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revision 211 by ph10, Thu Aug 9 09:52:43 2007 UTC revision 231 by ph10, Tue Sep 11 11:15:33 2007 UTC
# Line 361  CODE VALUE OF NEWLINE Line 361  CODE VALUE OF NEWLINE
361         conventional to use the standard for your operating system.         conventional to use the standard for your operating system.
362    
363    
364    WHAT \R MATCHES
365    
366           By default, the sequence \R in a pattern matches  any  Unicode  newline
367           sequence,  whatever  has  been selected as the line ending sequence. If
368           you specify
369    
370             --enable-bsr-anycrlf
371    
372           the default is changed so that \R matches only CR, LF, or  CRLF.  What-
373           ever  is selected when PCRE is built can be overridden when the library
374           functions are called.
375    
376    
377  BUILDING SHARED AND STATIC LIBRARIES  BUILDING SHARED AND STATIC LIBRARIES
378    
379         The PCRE building process uses libtool to build both shared and  static         The PCRE building process uses libtool to build both shared and  static
# Line 513  AUTHOR Line 526  AUTHOR
526    
527  REVISION  REVISION
528    
529         Last updated: 30 July 2007         Last updated: 11 September 2007
530         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
531  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
532    
# Line 908  NEWLINES Line 921  NEWLINES
921         dard. When PCRE is run, the default can be overridden,  either  when  a         dard. When PCRE is run, the default can be overridden,  either  when  a
922         pattern is compiled, or when it is matched.         pattern is compiled, or when it is matched.
923    
924           At compile time, the newline convention can be specified by the options
925           argument of pcre_compile(), or it can be specified by special  text  at
926           the start of the pattern itself; this overrides any other settings. See
927           the pcrepattern page for details of the special character sequences.
928    
929         In the PCRE documentation the word "newline" is used to mean "the char-         In the PCRE documentation the word "newline" is used to mean "the char-
930         acter or pair of characters that indicate a line break". The choice  of         acter  or pair of characters that indicate a line break". The choice of
931         newline  convention  affects  the  handling of the dot, circumflex, and         newline convention affects the handling of  the  dot,  circumflex,  and
932         dollar metacharacters, the handling of #-comments in /x mode, and, when         dollar metacharacters, the handling of #-comments in /x mode, and, when
933         CRLF  is a recognized line ending sequence, the match position advance-         CRLF is a recognized line ending sequence, the match position  advance-
934         ment for a non-anchored pattern. The choice of newline convention  does         ment for a non-anchored pattern. There is more detail about this in the
935         not affect the interpretation of the \n or \r escape sequences.         section on pcre_exec() options below.
936    
937           The choice of newline convention does not affect the interpretation  of
938           the  \n  or  \r  escape  sequences, nor does it affect what \R matches,
939           which is controlled in a similar way, but by separate options.
940    
941    
942  MULTITHREADING  MULTITHREADING
943    
944         The  PCRE  functions  can be used in multi-threading applications, with         The PCRE functions can be used in  multi-threading  applications,  with
945         the  proviso  that  the  memory  management  functions  pointed  to  by         the  proviso  that  the  memory  management  functions  pointed  to  by
946         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
947         callout function pointed to by pcre_callout, are shared by all threads.         callout function pointed to by pcre_callout, are shared by all threads.
948    
949         The  compiled form of a regular expression is not altered during match-         The compiled form of a regular expression is not altered during  match-
950         ing, so the same compiled pattern can safely be used by several threads         ing, so the same compiled pattern can safely be used by several threads
951         at once.         at once.
952    
# Line 932  MULTITHREADING Line 954  MULTITHREADING
954  SAVING PRECOMPILED PATTERNS FOR LATER USE  SAVING PRECOMPILED PATTERNS FOR LATER USE
955    
956         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
957         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
958         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
959         pcreprecompile documentation. However, compiling a  regular  expression         pcreprecompile  documentation.  However, compiling a regular expression
960         with  one version of PCRE for use with a different version is not guar-         with one version of PCRE for use with a different version is not  guar-
961         anteed to work and may cause crashes.         anteed to work and may cause crashes.
962    
963    
# Line 943  CHECKING BUILD-TIME OPTIONS Line 965  CHECKING BUILD-TIME OPTIONS
965    
966         int pcre_config(int what, void *where);         int pcre_config(int what, void *where);
967    
968         The function pcre_config() makes it possible for a PCRE client to  dis-         The  function pcre_config() makes it possible for a PCRE client to dis-
969         cover which optional features have been compiled into the PCRE library.         cover which optional features have been compiled into the PCRE library.
970         The pcrebuild documentation has more details about these optional  fea-         The  pcrebuild documentation has more details about these optional fea-
971         tures.         tures.
972    
973         The  first  argument  for pcre_config() is an integer, specifying which         The first argument for pcre_config() is an  integer,  specifying  which
974         information is required; the second argument is a pointer to a variable         information is required; the second argument is a pointer to a variable
975         into  which  the  information  is  placed. The following information is         into which the information is  placed.  The  following  information  is
976         available:         available:
977    
978           PCRE_CONFIG_UTF8           PCRE_CONFIG_UTF8
979    
980         The output is an integer that is set to one if UTF-8 support is  avail-         The  output is an integer that is set to one if UTF-8 support is avail-
981         able; otherwise it is set to zero.         able; otherwise it is set to zero.
982    
983           PCRE_CONFIG_UNICODE_PROPERTIES           PCRE_CONFIG_UNICODE_PROPERTIES
984    
985         The  output  is  an  integer  that is set to one if support for Unicode         The output is an integer that is set to  one  if  support  for  Unicode
986         character properties is available; otherwise it is set to zero.         character properties is available; otherwise it is set to zero.
987    
988           PCRE_CONFIG_NEWLINE           PCRE_CONFIG_NEWLINE
989    
990         The output is an integer whose value specifies  the  default  character         The  output  is  an integer whose value specifies the default character
991         sequence  that is recognized as meaning "newline". The four values that         sequence that is recognized as meaning "newline". The four values  that
992         are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,         are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,
993         and  -1  for  ANY. The default should normally be the standard sequence         and -1 for ANY. The default should normally be  the  standard  sequence
994         for your operating system.         for your operating system.
995    
996             PCRE_CONFIG_BSR
997    
998           The output is an integer whose value indicates what character sequences
999           the \R escape sequence matches by default. A value of 0 means  that  \R
1000           matches  any  Unicode  line ending sequence; a value of 1 means that \R
1001           matches only CR, LF, or CRLF. The default can be overridden when a pat-
1002           tern is compiled or matched.
1003    
1004           PCRE_CONFIG_LINK_SIZE           PCRE_CONFIG_LINK_SIZE
1005    
1006         The output is an integer that contains the number  of  bytes  used  for         The  output  is  an  integer that contains the number of bytes used for
1007         internal linkage in compiled regular expressions. The value is 2, 3, or         internal linkage in compiled regular expressions. The value is 2, 3, or
1008         4. Larger values allow larger regular expressions to  be  compiled,  at         4.  Larger  values  allow larger regular expressions to be compiled, at
1009         the  expense  of  slower matching. The default value of 2 is sufficient         the expense of slower matching. The default value of  2  is  sufficient
1010         for all but the most massive patterns, since  it  allows  the  compiled         for  all  but  the  most massive patterns, since it allows the compiled
1011         pattern to be up to 64K in size.         pattern to be up to 64K in size.
1012    
1013           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
1014    
1015         The  output  is  an integer that contains the threshold above which the         The output is an integer that contains the threshold  above  which  the
1016         POSIX interface uses malloc() for output vectors. Further  details  are         POSIX  interface  uses malloc() for output vectors. Further details are
1017         given in the pcreposix documentation.         given in the pcreposix documentation.
1018    
1019           PCRE_CONFIG_MATCH_LIMIT           PCRE_CONFIG_MATCH_LIMIT
1020    
1021         The output is an integer that gives the default limit for the number of         The output is an integer that gives the default limit for the number of
1022         internal matching function calls in a  pcre_exec()  execution.  Further         internal  matching  function  calls in a pcre_exec() execution. Further
1023         details are given with pcre_exec() below.         details are given with pcre_exec() below.
1024    
1025           PCRE_CONFIG_MATCH_LIMIT_RECURSION           PCRE_CONFIG_MATCH_LIMIT_RECURSION
1026    
1027         The  output is an integer that gives the default limit for the depth of         The output is an integer that gives the default limit for the depth  of
1028         recursion when calling the internal matching function in a  pcre_exec()         recursion  when calling the internal matching function in a pcre_exec()
1029         execution. Further details are given with pcre_exec() below.         execution. Further details are given with pcre_exec() below.
1030    
1031           PCRE_CONFIG_STACKRECURSE           PCRE_CONFIG_STACKRECURSE
1032    
1033         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
1034         running pcre_exec() is implemented by recursive function calls that use         running pcre_exec() is implemented by recursive function calls that use
1035         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
1036         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
1037         on  the  heap  instead  of  recursive  function  calls.  In  this case,         on the  heap  instead  of  recursive  function  calls.  In  this  case,
1038         pcre_stack_malloc and  pcre_stack_free  are  called  to  manage  memory         pcre_stack_malloc  and  pcre_stack_free  are  called  to  manage memory
1039         blocks on the heap, thus avoiding the use of the stack.         blocks on the heap, thus avoiding the use of the stack.
1040    
1041    
# Line 1022  COMPILING A PATTERN Line 1052  COMPILING A PATTERN
1052    
1053         Either of the functions pcre_compile() or pcre_compile2() can be called         Either of the functions pcre_compile() or pcre_compile2() can be called
1054         to compile a pattern into an internal form. The only difference between         to compile a pattern into an internal form. The only difference between
1055         the  two interfaces is that pcre_compile2() has an additional argument,         the two interfaces is that pcre_compile2() has an additional  argument,
1056         errorcodeptr, via which a numerical error code can be returned.         errorcodeptr, via which a numerical error code can be returned.
1057    
1058         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
1059         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
1060         obtained via pcre_malloc is returned. This contains the  compiled  code         obtained  via  pcre_malloc is returned. This contains the compiled code
1061         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
1062         is a typedef for a structure whose contents are not externally defined.         is a typedef for a structure whose contents are not externally defined.
1063         It is up to the caller to free the memory (via pcre_free) when it is no         It is up to the caller to free the memory (via pcre_free) when it is no
1064         longer required.         longer required.
1065    
1066         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
1067         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
1068         fully relocatable, because it may contain a copy of the tableptr  argu-         fully  relocatable, because it may contain a copy of the tableptr argu-
1069         ment, which is an address (see below).         ment, which is an address (see below).
1070    
1071         The options argument contains various bit settings that affect the com-         The options argument contains various bit settings that affect the com-
1072         pilation. It should be zero if no options are required.  The  available         pilation.  It  should be zero if no options are required. The available
1073         options  are  described  below. Some of them, in particular, those that         options are described below. Some of them, in  particular,  those  that
1074         are compatible with Perl, can also be set and  unset  from  within  the         are  compatible  with  Perl,  can also be set and unset from within the
1075         pattern  (see  the  detailed  description in the pcrepattern documenta-         pattern (see the detailed description  in  the  pcrepattern  documenta-
1076         tion). For these options, the contents of the options  argument  speci-         tion).  For  these options, the contents of the options argument speci-
1077         fies  their initial settings at the start of compilation and execution.         fies their initial settings at the start of compilation and  execution.
1078         The PCRE_ANCHORED and PCRE_NEWLINE_xxx options can be set at  the  time         The  PCRE_ANCHORED  and PCRE_NEWLINE_xxx options can be set at the time
1079         of matching as well as at compile time.         of matching as well as at compile time.
1080    
1081         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
1082         if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and
1083         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-
1084         sage. This is a static string that is part of the library. You must not         sage. This is a static string that is part of the library. You must not
1085         try to free it. The offset from the start of the pattern to the charac-         try to free it. The offset from the start of the pattern to the charac-
1086         ter where the error was discovered is placed in the variable pointed to         ter where the error was discovered is placed in the variable pointed to
1087         by  erroffset,  which must not be NULL. If it is, an immediate error is         by erroffset, which must not be NULL. If it is, an immediate  error  is
1088         given.         given.
1089    
1090         If pcre_compile2() is used instead of pcre_compile(),  and  the  error-         If  pcre_compile2()  is  used instead of pcre_compile(), and the error-
1091         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
1092         via this argument in the event of an error. This is in addition to  the         via  this argument in the event of an error. This is in addition to the
1093         textual error message. Error codes and messages are listed below.         textual error message. Error codes and messages are listed below.
1094    
1095         If  the  final  argument, tableptr, is NULL, PCRE uses a default set of         If the final argument, tableptr, is NULL, PCRE uses a  default  set  of
1096         character tables that are  built  when  PCRE  is  compiled,  using  the         character  tables  that  are  built  when  PCRE  is compiled, using the
1097         default  C  locale.  Otherwise, tableptr must be an address that is the         default C locale. Otherwise, tableptr must be an address  that  is  the
1098         result of a call to pcre_maketables(). This value is  stored  with  the         result  of  a  call to pcre_maketables(). This value is stored with the
1099         compiled  pattern,  and used again by pcre_exec(), unless another table         compiled pattern, and used again by pcre_exec(), unless  another  table
1100         pointer is passed to it. For more discussion, see the section on locale         pointer is passed to it. For more discussion, see the section on locale
1101         support below.         support below.
1102    
1103         This  code  fragment  shows a typical straightforward call to pcre_com-         This code fragment shows a typical straightforward  call  to  pcre_com-
1104         pile():         pile():
1105    
1106           pcre *re;           pcre *re;
# Line 1083  COMPILING A PATTERN Line 1113  COMPILING A PATTERN
1113             &erroffset,       /* for error offset */             &erroffset,       /* for error offset */
1114             NULL);            /* use default character tables */             NULL);            /* use default character tables */
1115    
1116         The following names for option bits are defined in  the  pcre.h  header         The  following  names  for option bits are defined in the pcre.h header
1117         file:         file:
1118    
1119           PCRE_ANCHORED           PCRE_ANCHORED
1120    
1121         If this bit is set, the pattern is forced to be "anchored", that is, it         If this bit is set, the pattern is forced to be "anchored", that is, it
1122         is constrained to match only at the first matching point in the  string         is  constrained to match only at the first matching point in the string
1123         that  is being searched (the "subject string"). This effect can also be         that is being searched (the "subject string"). This effect can also  be
1124         achieved by appropriate constructs in the pattern itself, which is  the         achieved  by appropriate constructs in the pattern itself, which is the
1125         only way to do it in Perl.         only way to do it in Perl.
1126    
1127           PCRE_AUTO_CALLOUT           PCRE_AUTO_CALLOUT
1128    
1129         If this bit is set, pcre_compile() automatically inserts callout items,         If this bit is set, pcre_compile() automatically inserts callout items,
1130         all with number 255, before each pattern item. For  discussion  of  the         all  with  number  255, before each pattern item. For discussion of the
1131         callout facility, see the pcrecallout documentation.         callout facility, see the pcrecallout documentation.
1132    
1133             PCRE_BSR_ANYCRLF
1134             PCRE_BSR_UNICODE
1135    
1136           These options (which are mutually exclusive) control what the \R escape
1137           sequence  matches.  The choice is either to match only CR, LF, or CRLF,
1138           or to match any Unicode newline sequence. The default is specified when
1139           PCRE is built. It can be overridden from within the pattern, or by set-
1140           ting an option when a compiled pattern is matched.
1141    
1142           PCRE_CASELESS           PCRE_CASELESS
1143    
1144         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
1145         case letters. It is equivalent to Perl's  /i  option,  and  it  can  be         case  letters.  It  is  equivalent  to  Perl's /i option, and it can be
1146         changed  within a pattern by a (?i) option setting. In UTF-8 mode, PCRE         changed within a pattern by a (?i) option setting. In UTF-8 mode,  PCRE
1147         always understands the concept of case for characters whose values  are         always  understands the concept of case for characters whose values are
1148         less  than 128, so caseless matching is always possible. For characters         less than 128, so caseless matching is always possible. For  characters
1149         with higher values, the concept of case is supported if  PCRE  is  com-         with  higher  values,  the concept of case is supported if PCRE is com-
1150         piled  with Unicode property support, but not otherwise. If you want to         piled with Unicode property support, but not otherwise. If you want  to
1151         use caseless matching for characters 128 and  above,  you  must  ensure         use  caseless  matching  for  characters 128 and above, you must ensure
1152         that  PCRE  is  compiled  with Unicode property support as well as with         that PCRE is compiled with Unicode property support  as  well  as  with
1153         UTF-8 support.         UTF-8 support.
1154    
1155           PCRE_DOLLAR_ENDONLY           PCRE_DOLLAR_ENDONLY
1156    
1157         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
1158         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
1159         matches immediately before a newline at the end of the string (but  not         matches  immediately before a newline at the end of the string (but not
1160         before  any  other newlines). The PCRE_DOLLAR_ENDONLY option is ignored         before any other newlines). The PCRE_DOLLAR_ENDONLY option  is  ignored
1161         if PCRE_MULTILINE is set.  There is no equivalent  to  this  option  in         if  PCRE_MULTILINE  is  set.   There is no equivalent to this option in
1162         Perl, and no way to set it within a pattern.         Perl, and no way to set it within a pattern.
1163    
1164           PCRE_DOTALL           PCRE_DOTALL
1165    
1166         If this bit is set, a dot metacharater in the pattern matches all char-         If this bit is set, a dot metacharater in the pattern matches all char-
1167         acters, including those that indicate newline. Without it, a  dot  does         acters,  including  those that indicate newline. Without it, a dot does
1168         not  match  when  the  current position is at a newline. This option is         not match when the current position is at a  newline.  This  option  is
1169         equivalent to Perl's /s option, and it can be changed within a  pattern         equivalent  to Perl's /s option, and it can be changed within a pattern
1170         by  a (?s) option setting. A negative class such as [^a] always matches         by a (?s) option setting. A negative class such as [^a] always  matches
1171         newline characters, independent of the setting of this option.         newline characters, independent of the setting of this option.
1172    
1173           PCRE_DUPNAMES           PCRE_DUPNAMES
1174    
1175         If this bit is set, names used to identify capturing  subpatterns  need         If  this  bit is set, names used to identify capturing subpatterns need
1176         not be unique. This can be helpful for certain types of pattern when it         not be unique. This can be helpful for certain types of pattern when it
1177         is known that only one instance of the named  subpattern  can  ever  be         is  known  that  only  one instance of the named subpattern can ever be
1178         matched.  There  are  more details of named subpatterns below; see also         matched. There are more details of named subpatterns  below;  see  also
1179         the pcrepattern documentation.         the pcrepattern documentation.
1180    
1181           PCRE_EXTENDED           PCRE_EXTENDED
1182    
1183         If this bit is set, whitespace  data  characters  in  the  pattern  are         If  this  bit  is  set,  whitespace  data characters in the pattern are
1184         totally ignored except when escaped or inside a character class. White-         totally ignored except when escaped or inside a character class. White-
1185         space does not include the VT character (code 11). In addition, charac-         space does not include the VT character (code 11). In addition, charac-
1186         ters between an unescaped # outside a character class and the next new-         ters between an unescaped # outside a character class and the next new-
1187         line, inclusive, are also ignored. This  is  equivalent  to  Perl's  /x         line,  inclusive,  are  also  ignored.  This is equivalent to Perl's /x
1188         option,  and  it  can be changed within a pattern by a (?x) option set-         option, and it can be changed within a pattern by a  (?x)  option  set-
1189         ting.         ting.
