  (which may be positive or negative) to it. The
1908         yield of the function is the new value. However, the value of the count         yield of the function is the new value. However, the value of the count
1909         is constrained to lie between 0 and 65535, inclusive. If the new  value         is  constrained to lie between 0 and 65535, inclusive. If the new value
1910         is outside these limits, it is forced to the appropriate limit value.         is outside these limits, it is forced to the appropriate limit value.
1911    
1912         Except  when it is zero, the reference count is not correctly preserved         Except when it is zero, the reference count is not correctly  preserved
1913         if a pattern is compiled on one host and then  transferred  to  a  host         if  a  pattern  is  compiled on one host and then transferred to a host
1914         whose byte-order is different. (This seems a highly unlikely scenario.)         whose byte-order is different. (This seems a highly unlikely scenario.)
1915    
1916    
# Line 1397  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1922  MATCHING A PATTERN: THE TRADITIONAL FUNC
1922    
1923         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
1924         compiled  pattern, which is passed in the code argument. If the pattern         compiled  pattern, which is passed in the code argument. If the pattern
1925         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
1926         argument.  This  function is the main matching facility of the library,         argument.  This  function is the main matching facility of the library,
1927         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
1928         an  alternative matching function, which is described below in the sec-         an  alternative matching function, which is described below in the sec-
# Line 1428  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1953  MATCHING A PATTERN: THE TRADITIONAL FUNC
1953         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
1954         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
1955         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-
1956         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
1957         lows:         fields (not necessarily in this order):
1958    
1959           unsigned long int flags;           unsigned long int flags;
1960           void *study_data;           void *study_data;
1961           unsigned long int match_limit;           unsigned long int match_limit;
1962             unsigned long int match_limit_recursion;
1963           void *callout_data;           void *callout_data;
1964           const unsigned char *tables;           const unsigned char *tables;
1965             unsigned char **mark;
1966    
1967         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
1968         are set. The flag bits are:         are set. The flag bits are:
1969    
1970           PCRE_EXTRA_STUDY_DATA           PCRE_EXTRA_STUDY_DATA
1971           PCRE_EXTRA_MATCH_LIMIT           PCRE_EXTRA_MATCH_LIMIT
1972             PCRE_EXTRA_MATCH_LIMIT_RECURSION
1973           PCRE_EXTRA_CALLOUT_DATA           PCRE_EXTRA_CALLOUT_DATA
1974           PCRE_EXTRA_TABLES           PCRE_EXTRA_TABLES
1975             PCRE_EXTRA_MARK
1976    
1977         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
1978         the pcre_extra block that is returned by  pcre_study(),  together  with         the pcre_extra block that is returned by  pcre_study(),  together  with
# Line 1454  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1983  MATCHING A PATTERN: THE TRADITIONAL FUNC
1983         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
1984         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
1985         match,  but  which  have  a very large number of possibilities in their         match,  but  which  have  a very large number of possibilities in their
1986         search trees. The classic  example  is  the  use  of  nested  unlimited         search trees. The classic example is a pattern that uses nested  unlim-
1987         repeats.         ited repeats.
1988    
1989         Internally,  PCRE uses a function called match() which it calls repeat-         Internally,  PCRE uses a function called match() which it calls repeat-
1990         edly (sometimes recursively). The limit is imposed  on  the  number  of         edly (sometimes recursively). The limit set by match_limit  is  imposed
1991         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
1992         limiting the amount of recursion and backtracking that can take  place.         has the effect of limiting the amount of  backtracking  that  can  take
1993         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
1994         position in the subject string.         for each position in the subject string.
1995    
1996         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
1997         default  default  is 10 million, which handles all but the most extreme         default  default  is 10 million, which handles all but the most extreme
1998         cases. You can reduce  the  default  by  suppling  pcre_exec()  with  a         cases. You can override the default  by  suppling  pcre_exec()  with  a
1999         pcre_extra  block  in  which match_limit is set to a smaller value, and         pcre_extra     block    in    which    match_limit    is    set,    and
2000         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
2001         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
2002    
2003         The  pcre_callout  field is used in conjunction with the "callout" fea-         The  match_limit_recursion field is similar to match_limit, but instead
2004         ture, which is described in the pcrecallout documentation.         of limiting the total number of times that match() is called, it limits
2005           the  depth  of  recursion. The recursion depth is a smaller number than
2006         The tables field  is  used  to  pass  a  character  tables  pointer  to         the total number of calls, because not all calls to match() are  recur-
2007         pcre_exec();  this overrides the value that is stored with the compiled         sive.  This limit is of use only if it is set smaller than match_limit.
2008         pattern. A non-NULL value is stored with the compiled pattern  only  if  
2009         custom  tables  were  supplied to pcre_compile() via its tableptr argu-         Limiting  the  recursion  depth  limits the amount of stack that can be
2010           used, or, when PCRE has been compiled to use memory on the heap instead
2011           of the stack, the amount of heap memory that can be used.
2012    
2013           The  default  value  for  match_limit_recursion can be set when PCRE is
2014           built; the default default  is  the  same  value  as  the  default  for
2015           match_limit.  You can override the default by suppling pcre_exec() with
2016           a  pcre_extra  block  in  which  match_limit_recursion  is   set,   and
2017           PCRE_EXTRA_MATCH_LIMIT_RECURSION  is  set  in  the  flags field. If the
2018           limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
2019    
2020           The callout_data field is used in conjunction with the  "callout"  fea-
2021           ture, and is described in the pcrecallout documentation.
2022    
2023           The  tables  field  is  used  to  pass  a  character  tables pointer to
2024           pcre_exec(); this overrides the value that is stored with the  compiled
2025           pattern.  A  non-NULL value is stored with the compiled pattern only if
2026           custom tables were supplied to pcre_compile() via  its  tableptr  argu-
2027         ment.  If NULL is passed to pcre_exec() using this mechanism, it forces         ment.  If NULL is passed to pcre_exec() using this mechanism, it forces
2028         PCRE's  internal  tables  to be used. This facility is helpful when re-         PCRE's internal tables to be used. This facility is  helpful  when  re-
2029         using patterns that have been saved after compiling  with  an  external         using  patterns  that  have been saved after compiling with an external
2030         set  of  tables,  because  the  external tables might be at a different         set of tables, because the external tables  might  be  at  a  different
2031         address when pcre_exec() is called. See the  pcreprecompile  documenta-         address  when  pcre_exec() is called. See the pcreprecompile documenta-
2032         tion for a discussion of saving compiled patterns for later use.         tion for a discussion of saving compiled patterns for later use.
2033    
2034           If PCRE_EXTRA_MARK is set in the flags field, the mark  field  must  be
2035           set  to  point  to a char * variable. If the pattern contains any back-
2036           tracking control verbs such as (*MARK:NAME), and the execution ends  up
2037           with  a  name  to  pass back, a pointer to the name string (zero termi-
2038           nated) is placed in the variable pointed to  by  the  mark  field.  The
2039           names  are  within  the  compiled pattern; if you wish to retain such a
2040           name you must copy it before freeing the memory of a compiled  pattern.
2041           If  there  is no name to pass back, the variable pointed to by the mark
2042           field set to NULL. For details of the backtracking control  verbs,  see
2043           the section entitled "Backtracking control" in the pcrepattern documen-
2044           tation.
2045    
2046     Option bits for pcre_exec()     Option bits for pcre_exec()
2047    
2048         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.
2049         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,
2050         PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK and PCRE_PARTIAL.         PCRE_NOTBOL,   PCRE_NOTEOL,    PCRE_NOTEMPTY,    PCRE_NOTEMPTY_ATSTART,
2051           PCRE_NO_START_OPTIMIZE,   PCRE_NO_UTF8_CHECK,   PCRE_PARTIAL_SOFT,  and
2052           PCRE_PARTIAL_HARD.
2053    
2054           PCRE_ANCHORED           PCRE_ANCHORED
2055    
2056         The  PCRE_ANCHORED  option  limits pcre_exec() to matching at the first         The PCRE_ANCHORED option limits pcre_exec() to matching  at  the  first
2057         matching position. If a pattern was  compiled  with  PCRE_ANCHORED,  or         matching  position.  If  a  pattern was compiled with PCRE_ANCHORED, or
2058         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
2059         unachored at matching time.         unachored at matching time.
2060    
2061             PCRE_BSR_ANYCRLF
2062             PCRE_BSR_UNICODE
2063    
2064           These options (which are mutually exclusive) control what the \R escape
2065           sequence matches. The choice is either to match only CR, LF,  or  CRLF,
2066           or  to  match  any Unicode newline sequence. These options override the
2067           choice that was made or defaulted when the pattern was compiled.
2068    
2069             PCRE_NEWLINE_CR
2070             PCRE_NEWLINE_LF
2071             PCRE_NEWLINE_CRLF
2072             PCRE_NEWLINE_ANYCRLF
2073             PCRE_NEWLINE_ANY
2074    
2075           These options override  the  newline  definition  that  was  chosen  or
2076           defaulted  when the pattern was compiled. For details, see the descrip-
2077           tion of pcre_compile()  above.  During  matching,  the  newline  choice
2078           affects  the  behaviour  of the dot, circumflex, and dollar metacharac-
2079           ters. It may also alter the way the match position is advanced after  a
2080           match failure for an unanchored pattern.
2081    
2082           When  PCRE_NEWLINE_CRLF,  PCRE_NEWLINE_ANYCRLF,  or PCRE_NEWLINE_ANY is
2083           set, and a match attempt for an unanchored pattern fails when the  cur-
2084           rent  position  is  at  a  CRLF  sequence,  and the pattern contains no
2085           explicit matches for  CR  or  LF  characters,  the  match  position  is
2086           advanced by two characters instead of one, in other words, to after the
2087           CRLF.
2088    
2089           The above rule is a compromise that makes the most common cases work as
2090           expected.  For  example,  if  the  pattern  is .+A (and the PCRE_DOTALL
2091           option is not set), it does not match the string "\r\nA" because, after
2092           failing  at the start, it skips both the CR and the LF before retrying.