1190    
1191         This option makes it possible to include  comments  inside  complicated         This  option  makes  it possible to include comments inside complicated
1192         patterns.   Note,  however,  that this applies only to data characters.         patterns.  Note, however, that this applies only  to  data  characters.
1193         Whitespace  characters  may  never  appear  within  special   character         Whitespace   characters  may  never  appear  within  special  character
1194         sequences  in  a  pattern,  for  example  within the sequence (?( which         sequences in a pattern, for  example  within  the  sequence  (?(  which
1195         introduces a conditional subpattern.         introduces a conditional subpattern.
1196    
1197           PCRE_EXTRA           PCRE_EXTRA
1198    
1199         This option was invented in order to turn on  additional  functionality         This  option  was invented in order to turn on additional functionality
1200         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
1201         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
1202         letter  that  has  no  special  meaning causes an error, thus reserving         letter that has no special meaning  causes  an  error,  thus  reserving
1203         these combinations for future expansion. By  default,  as  in  Perl,  a         these  combinations  for  future  expansion.  By default, as in Perl, a
1204         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
1205         literal. (Perl can, however, be persuaded to give a warning for  this.)         literal.  (Perl can, however, be persuaded to give a warning for this.)
1206         There  are  at  present no other features controlled by this option. It         There are at present no other features controlled by  this  option.  It
1207         can also be set by a (?X) option setting within a pattern.         can also be set by a (?X) option setting within a pattern.
1208    
1209           PCRE_FIRSTLINE           PCRE_FIRSTLINE
1210    
1211         If this option is set, an  unanchored  pattern  is  required  to  match         If  this  option  is  set,  an  unanchored pattern is required to match
1212         before  or  at  the  first  newline  in  the subject string, though the         before or at the first  newline  in  the  subject  string,  though  the
1213         matched text may continue over the newline.         matched text may continue over the newline.
1214    
1215           PCRE_MULTILINE           PCRE_MULTILINE
1216    
1217         By default, PCRE treats the subject string as consisting  of  a  single         By  default,  PCRE  treats the subject string as consisting of a single
1218         line  of characters (even if it actually contains newlines). The "start         line of characters (even if it actually contains newlines). The  "start
1219         of line" metacharacter (^) matches only at the  start  of  the  string,         of  line"  metacharacter  (^)  matches only at the start of the string,
1220         while  the  "end  of line" metacharacter ($) matches only at the end of         while the "end of line" metacharacter ($) matches only at  the  end  of
1221         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY
1222         is set). This is the same as Perl.         is set). This is the same as Perl.
1223    
1224         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"
1225         constructs match immediately following or immediately  before  internal         constructs  match  immediately following or immediately before internal
1226         newlines  in  the  subject string, respectively, as well as at the very         newlines in the subject string, respectively, as well as  at  the  very
1227         start and end. This is equivalent to Perl's /m option, and  it  can  be         start  and  end.  This is equivalent to Perl's /m option, and it can be
1228         changed within a pattern by a (?m) option setting. If there are no new-         changed within a pattern by a (?m) option setting. If there are no new-
1229         lines in a subject string, or no occurrences of ^ or $  in  a  pattern,         lines  in  a  subject string, or no occurrences of ^ or $ in a pattern,
1230         setting PCRE_MULTILINE has no effect.         setting PCRE_MULTILINE has no effect.
1231    
1232           PCRE_NEWLINE_CR           PCRE_NEWLINE_CR
# Line 1196  COMPILING A PATTERN Line 1235  COMPILING A PATTERN
1235           PCRE_NEWLINE_ANYCRLF           PCRE_NEWLINE_ANYCRLF
1236           PCRE_NEWLINE_ANY           PCRE_NEWLINE_ANY
1237    
1238         These  options  override the default newline definition that was chosen         These options override the default newline definition that  was  chosen
1239         when PCRE was built. Setting the first or the second specifies  that  a         when  PCRE  was built. Setting the first or the second specifies that a
1240         newline  is  indicated  by a single character (CR or LF, respectively).         newline is indicated by a single character (CR  or  LF,  respectively).
1241         Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by  the         Setting  PCRE_NEWLINE_CRLF specifies that a newline is indicated by the
1242         two-character  CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF specifies         two-character CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF  specifies
1243         that any of the three preceding sequences should be recognized. Setting         that any of the three preceding sequences should be recognized. Setting
1244         PCRE_NEWLINE_ANY  specifies that any Unicode newline sequence should be         PCRE_NEWLINE_ANY specifies that any Unicode newline sequence should  be
1245         recognized. The Unicode newline sequences are the three just mentioned,         recognized. The Unicode newline sequences are the three just mentioned,
1246         plus  the  single  characters  VT (vertical tab, U+000B), FF (formfeed,         plus the single characters VT (vertical  tab,  U+000B),  FF  (formfeed,
1247         U+000C), NEL (next line, U+0085), LS (line separator, U+2028),  and  PS         U+000C),  NEL  (next line, U+0085), LS (line separator, U+2028), and PS
1248         (paragraph  separator,  U+2029).  The  last  two are recognized only in         (paragraph separator, U+2029). The last  two  are  recognized  only  in
1249         UTF-8 mode.         UTF-8 mode.
1250    
1251         The newline setting in the  options  word  uses  three  bits  that  are         The  newline  setting  in  the  options  word  uses three bits that are
1252         treated as a number, giving eight possibilities. Currently only six are         treated as a number, giving eight possibilities. Currently only six are
1253         used (default plus the five values above). This means that if  you  set         used  (default  plus the five values above). This means that if you set
1254         more  than one newline option, the combination may or may not be sensi-         more than one newline option, the combination may or may not be  sensi-
1255         ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to         ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
1256         PCRE_NEWLINE_CRLF,  but other combinations may yield unused numbers and         PCRE_NEWLINE_CRLF, but other combinations may yield unused numbers  and
1257         cause an error.         cause an error.
1258    
1259         The only time that a line break is specially recognized when  compiling         The  only time that a line break is specially recognized when compiling
1260         a  pattern  is  if  PCRE_EXTENDED  is set, and an unescaped # outside a         a pattern is if PCRE_EXTENDED is set, and  an  unescaped  #  outside  a
1261         character class is encountered. This indicates  a  comment  that  lasts         character  class  is  encountered.  This indicates a comment that lasts
1262         until  after the next line break sequence. In other circumstances, line         until after the next line break sequence. In other circumstances,  line
1263         break  sequences  are  treated  as  literal  data,   except   that   in         break   sequences   are   treated  as  literal  data,  except  that  in
1264         PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters         PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters
1265         and are therefore ignored.         and are therefore ignored.
1266    
1267         The newline option that is set at compile time becomes the default that         The newline option that is set at compile time becomes the default that
1268         is  used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.         is used for pcre_exec() and pcre_dfa_exec(), but it can be  overridden.
1269    
1270           PCRE_NO_AUTO_CAPTURE           PCRE_NO_AUTO_CAPTURE
1271    
1272         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-
1273         theses  in the pattern. Any opening parenthesis that is not followed by         theses in the pattern. Any opening parenthesis that is not followed  by
1274         ? behaves as if it were followed by ?: but named parentheses can  still         ?  behaves as if it were followed by ?: but named parentheses can still
1275         be  used  for  capturing  (and  they acquire numbers in the usual way).         be used for capturing (and they acquire  numbers  in  the  usual  way).
1276         There is no equivalent of this option in Perl.         There is no equivalent of this option in Perl.
1277    
1278           PCRE_UNGREEDY           PCRE_UNGREEDY
1279    
1280         This option inverts the "greediness" of the quantifiers  so  that  they         This  option  inverts  the "greediness" of the quantifiers so that they
1281         are  not greedy by default, but become greedy if followed by "?". It is         are not greedy by default, but become greedy if followed by "?". It  is
1282         not compatible with Perl. It can also be set by a (?U)  option  setting         not  compatible  with Perl. It can also be set by a (?U) option setting
1283         within the pattern.         within the pattern.
1284    
1285           PCRE_UTF8           PCRE_UTF8
1286    
1287         This  option  causes PCRE to regard both the pattern and the subject as         This option causes PCRE to regard both the pattern and the  subject  as
1288         strings of UTF-8 characters instead of single-byte  character  strings.         strings  of  UTF-8 characters instead of single-byte character strings.
1289         However,  it is available only when PCRE is built to include UTF-8 sup-         However, it is available only when PCRE is built to include UTF-8  sup-
1290         port. If not, the use of this option provokes an error. Details of  how         port.  If not, the use of this option provokes an error. Details of how
1291         this  option  changes the behaviour of PCRE are given in the section on         this option changes the behaviour of PCRE are given in the  section  on
1292         UTF-8 support in the main pcre page.         UTF-8 support in the main pcre page.
1293    
1294           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
1295    
1296         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
1297         automatically  checked.  There  is  a  discussion about the validity of         automatically checked. There is a  discussion  about  the  validity  of
1298         UTF-8 strings in the main pcre page. If an invalid  UTF-8  sequence  of         UTF-8  strings  in  the main pcre page. If an invalid UTF-8 sequence of
1299         bytes  is  found,  pcre_compile() returns an error. If you already know         bytes is found, pcre_compile() returns an error. If  you  already  know
1300         that your pattern is valid, and you want to skip this check for perfor-         that your pattern is valid, and you want to skip this check for perfor-
1301         mance  reasons,  you  can set the PCRE_NO_UTF8_CHECK option. When it is         mance reasons, you can set the PCRE_NO_UTF8_CHECK option.  When  it  is
1302         set, the effect of passing an invalid UTF-8  string  as  a  pattern  is         set,  the  effect  of  passing  an invalid UTF-8 string as a pattern is
1303         undefined.  It  may  cause your program to crash. Note that this option         undefined. It may cause your program to crash. Note  that  this  option
1304         can also be passed to pcre_exec() and pcre_dfa_exec(), to suppress  the         can  also be passed to pcre_exec() and pcre_dfa_exec(), to suppress the
1305         UTF-8 validity checking of subject strings.         UTF-8 validity checking of subject strings.
1306    
1307    
1308  COMPILATION ERROR CODES  COMPILATION ERROR CODES
1309    
1310         The  following  table  lists  the  error  codes than may be returned by         The following table lists the error  codes  than  may  be  returned  by
1311         pcre_compile2(), along with the error messages that may be returned  by         pcre_compile2(),  along with the error messages that may be returned by
1312         both  compiling functions. As PCRE has developed, some error codes have         both compiling functions. As PCRE has developed, some error codes  have
1313         fallen out of use. To avoid confusion, they have not been re-used.         fallen out of use. To avoid confusion, they have not been re-used.
1314    
1315            0  no error            0  no error
# Line 1326  COMPILATION ERROR CODES Line 1365  COMPILATION ERROR CODES
1365           50  [this code is not in use]           50  [this code is not in use]
1366           51  octal value is greater than \377 (not in UTF-8 mode)           51  octal value is greater than \377 (not in UTF-8 mode)
1367           52  internal error: overran compiling workspace           52  internal error: overran compiling workspace
1368           53  internal  error:  previously-checked  referenced  subpattern  not           53   internal  error:  previously-checked  referenced  subpattern not
1369         found         found
1370           54  DEFINE group contains more than one branch           54  DEFINE group contains more than one branch
1371           55  repeating a DEFINE group is not allowed           55  repeating a DEFINE group is not allowed
1372           56  inconsistent NEWLINE options"           56  inconsistent NEWLINE options
1373           57  \g is not followed by a braced name or an optionally braced           57  \g is not followed by a braced name or an optionally braced
1374                 non-zero number                 non-zero number
1375           58  (?+ or (?- or (?(+ or (?(- must be followed by a non-zero number           58  (?+ or (?- or (?(+ or (?(- must be followed by a non-zero number
# Line 1341  STUDYING A PATTERN Line 1380  STUDYING A PATTERN
1380         pcre_extra *pcre_study(const pcre *code, int options         pcre_extra *pcre_study(const pcre *code, int options
1381              const char **errptr);              const char **errptr);
1382    
1383         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
1384         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
1385         matching.  The function pcre_study() takes a pointer to a compiled pat-         matching. The function pcre_study() takes a pointer to a compiled  pat-
1386         tern as its first argument. If studying the pattern produces additional         tern as its first argument. If studying the pattern produces additional
1387         information  that  will  help speed up matching, pcre_study() returns a         information that will help speed up matching,  pcre_study()  returns  a
1388         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
1389         the results of the study.         the results of the study.
1390    
1391         The  returned  value  from  pcre_study()  can  be  passed  directly  to         The  returned  value  from  pcre_study()  can  be  passed  directly  to
1392         pcre_exec(). However, a pcre_extra block  also  contains  other  fields         pcre_exec().  However,  a  pcre_extra  block also contains other fields
1393         that  can  be  set  by the caller before the block is passed; these are         that can be set by the caller before the block  is  passed;  these  are
1394         described below in the section on matching a pattern.         described below in the section on matching a pattern.
1395    
1396         If studying the pattern does not  produce  any  additional  information         If  studying  the  pattern  does not produce any additional information
1397         pcre_study() returns NULL. In that circumstance, if the calling program         pcre_study() returns NULL. In that circumstance, if the calling program
1398         wants to pass any of the other fields to pcre_exec(), it  must  set  up         wants  to  pass  any of the other fields to pcre_exec(), it must set up
1399         its own pcre_extra block.         its own pcre_extra block.
1400    
1401         The  second  argument of pcre_study() contains option bits. At present,         The second argument of pcre_study() contains option bits.  At  present,
1402         no options are defined, and this argument should always be zero.         no options are defined, and this argument should always be zero.
1403    
1404         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.
1405         If  studying  succeeds  (even  if no data is returned), the variable it         If studying succeeds (even if no data is  returned),  the  variable  it
1406         points to is set to NULL. Otherwise it is set to  point  to  a  textual         points  to  is  set  to NULL. Otherwise it is set to point to a textual
1407         error message. This is a static string that is part of the library. You         error message. This is a static string that is part of the library. You
1408         must not try to free it. You should test the  error  pointer  for  NULL         must  not  try  to  free it. You should test the error pointer for NULL
1409         after calling pcre_study(), to be sure that it has run successfully.         after calling pcre_study(), to be sure that it has run successfully.
1410    
1411         This is a typical call to pcre_study():         This is a typical call to pcre_study():
# Line 1378  STUDYING A PATTERN Line 1417  STUDYING A PATTERN
1417             &error);        /* set to NULL or points to a message */             &error);        /* set to NULL or points to a message */
1418    
1419         At present, studying a pattern is useful only for non-anchored patterns         At present, studying a pattern is useful only for non-anchored patterns
1420         that do not have a single fixed starting character. A bitmap of  possi-         that  do not have a single fixed starting character. A bitmap of possi-
1421         ble starting bytes is created.         ble starting bytes is created.
1422    
1423    
1424  LOCALE SUPPORT  LOCALE SUPPORT
1425    
1426         PCRE  handles  caseless matching, and determines whether characters are         PCRE handles caseless matching, and determines whether  characters  are
1427         letters, digits, or whatever, by reference to a set of tables,  indexed         letters,  digits, or whatever, by reference to a set of tables, indexed
1428         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
1429         characters with codes less than 128. Higher-valued  codes  never  match         characters  with  codes  less than 128. Higher-valued codes never match
1430         escapes  such  as  \w or \d, but can be tested with \p if PCRE is built         escapes such as \w or \d, but can be tested with \p if  PCRE  is  built
1431         with Unicode character property support. The use of locales  with  Uni-         with  Unicode  character property support. The use of locales with Uni-
1432         code  is discouraged. If you are handling characters with codes greater         code is discouraged. If you are handling characters with codes  greater
1433         than 128, you should either use UTF-8 and Unicode, or use locales,  but         than  128, you should either use UTF-8 and Unicode, or use locales, but
1434         not try to mix the two.         not try to mix the two.
1435    
1436         PCRE  contains  an  internal set of tables that are used when the final         PCRE contains an internal set of tables that are used  when  the  final
1437         argument of pcre_compile() is  NULL.  These  are  sufficient  for  many         argument  of  pcre_compile()  is  NULL.  These  are sufficient for many
1438         applications.  Normally, the internal tables recognize only ASCII char-         applications.  Normally, the internal tables recognize only ASCII char-
1439         acters. However, when PCRE is built, it is possible to cause the inter-         acters. However, when PCRE is built, it is possible to cause the inter-
1440         nal tables to be rebuilt in the default "C" locale of the local system,         nal tables to be rebuilt in the default "C" locale of the local system,
1441         which may cause them to be different.         which may cause them to be different.
1442    
1443         The internal tables can always be overridden by tables supplied by  the         The  internal tables can always be overridden by tables supplied by the
1444         application that calls PCRE. These may be created in a different locale         application that calls PCRE. These may be created in a different locale
1445         from the default. As more and more applications change  to  using  Uni-         from  the  default.  As more and more applications change to using Uni-
1446         code, the need for this locale support is expected to die away.         code, the need for this locale support is expected to die away.
1447    
1448         External  tables  are  built by calling the pcre_maketables() function,         External tables are built by calling  the  pcre_maketables()  function,
1449         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
1450         passed  to  pcre_compile()  or  pcre_exec()  as often as necessary. For         passed to pcre_compile() or pcre_exec()  as  often  as  necessary.  For
1451         example, to build and use tables that are appropriate  for  the  French         example,  to  build  and use tables that are appropriate for the French
1452         locale  (where  accented  characters  with  values greater than 128 are         locale (where accented characters with  values  greater  than  128  are
1453         treated as letters), the following code could be used:         treated as letters), the following code could be used:
1454    
1455           setlocale(LC_CTYPE, "fr_FR");           setlocale(LC_CTYPE, "fr_FR");
1456           tables = pcre_maketables();           tables = pcre_maketables();
1457           re = pcre_compile(..., tables);           re = pcre_compile(..., tables);
1458    
1459         The locale name "fr_FR" is used on Linux and other  Unix-like  systems;         The  locale  name "fr_FR" is used on Linux and other Unix-like systems;
1460         if you are using Windows, the name for the French locale is "french".         if you are using Windows, the name for the French locale is "french".
1461    
1462         When  pcre_maketables()  runs,  the  tables are built in memory that is         When pcre_maketables() runs, the tables are built  in  memory  that  is
1463         obtained via pcre_malloc. It is the caller's responsibility  to  ensure         obtained  via  pcre_malloc. It is the caller's responsibility to ensure
1464         that  the memory containing the tables remains available for as long as         that the memory containing the tables remains available for as long  as
1465         it is needed.         it is needed.
1466    
1467         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
1468         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()
1469         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-
1470         tern, compilation, studying and matching all happen in the same locale,         tern, compilation, studying and matching all happen in the same locale,
1471         but different patterns can be compiled in different locales.         but different patterns can be compiled in different locales.
1472    
1473         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
1474         the  internal  tables)  to  pcre_exec(). Although not intended for this         the internal tables) to pcre_exec(). Although  not  intended  for  this
1475         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
1476         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
1477         run time is discussed below in the section on matching a pattern.         run time is discussed below in the section on matching a pattern.
1478    
# Line 1443  INFORMATION ABOUT A PATTERN Line 1482  INFORMATION ABOUT A PATTERN
1482         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
1483              int what, void *where);              int what, void *where);
1484    
1485         The pcre_fullinfo() function returns information about a compiled  pat-         The  pcre_fullinfo() function returns information about a compiled pat-
1486         tern. It replaces the obsolete pcre_info() function, which is neverthe-         tern. It replaces the obsolete pcre_info() function, which is neverthe-
1487         less retained for backwards compability (and is documented below).         less retained for backwards compability (and is documented below).