2093           However, the pattern [\r\n]A does match that string,  because  it  con-
2094           tains an explicit CR or LF reference, and so advances only by one char-
2095           acter after the first failure.
2096    
2097           An explicit match for CR of LF is either a literal appearance of one of
2098           those  characters,  or  one  of the \r or \n escape sequences. Implicit
2099           matches such as [^X] do not count, nor does \s (which includes  CR  and
2100           LF in the characters that it matches).
2101    
2102           Notwithstanding  the above, anomalous effects may still occur when CRLF
2103           is a valid newline sequence and explicit \r or \n escapes appear in the
2104           pattern.
2105    
2106           PCRE_NOTBOL           PCRE_NOTBOL
2107    
2108         This option specifies that first character of the subject string is not         This option specifies that first character of the subject string is not
2109         the  beginning  of  a  line, so the circumflex metacharacter should not         the beginning of a line, so the  circumflex  metacharacter  should  not
2110         match before it. Setting this without PCRE_MULTILINE (at compile  time)         match  before it. Setting this without PCRE_MULTILINE (at compile time)
2111         causes  circumflex  never to match. This option affects only the behav-         causes circumflex never to match. This option affects only  the  behav-
2112         iour of the circumflex metacharacter. It does not affect \A.         iour of the circumflex metacharacter. It does not affect \A.
2113    
2114           PCRE_NOTEOL           PCRE_NOTEOL
2115    
2116         This option specifies that the end of the subject string is not the end         This option specifies that the end of the subject string is not the end
2117         of  a line, so the dollar metacharacter should not match it nor (except         of a line, so the dollar metacharacter should not match it nor  (except
2118         in multiline mode) a newline immediately before it. Setting this  with-         in  multiline mode) a newline immediately before it. Setting this with-
2119         out PCRE_MULTILINE (at compile time) causes dollar never to match. This         out PCRE_MULTILINE (at compile time) causes dollar never to match. This
2120         option affects only the behaviour of the dollar metacharacter. It  does         option  affects only the behaviour of the dollar metacharacter. It does
2121         not affect \Z or \z.         not affect \Z or \z.
2122    
2123           PCRE_NOTEMPTY           PCRE_NOTEMPTY
2124    
2125         An empty string is not considered to be a valid match if this option is         An empty string is not considered to be a valid match if this option is
2126         set. If there are alternatives in the pattern, they are tried.  If  all         set.  If  there are alternatives in the pattern, they are tried. If all
2127         the  alternatives  match  the empty string, the entire match fails. For         the alternatives match the empty string, the entire  match  fails.  For
2128         example, if the pattern         example, if the pattern
2129    
2130           a?b?           a?b?
2131    
2132         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
2133         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
2134         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-
2135         rences of "a" or "b".         rences of "a" or "b".
2136    
2137         Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a spe-           PCRE_NOTEMPTY_ATSTART
2138         cial case of a pattern match of the empty  string  within  its  split()  
2139         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
2140         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
2141         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.
2142         if that fails by advancing the starting offset (see below)  and  trying  
2143         an ordinary match again. There is some code that demonstrates how to do         Perl    has    no    direct    equivalent    of    PCRE_NOTEMPTY     or
2144         this in the pcredemo.c sample program.         PCRE_NOTEMPTY_ATSTART,  but  it  does  make a special case of a pattern
2145           match of the empty string within its split() function, and  when  using
2146           the  /g  modifier.  It  is  possible  to emulate Perl's behaviour after
2147           matching a null string by first trying the match again at the same off-
2148           set  with  PCRE_NOTEMPTY_ATSTART  and  PCRE_ANCHORED,  and then if that
2149           fails, by advancing the starting offset (see below) and trying an ordi-
2150           nary  match  again. There is some code that demonstrates how to do this
2151           in the pcredemo sample program. In the most general case, you  have  to
2152           check  to  see  if the newline convention recognizes CRLF as a newline,
2153           and if so, and the current character is CR followed by LF, advance  the
2154           starting offset by two characters instead of one.
2155    
2156             PCRE_NO_START_OPTIMIZE
2157    
2158           There  are a number of optimizations that pcre_exec() uses at the start
2159           of a match, in order to speed up the process. For  example,  if  it  is
2160           known that an unanchored match must start with a specific character, it
2161           searches the subject for that character, and fails  immediately  if  it
2162           cannot  find  it,  without actually running the main matching function.
2163           This means that a special item such as (*COMMIT) at the start of a pat-
2164           tern  is  not  considered until after a suitable starting point for the
2165           match has been found. When callouts or (*MARK) items are in use,  these
2166           "start-up" optimizations can cause them to be skipped if the pattern is
2167           never actually used. The start-up optimizations are in  effect  a  pre-
2168           scan of the subject that takes place before the pattern is run.
2169    
2170           The  PCRE_NO_START_OPTIMIZE option disables the start-up optimizations,
2171           possibly causing performance to suffer,  but  ensuring  that  in  cases
2172           where  the  result is "no match", the callouts do occur, and that items
2173           such as (*COMMIT) and (*MARK) are considered at every possible starting
2174           position  in  the  subject  string. If PCRE_NO_START_OPTIMIZE is set at
2175           compile time, it cannot be unset at matching time.
2176    
2177           Setting PCRE_NO_START_OPTIMIZE can change the  outcome  of  a  matching
2178           operation.  Consider the pattern
2179    
2180             (*COMMIT)ABC
2181    
2182           When  this  is  compiled, PCRE records the fact that a match must start
2183           with the character "A". Suppose the subject  string  is  "DEFABC".  The
2184           start-up  optimization  scans along the subject, finds "A" and runs the
2185           first match attempt from there. The (*COMMIT) item means that the  pat-
2186           tern  must  match the current starting position, which in this case, it
2187           does. However, if the same match  is  run  with  PCRE_NO_START_OPTIMIZE
2188           set,  the  initial  scan  along the subject string does not happen. The
2189           first match attempt is run starting  from  "D"  and  when  this  fails,
2190           (*COMMIT)  prevents  any  further  matches  being tried, so the overall
2191           result is "no match". If the pattern is studied,  more  start-up  opti-
2192           mizations  may  be  used. For example, a minimum length for the subject
2193           may be recorded. Consider the pattern
2194    
2195             (*MARK:A)(X|Y)
2196    
2197           The minimum length for a match is one  character.  If  the  subject  is
2198           "ABC",  there  will  be  attempts  to  match "ABC", "BC", "C", and then
2199           finally an empty string.  If the pattern is studied, the final  attempt
2200           does  not take place, because PCRE knows that the subject is too short,
2201           and so the (*MARK) is never encountered.  In this  case,  studying  the
2202           pattern  does  not  affect the overall match result, which is still "no
2203           match", but it does affect the auxiliary information that is returned.
2204    
2205           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
2206    
2207         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
2208         UTF-8  string is automatically checked when pcre_exec() is subsequently         UTF-8  string is automatically checked when pcre_exec() is subsequently
2209         called.  The value of startoffset is also checked  to  ensure  that  it         called.  The value of startoffset is also checked  to  ensure  that  it
2210         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
2211         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
2212         startoffset  contains  an  invalid  value, PCRE_ERROR_BADUTF8_OFFSET is         main  pcre  page.  If  an  invalid  UTF-8  sequence  of bytes is found,
2213         returned.         pcre_exec() returns  the  error  PCRE_ERROR_BADUTF8  or,  if  PCRE_PAR-
2214           TIAL_HARD  is set and the problem is a truncated UTF-8 character at the
2215           end of the subject, PCRE_ERROR_SHORTUTF8.  If  startoffset  contains  a
2216           value  that does not point to the start of a UTF-8 character (or to the
2217           end of the subject), PCRE_ERROR_BADUTF8_OFFSET is returned.
2218    
2219         If you already know that your subject is valid, and you  want  to  skip         If you already know that your subject is valid, and you  want  to  skip
2220         these    checks    for   performance   reasons,   you   can   set   the         these    checks    for   performance   reasons,   you   can   set   the
# Line 1554  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2222  MATCHING A PATTERN: THE TRADITIONAL FUNC
2222         do  this  for the second and subsequent calls to pcre_exec() if you are         do  this  for the second and subsequent calls to pcre_exec() if you are
2223         making repeated calls to find all  the  matches  in  a  single  subject         making repeated calls to find all  the  matches  in  a  single  subject
2224         string.  However,  you  should  be  sure  that the value of startoffset         string.  However,  you  should  be  sure  that the value of startoffset
2225         points to the start of a UTF-8 character.  When  PCRE_NO_UTF8_CHECK  is         points to the start of a UTF-8 character (or the end of  the  subject).
2226         set,  the  effect of passing an invalid UTF-8 string as a subject, or a         When  PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid UTF-8
2227         value of startoffset that does not point to the start of a UTF-8  char-         string as a subject or an invalid value of  startoffset  is  undefined.
2228         acter, is undefined. Your program may crash.         Your program may crash.
2229    
2230           PCRE_PARTIAL           PCRE_PARTIAL_HARD
2231             PCRE_PARTIAL_SOFT
2232         This  option  turns  on  the  partial  matching feature. If the subject  
2233         string fails to match the pattern, but at some point during the  match-         These  options turn on the partial matching feature. For backwards com-
2234         ing  process  the  end of the subject was reached (that is, the subject         patibility, PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A  partial
2235         partially matches the pattern and the failure to  match  occurred  only         match  occurs if the end of the subject string is reached successfully,
2236         because  there were not enough subject characters), pcre_exec() returns         but there are not enough subject characters to complete the  match.  If
2237         PCRE_ERROR_PARTIAL instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL  is         this happens when PCRE_PARTIAL_SOFT (but not PCRE_PARTIAL_HARD) is set,
2238         used,  there  are restrictions on what may appear in the pattern. These         matching continues by testing any remaining alternatives.  Only  if  no
2239         are discussed in the pcrepartial documentation.         complete  match  can be found is PCRE_ERROR_PARTIAL returned instead of
2240           PCRE_ERROR_NOMATCH. In other words,  PCRE_PARTIAL_SOFT  says  that  the
2241           caller  is  prepared to handle a partial match, but only if no complete
2242           match can be found.