1488    
1489         The first argument for pcre_fullinfo() is a  pointer  to  the  compiled         The  first  argument  for  pcre_fullinfo() is a pointer to the compiled
1490         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
1491         the pattern was not studied. The third argument specifies  which  piece         the  pattern  was not studied. The third argument specifies which piece
1492         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
1493         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
1494         success, or one of the following negative numbers:         success, or one of the following negative numbers:
1495    
1496           PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_NULL       the argument code was NULL
# Line 1459  INFORMATION ABOUT A PATTERN Line 1498  INFORMATION ABOUT A PATTERN
1498           PCRE_ERROR_BADMAGIC   the "magic number" was not found           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1499           PCRE_ERROR_BADOPTION  the value of what was invalid           PCRE_ERROR_BADOPTION  the value of what was invalid
1500    
1501         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
1502         an simple check against passing an arbitrary memory pointer. Here is  a         an  simple check against passing an arbitrary memory pointer. Here is a
1503         typical  call  of pcre_fullinfo(), to obtain the length of the compiled         typical call of pcre_fullinfo(), to obtain the length of  the  compiled
1504         pattern:         pattern:
1505    
1506           int rc;           int rc;
# Line 1472  INFORMATION ABOUT A PATTERN Line 1511  INFORMATION ABOUT A PATTERN
1511             PCRE_INFO_SIZE,   /* what is required */             PCRE_INFO_SIZE,   /* what is required */
1512             &length);         /* where to put the data */             &length);         /* where to put the data */
1513    
1514         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
1515         are as follows:         are as follows:
1516    
1517           PCRE_INFO_BACKREFMAX           PCRE_INFO_BACKREFMAX
1518    
1519         Return  the  number  of  the highest back reference in the pattern. The         Return the number of the highest back reference  in  the  pattern.  The
1520         fourth argument should point to an int variable. Zero  is  returned  if         fourth  argument  should  point to an int variable. Zero is returned if
1521         there are no back references.         there are no back references.
1522    
1523           PCRE_INFO_CAPTURECOUNT           PCRE_INFO_CAPTURECOUNT
1524    
1525         Return  the  number of capturing subpatterns in the pattern. The fourth         Return the number of capturing subpatterns in the pattern.  The  fourth
1526         argument should point to an int variable.         argument should point to an int variable.
1527    
1528           PCRE_INFO_DEFAULT_TABLES           PCRE_INFO_DEFAULT_TABLES
1529    
1530         Return a pointer to the internal default character tables within  PCRE.         Return  a pointer to the internal default character tables within PCRE.
1531         The  fourth  argument should point to an unsigned char * variable. This         The fourth argument should point to an unsigned char *  variable.  This
1532         information call is provided for internal use by the pcre_study() func-         information call is provided for internal use by the pcre_study() func-
1533         tion.  External  callers  can  cause PCRE to use its internal tables by         tion. External callers can cause PCRE to use  its  internal  tables  by
1534         passing a NULL table pointer.         passing a NULL table pointer.
1535    
1536           PCRE_INFO_FIRSTBYTE           PCRE_INFO_FIRSTBYTE
1537    
1538         Return information about the first byte of any matched  string,  for  a         Return  information  about  the first byte of any matched string, for a
1539         non-anchored  pattern. The fourth argument should point to an int vari-         non-anchored pattern. The fourth argument should point to an int  vari-
1540         able. (This option used to be called PCRE_INFO_FIRSTCHAR; the old  name         able.  (This option used to be called PCRE_INFO_FIRSTCHAR; the old name
1541         is still recognized for backwards compatibility.)         is still recognized for backwards compatibility.)
1542    
1543         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
1544         (cat|cow|coyote), its value is returned. Otherwise, if either         (cat|cow|coyote), its value is returned. Otherwise, if either
1545    
1546         (a) the pattern was compiled with the PCRE_MULTILINE option, and  every         (a)  the pattern was compiled with the PCRE_MULTILINE option, and every
1547         branch starts with "^", or         branch starts with "^", or
1548    
1549         (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not         (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
1550         set (if it were set, the pattern would be anchored),         set (if it were set, the pattern would be anchored),
1551    
1552         -1 is returned, indicating that the pattern matches only at  the  start         -1  is  returned, indicating that the pattern matches only at the start
1553         of  a  subject string or after any newline within the string. Otherwise         of a subject string or after any newline within the  string.  Otherwise
1554         -2 is returned. For anchored patterns, -2 is returned.         -2 is returned. For anchored patterns, -2 is returned.
1555    
1556           PCRE_INFO_FIRSTTABLE           PCRE_INFO_FIRSTTABLE
1557    
1558         If the pattern was studied, and this resulted in the construction of  a         If  the pattern was studied, and this resulted in the construction of a
1559         256-bit table indicating a fixed set of bytes for the first byte in any         256-bit table indicating a fixed set of bytes for the first byte in any
1560         matching string, a pointer to the table is returned. Otherwise NULL  is         matching  string, a pointer to the table is returned. Otherwise NULL is
1561         returned.  The fourth argument should point to an unsigned char * vari-         returned. The fourth argument should point to an unsigned char *  vari-
1562         able.         able.
1563    
1564             PCRE_INFO_HASCRORLF
1565    
1566           Return  1  if  the  pattern  contains any explicit matches for CR or LF
1567           characters, otherwise 0. The fourth argument should  point  to  an  int
1568           variable.
1569    
1570           PCRE_INFO_JCHANGED           PCRE_INFO_JCHANGED
1571    
1572         Return 1 if the (?J) option setting is used in the  pattern,  otherwise         Return  1  if the (?J) option setting is used in the pattern, otherwise
1573         0. The fourth argument should point to an int variable. The (?J) inter-         0. The fourth argument should point to an int variable. The (?J) inter-
1574         nal option setting changes the local PCRE_DUPNAMES option.         nal option setting changes the local PCRE_DUPNAMES option.
1575    
1576           PCRE_INFO_LASTLITERAL           PCRE_INFO_LASTLITERAL
1577    
1578         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
1579         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
1580         recorded. The fourth argument should point to an int variable. If there         recorded. The fourth argument should point to an int variable. If there
1581         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
1582         byte is recorded only if it follows something of variable  length.  For         byte  is  recorded only if it follows something of variable length. For
1583         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
1584         /^a\dz\d/ the returned value is -1.         /^a\dz\d/ the returned value is -1.
1585    
# Line 1542  INFORMATION ABOUT A PATTERN Line 1587  INFORMATION ABOUT A PATTERN
1587           PCRE_INFO_NAMEENTRYSIZE           PCRE_INFO_NAMEENTRYSIZE
1588           PCRE_INFO_NAMETABLE           PCRE_INFO_NAMETABLE
1589    
1590         PCRE supports the use of named as well as numbered capturing  parenthe-         PCRE  supports the use of named as well as numbered capturing parenthe-
1591         ses.  The names are just an additional way of identifying the parenthe-         ses. The names are just an additional way of identifying the  parenthe-
1592         ses, which still acquire numbers. Several convenience functions such as         ses, which still acquire numbers. Several convenience functions such as
1593         pcre_get_named_substring()  are  provided  for extracting captured sub-         pcre_get_named_substring() are provided for  extracting  captured  sub-
1594         strings by name. It is also possible to extract the data  directly,  by         strings  by  name. It is also possible to extract the data directly, by
1595         first  converting  the  name to a number in order to access the correct         first converting the name to a number in order to  access  the  correct
1596         pointers in the output vector (described with pcre_exec() below). To do         pointers in the output vector (described with pcre_exec() below). To do
1597         the  conversion,  you  need  to  use  the  name-to-number map, which is         the conversion, you need  to  use  the  name-to-number  map,  which  is
1598         described by these three values.         described by these three values.
1599    
1600         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
1601         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
1602         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
1603         depends  on the length of the longest name. PCRE_INFO_NAMETABLE returns         depends on the length of the longest name. PCRE_INFO_NAMETABLE  returns
1604         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
1605         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-
1606         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-
1607         sponding  name,  zero  terminated. The names are in alphabetical order.         sponding name, zero terminated. The names are  in  alphabetical  order.
1608         When PCRE_DUPNAMES is set, duplicate names are in order of their paren-         When PCRE_DUPNAMES is set, duplicate names are in order of their paren-
1609         theses  numbers.  For  example,  consider the following pattern (assume         theses numbers. For example, consider  the  following  pattern  (assume
1610         PCRE_EXTENDED is  set,  so  white  space  -  including  newlines  -  is         PCRE_EXTENDED  is  set,  so  white  space  -  including  newlines  - is
1611         ignored):         ignored):
1612    
1613           (?<date> (?<year>(\d\d)?\d\d) -           (?<date> (?<year>(\d\d)?\d\d) -
1614           (?<month>\d\d) - (?<day>\d\d) )           (?<month>\d\d) - (?<day>\d\d) )
1615    
1616         There  are  four  named subpatterns, so the table has four entries, and         There are four named subpatterns, so the table has  four  entries,  and
1617         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,
1618         with non-printing bytes shows in hexadecimal, and undefined bytes shown         with non-printing bytes shows in hexadecimal, and undefined bytes shown
1619         as ??:         as ??:
1620    
# Line 1578  INFORMATION ABOUT A PATTERN Line 1623  INFORMATION ABOUT A PATTERN
1623           00 04 m  o  n  t  h  00           00 04 m  o  n  t  h  00
1624           00 02 y  e  a  r  00 ??           00 02 y  e  a  r  00 ??
1625    
1626         When writing code to extract data  from  named  subpatterns  using  the         When  writing  code  to  extract  data from named subpatterns using the
1627         name-to-number  map,  remember that the length of the entries is likely         name-to-number map, remember that the length of the entries  is  likely
1628         to be different for each compiled pattern.         to be different for each compiled pattern.
1629    
1630           PCRE_INFO_OKPARTIAL           PCRE_INFO_OKPARTIAL
1631    
1632         Return 1 if the pattern can be used for partial matching, otherwise  0.         Return  1 if the pattern can be used for partial matching, otherwise 0.
1633         The  fourth  argument  should point to an int variable. The pcrepartial         The fourth argument should point to an int  variable.  The  pcrepartial
1634         documentation lists the restrictions that apply to patterns  when  par-         documentation  lists  the restrictions that apply to patterns when par-
1635         tial matching is used.         tial matching is used.
1636    
1637           PCRE_INFO_OPTIONS           PCRE_INFO_OPTIONS
1638    
1639         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
1640         fourth argument should point to an unsigned long  int  variable.  These         fourth  argument  should  point to an unsigned long int variable. These
1641         option bits are those specified in the call to pcre_compile(), modified         option bits are those specified in the call to pcre_compile(), modified
1642         by any top-level option settings at the start of the pattern itself. In         by any top-level option settings at the start of the pattern itself. In
1643         other  words,  they are the options that will be in force when matching         other words, they are the options that will be in force  when  matching
1644         starts. For example, if the pattern /(?im)abc(?-i)d/ is  compiled  with         starts.  For  example, if the pattern /(?im)abc(?-i)d/ is compiled with
1645         the  PCRE_EXTENDED option, the result is PCRE_CASELESS, PCRE_MULTILINE,         the PCRE_EXTENDED option, the result is PCRE_CASELESS,  PCRE_MULTILINE,
1646         and PCRE_EXTENDED.         and PCRE_EXTENDED.
1647    
1648         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
1649         alternatives begin with one of the following:         alternatives begin with one of the following:
1650    
1651           ^     unless PCRE_MULTILINE is set           ^     unless PCRE_MULTILINE is set
# Line 1614  INFORMATION ABOUT A PATTERN Line 1659  INFORMATION ABOUT A PATTERN
1659    
1660           PCRE_INFO_SIZE           PCRE_INFO_SIZE
1661    
1662         Return the size of the compiled pattern, that is, the  value  that  was         Return  the  size  of the compiled pattern, that is, the value that was
1663         passed as the argument to pcre_malloc() when PCRE was getting memory in         passed as the argument to pcre_malloc() when PCRE was getting memory in
1664         which to place the compiled data. The fourth argument should point to a         which to place the compiled data. The fourth argument should point to a
1665         size_t variable.         size_t variable.
# Line 1622  INFORMATION ABOUT A PATTERN Line 1667  INFORMATION ABOUT A PATTERN
1667           PCRE_INFO_STUDYSIZE           PCRE_INFO_STUDYSIZE
1668    
1669         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
1670         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
1671         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
1672         created by pcre_study(). The fourth argument should point to  a  size_t         created  by  pcre_study(). The fourth argument should point to a size_t
1673         variable.         variable.
1674    
1675    
# Line 1632  OBSOLETE INFO FUNCTION Line 1677  OBSOLETE INFO FUNCTION
1677    
1678         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
1679    
1680         The  pcre_info()  function is now obsolete because its interface is too         The pcre_info() function is now obsolete because its interface  is  too
1681         restrictive to return all the available data about a compiled  pattern.         restrictive  to return all the available data about a compiled pattern.
1682         New   programs   should  use  pcre_fullinfo()  instead.  The  yield  of         New  programs  should  use  pcre_fullinfo()  instead.  The   yield   of
1683         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-
1684         lowing negative numbers:         lowing negative numbers:
1685    
1686           PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_NULL       the argument code was NULL
1687           PCRE_ERROR_BADMAGIC   the "magic number" was not found           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1688    
1689         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
1690         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
1691         PCRE_INFO_OPTIONS above).         PCRE_INFO_OPTIONS above).
1692    
1693         If  the  pattern  is  not anchored and the firstcharptr argument is not         If the pattern is not anchored and the  firstcharptr  argument  is  not
1694         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
1695         any matched string (see PCRE_INFO_FIRSTBYTE above).         any matched string (see PCRE_INFO_FIRSTBYTE above).
1696    
1697    
# Line 1654  REFERENCE COUNTS Line 1699  REFERENCE COUNTS
1699    
1700         int pcre_refcount(pcre *code, int adjust);         int pcre_refcount(pcre *code, int adjust);
1701    
1702         The  pcre_refcount()  function is used to maintain a reference count in         The pcre_refcount() function is used to maintain a reference  count  in
1703         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
1704         benefit  of  applications  that  operate  in an object-oriented manner,         benefit of applications that  operate  in  an  object-oriented  manner,
1705         where different parts of the application may be using the same compiled         where different parts of the application may be using the same compiled
1706         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.
1707    
1708         When a pattern is compiled, the reference count field is initialized to         When a pattern is compiled, the reference count field is initialized to
1709         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
1710         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
1711         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
1712         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
1713         is outside these limits, it is forced to the appropriate limit value.         is outside these limits, it is forced to the appropriate limit value.
1714    
1715         Except when it is zero, the reference count is not correctly  preserved         Except  when it is zero, the reference count is not correctly preserved
1716         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
1717         whose byte-order is different. (This seems a highly unlikely scenario.)         whose byte-order is different. (This seems a highly unlikely scenario.)
1718    
1719    
# Line 1678  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1723  MATCHING A PATTERN: THE TRADITIONAL FUNC
1723              const char *subject, int length, int startoffset,              const char *subject, int length, int startoffset,
1724              int options, int *ovector, int ovecsize);              int options, int *ovector, int ovecsize);
1725    
1726         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
1727         compiled pattern, which is passed in the code argument. If the  pattern         compiled  pattern, which is passed in the code argument. If the pattern
1728         has been studied, the result of the study should be passed in the extra         has been studied, the result of the study should be passed in the extra
1729         argument. This function is the main matching facility of  the  library,         argument.  This  function is the main matching facility of the library,
1730         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
1731         an alternative matching function, which is described below in the  sec-         an  alternative matching function, which is described below in the sec-
1732         tion about the pcre_dfa_exec() function.         tion about the pcre_dfa_exec() function.
1733    
1734         In  most applications, the pattern will have been compiled (and option-         In most applications, the pattern will have been compiled (and  option-
1735         ally studied) in the same process that calls pcre_exec().  However,  it         ally  studied)  in the same process that calls pcre_exec(). However, it
1736         is possible to save compiled patterns and study data, and then use them         is possible to save compiled patterns and study data, and then use them
1737         later in different processes, possibly even on different hosts.  For  a         later  in  different processes, possibly even on different hosts. For a
1738         discussion about this, see the pcreprecompile documentation.         discussion about this, see the pcreprecompile documentation.
1739    
1740         Here is an example of a simple call to pcre_exec():         Here is an example of a simple call to pcre_exec():
# Line 1708  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1753  MATCHING A PATTERN: THE TRADITIONAL FUNC
1753    
1754     Extra data for pcre_exec()     Extra data for pcre_exec()
1755    
1756         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
1757         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
1758         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-
1759         tional information in it. The pcre_extra block contains  the  following         tional  information  in it. The pcre_extra block contains the following
1760         fields (not necessarily in this order):         fields (not necessarily in this order):
1761    
1762           unsigned long int flags;           unsigned long int flags;
# Line 1721  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1766  MATCHING A PATTERN: THE TRADITIONAL FUNC
1766           void *callout_data;           void *callout_data;
1767           const unsigned char *tables;           const unsigned char *tables;
1768    
1769         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
1770         are set. The flag bits are:         are set. The flag bits are:
1771    
1772           PCRE_EXTRA_STUDY_DATA           PCRE_EXTRA_STUDY_DATA
# Line 1730  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1775  MATCHING A PATTERN: THE TRADITIONAL FUNC
1775           PCRE_EXTRA_CALLOUT_DATA           PCRE_EXTRA_CALLOUT_DATA
1776           PCRE_EXTRA_TABLES           PCRE_EXTRA_TABLES
1777    
1778         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
1779         the  pcre_extra  block  that is returned by pcre_study(), together with         the pcre_extra block that is returned by  pcre_study(),  together  with
1780         the appropriate flag bit. You should not set this yourself, but you may         the appropriate flag bit. You should not set this yourself, but you may
1781         add  to  the  block by setting the other fields and their corresponding         add to the block by setting the other fields  and  their  corresponding
1782         flag bits.         flag bits.
1783    
1784         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
1785         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
1786         match, but which have a very large number  of  possibilities  in  their         match,  but  which  have  a very large number of possibilities in their
1787         search  trees.  The  classic  example  is  the  use of nested unlimited         search trees. The classic  example  is  the  use  of  nested  unlimited
1788         repeats.         repeats.
1789    
1790         Internally, PCRE uses a function called match() which it calls  repeat-         Internally,  PCRE uses a function called match() which it calls repeat-
1791         edly  (sometimes  recursively). The limit set by match_limit is imposed         edly (sometimes recursively). The limit set by match_limit  is  imposed
1792         on the number of times this function is called during  a  match,  which         on  the  number  of times this function is called during a match, which
1793         has  the  effect  of  limiting the amount of backtracking that can take         has the effect of limiting the amount of  backtracking  that  can  take
1794         place. For patterns that are not anchored, the count restarts from zero         place. For patterns that are not anchored, the count restarts from zero
1795         for each position in the subject string.         for each position in the subject string.
1796    
1797         The  default  value  for  the  limit can be set when PCRE is built; the         The default value for the limit can be set  when  PCRE  is  built;  the
1798         default default is 10 million, which handles all but the  most  extreme         default  default  is 10 million, which handles all but the most extreme
1799         cases.  You  can  override  the  default by suppling pcre_exec() with a         cases. You can override the default  by  suppling  pcre_exec()  with  a
1800         pcre_extra    block    in    which    match_limit    is    set,     and         pcre_extra     block    in    which    match_limit    is    set,    and
1801         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
1802         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1803    
1804         The match_limit_recursion field is similar to match_limit, but  instead         The  match_limit_recursion field is similar to match_limit, but instead
1805         of limiting the total number of times that match() is called, it limits         of limiting the total number of times that match() is called, it limits
1806         the depth of recursion. The recursion depth is a  smaller  number  than         the  depth  of  recursion. The recursion depth is a smaller number than
1807         the  total number of calls, because not all calls to match() are recur-         the total number of calls, because not all calls to match() are  recur-
1808         sive.  This limit is of use only if it is set smaller than match_limit.         sive.  This limit is of use only if it is set smaller than match_limit.
1809    
1810         Limiting  the  recursion  depth  limits the amount of stack that can be         Limiting the recursion depth limits the amount of  stack  that  can  be
1811         used, or, when PCRE has been compiled to use memory on the heap instead         used, or, when PCRE has been compiled to use memory on the heap instead
1812         of the stack, the amount of heap memory that can be used.         of the stack, the amount of heap memory that can be used.
1813    
1814         The  default  value  for  match_limit_recursion can be set when PCRE is         The default value for match_limit_recursion can be  set  when  PCRE  is
1815         built; the default default  is  the  same  value  as  the  default  for         built;  the  default  default  is  the  same  value  as the default for
1816         match_limit.  You can override the default by suppling pcre_exec() with         match_limit. You can override the default by suppling pcre_exec()  with
1817         a  pcre_extra  block  in  which  match_limit_recursion  is   set,   and         a   pcre_extra   block  in  which  match_limit_recursion  is  set,  and
1818         PCRE_EXTRA_MATCH_LIMIT_RECURSION  is  set  in  the  flags field. If the         PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in  the  flags  field.  If  the
1819         limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.         limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1820    
1821         The pcre_callout field is used in conjunction with the  "callout"  fea-         The  pcre_callout  field is used in conjunction with the "callout" fea-
1822         ture, which is described in the pcrecallout documentation.         ture, which is described in the pcrecallout documentation.
1823    
1824         The  tables  field  is  used  to  pass  a  character  tables pointer to         The tables field  is  used  to  pass  a  character  tables  pointer  to
1825         pcre_exec(); this overrides the value that is stored with the  compiled         pcre_exec();  this overrides the value that is stored with the compiled
1826         pattern.  A  non-NULL value is stored with the compiled pattern only if         pattern. A non-NULL value is stored with the compiled pattern  only  if
1827         custom tables were supplied to pcre_compile() via  its  tableptr  argu-         custom  tables  were  supplied to pcre_compile() via its tableptr argu-
1828         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
1829         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-
1830         using  patterns  that  have been saved after compiling with an external         using patterns that have been saved after compiling  with  an  external
1831         set of tables, because the external tables  might  be  at  a  different         set  of  tables,  because  the  external tables might be at a different
1832         address  when  pcre_exec() is called. See the pcreprecompile documenta-         address when pcre_exec() is called. See the  pcreprecompile  documenta-
1833         tion for a discussion of saving compiled patterns for later use.         tion for a discussion of saving compiled patterns for later use.
1834    
1835     Option bits for pcre_exec()     Option bits for pcre_exec()
1836    
1837         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.
1838         The  only  bits  that  may  be set are PCRE_ANCHORED, PCRE_NEWLINE_xxx,         The only bits that may  be  set  are  PCRE_ANCHORED,  PCRE_NEWLINE_xxx,
1839         PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and         PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and
1840         PCRE_PARTIAL.         PCRE_PARTIAL.
1841    
1842           PCRE_ANCHORED           PCRE_ANCHORED
1843    
1844         The  PCRE_ANCHORED  option  limits pcre_exec() to matching at the first         The PCRE_ANCHORED option limits pcre_exec() to matching  at  the  first
1845         matching position. If a pattern was  compiled  with  PCRE_ANCHORED,  or         matching  position.  If  a  pattern was compiled with PCRE_ANCHORED, or
1846         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
1847         unachored at matching time.         unachored at matching time.
1848    
1849             PCRE_BSR_ANYCRLF
1850             PCRE_BSR_UNICODE
1851    
1852           These options (which are mutually exclusive) control what the \R escape
1853           sequence matches. The choice is either to match only CR, LF,  or  CRLF,
1854           or  to  match  any Unicode newline sequence. These options override the
1855           choice that was made or defaulted when the pattern was compiled.
1856    
1857           PCRE_NEWLINE_CR           PCRE_NEWLINE_CR
1858           PCRE_NEWLINE_LF           PCRE_NEWLINE_LF
1859           PCRE_NEWLINE_CRLF           PCRE_NEWLINE_CRLF
# Line 1812  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1865  MATCHING A PATTERN: THE TRADITIONAL FUNC
1865         tion of pcre_compile()  above.  During  matching,  the  newline  choice         tion of pcre_compile()  above.  During  matching,  the  newline  choice
1866         affects  the  behaviour  of the dot, circumflex, and dollar metacharac-         affects  the  behaviour  of the dot, circumflex, and dollar metacharac-
1867         ters. It may also alter the way the match position is advanced after  a         ters. It may also alter the way the match position is advanced after  a
1868         match  failure  for  an  unanchored  pattern.  When  PCRE_NEWLINE_CRLF,         match failure for an unanchored pattern.
1869         PCRE_NEWLINE_ANYCRLF, or PCRE_NEWLINE_ANY is set, and a  match  attempt  
1870         fails  when the current position is at a CRLF sequence, the match posi-         When  PCRE_NEWLINE_CRLF,  PCRE_NEWLINE_ANYCRLF,  or PCRE_NEWLINE_ANY is
1871         tion is advanced by two characters instead of one, in other  words,  to         set, and a match attempt for an unanchored pattern fails when the  cur-
1872         after the CRLF.         rent  position  is  at  a  CRLF  sequence,  and the pattern contains no
1873           explicit matches for  CR  or  LF  characters,  the  match  position  is
1874           advanced by two characters instead of one, in other words, to after the
1875           CRLF.
1876    
1877           The above rule is a compromise that makes the most common cases work as
1878           expected.  For  example,  if  the  pattern  is .+A (and the PCRE_DOTALL
1879           option is not set), it does not match the string "\r\nA" because, after
1880           failing  at the start, it skips both the CR and the LF before retrying.
1881           However, the pattern [\r\n]A does match that string,  because  it  con-
1882           tains an explicit CR or LF reference, and so advances only by one char-
1883           acter after the first failure.
1884    
1885           An explicit match for CR of LF is either a literal appearance of one of
1886           those  characters,  or  one  of the \r or \n escape sequences. Implicit
1887           matches such as [^X] do not count, nor does \s (which includes  CR  and
1888           LF in the characters that it matches).
1889    
1890           Notwithstanding  the above, anomalous effects may still occur when CRLF
1891           is a valid newline sequence and explicit \r or \n escapes appear in the
1892           pattern.
1893    
1894           PCRE_NOTBOL           PCRE_NOTBOL
1895    
# Line 2451  AUTHOR Line 2524  AUTHOR
2524    
2525  REVISION  REVISION
2526    
2527         Last updated: 09 August 2007         Last updated: 11 September 2007
2528         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
2529  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2530    
# Line 2736  DIFFERENCES BETWEEN PCRE AND PERL Line 2809  DIFFERENCES BETWEEN PCRE AND PERL
2809         (f)  The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAP-         (f)  The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAP-
2810         TURE options for pcre_exec() have no Perl equivalents.         TURE options for pcre_exec() have no Perl equivalents.
2811    
2812         (g) The callout facility is PCRE-specific.         (g) The \R escape sequence can be restricted to match only CR,  LF,  or
2813           CRLF by the PCRE_BSR_ANYCRLF option.
2814    
2815         (h) The partial matching facility is PCRE-specific.         (h) The callout facility is PCRE-specific.
2816    
2817         (i) Patterns compiled by PCRE can be saved and re-used at a later time,         (i) The partial matching facility is PCRE-specific.
2818    
2819           (j) Patterns compiled by PCRE can be saved and re-used at a later time,
2820         even on different hosts that have the other endianness.         even on different hosts that have the other endianness.
2821    
2822         (j)  The  alternative  matching function (pcre_dfa_exec()) matches in a         (k) The alternative matching function (pcre_dfa_exec())  matches  in  a
2823         different way and is not Perl-compatible.         different way and is not Perl-compatible.
2824    
2825           (l)  PCRE  recognizes some special sequences such as (*CR) at the start
2826           of a pattern that set overall options that cannot be changed within the
2827           pattern.
2828    
2829    
2830  AUTHOR  AUTHOR
2831    
# Line 2756  AUTHOR Line 2836  AUTHOR
2836    
2837  REVISION  REVISION
2838    
2839         Last updated: 08 August 2007         Last updated: 11 September 2007
2840         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
2841  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2842    
# Line 2797  PCRE REGULAR EXPRESSION DETAILS Line 2877  PCRE REGULAR EXPRESSION DETAILS
2877         discussed in the pcrematching page.         discussed in the pcrematching page.
2878    
2879    
2880    NEWLINE CONVENTIONS
2881    
2882           PCRE  supports five different conventions for indicating line breaks in
2883           strings: a single CR (carriage return) character, a  single  LF  (line-
2884           feed) character, the two-character sequence CRLF, any of the three pre-
2885           ceding, or any Unicode newline sequence. The pcreapi page  has  further
2886           discussion  about newlines, and shows how to set the newline convention
2887           in the options arguments for the compiling and matching functions.
2888    
2889           It is also possible to specify a newline convention by starting a  pat-
2890           tern string with one of the following five sequences:
2891    
2892             (*CR)        carriage return
2893             (*LF)        linefeed
2894             (*CRLF)      carriage return, followed by linefeed
2895             (*ANYCRLF)   any of the three above
2896             (*ANY)       all Unicode newline sequences
2897    
2898           These override the default and the options given to pcre_compile(). For
2899           example, on a Unix system where LF is the default newline sequence, the
2900           pattern
2901    
2902             (*CR)a.b
2903    
2904           changes the convention to CR. That pattern matches "a\nb" because LF is
2905           no longer a newline. Note that these special settings,  which  are  not
2906           Perl-compatible,  are  recognized  only at the very start of a pattern,
2907           and that they must be in upper case.  If  more  than  one  of  them  is
2908           present, the last one is used.
2909    
2910           The  newline  convention  does  not  affect what the \R escape sequence
2911           matches. By default, this is any Unicode  newline  sequence,  for  Perl
2912           compatibility.  However, this can be changed; see the description of \R
2913           in the section entitled "Newline sequences" below.
2914    
2915    
2916  CHARACTERS AND METACHARACTERS  CHARACTERS AND METACHARACTERS
2917    
2918         A  regular  expression  is  a pattern that is matched against a subject         A regular expression is a pattern that is  matched  against  a  subject
2919         string from left to right. Most characters stand for  themselves  in  a         string  from  left  to right. Most characters stand for themselves in a
2920         pattern,  and  match  the corresponding characters in the subject. As a         pattern, and match the corresponding characters in the  subject.  As  a
2921         trivial example, the pattern         trivial example, the pattern
2922    
2923           The quick brown fox           The quick brown fox
2924    
2925         matches a portion of a subject string that is identical to itself. When         matches a portion of a subject string that is identical to itself. When
2926         caseless  matching is specified (the PCRE_CASELESS option), letters are         caseless matching is specified (the PCRE_CASELESS option), letters  are
2927         matched independently of case. In UTF-8 mode, PCRE  always  understands         matched  independently  of case. In UTF-8 mode, PCRE always understands
2928         the  concept  of case for characters whose values are less than 128, so         the concept of case for characters whose values are less than  128,  so
2929         caseless matching is always possible. For characters with  higher  val-         caseless  matching  is always possible. For characters with higher val-
2930         ues,  the concept of case is supported if PCRE is compiled with Unicode         ues, the concept of case is supported if PCRE is compiled with  Unicode
2931         property support, but not otherwise.   If  you  want  to  use  caseless         property  support,  but  not  otherwise.   If  you want to use caseless
2932         matching  for  characters  128  and above, you must ensure that PCRE is         matching for characters 128 and above, you must  ensure  that  PCRE  is
2933         compiled with Unicode property support as well as with UTF-8 support.         compiled with Unicode property support as well as with UTF-8 support.
2934    
2935         The power of regular expressions comes  from  the  ability  to  include         The  power  of  regular  expressions  comes from the ability to include
2936         alternatives  and  repetitions in the pattern. These are encoded in the         alternatives and repetitions in the pattern. These are encoded  in  the
2937         pattern by the use of metacharacters, which do not stand for themselves         pattern by the use of metacharacters, which do not stand for themselves
2938         but instead are interpreted in some special way.         but instead are interpreted in some special way.
2939    
2940         There  are  two different sets of metacharacters: those that are recog-         There are two different sets of metacharacters: those that  are  recog-
2941         nized anywhere in the pattern except within square brackets, and  those         nized  anywhere in the pattern except within square brackets, and those
2942         that  are  recognized  within square brackets. Outside square brackets,         that are recognized within square brackets.  Outside  square  brackets,
2943         the metacharacters are as follows:         the metacharacters are as follows:
2944    
2945           \      general escape character with several uses           \      general escape character with several uses
# Line 2842  CHARACTERS AND METACHARACTERS Line 2958  CHARACTERS AND METACHARACTERS
2958                  also "possessive quantifier"                  also "possessive quantifier"
2959           {      start min/max quantifier           {      start min/max quantifier
2960    
2961         Part of a pattern that is in square brackets  is  called  a  "character         Part  of  a  pattern  that is in square brackets is called a "character
2962         class". In a character class the only metacharacters are:         class". In a character class the only metacharacters are:
2963    
2964           \      general escape character           \      general escape character
# Line 2852  CHARACTERS AND METACHARACTERS Line 2968  CHARACTERS AND METACHARACTERS
2968                    syntax)                    syntax)
2969           ]      terminates the character class           ]      terminates the character class
2970    
2971         The  following sections describe the use of each of the metacharacters.         The following sections describe the use of each of the  metacharacters.
2972    
2973    
2974  BACKSLASH  BACKSLASH
2975    
2976         The backslash character has several uses. Firstly, if it is followed by         The backslash character has several uses. Firstly, if it is followed by
2977         a  non-alphanumeric  character,  it takes away any special meaning that         a non-alphanumeric character, it takes away any  special  meaning  that
2978         character may have. This  use  of  backslash  as  an  escape  character         character  may  have.  This  use  of  backslash  as an escape character
2979         applies both inside and outside character classes.         applies both inside and outside character classes.
2980    
2981         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
2982         pattern.  This escaping action applies whether  or  not  the  following         pattern.   This  escaping  action  applies whether or not the following
2983         character  would  otherwise be interpreted as a metacharacter, so it is         character would otherwise be interpreted as a metacharacter, so  it  is
2984         always safe to precede a non-alphanumeric  with  backslash  to  specify         always  safe  to  precede  a non-alphanumeric with backslash to specify
2985         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-
2986         slash, you write \\.         slash, you write \\.
2987    
2988         If a pattern is compiled with the PCRE_EXTENDED option,  whitespace  in         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in
2989         the  pattern (other than in a character class) and characters between a         the pattern (other than in a character class) and characters between  a
2990         # outside a character class and the next newline are ignored. An escap-         # outside a character class and the next newline are ignored. An escap-
2991         ing  backslash  can  be  used to include a whitespace or # character as         ing backslash can be used to include a whitespace  or  #  character  as
2992         part of the pattern.         part of the pattern.
2993    
2994         If you want to remove the special meaning from a  sequence  of  charac-         If  you  want  to remove the special meaning from a sequence of charac-
2995         ters,  you can do so by putting them between \Q and \E. This is differ-         ters, you can do so by putting them between \Q and \E. This is  differ-
2996         ent from Perl in that $ and  @  are  handled  as  literals  in  \Q...\E         ent  from  Perl  in  that  $  and  @ are handled as literals in \Q...\E
2997         sequences  in  PCRE, whereas in Perl, $ and @ cause variable interpola-         sequences in PCRE, whereas in Perl, $ and @ cause  variable  interpola-
2998         tion. Note the following examples:         tion. Note the following examples:
2999    
3000           Pattern            PCRE matches   Perl matches           Pattern            PCRE matches   Perl matches
# Line 2888  BACKSLASH Line 3004  BACKSLASH
3004           \Qabc\$xyz\E       abc\$xyz       abc\$xyz           \Qabc\$xyz\E       abc\$xyz       abc\$xyz
3005           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz
3006    
3007         The \Q...\E sequence is recognized both inside  and  outside  character         The  \Q...\E  sequence  is recognized both inside and outside character
3008         classes.         classes.
3009    
3010     Non-printing characters     Non-printing characters
3011    
3012         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-
3013         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
3014         appearance  of non-printing characters, apart from the binary zero that         appearance of non-printing characters, apart from the binary zero  that
3015         terminates a pattern, but when a pattern  is  being  prepared  by  text         terminates  a  pattern,  but  when  a pattern is being prepared by text
3016         editing,  it  is  usually  easier  to  use  one of the following escape         editing, it is usually easier  to  use  one  of  the  following  escape
3017         sequences than the binary character it represents:         sequences than the binary character it represents:
3018    
3019           \a        alarm, that is, the BEL character (hex 07)           \a        alarm, that is, the BEL character (hex 07)
3020           \cx       "control-x", where x is any character           \cx       "control-x", where x is any character
3021           \e        escape (hex 1B)           \e        escape (hex 1B)
3022           \f        formfeed (hex 0C)           \f        formfeed (hex 0C)
3023           \n        newline (hex 0A)           \n        linefeed (hex 0A)
3024           \r        carriage return (hex 0D)           \r        carriage return (hex 0D)
3025           \t        tab (hex 09)           \t        tab (hex 09)
3026           \ddd      character with octal code ddd, or backreference           \ddd      character with octal code ddd, or backreference
3027           \xhh      character with hex code hh           \xhh      character with hex code hh
3028           \x{hhh..} character with hex code hhh..           \x{hhh..} character with hex code hhh..
3029    
3030         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,
3031         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
3032         inverted.  Thus \cz becomes hex 1A, but \c{ becomes hex 3B,  while  \c;         inverted.   Thus  \cz becomes hex 1A, but \c{ becomes hex 3B, while \c;
3033         becomes hex 7B.         becomes hex 7B.
3034    
3035         After  \x, from zero to two hexadecimal digits are read (letters can be         After \x, from zero to two hexadecimal digits are read (letters can  be
3036         in upper or lower case). Any number of hexadecimal  digits  may  appear         in  upper  or  lower case). Any number of hexadecimal digits may appear
3037         between  \x{  and  },  but the value of the character code must be less         between \x{ and }, but the value of the character  code  must  be  less
3038         than 256 in non-UTF-8 mode, and less than 2**31 in UTF-8 mode. That is,         than 256 in non-UTF-8 mode, and less than 2**31 in UTF-8 mode. That is,
3039         the  maximum value in hexadecimal is 7FFFFFFF. Note that this is bigger         the maximum value in hexadecimal is 7FFFFFFF. Note that this is  bigger
3040         than the largest Unicode code point, which is 10FFFF.         than the largest Unicode code point, which is 10FFFF.
3041    
3042         If characters other than hexadecimal digits appear between \x{  and  },         If  characters  other than hexadecimal digits appear between \x{ and },
3043         or if there is no terminating }, this form of escape is not recognized.         or if there is no terminating }, this form of escape is not recognized.