2243    
2244           If PCRE_PARTIAL_HARD is set, it overrides  PCRE_PARTIAL_SOFT.  In  this
2245           case,  if  a  partial  match  is found, pcre_exec() immediately returns
2246           PCRE_ERROR_PARTIAL, without  considering  any  other  alternatives.  In
2247           other  words, when PCRE_PARTIAL_HARD is set, a partial match is consid-
2248           ered to be more important that an alternative complete match.
2249    
2250           In both cases, the portion of the string that was  inspected  when  the
2251           partial match was found is set as the first matching string. There is a
2252           more detailed discussion of partial and  multi-segment  matching,  with
2253           examples, in the pcrepartial documentation.
2254    
2255     The string to be matched by pcre_exec()     The string to be matched by pcre_exec()
2256    
2257         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
2258         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.
2259         mode, the byte offset must point to the start  of  a  UTF-8  character.         If  this  is  negative  or  greater  than  the  length  of the subject,
2260         Unlike  the  pattern string, the subject may contain binary zero bytes.         pcre_exec() returns PCRE_ERROR_BADOFFSET. When the starting  offset  is
2261         When the starting offset is zero, the search for a match starts at  the         zero,  the  search  for a match starts at the beginning of the subject,
2262         beginning of the subject, and this is by far the most common case.         and this is by far the most common case. In UTF-8 mode, the byte offset
2263           must  point  to  the start of a UTF-8 character (or the end of the sub-
2264           ject). Unlike the pattern string, the subject may contain  binary  zero
2265           bytes.
2266    
2267         A  non-zero  starting offset is useful when searching for another match         A  non-zero  starting offset is useful when searching for another match
2268         in the same subject by calling pcre_exec() again after a previous  suc-         in the same subject by calling pcre_exec() again after a previous  suc-
# Line 1598  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2283  MATCHING A PATTERN: THE TRADITIONAL FUNC
2283         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
2284         discover that it is preceded by a letter.         discover that it is preceded by a letter.
2285    
2286         If a non-zero starting offset is passed when the pattern  is  anchored,         Finding all the matches in a subject is tricky  when  the  pattern  can
2287           match an empty string. It is possible to emulate Perl's /g behaviour by
2288           first  trying  the  match  again  at  the   same   offset,   with   the
2289           PCRE_NOTEMPTY_ATSTART  and  PCRE_ANCHORED  options,  and  then  if that
2290           fails, advancing the starting  offset  and  trying  an  ordinary  match
2291           again. There is some code that demonstrates how to do this in the pcre-
2292           demo sample program. In the most general case, you have to check to see
2293           if  the newline convention recognizes CRLF as a newline, and if so, and
2294           the current character is CR followed by LF, advance the starting offset
2295           by two characters instead of one.
2296    
2297           If  a  non-zero starting offset is passed when the pattern is anchored,
2298         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
2299         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
2300         subject.         subject.
2301    
2302     How pcre_exec() returns captured substrings     How pcre_exec() returns captured substrings
2303    
2304         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
2305         addition, further substrings from the subject  may  be  picked  out  by         addition,  further  substrings  from  the  subject may be picked out by
2306         parts  of  the  pattern.  Following the usage in Jeffrey Friedl's book,         parts of the pattern. Following the usage  in  Jeffrey  Friedl's  book,
2307         this is called "capturing" in what follows, and the  phrase  "capturing         this  is  called "capturing" in what follows, and the phrase "capturing
2308         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-
2309         string. PCRE supports several other kinds of  parenthesized  subpattern         string.  PCRE  supports several other kinds of parenthesized subpattern
2310         that do not cause substrings to be captured.         that do not cause substrings to be captured.
2311    
2312         Captured  substrings are returned to the caller via a vector of integer         Captured substrings are returned to the caller via a vector of integers
2313         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-
2314         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:
2315         Note: this argument is NOT the size of ovector in bytes.         this argument is NOT the size of ovector in bytes.
2316    
2317         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-
2318         strings,  each  substring using a pair of integers. The remaining third         strings, each substring using a pair of integers. The  remaining  third
2319         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-
2320         turing  subpatterns, and is not available for passing back information.         turing subpatterns, and is not available for passing back  information.
2321         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
2322         it is not, it is rounded down.         it is not, it is rounded down.
2323    
2324         When  a  match  is successful, information about captured substrings is         When a match is successful, information about  captured  substrings  is
2325         returned in pairs of integers, starting at the  beginning  of  ovector,         returned  in  pairs  of integers, starting at the beginning of ovector,
2326         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
2327         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
2328         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
2329         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
2330         tor[1],  identify  the  portion  of  the  subject string matched by the         byte offsets, even in UTF-8 mode. They are not character counts.
2331         entire pattern. The next pair is used for the first  capturing  subpat-  
2332         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
2333         pairs that have been set. If there are no  capturing  subpatterns,  the         portion  of  the subject string matched by the entire pattern. The next
2334         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
2335         first pair of offsets has been set.         returned by pcre_exec() is one more than the highest numbered pair that
2336           has been set.  For example, if two substrings have been  captured,  the
2337         Some convenience functions are provided  for  extracting  the  captured         returned  value is 3. If there are no capturing subpatterns, the return
2338         substrings  as  separate  strings. These are described in the following         value from a successful match is 1, indicating that just the first pair
2339         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.  
2340    
2341         If a capturing subpattern is matched repeatedly, it is the last portion         If a capturing subpattern is matched repeatedly, it is the last portion
2342         of the string that it matched that is returned.         of the string that it matched that is returned.
2343    
2344         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,
2345         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
2346         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
2347         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
2348         as  NULL  and  ovecsize  as zero. However, if the pattern contains back         ovecsize as zero. However, if the pattern contains back references  and
2349         references and the ovector is not big enough to  remember  the  related         the  ovector is not big enough to remember the related substrings, PCRE
2350         substrings,  PCRE has to get additional memory for use during matching.         has to get additional memory for use during matching. Thus it  is  usu-
2351         Thus it is usually advisable to supply an ovector.         ally advisable to supply an ovector.
2352    
2353         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
2354         patterns there are in a compiled pattern. The smallest size for ovector         subpatterns there are in a compiled  pattern.  The  smallest  size  for
2355         that will allow for n captured substrings, in addition to  the  offsets         ovector  that  will allow for n captured substrings, in addition to the
2356         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.
2357    
2358           It is possible for capturing subpattern number n+1 to match  some  part
2359           of the subject when subpattern n has not been used at all. For example,
2360           if the string "abc" is matched  against  the  pattern  (a|(z))(bc)  the
2361           return from the function is 4, and subpatterns 1 and 3 are matched, but
2362           2 is not. When this happens, both values in  the  offset  pairs  corre-
2363           sponding to unused subpatterns are set to -1.
2364    
2365           Offset  values  that correspond to unused subpatterns at the end of the
2366           expression are also set to -1. For example,  if  the  string  "abc"  is
2367           matched  against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not
2368           matched. The return from the function is 2, because  the  highest  used
2369           capturing  subpattern  number  is 1, and the offsets for for the second
2370           and third capturing subpatterns (assuming the vector is  large  enough,
2371           of course) are set to -1.
2372    
2373           Note: Elements of ovector that do not correspond to capturing parenthe-
2374           ses in the pattern are never changed. That is, if a pattern contains  n
2375           capturing parentheses, no more than ovector[0] to ovector[2n+1] are set
2376           by pcre_exec(). The other elements retain whatever values  they  previ-
2377           ously had.
2378    
2379     Return values from pcre_exec()         Some  convenience  functions  are  provided for extracting the captured
2380           substrings as separate strings. These are described below.
2381    
2382         If  pcre_exec()  fails, it returns a negative number. The following are     Error return values from pcre_exec()
2383    
2384           If pcre_exec() fails, it returns a negative number. The  following  are
2385         defined in the header file:         defined in the header file:
2386    
2387           PCRE_ERROR_NOMATCH        (-1)           PCRE_ERROR_NOMATCH        (-1)
# Line 1676  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2390  MATCHING A PATTERN: THE TRADITIONAL FUNC
2390    
2391           PCRE_ERROR_NULL           (-2)           PCRE_ERROR_NULL           (-2)
2392    
2393         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
2394         ovecsize was not zero.         ovecsize was not zero.
2395    
2396           PCRE_ERROR_BADOPTION      (-3)           PCRE_ERROR_BADOPTION      (-3)
# Line 1685  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2399  MATCHING A PATTERN: THE TRADITIONAL FUNC
2399    
2400           PCRE_ERROR_BADMAGIC       (-4)           PCRE_ERROR_BADMAGIC       (-4)
2401    
2402         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,
2403         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
2404         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
2405         an environment with the other endianness. This is the error  that  PCRE         an  environment  with the other endianness. This is the error that PCRE
2406         gives when the magic number is not present.         gives when the magic number is not present.
2407    
2408           PCRE_ERROR_UNKNOWN_NODE   (-5)           PCRE_ERROR_UNKNOWN_OPCODE (-5)
2409    
2410         While running the pattern match, an unknown item was encountered in the         While running the pattern match, an unknown item was encountered in the
2411         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
2412         overwriting of the compiled pattern.         overwriting of the compiled pattern.
2413    
2414           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2415    
2416         If  a  pattern contains back references, but the ovector that is passed         If a pattern contains back references, but the ovector that  is  passed
2417         to pcre_exec() is not big enough to remember the referenced substrings,         to pcre_exec() is not big enough to remember the referenced substrings,
2418         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
2419         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
2420         memory is automatically freed at the end of matching.         memory is automatically freed at the end of matching.