3044         Instead, the initial \x will be  interpreted  as  a  basic  hexadecimal         Instead,  the  initial  \x  will  be interpreted as a basic hexadecimal
3045         escape,  with  no  following  digits, giving a character whose value is         escape, with no following digits, giving a  character  whose  value  is
3046         zero.         zero.
3047    
3048         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
3049         two  syntaxes  for  \x. There is no difference in the way they are han-         two syntaxes for \x. There is no difference in the way  they  are  han-
3050         dled. For example, \xdc is exactly the same as \x{dc}.         dled. For example, \xdc is exactly the same as \x{dc}.
3051    
3052         After \0 up to two further octal digits are read. If  there  are  fewer         After  \0  up  to two further octal digits are read. If there are fewer
3053         than  two  digits,  just  those  that  are  present  are used. Thus the         than two digits, just  those  that  are  present  are  used.  Thus  the
3054         sequence \0\x\07 specifies two binary zeros followed by a BEL character         sequence \0\x\07 specifies two binary zeros followed by a BEL character
3055         (code  value 7). Make sure you supply two digits after the initial zero         (code value 7). Make sure you supply two digits after the initial  zero
3056         if the pattern character that follows is itself an octal digit.         if the pattern character that follows is itself an octal digit.
3057    
3058         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-
3059         cated.  Outside a character class, PCRE reads it and any following dig-         cated.  Outside a character class, PCRE reads it and any following dig-
3060         its as a decimal number. If the number is less than  10,  or  if  there         its  as  a  decimal  number. If the number is less than 10, or if there
3061         have been at least that many previous capturing left parentheses in the         have been at least that many previous capturing left parentheses in the
3062         expression, the entire  sequence  is  taken  as  a  back  reference.  A         expression,  the  entire  sequence  is  taken  as  a  back reference. A
3063         description  of how this works is given later, following the discussion         description of how this works is given later, following the  discussion
3064         of parenthesized subpatterns.         of parenthesized subpatterns.
3065    
3066         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
3067         and  there have not been that many capturing subpatterns, PCRE re-reads         and there have not been that many capturing subpatterns, PCRE  re-reads
3068         up to three octal digits following the backslash, and uses them to gen-         up to three octal digits following the backslash, and uses them to gen-
3069         erate  a data character. Any subsequent digits stand for themselves. In         erate a data character. Any subsequent digits stand for themselves.  In
3070         non-UTF-8 mode, the value of a character specified  in  octal  must  be         non-UTF-8  mode,  the  value  of a character specified in octal must be
3071         less  than  \400.  In  UTF-8 mode, values up to \777 are permitted. For         less than \400. In UTF-8 mode, values up to  \777  are  permitted.  For
3072         example:         example:
3073    
3074           \040   is another way of writing a space           \040   is another way of writing a space
# Line 2970  BACKSLASH Line 3086  BACKSLASH
3086           \81    is either a back reference, or a binary zero           \81    is either a back reference, or a binary zero
3087                     followed by the two characters "8" and "1"                     followed by the two characters "8" and "1"
3088    
3089         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
3090         leading zero, because no more than three octal digits are ever read.         leading zero, because no more than three octal digits are ever read.
3091    
3092         All the sequences that define a single character value can be used both         All the sequences that define a single character value can be used both
3093         inside and outside character classes. In addition, inside  a  character         inside  and  outside character classes. In addition, inside a character
3094         class,  the  sequence \b is interpreted as the backspace character (hex         class, the sequence \b is interpreted as the backspace  character  (hex
3095         08), and the sequences \R and \X are interpreted as the characters  "R"         08),  and the sequences \R and \X are interpreted as the characters "R"
3096         and  "X", respectively. Outside a character class, these sequences have         and "X", respectively. Outside a character class, these sequences  have
3097         different meanings (see below).         different meanings (see below).
3098    
3099     Absolute and relative back references     Absolute and relative back references
3100    
3101         The sequence \g followed by an unsigned or a negative  number,  option-         The  sequence  \g followed by an unsigned or a negative number, option-
3102         ally  enclosed  in braces, is an absolute or relative back reference. A         ally enclosed in braces, is an absolute or relative back  reference.  A
3103         named back reference can be coded as \g{name}. Back references are dis-         named back reference can be coded as \g{name}. Back references are dis-
3104         cussed later, following the discussion of parenthesized subpatterns.         cussed later, following the discussion of parenthesized subpatterns.
3105    
# Line 3004  BACKSLASH Line 3120  BACKSLASH
3120           \W     any "non-word" character           \W     any "non-word" character
3121    
3122         Each pair of escape sequences partitions the complete set of characters         Each pair of escape sequences partitions the complete set of characters
3123         into  two disjoint sets. Any given character matches one, and only one,         into two disjoint sets. Any given character matches one, and only  one,
3124         of each pair.         of each pair.
3125    
3126         These character type sequences can appear both inside and outside char-         These character type sequences can appear both inside and outside char-
3127         acter  classes.  They each match one character of the appropriate type.         acter classes. They each match one character of the  appropriate  type.
3128         If the current matching point is at the end of the subject string,  all         If  the current matching point is at the end of the subject string, all
3129         of them fail, since there is no character to match.         of them fail, since there is no character to match.
3130    
3131         For  compatibility  with Perl, \s does not match the VT character (code         For compatibility with Perl, \s does not match the VT  character  (code
3132         11).  This makes it different from the the POSIX "space" class. The  \s         11).   This makes it different from the the POSIX "space" class. The \s
3133         characters  are  HT  (9), LF (10), FF (12), CR (13), and space (32). If         characters are HT (9), LF (10), FF (12), CR (13), and  space  (32).  If
3134         "use locale;" is included in a Perl script, \s may match the VT charac-         "use locale;" is included in a Perl script, \s may match the VT charac-
3135         ter. In PCRE, it never does.         ter. In PCRE, it never does.
3136    
3137         In  UTF-8 mode, characters with values greater than 128 never match \d,         In UTF-8 mode, characters with values greater than 128 never match  \d,
3138         \s, or \w, and always match \D, \S, and \W. This is true even when Uni-         \s, or \w, and always match \D, \S, and \W. This is true even when Uni-
3139         code  character  property  support is available. These sequences retain         code character property support is available.  These  sequences  retain
3140         their original meanings from before UTF-8 support was available, mainly         their original meanings from before UTF-8 support was available, mainly
3141         for efficiency reasons.         for efficiency reasons.
3142    
3143         The sequences \h, \H, \v, and \V are Perl 5.10 features. In contrast to         The sequences \h, \H, \v, and \V are Perl 5.10 features. In contrast to
3144         the other sequences, these do match certain high-valued  codepoints  in         the  other  sequences, these do match certain high-valued codepoints in
3145         UTF-8 mode.  The horizontal space characters are:         UTF-8 mode.  The horizontal space characters are:
3146    
3147           U+0009     Horizontal tab           U+0009     Horizontal tab
# Line 3059  BACKSLASH Line 3175  BACKSLASH
3175           U+2029     Paragraph separator           U+2029     Paragraph separator
3176    
3177         A "word" character is an underscore or any character less than 256 that         A "word" character is an underscore or any character less than 256 that
3178         is a letter or digit. The definition of  letters  and  digits  is  con-         is  a  letter  or  digit.  The definition of letters and digits is con-
3179         trolled  by PCRE's low-valued character tables, and may vary if locale-         trolled by PCRE's low-valued character tables, and may vary if  locale-
3180         specific matching is taking place (see "Locale support" in the  pcreapi         specific  matching is taking place (see "Locale support" in the pcreapi
3181         page).  For  example,  in  a French locale such as "fr_FR" in Unix-like         page). For example, in a French locale such  as  "fr_FR"  in  Unix-like
3182         systems, or "french" in Windows, some character codes greater than  128         systems,  or "french" in Windows, some character codes greater than 128
3183         are  used for accented letters, and these are matched by \w. The use of         are used for accented letters, and these are matched by \w. The use  of
3184         locales with Unicode is discouraged.         locales with Unicode is discouraged.
3185    
3186     Newline sequences     Newline sequences
3187    
3188         Outside a character class, the escape sequence \R matches  any  Unicode         Outside  a  character class, by default, the escape sequence \R matches
3189         newline  sequence. This is a Perl 5.10 feature. In non-UTF-8 mode \R is         any Unicode newline sequence. This is a Perl 5.10 feature. In non-UTF-8
3190         equivalent to the following:         mode \R is equivalent to the following:
3191    
3192           (?>\r\n|\n|\x0b|\f|\r|\x85)           (?>\r\n|\n|\x0b|\f|\r|\x85)
3193    
3194         This is an example of an "atomic group", details  of  which  are  given         This  is  an  example  of an "atomic group", details of which are given
3195         below.  This particular group matches either the two-character sequence         below.  This particular group matches either the two-character sequence
3196         CR followed by LF, or  one  of  the  single  characters  LF  (linefeed,         CR  followed  by  LF,  or  one  of  the single characters LF (linefeed,
3197         U+000A), VT (vertical tab, U+000B), FF (formfeed, U+000C), CR (carriage         U+000A), VT (vertical tab, U+000B), FF (formfeed, U+000C), CR (carriage
3198         return, U+000D), or NEL (next line, U+0085). The two-character sequence         return, U+000D), or NEL (next line, U+0085). The two-character sequence
3199         is treated as a single unit that cannot be split.         is treated as a single unit that cannot be split.
3200    
3201         In  UTF-8  mode, two additional characters whose codepoints are greater         In UTF-8 mode, two additional characters whose codepoints  are  greater
3202         than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa-         than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa-
3203         rator,  U+2029).   Unicode character property support is not needed for         rator, U+2029).  Unicode character property support is not  needed  for
3204         these characters to be recognized.         these characters to be recognized.
3205    
3206           It is possible to restrict \R to match only CR, LF, or CRLF (instead of
3207           the complete set  of  Unicode  line  endings)  by  setting  the  option
3208           PCRE_BSR_ANYCRLF either at compile time or when the pattern is matched.
3209           This can be made the default when PCRE is built; if this is  the  case,
3210           the  other  behaviour can be requested via the PCRE_BSR_UNICODE option.
3211           It is also possible to specify these settings  by  starting  a  pattern
3212           string with one of the following sequences:
3213    
3214             (*BSR_ANYCRLF)   CR, LF, or CRLF only
3215             (*BSR_UNICODE)   any Unicode newline sequence
3216    
3217           These override the default and the options given to pcre_compile(), but
3218           they can be overridden by options given to pcre_exec(). Note that these
3219           special settings, which are not Perl-compatible, are recognized only at
3220           the very start of a pattern, and that they must be in  upper  case.  If
3221           more than one of them is present, the last one is used.
3222    
3223         Inside a character class, \R matches the letter "R".         Inside a character class, \R matches the letter "R".
3224    
3225     Unicode character properties     Unicode character properties
3226    
3227         When PCRE is built with Unicode character property support, three addi-         When PCRE is built with Unicode character property support, three addi-
3228         tional  escape sequences that match characters with specific properties         tional escape sequences that match characters with specific  properties
3229         are available.  When not in UTF-8 mode, these sequences are  of  course         are  available.   When not in UTF-8 mode, these sequences are of course
3230         limited  to  testing characters whose codepoints are less than 256, but         limited to testing characters whose codepoints are less than  256,  but
3231         they do work in this mode.  The extra escape sequences are:         they do work in this mode.  The extra escape sequences are:
3232    
3233           \p{xx}   a character with the xx property           \p{xx}   a character with the xx property
3234           \P{xx}   a character without the xx property           \P{xx}   a character without the xx property
3235           \X       an extended Unicode sequence           \X       an extended Unicode sequence
3236    
3237         The property names represented by xx above are limited to  the  Unicode         The  property  names represented by xx above are limited to the Unicode
3238         script names, the general category properties, and "Any", which matches         script names, the general category properties, and "Any", which matches
3239         any character (including newline). Other properties such as "InMusical-         any character (including newline). Other properties such as "InMusical-
3240         Symbols"  are  not  currently supported by PCRE. Note that \P{Any} does         Symbols" are not currently supported by PCRE. Note  that  \P{Any}  does
3241         not match any characters, so always causes a match failure.         not match any characters, so always causes a match failure.
3242    
3243         Sets of Unicode characters are defined as belonging to certain scripts.         Sets of Unicode characters are defined as belonging to certain scripts.
3244         A  character from one of these sets can be matched using a script name.         A character from one of these sets can be matched using a script  name.
3245         For example:         For example:
3246    
3247           \p{Greek}           \p{Greek}
3248           \P{Han}           \P{Han}
3249    
3250         Those that are not part of an identified script are lumped together  as         Those  that are not part of an identified script are lumped together as
3251         "Common". The current list of scripts is:         "Common". The current list of scripts is:
3252    
3253         Arabic,  Armenian,  Balinese,  Bengali,  Bopomofo,  Braille,  Buginese,         Arabic,  Armenian,  Balinese,  Bengali,  Bopomofo,  Braille,  Buginese,
3254         Buhid,  Canadian_Aboriginal,  Cherokee,  Common,   Coptic,   Cuneiform,         Buhid,   Canadian_Aboriginal,   Cherokee,  Common,  Coptic,  Cuneiform,
3255         Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,         Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,
3256         Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew,  Hira-         Gothic,  Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hira-
3257         gana,  Inherited,  Kannada,  Katakana,  Kharoshthi,  Khmer, Lao, Latin,         gana, Inherited, Kannada,  Katakana,  Kharoshthi,  Khmer,  Lao,  Latin,
3258         Limbu,  Linear_B,  Malayalam,  Mongolian,  Myanmar,  New_Tai_Lue,  Nko,         Limbu,  Linear_B,  Malayalam,  Mongolian,  Myanmar,  New_Tai_Lue,  Nko,
3259         Ogham,  Old_Italic,  Old_Persian, Oriya, Osmanya, Phags_Pa, Phoenician,         Ogham, Old_Italic, Old_Persian, Oriya, Osmanya,  Phags_Pa,  Phoenician,
3260         Runic,  Shavian,  Sinhala,  Syloti_Nagri,  Syriac,  Tagalog,  Tagbanwa,         Runic,  Shavian,  Sinhala,  Syloti_Nagri,  Syriac,  Tagalog,  Tagbanwa,
3261         Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.         Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.
3262    
3263         Each  character has exactly one general category property, specified by         Each character has exactly one general category property, specified  by
3264         a two-letter abbreviation. For compatibility with Perl, negation can be         a two-letter abbreviation. For compatibility with Perl, negation can be
3265         specified  by  including a circumflex between the opening brace and the         specified by including a circumflex between the opening brace  and  the
3266         property name. For example, \p{^Lu} is the same as \P{Lu}.         property name. For example, \p{^Lu} is the same as \P{Lu}.
3267    
3268         If only one letter is specified with \p or \P, it includes all the gen-         If only one letter is specified with \p or \P, it includes all the gen-
3269         eral  category properties that start with that letter. In this case, in         eral category properties that start with that letter. In this case,  in
3270         the absence of negation, the curly brackets in the escape sequence  are         the  absence of negation, the curly brackets in the escape sequence are
3271         optional; these two examples have the same effect:         optional; these two examples have the same effect:
3272    
3273           \p{L}           \p{L}
# Line 3186  BACKSLASH Line 3319  BACKSLASH
3319           Zp    Paragraph separator           Zp    Paragraph separator
3320           Zs    Space separator           Zs    Space separator
3321    
3322         The  special property L& is also supported: it matches a character that         The special property L& is also supported: it matches a character  that
3323         has the Lu, Ll, or Lt property, in other words, a letter  that  is  not         has  the  Lu,  Ll, or Lt property, in other words, a letter that is not
3324         classified as a modifier or "other".         classified as a modifier or "other".
3325    
3326         The  Cs  (Surrogate)  property  applies only to characters in the range         The Cs (Surrogate) property applies only to  characters  in  the  range
3327         U+D800 to U+DFFF. Such characters are not valid in UTF-8  strings  (see         U+D800  to  U+DFFF. Such characters are not valid in UTF-8 strings (see
3328         RFC 3629) and so cannot be tested by PCRE, unless UTF-8 validity check-         RFC 3629) and so cannot be tested by PCRE, unless UTF-8 validity check-
3329         ing has been turned off (see the discussion  of  PCRE_NO_UTF8_CHECK  in         ing  has  been  turned off (see the discussion of PCRE_NO_UTF8_CHECK in
3330         the pcreapi page).         the pcreapi page).
3331    
3332         The  long  synonyms  for  these  properties that Perl supports (such as         The long synonyms for these properties  that  Perl  supports  (such  as
3333         \p{Letter}) are not supported by PCRE, nor is it  permitted  to  prefix         \p{Letter})  are  not  supported by PCRE, nor is it permitted to prefix
3334         any of these properties with "Is".         any of these properties with "Is".
3335    
3336         No character that is in the Unicode table has the Cn (unassigned) prop-         No character that is in the Unicode table has the Cn (unassigned) prop-
3337         erty.  Instead, this property is assumed for any code point that is not         erty.  Instead, this property is assumed for any code point that is not
3338         in the Unicode table.         in the Unicode table.
3339    
3340         Specifying  caseless  matching  does not affect these escape sequences.         Specifying caseless matching does not affect  these  escape  sequences.
3341         For example, \p{Lu} always matches only upper case letters.         For example, \p{Lu} always matches only upper case letters.
3342    
3343         The \X escape matches any number of Unicode  characters  that  form  an         The  \X  escape  matches  any number of Unicode characters that form an
3344         extended Unicode sequence. \X is equivalent to         extended Unicode sequence. \X is equivalent to
3345    
3346           (?>\PM\pM*)           (?>\PM\pM*)
3347    
3348         That  is,  it matches a character without the "mark" property, followed         That is, it matches a character without the "mark"  property,  followed
3349         by zero or more characters with the "mark"  property,  and  treats  the         by  zero  or  more  characters with the "mark" property, and treats the
3350         sequence  as  an  atomic group (see below).  Characters with the "mark"         sequence as an atomic group (see below).  Characters  with  the  "mark"
3351         property are typically accents that  affect  the  preceding  character.         property  are  typically  accents  that affect the preceding character.
3352         None  of  them  have  codepoints less than 256, so in non-UTF-8 mode \X         None of them have codepoints less than 256, so  in  non-UTF-8  mode  \X
3353         matches any one character.         matches any one character.
3354    
3355         Matching characters by Unicode property is not fast, because  PCRE  has         Matching  characters  by Unicode property is not fast, because PCRE has
3356         to  search  a  structure  that  contains data for over fifteen thousand         to search a structure that contains  data  for  over  fifteen  thousand
3357         characters. That is why the traditional escape sequences such as \d and         characters. That is why the traditional escape sequences such as \d and
3358         \w do not use Unicode properties in PCRE.         \w do not use Unicode properties in PCRE.