2421    
2422           This error is also given if pcre_stack_malloc() fails  in  pcre_exec().
2423           This  can happen only when PCRE has been compiled with --disable-stack-
2424           for-recursion.
2425    
2426           PCRE_ERROR_NOSUBSTRING    (-7)           PCRE_ERROR_NOSUBSTRING    (-7)
2427    
2428         This  error is used by the pcre_copy_substring(), pcre_get_substring(),         This error is used by the pcre_copy_substring(),  pcre_get_substring(),
2429         and  pcre_get_substring_list()  functions  (see  below).  It  is  never         and  pcre_get_substring_list()  functions  (see  below).  It  is  never
2430         returned by pcre_exec().         returned by pcre_exec().
2431    
2432           PCRE_ERROR_MATCHLIMIT     (-8)           PCRE_ERROR_MATCHLIMIT     (-8)
2433    
2434         The  recursion  and backtracking limit, as specified by the match_limit         The backtracking limit, as specified by  the  match_limit  field  in  a
2435         field in a pcre_extra structure (or defaulted)  was  reached.  See  the         pcre_extra  structure  (or  defaulted) was reached. See the description
2436         description above.         above.
2437    
2438           PCRE_ERROR_CALLOUT        (-9)           PCRE_ERROR_CALLOUT        (-9)
2439    
2440         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
2441         use by callout functions that want to yield a distinctive  error  code.         use  by  callout functions that want to yield a distinctive error code.
2442         See the pcrecallout documentation for details.         See the pcrecallout documentation for details.
2443    
2444           PCRE_ERROR_BADUTF8        (-10)           PCRE_ERROR_BADUTF8        (-10)
2445    
2446         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
2447         subject.         subject.   However,  if  PCRE_PARTIAL_HARD  is set and the problem is a
2448           truncated UTF-8 character at the end of the subject,  PCRE_ERROR_SHORT-
2449           UTF8 is used instead.
2450    
2451           PCRE_ERROR_BADUTF8_OFFSET (-11)           PCRE_ERROR_BADUTF8_OFFSET (-11)
2452    
2453         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
2454         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-
2455         ter.         ter or the end of the subject.
2456    
2457           PCRE_ERROR_PARTIAL        (-12)           PCRE_ERROR_PARTIAL        (-12)
2458    
2459         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
2460         pcrepartial documentation for details of partial matching.         pcrepartial documentation for details of partial matching.
2461    
2462           PCRE_ERROR_BADPARTIAL     (-13)           PCRE_ERROR_BADPARTIAL     (-13)
2463    
2464         The  PCRE_PARTIAL  option  was  used with a compiled pattern containing         This code is no longer in  use.  It  was  formerly  returned  when  the
2465         items that are not supported for partial matching. See the  pcrepartial         PCRE_PARTIAL  option  was used with a compiled pattern containing items
2466         documentation for details of partial matching.         that were  not  supported  for  partial  matching.  From  release  8.00
2467           onwards, there are no restrictions on partial matching.
2468    
2469           PCRE_ERROR_INTERNAL       (-14)           PCRE_ERROR_INTERNAL       (-14)
2470    
# Line 1752  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2473  MATCHING A PATTERN: THE TRADITIONAL FUNC
2473    
2474           PCRE_ERROR_BADCOUNT       (-15)           PCRE_ERROR_BADCOUNT       (-15)
2475    
2476         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.
2477    
2478             PCRE_ERROR_RECURSIONLIMIT (-21)
2479    
2480           The internal recursion limit, as specified by the match_limit_recursion
2481           field  in  a  pcre_extra  structure (or defaulted) was reached. See the
2482           description above.
2483    
2484             PCRE_ERROR_BADNEWLINE     (-23)
2485    
2486           An invalid combination of PCRE_NEWLINE_xxx options was given.
2487    
2488             PCRE_ERROR_BADOFFSET      (-24)
2489    
2490           The value of startoffset was negative or greater than the length of the
2491           subject, that is, the value in length.
2492    
2493             PCRE_ERROR_SHORTUTF8      (-25)
2494    
2495           The  subject  string ended with an incomplete (truncated) UTF-8 charac-
2496           ter, and the PCRE_PARTIAL_HARD option was  set.  Without  this  option,
2497           PCRE_ERROR_BADUTF8 is returned in this situation.
2498    
2499           Error numbers -16 to -20 and -22 are not used by pcre_exec().
2500    
2501    
2502  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
# Line 1774  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2518  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2518         string_list() are provided for extracting captured substrings  as  new,         string_list() are provided for extracting captured substrings  as  new,
2519         separate,  zero-terminated strings. These functions identify substrings         separate,  zero-terminated strings. These functions identify substrings
2520         by number. The next section describes functions  for  extracting  named         by number. The next section describes functions  for  extracting  named
2521         substrings.  A  substring  that  contains  a  binary  zero is correctly         substrings.
2522         extracted and has a further zero added on the end, but  the  result  is  
2523         not, of course, a C string.         A  substring that contains a binary zero is correctly extracted and has
2524           a further zero added on the end, but the result is not, of course, a  C
2525           string.   However,  you  can  process such a string by referring to the
2526           length that is  returned  by  pcre_copy_substring()  and  pcre_get_sub-
2527           string().  Unfortunately, the interface to pcre_get_substring_list() is
2528           not adequate for handling strings containing binary zeros, because  the
2529           end of the final string is not independently indicated.
2530    
2531         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-
2532         tions: subject is the subject string that has  just  been  successfully         tions: subject is the subject string that has  just  been  successfully
# Line 1796  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2546  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2546         buffersize, while for pcre_get_substring() a new  block  of  memory  is         buffersize, while for pcre_get_substring() a new  block  of  memory  is
2547         obtained  via  pcre_malloc,  and its address is returned via stringptr.         obtained  via  pcre_malloc,  and its address is returned via stringptr.
2548         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
2549         the terminating zero, or one of         the terminating zero, or one of these error codes:
2550    
2551           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2552    
# Line 1812  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2562  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2562         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
2563         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
2564         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
2565         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
2566           error code
2567    
2568           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2569    
2570         if the attempt to get the memory block failed.         if the attempt to get the memory block failed.
2571    
2572         When  any of these functions encounter a substring that is unset, which         When any of these functions encounter a substring that is unset,  which
2573         can happen when capturing subpattern number n+1 matches  some  part  of         can  happen  when  capturing subpattern number n+1 matches some part of
2574         the  subject, but subpattern n has not been used at all, they return an         the subject, but subpattern n has not been used at all, they return  an
2575         empty string. This can be distinguished from a genuine zero-length sub-         empty string. This can be distinguished from a genuine zero-length sub-
2576         string  by inspecting the appropriate offset in ovector, which is nega-         string by inspecting the appropriate offset in ovector, which is  nega-
2577         tive for unset substrings.         tive for unset substrings.
2578    
2579         The two convenience functions pcre_free_substring() and  pcre_free_sub-         The  two convenience functions pcre_free_substring() and pcre_free_sub-
2580         string_list()  can  be  used  to free the memory returned by a previous         string_list() can be used to free the memory  returned  by  a  previous
2581         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-
2582         tively.  They  do  nothing  more  than  call the function pointed to by         tively. They do nothing more than  call  the  function  pointed  to  by
2583         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.
2584         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-
2585         cial  interface  to  another  programming  language  which  cannot  use         cial   interface  to  another  programming  language  that  cannot  use
2586         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-
2587         vided.         vided.
2588    
2589    
# Line 1851  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2602  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2602              int stringcount, const char *stringname,              int stringcount, const char *stringname,
2603              const char **stringptr);              const char **stringptr);
2604    
2605         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-
2606         ber.  For example, for this pattern         ber.  For example, for this pattern
2607    
2608           (a+)b(?P<xxx>\d+)...           (a+)b(?<xxx>\d+)...
2609    
2610         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
2611         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
2612         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-
2613         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
2614         there is no subpattern of that name.         the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if  there  is  no
2615           subpattern of that name.
2616    
2617         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
2618         the functions described in the previous section. For convenience, there         the functions described in the previous section. For convenience, there
# Line 1879  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2631  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2631    
2632         These functions call pcre_get_stringnumber(), and if it succeeds,  they         These functions call pcre_get_stringnumber(), and if it succeeds,  they
2633         then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-         then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-
2634         ate.         ate. NOTE: If PCRE_DUPNAMES is set and there are duplicate  names,  the
2635           behaviour may not be what you want (see the next section).
2636    
2637           Warning: If the pattern uses the (?| feature to set up multiple subpat-
2638           terns with the same number, as described in the  section  on  duplicate
2639           subpattern  numbers  in  the  pcrepattern page, you cannot use names to
2640           distinguish the different subpatterns, because names are  not  included
2641           in  the compiled code. The matching process uses only numbers. For this
2642           reason, the use of different names for subpatterns of the  same  number
2643           causes an error at compile time.
2644    
2645    
2646    DUPLICATE SUBPATTERN NAMES
2647    
2648           int pcre_get_stringtable_entries(const pcre *code,
2649                const char *name, char **first, char **last);
2650    
2651           When  a  pattern  is  compiled with the PCRE_DUPNAMES option, names for
2652           subpatterns are not required to be unique. (Duplicate names are  always
2653           allowed  for subpatterns with the same number, created by using the (?|
2654           feature. Indeed, if such subpatterns are named, they  are  required  to
2655           use the same names.)
2656    
2657           Normally, patterns with duplicate names are such that in any one match,
2658           only one of the named subpatterns participates. An example is shown  in
2659           the pcrepattern documentation.