3359    
3360     Resetting the match start     Resetting the match start
3361    
3362         The escape sequence \K, which is a Perl 5.10 feature, causes any previ-         The escape sequence \K, which is a Perl 5.10 feature, causes any previ-
3363         ously matched characters not  to  be  included  in  the  final  matched         ously  matched  characters  not  to  be  included  in the final matched
3364         sequence. For example, the pattern:         sequence. For example, the pattern:
3365    
3366           foo\Kbar           foo\Kbar
3367    
3368         matches  "foobar",  but reports that it has matched "bar". This feature         matches "foobar", but reports that it has matched "bar".  This  feature
3369         is similar to a lookbehind assertion (described  below).   However,  in         is  similar  to  a lookbehind assertion (described below).  However, in
3370         this  case, the part of the subject before the real match does not have         this case, the part of the subject before the real match does not  have
3371         to be of fixed length, as lookbehind assertions do. The use of \K  does         to  be of fixed length, as lookbehind assertions do. The use of \K does
3372         not  interfere  with  the setting of captured substrings.  For example,         not interfere with the setting of captured  substrings.   For  example,
3373         when the pattern         when the pattern
3374    
3375           (foo)\Kbar           (foo)\Kbar
# Line 3245  BACKSLASH Line 3378  BACKSLASH
3378    
3379     Simple assertions     Simple assertions
3380    
3381         The final use of backslash is for certain simple assertions. An  asser-         The  final use of backslash is for certain simple assertions. An asser-
3382         tion  specifies a condition that has to be met at a particular point in         tion specifies a condition that has to be met at a particular point  in
3383         a match, without consuming any characters from the subject string.  The         a  match, without consuming any characters from the subject string. The
3384         use  of subpatterns for more complicated assertions is described below.         use of subpatterns for more complicated assertions is described  below.
3385         The backslashed assertions are:         The backslashed assertions are:
3386    
3387           \b     matches at a word boundary           \b     matches at a word boundary
# Line 3259  BACKSLASH Line 3392  BACKSLASH
3392           \z     matches only at the end of the subject           \z     matches only at the end of the subject
3393           \G     matches at the first matching position in the subject           \G     matches at the first matching position in the subject
3394    
3395         These assertions may not appear in character classes (but note that  \b         These  assertions may not appear in character classes (but note that \b
3396         has a different meaning, namely the backspace character, inside a char-         has a different meaning, namely the backspace character, inside a char-
3397         acter class).         acter class).
3398    
3399         A word boundary is a position in the subject string where  the  current         A  word  boundary is a position in the subject string where the current
3400         character  and  the previous character do not both match \w or \W (i.e.         character and the previous character do not both match \w or  \W  (i.e.
3401         one matches \w and the other matches \W), or the start or  end  of  the         one  matches  \w  and the other matches \W), or the start or end of the
3402         string if the first or last character matches \w, respectively.         string if the first or last character matches \w, respectively.
3403    
3404         The  \A,  \Z,  and \z assertions differ from the traditional circumflex         The \A, \Z, and \z assertions differ from  the  traditional  circumflex
3405         and dollar (described in the next section) in that they only ever match         and dollar (described in the next section) in that they only ever match
3406         at  the  very start and end of the subject string, whatever options are         at the very start and end of the subject string, whatever  options  are
3407         set. Thus, they are independent of multiline mode. These  three  asser-         set.  Thus,  they are independent of multiline mode. These three asser-
3408         tions are not affected by the PCRE_NOTBOL or PCRE_NOTEOL options, which         tions are not affected by the PCRE_NOTBOL or PCRE_NOTEOL options, which
3409         affect only the behaviour of the circumflex and dollar  metacharacters.         affect  only the behaviour of the circumflex and dollar metacharacters.
3410         However,  if the startoffset argument of pcre_exec() is non-zero, indi-         However, if the startoffset argument of pcre_exec() is non-zero,  indi-
3411         cating that matching is to start at a point other than the beginning of         cating that matching is to start at a point other than the beginning of
3412         the  subject,  \A  can never match. The difference between \Z and \z is         the subject, \A can never match. The difference between \Z  and  \z  is
3413         that \Z matches before a newline at the end of the string as well as at         that \Z matches before a newline at the end of the string as well as at
3414         the very end, whereas \z matches only at the end.         the very end, whereas \z matches only at the end.
3415    
3416         The  \G assertion is true only when the current matching position is at         The \G assertion is true only when the current matching position is  at
3417         the start point of the match, as specified by the startoffset  argument         the  start point of the match, as specified by the startoffset argument
3418         of  pcre_exec().  It  differs  from \A when the value of startoffset is         of pcre_exec(). It differs from \A when the  value  of  startoffset  is
3419         non-zero. By calling pcre_exec() multiple times with appropriate  argu-         non-zero.  By calling pcre_exec() multiple times with appropriate argu-
3420         ments, you can mimic Perl's /g option, and it is in this kind of imple-         ments, you can mimic Perl's /g option, and it is in this kind of imple-
3421         mentation where \G can be useful.         mentation where \G can be useful.
3422    
3423         Note, however, that PCRE's interpretation of \G, as the  start  of  the         Note,  however,  that  PCRE's interpretation of \G, as the start of the
3424         current match, is subtly different from Perl's, which defines it as the         current match, is subtly different from Perl's, which defines it as the
3425         end of the previous match. In Perl, these can  be  different  when  the         end  of  the  previous  match. In Perl, these can be different when the
3426         previously  matched  string was empty. Because PCRE does just one match         previously matched string was empty. Because PCRE does just  one  match
3427         at a time, it cannot reproduce this behaviour.         at a time, it cannot reproduce this behaviour.
3428    
3429         If all the alternatives of a pattern begin with \G, the  expression  is         If  all  the alternatives of a pattern begin with \G, the expression is
3430         anchored to the starting match position, and the "anchored" flag is set         anchored to the starting match position, and the "anchored" flag is set
3431         in the compiled regular expression.         in the compiled regular expression.
3432    
# Line 3301  BACKSLASH Line 3434  BACKSLASH
3434  CIRCUMFLEX AND DOLLAR  CIRCUMFLEX AND DOLLAR
3435    
3436         Outside a character class, in the default matching mode, the circumflex         Outside a character class, in the default matching mode, the circumflex
3437         character  is  an  assertion  that is true only if the current matching         character is an assertion that is true only  if  the  current  matching
3438         point is at the start of the subject string. If the  startoffset  argu-         point  is  at the start of the subject string. If the startoffset argu-
3439         ment  of  pcre_exec()  is  non-zero,  circumflex can never match if the         ment of pcre_exec() is non-zero, circumflex  can  never  match  if  the
3440         PCRE_MULTILINE option is unset. Inside a  character  class,  circumflex         PCRE_MULTILINE  option  is  unset. Inside a character class, circumflex
3441         has an entirely different meaning (see below).         has an entirely different meaning (see below).
3442    
3443         Circumflex  need  not be the first character of the pattern if a number         Circumflex need not be the first character of the pattern if  a  number
3444         of alternatives are involved, but it should be the first thing in  each         of  alternatives are involved, but it should be the first thing in each
3445         alternative  in  which  it appears if the pattern is ever to match that         alternative in which it appears if the pattern is ever  to  match  that
3446         branch. If all possible alternatives start with a circumflex, that  is,         branch.  If all possible alternatives start with a circumflex, that is,
3447         if  the  pattern  is constrained to match only at the start of the sub-         if the pattern is constrained to match only at the start  of  the  sub-
3448         ject, it is said to be an "anchored" pattern.  (There  are  also  other         ject,  it  is  said  to be an "anchored" pattern. (There are also other
3449         constructs that can cause a pattern to be anchored.)         constructs that can cause a pattern to be anchored.)
3450    
3451         A  dollar  character  is  an assertion that is true only if the current         A dollar character is an assertion that is true  only  if  the  current
3452         matching point is at the end of  the  subject  string,  or  immediately         matching  point  is  at  the  end of the subject string, or immediately
3453         before a newline at the end of the string (by default). Dollar need not         before a newline at the end of the string (by default). Dollar need not
3454         be the last character of the pattern if a number  of  alternatives  are         be  the  last  character of the pattern if a number of alternatives are
3455         involved,  but  it  should  be  the last item in any branch in which it         involved, but it should be the last item in  any  branch  in  which  it
3456         appears. Dollar has no special meaning in a character class.         appears. Dollar has no special meaning in a character class.
3457    
3458         The meaning of dollar can be changed so that it  matches  only  at  the         The  meaning  of  dollar  can be changed so that it matches only at the
3459         very  end  of  the string, by setting the PCRE_DOLLAR_ENDONLY option at         very end of the string, by setting the  PCRE_DOLLAR_ENDONLY  option  at
3460         compile time. This does not affect the \Z assertion.         compile time. This does not affect the \Z assertion.
3461    
3462         The meanings of the circumflex and dollar characters are changed if the         The meanings of the circumflex and dollar characters are changed if the
3463         PCRE_MULTILINE  option  is  set.  When  this  is the case, a circumflex         PCRE_MULTILINE option is set. When  this  is  the  case,  a  circumflex
3464         matches immediately after internal newlines as well as at the start  of         matches  immediately after internal newlines as well as at the start of
3465         the  subject  string.  It  does not match after a newline that ends the         the subject string. It does not match after a  newline  that  ends  the
3466         string. A dollar matches before any newlines in the string, as well  as         string.  A dollar matches before any newlines in the string, as well as
3467         at  the very end, when PCRE_MULTILINE is set. When newline is specified         at the very end, when PCRE_MULTILINE is set. When newline is  specified
3468         as the two-character sequence CRLF, isolated CR and  LF  characters  do         as  the  two-character  sequence CRLF, isolated CR and LF characters do
3469         not indicate newlines.         not indicate newlines.
3470    
3471         For  example, the pattern /^abc$/ matches the subject string "def\nabc"         For example, the pattern /^abc$/ matches the subject string  "def\nabc"
3472         (where \n represents a newline) in multiline mode, but  not  otherwise.         (where  \n  represents a newline) in multiline mode, but not otherwise.
3473         Consequently,  patterns  that  are anchored in single line mode because         Consequently, patterns that are anchored in single  line  mode  because
3474         all branches start with ^ are not anchored in  multiline  mode,  and  a         all  branches  start  with  ^ are not anchored in multiline mode, and a
3475         match  for  circumflex  is  possible  when  the startoffset argument of         match for circumflex is  possible  when  the  startoffset  argument  of
3476         pcre_exec() is non-zero. The PCRE_DOLLAR_ENDONLY option is  ignored  if         pcre_exec()  is  non-zero. The PCRE_DOLLAR_ENDONLY option is ignored if
3477         PCRE_MULTILINE is set.         PCRE_MULTILINE is set.
3478    
3479         Note  that  the sequences \A, \Z, and \z can be used to match the start         Note that the sequences \A, \Z, and \z can be used to match  the  start
3480         and end of the subject in both modes, and if all branches of a  pattern         and  end of the subject in both modes, and if all branches of a pattern
3481         start  with  \A it is always anchored, whether or not PCRE_MULTILINE is         start with \A it is always anchored, whether or not  PCRE_MULTILINE  is
3482         set.         set.
3483    
3484    
3485  FULL STOP (PERIOD, DOT)  FULL STOP (PERIOD, DOT)
3486    
3487         Outside a character class, a dot in the pattern matches any one charac-         Outside a character class, a dot in the pattern matches any one charac-
3488         ter  in  the subject string except (by default) a character that signi-         ter in the subject string except (by default) a character  that  signi-
3489         fies the end of a line. In UTF-8 mode, the  matched  character  may  be         fies  the  end  of  a line. In UTF-8 mode, the matched character may be
3490         more than one byte long.         more than one byte long.
3491    
3492         When  a line ending is defined as a single character, dot never matches         When a line ending is defined as a single character, dot never  matches
3493         that character; when the two-character sequence CRLF is used, dot  does         that  character; when the two-character sequence CRLF is used, dot does
3494         not  match  CR  if  it  is immediately followed by LF, but otherwise it         not match CR if it is immediately followed  by  LF,  but  otherwise  it
3495         matches all characters (including isolated CRs and LFs). When any  Uni-         matches  all characters (including isolated CRs and LFs). When any Uni-
3496         code  line endings are being recognized, dot does not match CR or LF or         code line endings are being recognized, dot does not match CR or LF  or
3497         any of the other line ending characters.         any of the other line ending characters.
3498    
3499         The behaviour of dot with regard to newlines can  be  changed.  If  the         The  behaviour  of  dot  with regard to newlines can be changed. If the
3500         PCRE_DOTALL  option  is  set,  a dot matches any one character, without         PCRE_DOTALL option is set, a dot matches  any  one  character,  without
3501         exception. If the two-character sequence CRLF is present in the subject         exception. If the two-character sequence CRLF is present in the subject
3502         string, it takes two dots to match it.         string, it takes two dots to match it.
3503    
3504         The  handling of dot is entirely independent of the handling of circum-         The handling of dot is entirely independent of the handling of  circum-
3505         flex and dollar, the only relationship being  that  they  both  involve         flex  and  dollar,  the  only relationship being that they both involve
3506         newlines. Dot has no special meaning in a character class.         newlines. Dot has no special meaning in a character class.
3507    
3508    
3509  MATCHING A SINGLE BYTE  MATCHING A SINGLE BYTE
3510    
3511         Outside a character class, the escape sequence \C matches any one byte,         Outside a character class, the escape sequence \C matches any one byte,
3512         both in and out of UTF-8 mode. Unlike a  dot,  it  always  matches  any         both  in  and  out  of  UTF-8 mode. Unlike a dot, it always matches any
3513         line-ending  characters.  The  feature  is provided in Perl in order to         line-ending characters. The feature is provided in  Perl  in  order  to
3514         match individual bytes in UTF-8 mode. Because it breaks up UTF-8  char-         match  individual bytes in UTF-8 mode. Because it breaks up UTF-8 char-
3515         acters  into individual bytes, what remains in the string may be a mal-         acters into individual bytes, what remains in the string may be a  mal-
3516         formed UTF-8 string. For this reason, the \C escape  sequence  is  best         formed  UTF-8  string.  For this reason, the \C escape sequence is best
3517         avoided.         avoided.
3518    
3519         PCRE  does  not  allow \C to appear in lookbehind assertions (described         PCRE does not allow \C to appear in  lookbehind  assertions  (described
3520         below), because in UTF-8 mode this would make it impossible  to  calcu-         below),  because  in UTF-8 mode this would make it impossible to calcu-
3521         late the length of the lookbehind.         late the length of the lookbehind.
3522    
3523    
# Line 3393  SQUARE BRACKETS AND CHARACTER CLASSES Line 3526  SQUARE BRACKETS AND CHARACTER CLASSES
3526         An opening square bracket introduces a character class, terminated by a         An opening square bracket introduces a character class, terminated by a
3527         closing square bracket. A closing square bracket on its own is not spe-         closing square bracket. A closing square bracket on its own is not spe-
3528         cial. If a closing square bracket is required as a member of the class,         cial. If a closing square bracket is required as a member of the class,
3529         it should be the first data character in the class  (after  an  initial         it  should  be  the first data character in the class (after an initial
3530         circumflex, if present) or escaped with a backslash.         circumflex, if present) or escaped with a backslash.
3531    
3532         A  character  class matches a single character in the subject. In UTF-8         A character class matches a single character in the subject.  In  UTF-8
3533         mode, the character may occupy more than one byte. A matched  character         mode,  the character may occupy more than one byte. A matched character
3534         must be in the set of characters defined by the class, unless the first         must be in the set of characters defined by the class, unless the first
3535         character in the class definition is a circumflex, in  which  case  the         character  in  the  class definition is a circumflex, in which case the
3536         subject  character  must  not  be in the set defined by the class. If a         subject character must not be in the set defined by  the  class.  If  a
3537         circumflex is actually required as a member of the class, ensure it  is         circumflex  is actually required as a member of the class, ensure it is
3538         not the first character, or escape it with a backslash.         not the first character, or escape it with a backslash.
3539    
3540         For  example, the character class [aeiou] matches any lower case vowel,         For example, the character class [aeiou] matches any lower case  vowel,
3541         while [^aeiou] matches any character that is not a  lower  case  vowel.         while  [^aeiou]  matches  any character that is not a lower case vowel.
3542         Note that a circumflex is just a convenient notation for specifying the         Note that a circumflex is just a convenient notation for specifying the
3543         characters that are in the class by enumerating those that are  not.  A         characters  that  are in the class by enumerating those that are not. A
3544         class  that starts with a circumflex is not an assertion: it still con-         class that starts with a circumflex is not an assertion: it still  con-
3545         sumes a character from the subject string, and therefore  it  fails  if         sumes  a  character  from the subject string, and therefore it fails if
3546         the current pointer is at the end of the string.         the current pointer is at the end of the string.
3547    
3548         In  UTF-8 mode, characters with values greater than 255 can be included         In UTF-8 mode, characters with values greater than 255 can be  included
3549         in a class as a literal string of bytes, or by using the  \x{  escaping         in  a  class as a literal string of bytes, or by using the \x{ escaping
3550         mechanism.         mechanism.
3551    
3552         When  caseless  matching  is set, any letters in a class represent both         When caseless matching is set, any letters in a  class  represent  both
3553         their upper case and lower case versions, so for  example,  a  caseless         their  upper  case  and lower case versions, so for example, a caseless
3554         [aeiou]  matches  "A"  as well as "a", and a caseless [^aeiou] does not         [aeiou] matches "A" as well as "a", and a caseless  [^aeiou]  does  not
3555         match "A", whereas a caseful version would. In UTF-8 mode, PCRE  always         match  "A", whereas a caseful version would. In UTF-8 mode, PCRE always
3556         understands  the  concept  of case for characters whose values are less         understands the concept of case for characters whose  values  are  less
3557         than 128, so caseless matching is always possible. For characters  with         than  128, so caseless matching is always possible. For characters with
3558         higher  values,  the  concept  of case is supported if PCRE is compiled         higher values, the concept of case is supported  if  PCRE  is  compiled
3559         with Unicode property support, but not otherwise.  If you want  to  use         with  Unicode  property support, but not otherwise.  If you want to use
3560         caseless  matching  for  characters 128 and above, you must ensure that         caseless matching for characters 128 and above, you  must  ensure  that
3561         PCRE is compiled with Unicode property support as well  as  with  UTF-8         PCRE  is  compiled  with Unicode property support as well as with UTF-8
3562         support.         support.
3563    
3564         Characters  that  might  indicate  line breaks are never treated in any         Characters that might indicate line breaks are  never  treated  in  any
3565         special way  when  matching  character  classes,  whatever  line-ending         special  way  when  matching  character  classes,  whatever line-ending
3566         sequence  is  in  use,  and  whatever  setting  of  the PCRE_DOTALL and         sequence is in  use,  and  whatever  setting  of  the  PCRE_DOTALL  and
3567         PCRE_MULTILINE options is used. A class such as [^a] always matches one         PCRE_MULTILINE options is used. A class such as [^a] always matches one
3568         of these characters.         of these characters.
3569    
3570         The  minus (hyphen) character can be used to specify a range of charac-         The minus (hyphen) character can be used to specify a range of  charac-
3571         ters in a character  class.  For  example,  [d-m]  matches  any  letter         ters  in  a  character  class.  For  example,  [d-m] matches any letter
3572         between  d  and  m,  inclusive.  If  a minus character is required in a         between d and m, inclusive. If a  minus  character  is  required  in  a
3573         class, it must be escaped with a backslash  or  appear  in  a  position         class,  it  must  be  escaped  with a backslash or appear in a position
3574         where  it cannot be interpreted as indicating a range, typically as the         where it cannot be interpreted as indicating a range, typically as  the
3575         first or last character in the class.         first or last character in the class.
3576    
3577         It is not possible to have the literal character "]" as the end charac-         It is not possible to have the literal character "]" as the end charac-
3578         ter  of a range. A pattern such as [W-]46] is interpreted as a class of         ter of a range. A pattern such as [W-]46] is interpreted as a class  of
3579         two characters ("W" and "-") followed by a literal string "46]", so  it         two  characters ("W" and "-") followed by a literal string "46]", so it
3580         would  match  "W46]"  or  "-46]". However, if the "]" is escaped with a         would match "W46]" or "-46]". However, if the "]"  is  escaped  with  a
3581         backslash it is interpreted as the end of range, so [W-\]46] is  inter-         backslash  it is interpreted as the end of range, so [W-\]46] is inter-
3582         preted  as a class containing a range followed by two other characters.         preted as a class containing a range followed by two other  characters.
3583         The octal or hexadecimal representation of "]" can also be used to  end         The  octal or hexadecimal representation of "]" can also be used to end
3584         a range.         a range.
3585    
3586         Ranges  operate in the collating sequence of character values. They can         Ranges operate in the collating sequence of character values. They  can
3587         also  be  used  for  characters  specified  numerically,  for   example         also   be  used  for  characters  specified  numerically,  for  example
3588         [\000-\037].  In UTF-8 mode, ranges can include characters whose values         [\000-\037]. In UTF-8 mode, ranges can include characters whose  values
3589         are greater than 255, for example [\x{100}-\x{2ff}].         are greater than 255, for example [\x{100}-\x{2ff}].
3590    
3591         If a range that includes letters is used when caseless matching is set,         If a range that includes letters is used when caseless matching is set,
3592         it matches the letters in either case. For example, [W-c] is equivalent         it matches the letters in either case. For example, [W-c] is equivalent
3593         to [][\\^_`wxyzabc], matched caselessly,  and  in  non-UTF-8  mode,  if         to  [][\\^_`wxyzabc],  matched  caselessly,  and  in non-UTF-8 mode, if
3594         character  tables  for  a French locale are in use, [\xc8-\xcb] matches         character tables for a French locale are in  use,  [\xc8-\xcb]  matches
3595         accented E characters in both cases. In UTF-8 mode, PCRE  supports  the         accented  E  characters in both cases. In UTF-8 mode, PCRE supports the
3596         concept  of  case for characters with values greater than 128 only when         concept of case for characters with values greater than 128  only  when
3597         it is compiled with Unicode property support.         it is compiled with Unicode property support.
3598    
3599         The character types \d, \D, \p, \P, \s, \S, \w, and \W may also  appear         The  character types \d, \D, \p, \P, \s, \S, \w, and \W may also appear
3600         in  a  character  class,  and add the characters that they match to the         in a character class, and add the characters that  they  match  to  the
3601         class. For example, [\dABCDEF] matches any hexadecimal digit. A circum-         class. For example, [\dABCDEF] matches any hexadecimal digit. A circum-
3602         flex  can  conveniently  be used with the upper case character types to         flex can conveniently be used with the upper case  character  types  to
3603         specify a more restricted set of characters  than  the  matching  lower         specify  a  more  restricted  set of characters than the matching lower
3604         case  type.  For example, the class [^\W_] matches any letter or digit,         case type. For example, the class [^\W_] matches any letter  or  digit,
3605         but not underscore.         but not underscore.
3606    
3607         The only metacharacters that are recognized in  character  classes  are         The  only  metacharacters  that are recognized in character classes are
3608         backslash,  hyphen  (only  where  it can be interpreted as specifying a         backslash, hyphen (only where it can be  interpreted  as  specifying  a
3609         range), circumflex (only at the start), opening  square  bracket  (only         range),  circumflex  (only  at the start), opening square bracket (only
3610         when  it can be interpreted as introducing a POSIX class name - see the         when it can be interpreted as introducing a POSIX class name - see  the
3611         next section), and the terminating  closing  square  bracket.  However,         next  section),  and  the  terminating closing square bracket. However,
3612         escaping other non-alphanumeric characters does no harm.         escaping other non-alphanumeric characters does no harm.
3613    
3614    
3615  POSIX CHARACTER CLASSES  POSIX CHARACTER CLASSES
3616    
3617         Perl supports the POSIX notation for character classes. This uses names         Perl supports the POSIX notation for character classes. This uses names
3618         enclosed by [: and :] within the enclosing square brackets.  PCRE  also         enclosed  by  [: and :] within the enclosing square brackets. PCRE also
3619         supports this notation. For example,         supports this notation. For example,
3620    
3621           [01[:alpha:]%]           [01[:alpha:]%]
# Line 3505  POSIX CHARACTER CLASSES Line 3638  POSIX CHARACTER CLASSES
3638           word     "word" characters (same as \w)           word     "word" characters (same as \w)
3639           xdigit   hexadecimal digits           xdigit   hexadecimal digits
3640    
3641         The "space" characters are HT (9), LF (10), VT (11), FF (12), CR  (13),         The  "space" characters are HT (9), LF (10), VT (11), FF (12), CR (13),
3642         and  space  (32). Notice that this list includes the VT character (code         and space (32). Notice that this list includes the VT  character  (code
3643         11). This makes "space" different to \s, which does not include VT (for         11). This makes "space" different to \s, which does not include VT (for
3644         Perl compatibility).         Perl compatibility).
3645    
3646         The  name  "word"  is  a Perl extension, and "blank" is a GNU extension         The name "word" is a Perl extension, and "blank"  is  a  GNU  extension
3647         from Perl 5.8. Another Perl extension is negation, which  is  indicated         from  Perl  5.8. Another Perl extension is negation, which is indicated
3648         by a ^ character after the colon. For example,         by a ^ character after the colon. For example,
3649    
3650           [12[:^digit:]]           [12[:^digit:]]
3651    
3652         matches  "1", "2", or any non-digit. PCRE (and Perl) also recognize the         matches "1", "2", or any non-digit. PCRE (and Perl) also recognize  the
3653         POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but         POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but
3654         these are not supported, and an error is given if they are encountered.         these are not supported, and an error is given if they are encountered.
3655    
# Line 3526  POSIX CHARACTER CLASSES Line 3659  POSIX CHARACTER CLASSES
3659    
3660  VERTICAL BAR  VERTICAL BAR
3661    
3662         Vertical  bar characters are used to separate alternative patterns. For         Vertical bar characters are used to separate alternative patterns.  For
3663         example, the pattern         example, the pattern
3664    
3665           gilbert|sullivan           gilbert|sullivan
3666    
3667         matches either "gilbert" or "sullivan". Any number of alternatives  may         matches  either "gilbert" or "sullivan". Any number of alternatives may
3668         appear,  and  an  empty  alternative  is  permitted (matching the empty         appear, and an empty  alternative  is  permitted  (matching  the  empty
3669         string). The matching process tries each alternative in turn, from left         string). The matching process tries each alternative in turn, from left
3670         to  right, and the first one that succeeds is used. If the alternatives         to right, and the first one that succeeds is used. If the  alternatives
3671         are within a subpattern (defined below), "succeeds" means matching  the         are  within a subpattern (defined below), "succeeds" means matching the
3672         rest  of the main pattern as well as the alternative in the subpattern.         rest of the main pattern as well as the alternative in the  subpattern.
3673    
3674    
3675  INTERNAL OPTION SETTING  INTERNAL OPTION SETTING
3676    
3677         The settings of the  PCRE_CASELESS,  PCRE_MULTILINE,  PCRE_DOTALL,  and         The  settings  of  the  PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and
3678         PCRE_EXTENDED  options  can  be  changed  from  within the pattern by a         PCRE_EXTENDED options can be changed  from  within  the  pattern  by  a
3679         sequence of Perl option letters enclosed  between  "(?"  and  ")".  The         sequence  of  Perl  option  letters  enclosed between "(?" and ")". The
3680         option letters are         option letters are
3681    
3682           i  for PCRE_CASELESS           i  for PCRE_CASELESS
# Line 3553  INTERNAL OPTION SETTING Line 3686  INTERNAL OPTION SETTING
3686    
3687         For example, (?im) sets caseless, multiline matching. It is also possi-         For example, (?im) sets caseless, multiline matching. It is also possi-
3688         ble to unset these options by preceding the letter with a hyphen, and a         ble to unset these options by preceding the letter with a hyphen, and a
3689         combined  setting and unsetting such as (?im-sx), which sets PCRE_CASE-         combined setting and unsetting such as (?im-sx), which sets  PCRE_CASE-
3690         LESS and PCRE_MULTILINE while unsetting PCRE_DOTALL and  PCRE_EXTENDED,         LESS  and PCRE_MULTILINE while unsetting PCRE_DOTALL and PCRE_EXTENDED,
3691         is  also  permitted.  If  a  letter  appears  both before and after the         is also permitted. If a  letter  appears  both  before  and  after  the
3692         hyphen, the option is unset.         hyphen, the option is unset.
3693    
3694         When an option change occurs at top level (that is, not inside  subpat-         When  an option change occurs at top level (that is, not inside subpat-
3695         tern  parentheses),  the change applies to the remainder of the pattern         tern parentheses), the change applies to the remainder of  the  pattern
3696         that follows.  If the change is placed right at the start of a pattern,         that follows.  If the change is placed right at the start of a pattern,
3697         PCRE extracts it into the global options (and it will therefore show up         PCRE extracts it into the global options (and it will therefore show up
3698         in data extracted by the pcre_fullinfo() function).         in data extracted by the pcre_fullinfo() function).
3699    
3700         An option change within a subpattern (see below for  a  description  of         An  option  change  within a subpattern (see below for a description of
3701         subpatterns) affects only that part of the current pattern that follows         subpatterns) affects only that part of the current pattern that follows
3702         it, so         it, so
3703    
3704           (a(?i)b)c           (a(?i)b)c
3705    
3706         matches abc and aBc and no other strings (assuming PCRE_CASELESS is not         matches abc and aBc and no other strings (assuming PCRE_CASELESS is not
3707         used).   By  this means, options can be made to have different settings         used).  By this means, options can be made to have  different  settings
3708         in different parts of the pattern. Any changes made in one  alternative         in  different parts of the pattern. Any changes made in one alternative
3709         do  carry  on  into subsequent branches within the same subpattern. For         do carry on into subsequent branches within the  same  subpattern.  For
3710         example,         example,
3711    
3712           (a(?i)b|c)           (a(?i)b|c)
3713    
3714         matches "ab", "aB", "c", and "C", even though  when  matching  "C"  the         matches  "ab",  "aB",  "c",  and "C", even though when matching "C" the
3715         first  branch  is  abandoned before the option setting. This is because         first branch is abandoned before the option setting.  This  is  because
3716         the effects of option settings happen at compile time. There  would  be         the  effects  of option settings happen at compile time. There would be
3717         some very weird behaviour otherwise.         some very weird behaviour otherwise.
3718    
3719         The  PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and PCRE_EXTRA         The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and  PCRE_EXTRA
3720         can be changed in the same way as the Perl-compatible options by  using         can  be changed in the same way as the Perl-compatible options by using
3721         the characters J, U and X respectively.         the characters J, U and X respectively.
3722    
3723    
# Line 3597  SUBPATTERNS Line 3730  SUBPATTERNS
3730    
3731           cat(aract|erpillar|)           cat(aract|erpillar|)
3732    
3733         matches one of the words "cat", "cataract", or  "caterpillar".  Without         matches  one  of the words "cat", "cataract", or "caterpillar". Without
3734         the  parentheses,  it  would  match  "cataract", "erpillar" or an empty         the parentheses, it would match  "cataract",  "erpillar"  or  an  empty
3735         string.         string.
3736    
3737         2. It sets up the subpattern as  a  capturing  subpattern.  This  means         2.  It  sets  up  the  subpattern as a capturing subpattern. This means
3738         that,  when  the  whole  pattern  matches,  that portion of the subject         that, when the whole pattern  matches,  that  portion  of  the  subject
3739         string that matched the subpattern is passed back to the caller via the         string that matched the subpattern is passed back to the caller via the
3740         ovector  argument  of pcre_exec(). Opening parentheses are counted from         ovector argument of pcre_exec(). Opening parentheses are  counted  from
3741         left to right (starting from 1) to obtain  numbers  for  the  capturing         left  to  right  (starting  from 1) to obtain numbers for the capturing
3742         subpatterns.         subpatterns.
3743    
3744         For  example,  if the string "the red king" is matched against the pat-         For example, if the string "the red king" is matched against  the  pat-
3745         tern         tern
3746    
3747           the ((red|white) (king|queen))           the ((red|white) (king|queen))
# Line 3616  SUBPATTERNS Line 3749  SUBPATTERNS
3749         the captured substrings are "red king", "red", and "king", and are num-         the captured substrings are "red king", "red", and "king", and are num-
3750         bered 1, 2, and 3, respectively.         bered 1, 2, and 3, respectively.
3751    
3752         The  fact  that  plain  parentheses  fulfil two functions is not always         The fact that plain parentheses fulfil  two  functions  is  not  always
3753         helpful.  There are often times when a grouping subpattern is  required         helpful.   There are often times when a grouping subpattern is required
3754         without  a capturing requirement. If an opening parenthesis is followed         without a capturing requirement. If an opening parenthesis is  followed
3755         by a question mark and a colon, the subpattern does not do any  captur-         by  a question mark and a colon, the subpattern does not do any captur-
3756         ing,  and  is  not  counted when computing the number of any subsequent         ing, and is not counted when computing the  number  of  any  subsequent
3757         capturing subpatterns. For example, if the string "the white queen"  is         capturing  subpatterns. For example, if the string "the white queen" is
3758         matched against the pattern         matched against the pattern
3759    
3760           the ((?:red|white) (king|queen))           the ((?:red|white) (king|queen))
# Line 3629  SUBPATTERNS Line 3762  SUBPATTERNS
3762         the captured substrings are "white queen" and "queen", and are numbered         the captured substrings are "white queen" and "queen", and are numbered
3763         1 and 2. The maximum number of capturing subpatterns is 65535.         1 and 2. The maximum number of capturing subpatterns is 65535.
3764    
3765         As a convenient shorthand, if any option settings are required  at  the         As  a  convenient shorthand, if any option settings are required at the
3766         start  of  a  non-capturing  subpattern,  the option letters may appear         start of a non-capturing subpattern,  the  option  letters  may  appear
3767         between the "?" and the ":". Thus the two patterns         between the "?" and the ":". Thus the two patterns
3768    
3769           (?i:saturday|sunday)           (?i:saturday|sunday)
3770           (?:(?i)saturday|sunday)           (?:(?i)saturday|sunday)
3771    
3772         match exactly the same set of strings. Because alternative branches are         match exactly the same set of strings. Because alternative branches are
3773         tried  from  left  to right, and options are not reset until the end of         tried from left to right, and options are not reset until  the  end  of
3774         the subpattern is reached, an option setting in one branch does  affect         the  subpattern is reached, an option setting in one branch does affect
3775         subsequent  branches,  so  the above patterns match "SUNDAY" as well as         subsequent branches, so the above patterns match "SUNDAY"  as  well  as
3776         "Saturday".         "Saturday".
3777    
3778    
3779  DUPLICATE SUBPATTERN NUMBERS  DUPLICATE SUBPATTERN NUMBERS
3780    
3781         Perl 5.10 introduced a feature whereby each alternative in a subpattern         Perl 5.10 introduced a feature whereby each alternative in a subpattern
3782         uses  the same numbers for its capturing parentheses. Such a subpattern         uses the same numbers for its capturing parentheses. Such a  subpattern
3783         starts with (?| and is itself a non-capturing subpattern. For  example,         starts  with (?| and is itself a non-capturing subpattern. For example,
3784         consider this pattern:         consider this pattern:
3785    
3786           (?|(Sat)ur|(Sun))day           (?|(Sat)ur|(Sun))day
3787    
3788         Because  the two alternatives are inside a (?| group, both sets of cap-         Because the two alternatives are inside a (?| group, both sets of  cap-
3789         turing parentheses are numbered one. Thus, when  the  pattern  matches,         turing  parentheses  are  numbered one. Thus, when the pattern matches,
3790         you  can  look  at captured substring number one, whichever alternative         you can look at captured substring number  one,  whichever  alternative
3791         matched. This construct is useful when you want to  capture  part,  but         matched.  This  construct  is useful when you want to capture part, but
3792         not all, of one of a number of alternatives. Inside a (?| group, paren-         not all, of one of a number of alternatives. Inside a (?| group, paren-
3793         theses are numbered as usual, but the number is reset at the  start  of         theses  are  numbered as usual, but the number is reset at the start of
3794         each  branch. The numbers of any capturing buffers that follow the sub-         each branch. The numbers of any capturing buffers that follow the  sub-
3795         pattern start after the highest number used in any branch. The  follow-         pattern  start after the highest number used in any branch. The follow-
3796         ing  example  is taken from the Perl documentation.  The numbers under-         ing example is taken from the Perl documentation.  The  numbers  under-
3797         neath show in which buffer the captured content will be stored.         neath show in which buffer the captured content will be stored.
3798    
3799           # before  ---------------branch-reset----------- after           # before  ---------------branch-reset----------- after
3800           / ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x           / ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x
3801           # 1            2         2  3        2     3     4           # 1            2         2  3        2     3     4
3802    
3803         A backreference or a recursive call to  a  numbered  subpattern  always         A  backreference  or  a  recursive call to a numbered subpattern always
3804         refers to the first one in the pattern with the given number.         refers to the first one in the pattern with the given number.
3805    
3806         An  alternative approach to using this "branch reset" feature is to use         An alternative approach to using this "branch reset" feature is to  use
3807         duplicate named subpatterns, as described in the next section.         duplicate named subpatterns, as described in the next section.
3808    
3809    
3810  NAMED SUBPATTERNS  NAMED SUBPATTERNS
3811    
3812         Identifying capturing parentheses by number is simple, but  it  can  be         Identifying  capturing  parentheses  by number is simple, but it can be
3813         very  hard  to keep track of the numbers in complicated regular expres-         very hard to keep track of the numbers in complicated  regular  expres-
3814         sions. Furthermore, if an  expression  is  modified,  the  numbers  may         sions.  Furthermore,  if  an  expression  is  modified, the numbers may
3815         change.  To help with this difficulty, PCRE supports the naming of sub-         change. To help with this difficulty, PCRE supports the naming of  sub-
3816         patterns. This feature was not added to Perl until release 5.10. Python         patterns. This feature was not added to Perl until release 5.10. Python
3817         had  the  feature earlier, and PCRE introduced it at release 4.0, using         had the feature earlier, and PCRE introduced it at release  4.0,  using
3818         the Python syntax. PCRE now supports both the Perl and the Python  syn-         the  Python syntax. PCRE now supports both the Perl and the Python syn-
3819         tax.         tax.
3820    
3821         In  PCRE,  a subpattern can be named in one of three ways: (?<name>...)         In PCRE, a subpattern can be named in one of three  ways:  (?<name>...)
3822         or (?'name'...) as in Perl, or (?P<name>...) as in  Python.  References         or  (?'name'...)  as in Perl, or (?P<name>...) as in Python. References
3823         to capturing parentheses from other parts of the pattern, such as back-         to capturing parentheses from other parts of the pattern, such as back-
3824         references, recursion, and conditions, can be made by name as  well  as         references,  recursion,  and conditions, can be made by name as well as
3825         by number.         by number.
3826    
3827         Names  consist  of  up  to  32 alphanumeric characters and underscores.         Names consist of up to  32  alphanumeric  characters  and  underscores.
3828         Named capturing parentheses are still  allocated  numbers  as  well  as         Named  capturing  parentheses  are  still  allocated numbers as well as
3829         names,  exactly as if the names were not present. The PCRE API provides         names, exactly as if the names were not present. The PCRE API  provides
3830         function calls for extracting the name-to-number translation table from         function calls for extracting the name-to-number translation table from
3831         a compiled pattern. There is also a convenience function for extracting         a compiled pattern. There is also a convenience function for extracting
3832         a captured substring by name.         a captured substring by name.