2660    
2661           When    duplicates   are   present,   pcre_copy_named_substring()   and
2662           pcre_get_named_substring() return the first substring corresponding  to
2663           the  given  name  that  is set. If none are set, PCRE_ERROR_NOSUBSTRING
2664           (-7) is returned; no  data  is  returned.  The  pcre_get_stringnumber()
2665           function  returns one of the numbers that are associated with the name,
2666           but it is not defined which it is.
2667    
2668           If you want to get full details of all captured substrings for a  given
2669           name,  you  must  use  the pcre_get_stringtable_entries() function. The
2670           first argument is the compiled pattern, and the second is the name. The
2671           third  and  fourth  are  pointers to variables which are updated by the
2672           function. After it has run, they point to the first and last entries in
2673           the  name-to-number  table  for  the  given  name.  The function itself
2674           returns the length of each entry,  or  PCRE_ERROR_NOSUBSTRING  (-7)  if
2675           there  are none. The format of the table is described above in the sec-
2676           tion entitled Information about a  pattern.   Given  all  the  relevant
2677           entries  for the name, you can extract each of their numbers, and hence
2678           the captured data, if any.
2679    
2680    
2681  FINDING ALL POSSIBLE MATCHES  FINDING ALL POSSIBLE MATCHES
# Line 1908  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2704  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2704              int *workspace, int wscount);              int *workspace, int wscount);
2705    
2706         The  function  pcre_dfa_exec()  is  called  to  match  a subject string         The  function  pcre_dfa_exec()  is  called  to  match  a subject string
2707         against a compiled pattern, using a "DFA" matching algorithm. This  has         against a compiled pattern, using a matching algorithm that  scans  the
2708         different  characteristics to the normal algorithm, and is not compati-         subject  string  just  once, and does not backtrack. This has different
2709         ble with Perl. Some of the features of PCRE patterns are not supported.         characteristics to the normal algorithm, and  is  not  compatible  with
2710         Nevertheless, there are times when this kind of matching can be useful.         Perl.  Some  of the features of PCRE patterns are not supported. Never-
2711         For a discussion of the two matching algorithms, see  the  pcrematching         theless, there are times when this kind of matching can be useful.  For
2712         documentation.         a  discussion  of  the  two matching algorithms, and a list of features
2713           that pcre_dfa_exec() does not support, see the pcrematching  documenta-
2714           tion.
2715    
2716         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
2717         pcre_exec(), plus two extras. The ovector argument is used in a differ-         pcre_exec(), plus two extras. The ovector argument is used in a differ-
# Line 1925  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2723  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2723         workspace vector should contain at least 20 elements. It  is  used  for         workspace vector should contain at least 20 elements. It  is  used  for
2724         keeping  track  of  multiple  paths  through  the  pattern  tree.  More         keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2725         workspace will be needed for patterns and subjects where  there  are  a         workspace will be needed for patterns and subjects where  there  are  a
2726         lot of possible matches.         lot of potential matches.
2727    
2728         Here is an example of a simple call to pcre_exec():         Here is an example of a simple call to pcre_dfa_exec():
2729    
2730           int rc;           int rc;
2731           int ovector[10];           int ovector[10];
2732           int wspace[20];           int wspace[20];
2733           rc = pcre_exec(           rc = pcre_dfa_exec(
2734             re,             /* result of pcre_compile() */             re,             /* result of pcre_compile() */
2735             NULL,           /* we didn't study the pattern */             NULL,           /* we didn't study the pattern */
2736             "some string",  /* the subject string */             "some string",  /* the subject string */
# Line 1947  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2745  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2745     Option bits for pcre_dfa_exec()     Option bits for pcre_dfa_exec()
2746    
2747         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
2748         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-
2749         PCRE_NOTEOL,     PCRE_NOTEMPTY,    PCRE_NO_UTF8_CHECK,    PCRE_PARTIAL,         LINE_xxx,        PCRE_NOTBOL,        PCRE_NOTEOL,        PCRE_NOTEMPTY,
2750         PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All  but  the  last  three  of         PCRE_NOTEMPTY_ATSTART,      PCRE_NO_UTF8_CHECK,       PCRE_BSR_ANYCRLF,
2751         these  are  the  same  as  for pcre_exec(), so their description is not         PCRE_BSR_UNICODE,  PCRE_NO_START_OPTIMIZE, PCRE_PARTIAL_HARD, PCRE_PAR-
2752         repeated here.         TIAL_SOFT, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART.  All but  the  last
2753           four  of  these  are  exactly  the  same  as  for pcre_exec(), so their
2754           PCRE_PARTIAL         description is not repeated here.
2755    
2756         This has the same general effect as it does for  pcre_exec(),  but  the           PCRE_PARTIAL_HARD
2757         details   are   slightly   different.  When  PCRE_PARTIAL  is  set  for           PCRE_PARTIAL_SOFT
2758         pcre_dfa_exec(), the return code PCRE_ERROR_NOMATCH is  converted  into  
2759         PCRE_ERROR_PARTIAL  if  the  end  of the subject is reached, there have         These have the same general effect as they do for pcre_exec(), but  the
2760         been no complete matches, but there is still at least one matching pos-         details  are  slightly  different.  When  PCRE_PARTIAL_HARD  is set for
2761         sibility.  The portion of the string that provided the partial match is         pcre_dfa_exec(), it returns PCRE_ERROR_PARTIAL if the end of  the  sub-
2762         set as the first matching string.         ject  is  reached  and there is still at least one matching possibility
2763           that requires additional characters. This happens even if some complete
2764           matches have also been found. When PCRE_PARTIAL_SOFT is set, the return
2765           code PCRE_ERROR_NOMATCH is converted into PCRE_ERROR_PARTIAL if the end
2766           of  the  subject  is  reached, there have been no complete matches, but
2767           there is still at least one matching possibility. The  portion  of  the
2768           string  that  was inspected when the longest partial match was found is
2769           set as the first matching string  in  both  cases.   There  is  a  more
2770           detailed  discussion  of partial and multi-segment matching, with exam-
2771           ples, in the pcrepartial documentation.
2772    
2773           PCRE_DFA_SHORTEST           PCRE_DFA_SHORTEST
2774    
2775         Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to         Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to
2776         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-
2777         algorithm works, this is necessarily the shortest possible match at the         tive algorithm works, this is necessarily the shortest  possible  match
2778         first possible matching point in the subject string.         at the first possible matching point in the subject string.
2779    
2780           PCRE_DFA_RESTART           PCRE_DFA_RESTART
2781    
2782         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
2783         returns a partial match, it is possible to call it  again,  with  addi-         again, with additional subject characters, and have  it  continue  with
2784         tional  subject  characters,  and have it continue with the same match.         the  same match. The PCRE_DFA_RESTART option requests this action; when
2785         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
2786         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
2787         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
2788         match.  There  is  more  discussion of this facility in the pcrepartial         pcrepartial documentation.
        documentation.  
2789    
2790     Successful returns from pcre_dfa_exec()     Successful returns from pcre_dfa_exec()
2791    
2792         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-
2793         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
2794         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
2795         matches  are all initial substrings of the longer matches. For example,         matches are all initial substrings of the longer matches. For  example,
2796         if the pattern         if the pattern
2797    
2798           <.*>           <.*>
# Line 2001  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2807  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2807           <something> <something else>           <something> <something else>
2808           <something> <something else> <something further>           <something> <something else> <something further>
2809    
2810         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,
2811         which  is  the  number of matched substrings. The substrings themselves         which is the number of matched substrings.  The  substrings  themselves
2812         are returned in ovector. Each string uses two elements;  the  first  is         are  returned  in  ovector. Each string uses two elements; the first is
2813         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
2814         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
2815         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
2816         with the way pcre_exec() returns data, even though the meaning  of  the         compatibility  with  the  way pcre_exec() returns data, even though the
2817         strings is different.)         meaning of the strings is different.)
2818    
2819         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-
2820         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
2821         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
2822         filled with the longest matches.         filled with the longest matches.
2823    
2824     Error returns from pcre_dfa_exec()     Error returns from pcre_dfa_exec()
2825    
2826         The pcre_dfa_exec() function returns a negative number when  it  fails.         The  pcre_dfa_exec()  function returns a negative number when it fails.
2827         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
2828         described above.  There are in addition the following errors  that  are         described  above.   There are in addition the following errors that are
2829         specific to pcre_dfa_exec():         specific to pcre_dfa_exec():
2830    
2831           PCRE_ERROR_DFA_UITEM      (-16)           PCRE_ERROR_DFA_UITEM      (-16)
2832    
2833         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-
2834         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
2835         reference.         reference.
2836    
2837           PCRE_ERROR_DFA_UCOND      (-17)           PCRE_ERROR_DFA_UCOND      (-17)
2838    
2839         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
2840         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
2841         supported.         in a specific group. These are not supported.
2842    
2843           PCRE_ERROR_DFA_UMLIMIT    (-18)           PCRE_ERROR_DFA_UMLIMIT    (-18)
2844    
2845         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
2846         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
2847         (it is meaningless).         (it is meaningless).
2848    
2849           PCRE_ERROR_DFA_WSSIZE     (-19)           PCRE_ERROR_DFA_WSSIZE     (-19)
2850    
2851         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
2852         workspace vector.         workspace vector.
2853    
2854           PCRE_ERROR_DFA_RECURSE    (-20)           PCRE_ERROR_DFA_RECURSE    (-20)
2855    
2856         When a recursive subpattern is processed, the matching  function  calls         When  a  recursive subpattern is processed, the matching function calls
2857         itself  recursively,  using  private vectors for ovector and workspace.         itself recursively, using private vectors for  ovector  and  workspace.
2858         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
2859         should be extremely rare, as a vector of size 1000 is used.         should be extremely rare, as a vector of size 1000 is used.
2860    
2861  Last updated: 16 May 2005  
2862  Copyright (c) 1997-2005 University of Cambridge.  SEE ALSO
2863    
2864           pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3),  pcrepar-
2865           tial(3), pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
2866    
2867    
2868    AUTHOR
2869    
2870           Philip Hazel
2871           University Computing Service
2872           Cambridge CB2 3QH, England.
2873    
2874    
2875    REVISION
2876    
2877           Last updated: 21 November 2010
2878           Copyright (c) 1997-2010 University of Cambridge.
2879  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2880    
2881    
# Line 2080  PCRE CALLOUTS Line 2902  PCRE CALLOUTS
2902         default value is zero.  For  example,  this  pattern  has  two  callout         default value is zero.  For  example,  this  pattern  has  two  callout
2903         points:         points:
2904    
2905           (?C1)eabc(?C2)def           (?C1)abc(?C2)def
2906    
2907         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
2908         called, PCRE automatically  inserts  callouts,  all  with  number  255,         pcre_compile2() is called, PCRE  automatically  inserts  callouts,  all
2909         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
2910         used with the pattern         PCRE_AUTO_CALLOUT is used with the pattern
2911    
2912           A(\d{2}|--)           A(\d{2}|--)
2913    
# Line 2104  PCRE CALLOUTS Line 2926  PCRE CALLOUTS
2926  MISSING CALLOUTS  MISSING CALLOUTS
2927    
2928         You  should  be  aware  that,  because of optimizations in the way PCRE         You  should  be  aware  that,  because of optimizations in the way PCRE
2929         matches patterns, callouts sometimes do not happen. For example, if the         matches patterns by default, callouts  sometimes  do  not  happen.  For
2930         pattern is         example, if the pattern is
2931    
2932           ab(?C4)cd           ab(?C4)cd
2933    
# Line 2114  MISSING CALLOUTS Line 2936  MISSING CALLOUTS
2936         ever  start,  and  the  callout is never reached. However, with "abyd",         ever  start,  and  the  callout is never reached. However, with "abyd",
2937         though the result is still no match, the callout is obeyed.         though the result is still no match, the callout is obeyed.
2938    
2939           If the pattern is studied, PCRE knows the minimum length of a  matching
2940           string,  and will immediately give a "no match" return without actually
2941           running a match if the subject is not long enough, or,  for  unanchored
2942           patterns, if it has been scanned far enough.
2943    
2944           You  can disable these optimizations by passing the PCRE_NO_START_OPTI-
2945           MIZE option to pcre_compile(), pcre_exec(), or pcre_dfa_exec(),  or  by
2946           starting the pattern with (*NO_START_OPT). This slows down the matching
2947           process, but does ensure that callouts such as the  example  above  are
2948           obeyed.
2949    
2950    
2951  THE CALLOUT INTERFACE  THE CALLOUT INTERFACE
2952    
2953         During matching, when PCRE reaches a callout point, the external  func-         During  matching, when PCRE reaches a callout point, the external func-
2954         tion  defined by pcre_callout is called (if it is set). This applies to         tion defined by pcre_callout is called (if it is set). This applies  to
2955         both the pcre_exec() and the pcre_dfa_exec()  matching  functions.  The         both  the  pcre_exec()  and the pcre_dfa_exec() matching functions. The
2956         only  argument  to  the callout function is a pointer to a pcre_callout         only argument to the callout function is a pointer  to  a  pcre_callout
2957         block. This structure contains the following fields:         block. This structure contains the following fields:
2958    
2959           int          version;           int          version;
# Line 2136  THE CALLOUT INTERFACE Line 2969  THE CALLOUT INTERFACE
2969           int          pattern_position;           int          pattern_position;
2970           int          next_item_length;           int          next_item_length;
2971    
2972         The version field is an integer containing the version  number  of  the         The  version  field  is an integer containing the version number of the
2973         block  format. The initial version was 0; the current version is 1. The         block format. The initial version was 0; the current version is 1.  The
2974         version number will change again in future  if  additional  fields  are         version  number  will  change  again in future if additional fields are
2975         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.
2976    
2977         The callout_number field contains the number of the  callout,  as  com-         The callout_number field contains the number of the  callout,  as  com-
# Line 2155  THE CALLOUT INTERFACE Line 2988  THE CALLOUT INTERFACE
2988         The subject and subject_length fields contain copies of the values that         The subject and subject_length fields contain copies of the values that
2989         were passed to pcre_exec().         were passed to pcre_exec().
2990    
2991         The start_match field contains the offset within the subject  at  which         The start_match field normally contains the offset within  the  subject
2992         the  current match attempt started. If the pattern is not anchored, the         at  which  the  current  match  attempt started. However, if the escape
2993         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
2994         pattern for different starting points in the subject.         modified  starting  point.  If the pattern is not anchored, the callout
2995           function may be called several times from the same point in the pattern
2996           for different starting points in the subject.
2997    
2998         The  current_position  field  contains the offset within the subject of         The  current_position  field  contains the offset within the subject of
2999         the current match pointer.         the current match pointer.
# Line 2203  RETURN VALUES Line 3038  RETURN VALUES
3038         zero, matching fails at the current point, but  the  testing  of  other         zero, matching fails at the current point, but  the  testing  of  other
3039         matching possibilities goes ahead, just as if a lookahead assertion had         matching possibilities goes ahead, just as if a lookahead assertion had
3040         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
3041         pcre_exec() (or pcre_dfa_exec()) returns the negative value.         pcre_exec() or pcre_dfa_exec() returns the negative value.
3042    
3043         Negative   values   should   normally   be   chosen  from  the  set  of         Negative   values   should   normally   be   chosen  from  the  set  of
3044         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-
# Line 2211  RETURN VALUES Line 3046  RETURN VALUES
3046         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
3047         itself.         itself.
3048    
3049  Last updated: 28 February 2005  
3050  Copyright (c) 1997-2005 University of Cambridge.  AUTHOR
3051    
3052           Philip Hazel
3053           University Computing Service
3054           Cambridge CB2 3QH, England.
3055    
3056    
3057    REVISION
3058    
3059           Last updated: 21 November 2010
3060           Copyright (c) 1997-2010 University of Cambridge.
3061  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
3062    
3063    
# Line 2227  DIFFERENCES BETWEEN PCRE AND PERL Line 3072  DIFFERENCES BETWEEN PCRE AND PERL
3072    
3073         This  document describes the differences in the ways that PCRE and Perl         This  document describes the differences in the ways that PCRE and Perl
3074         handle regular expressions. The differences  described  here  are  with         handle regular expressions. The differences  described  here  are  with
3075         respect to Perl 5.8.         respect to Perl versions 5.10 and above.
3076    
3077         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
3078         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
3079           main pcre page.
3080    
3081         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl
3082         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,
3083         (?!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
3084         just asserts that the next character is not "a" three times.         just asserts that the next character is not "a" three times.
3085    
3086         3.  Capturing  subpatterns  that occur inside negative lookahead asser-         3. Capturing subpatterns that occur inside  negative  lookahead  asser-
3087         tions are counted, but their entries in the offsets  vector  are  never         tions  are  counted,  but their entries in the offsets vector are never
3088         set.  Perl sets its numerical variables from any such patterns that are         set. Perl sets its numerical variables from any such patterns that  are
3089         matched before the assertion fails to match something (thereby succeed-         matched before the assertion fails to match something (thereby succeed-
3090         ing),  but  only  if the negative lookahead assertion contains just one         ing), but only if the negative lookahead assertion  contains  just  one
3091         branch.         branch.
3092    
3093         4. Though binary zero characters are supported in the  subject  string,         4.  Though  binary zero characters are supported in the subject string,
3094         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-
3095         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
3096         the pattern to represent a binary zero.         the pattern to represent a binary zero.
3097    
3098         5.  The  following Perl escape sequences are not supported: \l, \u, \L,         5. The following Perl escape sequences are not supported: \l,  \u,  \L,
3099         \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-
3100         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
3101         are encountered by PCRE, an error is generated.         are encountered by PCRE, an error is generated.
3102    
3103         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
3104         is  built  with Unicode character property support. The properties that         is built with Unicode character property support. The  properties  that
3105         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-
3106         erties such as Lu and Nd.         erties such as Lu and Nd, script names such as Greek or  Han,  and  the
3107           derived  properties  Any  and  L&. PCRE does support the Cs (surrogate)
3108           property, which Perl does not; the  Perl  documentation  says  "Because
3109           Perl hides the need for the user to understand the internal representa-
3110           tion of Unicode characters, there is no need to implement the  somewhat
3111           messy concept of surrogates."
3112    
3113         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
3114         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 3126  DIFFERENCES BETWEEN PCRE AND PERL
3126         The  \Q...\E  sequence  is recognized both inside and outside character         The  \Q...\E  sequence  is recognized both inside and outside character
3127         classes.         classes.
3128    
3129         8. Fairly obviously, PCRE does not support the (?{code}) and (?p{code})         8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
3130         constructions.  However,  there is support for recursive patterns using         constructions.  However,  there is support for recursive patterns. This
3131         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
3132         "callout"  feature allows an external function to be called during pat-         "callout"  feature allows an external function to be called during pat-
3133         tern matching. See the pcrecallout documentation for details.         tern matching. See the pcrecallout documentation for details.
3134    
3135         9. There are some differences that are concerned with the  settings  of         9. Subpatterns that are called  recursively  or  as  "subroutines"  are
3136           always  treated  as  atomic  groups  in  PCRE. This is like Python, but
3137           unlike Perl. There is a discussion of an example that explains this  in
3138           more  detail  in  the section on recursion differences from Perl in the
3139           pcrepattern page.
3140    
3141           10. There are some differences that are concerned with the settings  of
3142         captured  strings  when  part  of  a  pattern is repeated. For example,         captured  strings  when  part  of  a  pattern is repeated. For example,
3143         matching "aba" against the  pattern  /^(a(b)?)+$/  in  Perl  leaves  $2         matching "aba" against the  pattern  /^(a(b)?)+$/  in  Perl  leaves  $2
3144         unset, but in PCRE it is set to "b".         unset, but in PCRE it is set to "b".
3145    
3146         10. PCRE provides some extensions to the Perl regular expression facil-         11.  PCRE's handling of duplicate subpattern numbers and duplicate sub-
3147         ities:         pattern names is not as general as Perl's. This is a consequence of the
3148           fact the PCRE works internally just with numbers, using an external ta-
3149         (a) Although lookbehind assertions must  match  fixed  length  strings,         ble to translate between numbers and names. In  particular,  a  pattern
3150         each alternative branch of a lookbehind assertion can match a different         such  as  (?|(?<a>A)|(?<b)B),  where the two capturing parentheses have
3151         length of string. Perl requires them all to have the same length.         the same number but different names, is not supported,  and  causes  an
3152           error  at compile time. If it were allowed, it would not be possible to
3153           distinguish which parentheses matched, because both names map  to  cap-
3154           turing subpattern number 1. To avoid this confusing situation, an error
3155           is given at compile time.
3156    
3157           12. Perl recognizes comments in some  places  that  PCRE  doesn't,  for
3158           example, between the ( and ? at the start of a subpattern.
3159    
3160           13. PCRE provides some extensions to the Perl regular expression facil-
3161           ities.  Perl 5.10 includes new features that are not  in  earlier  ver-
3162           sions  of  Perl, some of which (such as named parentheses) have been in
3163           PCRE for some time. This list is with respect to Perl 5.10:
3164    
3165           (a) Although lookbehind assertions in  PCRE  must  match  fixed  length
3166           strings,  each alternative branch of a lookbehind assertion can match a
3167           different length of string. Perl requires them all  to  have  the  same
3168           length.
3169    
3170         (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 $
3171         meta-character matches only at the very end of the string.         meta-character matches only at the very end of the string.
3172    
3173         (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-
3174         cial meaning is faulted.         cial meaning is faulted. Otherwise, like Perl, the backslash is quietly
3175           ignored.  (Perl can be made to issue a warning.)
3176    
3177         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-
3178         fiers is inverted, that is, by default they are not greedy, but if fol-         fiers is inverted, that is, by default they are not greedy, but if fol-
# Line 2306  DIFFERENCES BETWEEN PCRE AND PERL Line 3181  DIFFERENCES BETWEEN PCRE AND PERL
3181         (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
3182         tried only at the first matching position in the subject string.         tried only at the first matching position in the subject string.
3183    
3184         (f)  The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAP-         (f) The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART,
3185         TURE options for pcre_exec() have no Perl equivalents.         and PCRE_NO_AUTO_CAPTURE options for pcre_exec() have no  Perl  equiva-
3186           lents.
3187    
3188         (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
3189         pattern  matching  (Perl  can  do  this using the (?p{code}) construct,         CRLF by the PCRE_BSR_ANYCRLF option.
        which PCRE cannot support.)  
3190    
3191         (h) PCRE supports named capturing substrings, using the Python  syntax.         (h) The callout facility is PCRE-specific.
3192    
3193         (i)  PCRE  supports  the  possessive quantifier "++" syntax, taken from         (i) The partial matching facility is PCRE-specific.
        Sun's Java package.  
3194    
3195         (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,
3196           even on different hosts that have the other endianness.
3197    
3198         (k) The callout facility is PCRE-specific.         (k)  The  alternative  matching function (pcre_dfa_exec()) matches in a
3199           different way and is not Perl-compatible.
3200    
3201         (l) The partial matching facility is PCRE-specific.         (l) PCRE recognizes some special sequences such as (*CR) at  the  start
3202           of a pattern that set overall options that cannot be changed within the
3203           pattern.
3204    
        (m) Patterns compiled by PCRE can be saved and re-used at a later time,  
        even on different hosts that have the other endianness.  
3205    
3206         (n)  The  alternative  matching function (pcre_dfa_exec()) matches in a  AUTHOR
3207         different way and is not Perl-compatible.  
3208           Philip Hazel
3209           University Computing Service
3210           Cambridge CB2 3QH, England.
3211    
3212  Last updated: 28 February 2005  
3213  Copyright (c) 1997-2005 University of Cambridge.  REVISION
3214    
3215           Last updated: 31 October 2010
3216           Copyright (c) 1997-2010 University of Cambridge.
3217  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
3218    
3219    
# Line 2344  NAME Line 3226  NAME
3226    
3227  PCRE REGULAR EXPRESSION DETAILS  PCRE REGULAR EXPRESSION DETAILS
3228    
3229         The  syntax  and semantics of the regular expressions supported by PCRE         The  syntax and semantics of the regular expressions that are supported
3230         are described below. Regular expressions are also described in the Perl         by PCRE are described in detail below. There is a quick-reference  syn-
3231         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
3232         examples.  Jeffrey Friedl's "Mastering Regular Expressions",  published         semantics as closely as it can. PCRE  also  supports  some  alternative
3233         by  O'Reilly, covers regular expressions in great detail. This descrip-         regular  expression  syntax (which does not conflict with the Perl syn-
3234         tion of PCRE's regular expressions is intended as reference material.         tax) in order to provide some compatibility with regular expressions in
3235           Python, .NET, and Oniguruma.
3236    
3237           Perl's  regular expressions are described in its own documentation, and
3238           regular expressions in general are covered in a number of  books,  some
3239           of  which  have  copious  examples. Jeffrey Friedl's "Mastering Regular
3240           Expressions", published by  O'Reilly,  covers  regular  expressions  in
3241           great  detail.  This  description  of  PCRE's  regular  expressions  is
3242           intended as reference material.
3243    
3244         The original operation of PCRE was on strings of  one-byte  characters.         The original operation of PCRE was on strings of  one-byte  characters.
3245         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
3246         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
3247         pcre_compile()  with  the  PCRE_UTF8  option.  How this affects pattern         pcre_compile()  or  pcre_compile2() with the PCRE_UTF8 option. There is
3248         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:
3249         of  UTF-8  features  in  the  section on UTF-8 support in the main pcre  
3250         page.           (*UTF8)
3251    
3252           Starting a pattern with this sequence  is  equivalent  to  setting  the
3253           PCRE_UTF8  option.  This  feature  is  not Perl-compatible. How setting
3254           UTF-8 mode affects pattern matching  is  mentioned  in  several  places
3255           below.  There  is  also  a  summary of UTF-8 features in the section on
3256           UTF-8 support in the main pcre page.
3257    
3258           Another special sequence that may appear at the start of a  pattern  or
3259           in combination with (*UTF8) is:
3260    
3261             (*UCP)
3262    
3263           This  has  the  same  effect  as setting the PCRE_UCP option: it causes
3264           sequences such as \d and \w to  use  Unicode  properties  to  determine
3265           character types, instead of recognizing only characters with codes less
3266           than 128 via a lookup table.
3267    
3268           If a pattern starts with (*NO_START_OPT), it has  the  same  effect  as
3269           setting the PCRE_NO_START_OPTIMIZE option either at compile or matching
3270           time. There are also some more of these special sequences that are con-
3271           cerned with the handling of newlines; they are described below.
3272    
3273           The  remainder  of  this  document discusses the patterns that are sup-
3274           ported by PCRE when its main matching function, pcre_exec(),  is  used.
3275           From   release   6.0,   PCRE   offers   a   second  matching  function,
3276           pcre_dfa_exec(), which matches using a different algorithm that is  not
3277           Perl-compatible. Some of the features discussed below are not available
3278           when pcre_dfa_exec() is used. The advantages and disadvantages  of  the
3279           alternative  function, and how it differs from the normal function, are
3280           discussed in the pcrematching page.
3281    
3282    
3283    NEWLINE CONVENTIONS
3284    
3285           PCRE supports five different conventions for indicating line breaks  in
3286           strings:  a  single  CR (carriage return) character, a single LF (line-
3287           feed) character, the two-character sequence CRLF, any of the three pre-
3288           ceding,  or  any Unicode newline sequence. The pcreapi page has further
3289           discussion about newlines, and shows how to set the newline  convention
3290           in the options arguments for the compiling and matching functions.
3291    
3292           It  is also possible to specify a newline convention by starting a pat-
3293           tern string with one of the following five sequences:
3294    
3295             (*CR)        carriage return
3296             (*LF)        linefeed
3297             (*CRLF)      carriage return, followed by linefeed
3298             (*ANYCRLF)   any of the three above
3299             (*ANY)       all Unicode newline sequences
3300    
3301           These override the default and the options given to  pcre_compile()  or
3302           pcre_compile2().  For example, on a Unix system where LF is the default
3303           newline sequence, the pattern
3304    
3305             (*CR)a.b
3306    
3307           changes the convention to CR. That pattern matches "a\nb" because LF is
3308           no  longer  a  newline. Note that these special settings, which are not
3309           Perl-compatible, are recognized only at the very start  of  a  pattern,
3310           and  that  they  must  be  in  upper  case. If more than one of them is
3311           present, the last one is used.
3312    
3313           The newline convention affects the interpretation of the dot  metachar-
3314           acter  when  PCRE_DOTALL is not set, and also the behaviour of \N. How-
3315           ever, it does not affect  what  the  \R  escape  sequence  matches.  By
3316           default,  this is any Unicode newline sequence, for Perl compatibility.
3317           However, this can be changed; see the description of \R in the  section
3318           entitled  "Newline sequences" below. A change of \R setting can be com-
3319           bined with a change of newline convention.
3320    
3321         The remainder of this document discusses the  patterns  that  are  sup-  
3322         ported  by  PCRE when its main matching function, pcre_exec(), is used.  CHARACTERS AND METACHARACTERS
        From  release  6.0,   PCRE   offers   a   second   matching   function,  
        pcre_dfa_exec(),  which matches using a different algorithm that is not  
        Perl-compatible. The advantages and disadvantages  of  the  alternative  
        function, and how it differs from the normal function, are discussed in  
        the pcrematching page.  
3323    
3324         A regular expression is a pattern that is  matched  against  a  subject         A regular expression is a pattern that is  matched  against  a  subject
3325         string  from  left  to right. Most characters stand for themselves in a         string  from  left  to right. Most characters stand for themselves in a
# Line 2391  PCRE REGULAR EXPRESSION DETAILS Line 3345  PCRE REGULAR EXPRESSION DETAILS
3345    
3346         There are two different sets of metacharacters: those that  are  recog-         There are two different sets of metacharacters: those that  are  recog-
3347         nized  anywhere in the pattern except within square brackets, and those         nized  anywhere in the pattern except within square brackets, and those
3348         that are recognized in square brackets. Outside  square  brackets,  the         that are recognized within square brackets.  Outside  square  brackets,
3349         metacharacters are as follows:         the metacharacters are as follows:
3350    
3351           \      general escape character with several uses           \      general escape character with several uses
3352           ^      assert start of string (or line, in multiline mode)           ^      assert start of string (or line, in multiline mode)
# Line 2420  PCRE REGULAR EXPRESSION DETAILS Line 3374  PCRE REGULAR EXPRESSION DETAILS
3374                    syntax)                    syntax)
3375           ]      terminates the character class           ]      terminates the character class
3376    
3377         The following sections describe the use of each of the  metacharacters.         The following sections describe the use of each of the metacharacters.
3378    
3379    
3380  BACKSLASH  BACKSLASH
3381    
3382         The backslash character has several uses. Firstly, if it is followed by         The backslash character has several uses. Firstly, if it is followed by
3383         a non-alphanumeric character, it takes away any  special  meaning  that         a character that is not a number or a letter, it takes away any special
3384         character  may  have.  This  use  of  backslash  as an escape character         meaning that character may have. This use of  backslash  as  an  escape
3385         applies both inside and outside character classes.         character applies both inside and outside character classes.
3386    
3387         For example, if you want to match a * character, you write  \*  in  the         For  example,  if  you want to match a * character, you write \* in the
3388         pattern.   This  escaping  action  applies whether or not the following         pattern.  This escaping action applies whether  or  not  the  following
3389         character would otherwise be interpreted as a metacharacter, so  it  is         character  would  otherwise be interpreted as a metacharacter, so it is
3390         always  safe  to  precede  a non-alphanumeric with backslash to specify         always safe to precede a non-alphanumeric  with  backslash  to  specify
3391         that it stands for itself. In particular, if you want to match a  back-         that  it stands for itself. In particular, if you want to match a back-
3392         slash, you write \\.         slash, you write \\.
3393    
3394         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in         In UTF-8 mode, only ASCII numbers and letters have any special  meaning
3395         the pattern (other than in a character class) and characters between  a         after  a  backslash.  All  other characters (in particular, those whose
3396         # outside a character class and the next newline character are ignored.         codepoints are greater than 127) are treated as literals.
3397         An escaping backslash can be used to include a whitespace or #  charac-  
3398         ter as part of the pattern.         If a pattern is compiled with the PCRE_EXTENDED option,  whitespace  in
3399           the  pattern (other than in a character class) and characters between a
3400         If  you  want  to remove the special meaning from a sequence of charac-         # outside a character class and the next newline are ignored. An escap-
3401         ters, you can do so by putting them between \Q and \E. This is  differ-         ing  backslash  can  be  used to include a whitespace or # character as
3402         ent  from  Perl  in  that  $  and  @ are handled as literals in \Q...\E         part of the pattern.
3403         sequences in PCRE, whereas in Perl, $ and @ cause  variable  interpola-  
3404           If you want to remove the special meaning from a  sequence  of  charac-
3405           ters,  you can do so by putting them between \Q and \E. This is differ-
3406           ent from Perl in that $ and  @  are  handled  as  literals  in  \Q...\E
3407           sequences  in  PCRE, whereas in Perl, $ and @ cause variable interpola-
3408         tion. Note the following examples:         tion. Note the following examples:
3409    
3410           Pattern            PCRE matches   Perl matches           Pattern            PCRE matches   Perl matches
# Line 2456  BACKSLASH Line 3414  BACKSLASH
3414           \Qabc\$xyz\E       abc\$xyz       abc\$xyz           \Qabc\$xyz\E       abc\$xyz       abc\$xyz
3415           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz
3416    
3417         The  \Q...\E  sequence  is recognized both inside and outside character         The \Q...\E sequence is recognized both inside  and  outside  character
3418         classes.         classes.  An isolated \E that is not preceded by \Q is ignored.
3419    
3420     Non-printing characters     Non-printing characters
3421    
3422         A second use of backslash provides a way of encoding non-printing char-         A second use of backslash provides a way of encoding non-printing char-
3423         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
3424         appearance of non-printing characters, apart from the binary zero  that         appearance  of non-printing characters, apart from the binary zero that
3425         terminates  a  pattern,  but  when  a pattern is being prepared by text         terminates a pattern, but when a pattern  is  being  prepared  by  text
3426         editing, it is usually easier  to  use  one  of  the  following  escape         editing,  it  is  often  easier  to  use  one  of  the following escape
3427         sequences than the binary character it represents:         sequences than the binary character it represents:
3428    
3429           \a        alarm, that is, the BEL character (hex 07)           \a        alarm, that is, the BEL character (hex 07)
3430           \cx       "control-x", where x is any character           \cx       "control-x", where x is any ASCII character
3431           \e        escape (hex 1B)           \e        escape (hex 1B)
3432           \f        formfeed (hex 0C)           \f        formfeed (hex 0C)
3433           \n        newline (hex 0A)           \n        linefeed (hex 0A)
3434           \r        carriage return (hex 0D)           \r        carriage return (hex 0D)
3435           \t        tab (hex 09)           \t        tab (hex 09)
3436           \ddd      character with octal code ddd, or backreference           \ddd      character with octal code ddd, or back reference
3437           \xhh      character with hex code hh           \xhh      character with hex code hh
3438           \x{hhh..} character with hex code hhh... (UTF-8 mode only)           \x{hhh..} character with hex code hhh..
3439    
3440         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,
3441         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
3442         inverted.   Thus  \cz becomes hex 1A, but \c{ becomes hex 3B, while \c;         inverted.  Thus \cz becomes hex 1A (z is 7A), but \c{ becomes hex 3B ({
3443         becomes hex 7B.         is  7B),  while  \c; becomes hex 7B (; is 3B). If the byte following \c
3444           has a value greater than 127, a compile-time error occurs.  This  locks
3445         After \x, from zero to two hexadecimal digits are read (letters can  be         out  non-ASCII  characters in both byte mode and UTF-8 mode. (When PCRE
3446         in  upper or lower case). In UTF-8 mode, any number of hexadecimal dig-         is compiled in EBCDIC mode, all byte values are  valid.  A  lower  case
3447         its may appear between \x{ and }, but the value of the  character  code         letter is converted to upper case, and then the 0xc0 bits are flipped.)
3448         must  be  less  than  2**31  (that is, the maximum hexadecimal value is  
3449         7FFFFFFF). If characters other than hexadecimal digits  appear  between         After  \x, from zero to two hexadecimal digits are read (letters can be
3450         \x{  and }, or if there is no terminating }, this form of escape is not         in upper or lower case). Any number of hexadecimal  digits  may  appear
3451         recognized. Instead, the initial \x will  be  interpreted  as  a  basic         between  \x{  and  },  but the value of the character code must be less
3452         hexadecimal  escape, with no following digits, giving a character whose         than 256 in non-UTF-8 mode, and less than 2**31 in UTF-8 mode. That is,
3453         value is zero.         the  maximum value in hexadecimal is 7FFFFFFF. Note that this is bigger
3454           than the largest Unicode code point, which is 10FFFF.
3455    
3456           If characters other than hexadecimal digits appear between \x{  and  },
3457           or if there is no terminating }, this form of escape is not recognized.
3458           Instead, the initial \x will be  interpreted  as  a  basic  hexadecimal
3459           escape,  with  no  following  digits, giving a character whose value is
3460           zero.
3461    
3462         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
3463         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-
3464         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}.
3465         \x{dc}.  
3466           After \0 up to two further octal digits are read. If  there  are  fewer
3467         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
3468         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
3469         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
3470         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.  
3471    
3472         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-
3473         cated.  Outside a character class, PCRE reads it and any following dig-         cated.  Outside a character class, PCRE reads it and any following dig-
# Line 2516  BACKSLASH Line 3479  BACKSLASH
3479    
3480         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
3481         and  there have not been that many capturing subpatterns, PCRE re-reads         and  there have not been that many capturing subpatterns, PCRE re-reads
3482         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-
3483         gle byte from the least significant 8 bits of the value. Any subsequent         erate  a data character. Any subsequent digits stand for themselves. In
3484         digits stand for themselves.  For example:         non-UTF-8 mode, the value of a character specified  in  octal  must  be
3485           less  than  \400.  In  UTF-8 mode, values up to \777 are permitted. For
3486           example:
3487    
3488           \040   is another way of writing a space           \040   is another way of writing a space
3489           \40    is the same, provided there are fewer than 40           \40    is the same, provided there are fewer than 40
# Line 2538  BACKSLASH Line 3503  BACKSLASH
3503         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
3504         leading zero, because no more than three octal digits are ever read.         leading zero, because no more than three octal digits are ever read.
3505    
3506         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
3507         character (in UTF-8 mode) can be used both inside and outside character         inside and outside character classes. In addition, inside  a  character
3508         classes.  In  addition,  inside  a  character class, the sequence \b is         class,  the  sequence \b is interpreted as the backspace character (hex
3509         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-
3510         interpreted  as  the  character  "X".  Outside a character class, these         ter  class.  Like  any  other  unrecognized  escape sequences, they are
3511         sequences have different meanings (see below).         treated as the literal characters "B", "N", "R", and  "X"  by  default,