3833    
3834         By default, a name must be unique within a pattern, but it is  possible         By  default, a name must be unique within a pattern, but it is possible
3835         to relax this constraint by setting the PCRE_DUPNAMES option at compile         to relax this constraint by setting the PCRE_DUPNAMES option at compile
3836         time. This can be useful for patterns where only one  instance  of  the         time.  This  can  be useful for patterns where only one instance of the
3837         named  parentheses  can  match. Suppose you want to match the name of a         named parentheses can match. Suppose you want to match the  name  of  a
3838         weekday, either as a 3-letter abbreviation or as the full name, and  in         weekday,  either as a 3-letter abbreviation or as the full name, and in
3839         both cases you want to extract the abbreviation. This pattern (ignoring         both cases you want to extract the abbreviation. This pattern (ignoring
3840         the line breaks) does the job:         the line breaks) does the job:
3841    
# Line 3712  NAMED SUBPATTERNS Line 3845  NAMED SUBPATTERNS
3845           (?<DN>Thu)(?:rsday)?|           (?<DN>Thu)(?:rsday)?|
3846           (?<DN>Sat)(?:urday)?           (?<DN>Sat)(?:urday)?
3847    
3848         There are five capturing substrings, but only one is ever set  after  a         There  are  five capturing substrings, but only one is ever set after a
3849         match.  (An alternative way of solving this problem is to use a "branch         match.  (An alternative way of solving this problem is to use a "branch
3850         reset" subpattern, as described in the previous section.)         reset" subpattern, as described in the previous section.)
3851    
3852         The convenience function for extracting the data by  name  returns  the         The  convenience  function  for extracting the data by name returns the
3853         substring  for  the first (and in this example, the only) subpattern of         substring for the first (and in this example, the only)  subpattern  of
3854         that name that matched. This saves searching  to  find  which  numbered         that  name  that  matched.  This saves searching to find which numbered
3855         subpattern  it  was. If you make a reference to a non-unique named sub-         subpattern it was. If you make a reference to a non-unique  named  sub-
3856         pattern from elsewhere in the pattern, the one that corresponds to  the         pattern  from elsewhere in the pattern, the one that corresponds to the
3857         lowest  number  is used. For further details of the interfaces for han-         lowest number is used. For further details of the interfaces  for  han-
3858         dling named subpatterns, see the pcreapi documentation.         dling named subpatterns, see the pcreapi documentation.
3859    
3860    
3861  REPETITION  REPETITION
3862    
3863         Repetition is specified by quantifiers, which can  follow  any  of  the         Repetition  is  specified  by  quantifiers, which can follow any of the
3864         following items:         following items:
3865    
3866           a literal data character           a literal data character
# Line 3740  REPETITION Line 3873  REPETITION
3873           a back reference (see next section)           a back reference (see next section)
3874           a parenthesized subpattern (unless it is an assertion)           a parenthesized subpattern (unless it is an assertion)
3875    
3876         The  general repetition quantifier specifies a minimum and maximum num-         The general repetition quantifier specifies a minimum and maximum  num-
3877         ber of permitted matches, by giving the two numbers in  curly  brackets         ber  of  permitted matches, by giving the two numbers in curly brackets
3878         (braces),  separated  by  a comma. The numbers must be less than 65536,         (braces), separated by a comma. The numbers must be  less  than  65536,
3879         and the first must be less than or equal to the second. For example:         and the first must be less than or equal to the second. For example:
3880    
3881           z{2,4}           z{2,4}
3882    
3883         matches "zz", "zzz", or "zzzz". A closing brace on its  own  is  not  a         matches  "zz",  "zzz",  or  "zzzz". A closing brace on its own is not a
3884         special  character.  If  the second number is omitted, but the comma is         special character. If the second number is omitted, but  the  comma  is
3885         present, there is no upper limit; if the second number  and  the  comma         present,  there  is  no upper limit; if the second number and the comma
3886         are  both omitted, the quantifier specifies an exact number of required         are both omitted, the quantifier specifies an exact number of  required
3887         matches. Thus         matches. Thus
3888    
3889           [aeiou]{3,}           [aeiou]{3,}
# Line 3759  REPETITION Line 3892  REPETITION
3892    
3893           \d{8}           \d{8}
3894    
3895         matches exactly 8 digits. An opening curly bracket that  appears  in  a         matches  exactly  8  digits. An opening curly bracket that appears in a
3896         position  where a quantifier is not allowed, or one that does not match         position where a quantifier is not allowed, or one that does not  match
3897         the syntax of a quantifier, is taken as a literal character. For  exam-         the  syntax of a quantifier, is taken as a literal character. For exam-
3898         ple, {,6} is not a quantifier, but a literal string of four characters.         ple, {,6} is not a quantifier, but a literal string of four characters.
3899    
3900         In UTF-8 mode, quantifiers apply to UTF-8  characters  rather  than  to         In  UTF-8  mode,  quantifiers  apply to UTF-8 characters rather than to
3901         individual bytes. Thus, for example, \x{100}{2} matches two UTF-8 char-         individual bytes. Thus, for example, \x{100}{2} matches two UTF-8 char-
3902         acters, each of which is represented by a two-byte sequence. Similarly,         acters, each of which is represented by a two-byte sequence. Similarly,
3903         when Unicode property support is available, \X{3} matches three Unicode         when Unicode property support is available, \X{3} matches three Unicode
3904         extended sequences, each of which may be several bytes long  (and  they         extended  sequences,  each of which may be several bytes long (and they
3905         may be of different lengths).         may be of different lengths).
3906    
3907         The quantifier {0} is permitted, causing the expression to behave as if         The quantifier {0} is permitted, causing the expression to behave as if
3908         the previous item and the quantifier were not present.         the previous item and the quantifier were not present.
3909    
3910         For convenience, the three most common quantifiers have  single-charac-         For  convenience, the three most common quantifiers have single-charac-
3911         ter abbreviations:         ter abbreviations:
3912    
3913           *    is equivalent to {0,}           *    is equivalent to {0,}
3914           +    is equivalent to {1,}           +    is equivalent to {1,}
3915           ?    is equivalent to {0,1}           ?    is equivalent to {0,1}
3916    
3917         It  is  possible  to construct infinite loops by following a subpattern         It is possible to construct infinite loops by  following  a  subpattern
3918         that can match no characters with a quantifier that has no upper limit,         that can match no characters with a quantifier that has no upper limit,
3919         for example:         for example:
3920    
3921           (a?)*           (a?)*
3922    
3923         Earlier versions of Perl and PCRE used to give an error at compile time         Earlier versions of Perl and PCRE used to give an error at compile time
3924         for such patterns. However, because there are cases where this  can  be         for  such  patterns. However, because there are cases where this can be
3925         useful,  such  patterns  are now accepted, but if any repetition of the         useful, such patterns are now accepted, but if any  repetition  of  the
3926         subpattern does in fact match no characters, the loop is forcibly  bro-         subpattern  does in fact match no characters, the loop is forcibly bro-
3927         ken.         ken.
3928    
3929         By  default,  the quantifiers are "greedy", that is, they match as much         By default, the quantifiers are "greedy", that is, they match  as  much
3930         as possible (up to the maximum  number  of  permitted  times),  without         as  possible  (up  to  the  maximum number of permitted times), without
3931         causing  the  rest of the pattern to fail. The classic example of where         causing the rest of the pattern to fail. The classic example  of  where
3932         this gives problems is in trying to match comments in C programs. These         this gives problems is in trying to match comments in C programs. These
3933         appear  between  /*  and  */ and within the comment, individual * and /         appear between /* and */ and within the comment,  individual  *  and  /
3934         characters may appear. An attempt to match C comments by  applying  the         characters  may  appear. An attempt to match C comments by applying the
3935         pattern         pattern
3936    
3937           /\*.*\*/           /\*.*\*/
# Line 3807  REPETITION Line 3940  REPETITION
3940    
3941           /* first comment */  not comment  /* second comment */           /* first comment */  not comment  /* second comment */
3942    
3943         fails,  because it matches the entire string owing to the greediness of         fails, because it matches the entire string owing to the greediness  of
3944         the .*  item.         the .*  item.
3945    
3946         However, if a quantifier is followed by a question mark, it  ceases  to         However,  if  a quantifier is followed by a question mark, it ceases to
3947         be greedy, and instead matches the minimum number of times possible, so         be greedy, and instead matches the minimum number of times possible, so
3948         the pattern         the pattern
3949    
3950           /\*.*?\*/           /\*.*?\*/
3951    
3952         does the right thing with the C comments. The meaning  of  the  various         does  the  right  thing with the C comments. The meaning of the various
3953         quantifiers  is  not  otherwise  changed,  just the preferred number of         quantifiers is not otherwise changed,  just  the  preferred  number  of
3954         matches.  Do not confuse this use of question mark with its  use  as  a         matches.   Do  not  confuse this use of question mark with its use as a
3955         quantifier  in its own right. Because it has two uses, it can sometimes         quantifier in its own right. Because it has two uses, it can  sometimes
3956         appear doubled, as in         appear doubled, as in
3957    
3958           \d??\d           \d??\d
# Line 3827  REPETITION Line 3960  REPETITION
3960         which matches one digit by preference, but can match two if that is the         which matches one digit by preference, but can match two if that is the
3961         only way the rest of the pattern matches.         only way the rest of the pattern matches.
3962    
3963         If  the PCRE_UNGREEDY option is set (an option that is not available in         If the PCRE_UNGREEDY option is set (an option that is not available  in
3964         Perl), the quantifiers are not greedy by default, but  individual  ones         Perl),  the  quantifiers are not greedy by default, but individual ones
3965         can  be  made  greedy  by following them with a question mark. In other         can be made greedy by following them with a  question  mark.  In  other
3966         words, it inverts the default behaviour.         words, it inverts the default behaviour.
3967    
3968         When a parenthesized subpattern is quantified  with  a  minimum  repeat         When  a  parenthesized  subpattern  is quantified with a minimum repeat
3969         count  that is greater than 1 or with a limited maximum, more memory is         count that is greater than 1 or with a limited maximum, more memory  is
3970         required for the compiled pattern, in proportion to  the  size  of  the         required  for  the  compiled  pattern, in proportion to the size of the
3971         minimum or maximum.         minimum or maximum.
3972    
3973         If a pattern starts with .* or .{0,} and the PCRE_DOTALL option (equiv-         If a pattern starts with .* or .{0,} and the PCRE_DOTALL option (equiv-
3974         alent to Perl's /s) is set, thus allowing the dot  to  match  newlines,         alent  to  Perl's  /s) is set, thus allowing the dot to match newlines,
3975         the  pattern  is  implicitly anchored, because whatever follows will be         the pattern is implicitly anchored, because whatever  follows  will  be
3976         tried against every character position in the subject string, so  there         tried  against every character position in the subject string, so there
3977         is  no  point  in  retrying the overall match at any position after the         is no point in retrying the overall match at  any  position  after  the
3978         first. PCRE normally treats such a pattern as though it  were  preceded         first.  PCRE  normally treats such a pattern as though it were preceded
3979         by \A.         by \A.
3980    
3981         In  cases  where  it  is known that the subject string contains no new-         In cases where it is known that the subject  string  contains  no  new-
3982         lines, it is worth setting PCRE_DOTALL in order to  obtain  this  opti-         lines,  it  is  worth setting PCRE_DOTALL in order to obtain this opti-
3983         mization, or alternatively using ^ to indicate anchoring explicitly.         mization, or alternatively using ^ to indicate anchoring explicitly.
3984    
3985         However,  there is one situation where the optimization cannot be used.         However, there is one situation where the optimization cannot be  used.
3986         When .*  is inside capturing parentheses that  are  the  subject  of  a         When  .*   is  inside  capturing  parentheses that are the subject of a
3987         backreference  elsewhere  in the pattern, a match at the start may fail         backreference elsewhere in the pattern, a match at the start  may  fail
3988         where a later one succeeds. Consider, for example:         where a later one succeeds. Consider, for example:
3989    
3990           (.*)abc\1           (.*)abc\1
3991    
3992         If the subject is "xyz123abc123" the match point is the fourth  charac-         If  the subject is "xyz123abc123" the match point is the fourth charac-
3993         ter. For this reason, such a pattern is not implicitly anchored.         ter. For this reason, such a pattern is not implicitly anchored.
3994    
3995         When a capturing subpattern is repeated, the value captured is the sub-         When a capturing subpattern is repeated, the value captured is the sub-
# Line 3865  REPETITION Line 3998  REPETITION
3998           (tweedle[dume]{3}\s*)+           (tweedle[dume]{3}\s*)+
3999    
4000         has matched "tweedledum tweedledee" the value of the captured substring         has matched "tweedledum tweedledee" the value of the captured substring
4001         is  "tweedledee".  However,  if there are nested capturing subpatterns,         is "tweedledee". However, if there are  nested  capturing  subpatterns,
4002         the corresponding captured values may have been set in previous  itera-         the  corresponding captured values may have been set in previous itera-
4003         tions. For example, after         tions. For example, after
4004    
4005           /(a|(b))+/           /(a|(b))+/
# Line 3876  REPETITION Line 4009  REPETITION
4009    
4010  ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS  ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS
4011    
4012         With  both  maximizing ("greedy") and minimizing ("ungreedy" or "lazy")         With both maximizing ("greedy") and minimizing ("ungreedy"  or  "lazy")
4013         repetition, failure of what follows normally causes the  repeated  item         repetition,  failure  of what follows normally causes the repeated item
4014         to  be  re-evaluated to see if a different number of repeats allows the         to be re-evaluated to see if a different number of repeats  allows  the
4015         rest of the pattern to match. Sometimes it is useful to  prevent  this,         rest  of  the pattern to match. Sometimes it is useful to prevent this,
4016         either  to  change the nature of the match, or to cause it fail earlier         either to change the nature of the match, or to cause it  fail  earlier
4017         than it otherwise might, when the author of the pattern knows there  is         than  it otherwise might, when the author of the pattern knows there is
4018         no point in carrying on.         no point in carrying on.
4019    
4020         Consider,  for  example, the pattern \d+foo when applied to the subject         Consider, for example, the pattern \d+foo when applied to  the  subject
4021         line         line
4022    
4023           123456bar           123456bar
4024    
4025         After matching all 6 digits and then failing to match "foo", the normal         After matching all 6 digits and then failing to match "foo", the normal
4026         action  of  the matcher is to try again with only 5 digits matching the         action of the matcher is to try again with only 5 digits  matching  the
4027         \d+ item, and then with  4,  and  so  on,  before  ultimately  failing.         \d+  item,  and  then  with  4,  and  so on, before ultimately failing.
4028         "Atomic  grouping"  (a  term taken from Jeffrey Friedl's book) provides         "Atomic grouping" (a term taken from Jeffrey  Friedl's  book)  provides
4029         the means for specifying that once a subpattern has matched, it is  not         the  means for specifying that once a subpattern has matched, it is not
4030         to be re-evaluated in this way.         to be re-evaluated in this way.
4031    
4032         If  we  use atomic grouping for the previous example, the matcher gives         If we use atomic grouping for the previous example, the  matcher  gives
4033         up immediately on failing to match "foo" the first time.  The  notation         up  immediately  on failing to match "foo" the first time. The notation
4034         is a kind of special parenthesis, starting with (?> as in this example:         is a kind of special parenthesis, starting with (?> as in this example:
4035    
4036           (?>\d+)foo           (?>\d+)foo
4037    
4038         This kind of parenthesis "locks up" the  part of the  pattern  it  con-         This  kind  of  parenthesis "locks up" the  part of the pattern it con-
4039         tains  once  it  has matched, and a failure further into the pattern is         tains once it has matched, and a failure further into  the  pattern  is
4040         prevented from backtracking into it. Backtracking past it  to  previous         prevented  from  backtracking into it. Backtracking past it to previous
4041         items, however, works as normal.         items, however, works as normal.
4042    
4043         An  alternative  description  is that a subpattern of this type matches         An alternative description is that a subpattern of  this  type  matches
4044         the string of characters that an  identical  standalone  pattern  would         the  string  of  characters  that an identical standalone pattern would
4045         match, if anchored at the current point in the subject string.         match, if anchored at the current point in the subject string.
4046    
4047         Atomic grouping subpatterns are not capturing subpatterns. Simple cases         Atomic grouping subpatterns are not capturing subpatterns. Simple cases
4048         such as the above example can be thought of as a maximizing repeat that         such as the above example can be thought of as a maximizing repeat that
4049         must  swallow  everything  it can. So, while both \d+ and \d+? are pre-         must swallow everything it can. So, while both \d+ and  \d+?  are  pre-
4050         pared to adjust the number of digits they match in order  to  make  the         pared  to  adjust  the number of digits they match in order to make the
4051         rest of the pattern match, (?>\d+) can only match an entire sequence of         rest of the pattern match, (?>\d+) can only match an entire sequence of
4052         digits.         digits.
4053    
4054         Atomic groups in general can of course contain arbitrarily  complicated         Atomic  groups in general can of course contain arbitrarily complicated
4055         subpatterns,  and  can  be  nested. However, when the subpattern for an         subpatterns, and can be nested. However, when  the  subpattern  for  an
4056         atomic group is just a single repeated item, as in the example above, a         atomic group is just a single repeated item, as in the example above, a
4057         simpler  notation,  called  a "possessive quantifier" can be used. This         simpler notation, called a "possessive quantifier" can  be  used.  This
4058         consists of an additional + character  following  a  quantifier.  Using         consists  of  an  additional  + character following a quantifier. Using
4059         this notation, the previous example can be rewritten as         this notation, the previous example can be rewritten as
4060    
4061           \d++foo           \d++foo
# Line 3932  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE Line 4065  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
4065    
4066           (abc|xyz){2,3}+           (abc|xyz){2,3}+
4067    
4068         Possessive  quantifiers  are  always  greedy;  the   setting   of   the         Possessive   quantifiers   are   always  greedy;  the  setting  of  the
4069         PCRE_UNGREEDY option is ignored. They are a convenient notation for the         PCRE_UNGREEDY option is ignored. They are a convenient notation for the
4070         simpler forms of atomic group. However, there is no difference  in  the         simpler  forms  of atomic group. However, there is no difference in the
4071         meaning  of  a  possessive  quantifier and the equivalent atomic group,         meaning of a possessive quantifier and  the  equivalent  atomic  group,
4072         though there may be a performance  difference;  possessive  quantifiers         though  there  may  be a performance difference; possessive quantifiers
4073         should be slightly faster.         should be slightly faster.
4074    
4075         The  possessive  quantifier syntax is an extension to the Perl 5.8 syn-         The possessive quantifier syntax is an extension to the Perl  5.8  syn-
4076         tax.  Jeffrey Friedl originated the idea (and the name)  in  the  first         tax.   Jeffrey  Friedl  originated the idea (and the name) in the first
4077         edition of his book. Mike McCloskey liked it, so implemented it when he         edition of his book. Mike McCloskey liked it, so implemented it when he
4078         built Sun's Java package, and PCRE copied it from there. It  ultimately         built  Sun's Java package, and PCRE copied it from there. It ultimately
4079         found its way into Perl at release 5.10.         found its way into Perl at release 5.10.
4080    
4081         PCRE has an optimization that automatically "possessifies" certain sim-         PCRE has an optimization that automatically "possessifies" certain sim-
4082         ple pattern constructs. For example, the sequence  A+B  is  treated  as         ple  pattern  constructs.  For  example, the sequence A+B is treated as
4083         A++B  because  there is no point in backtracking into a sequence of A's         A++B because there is no point in backtracking into a sequence  of  A's
4084         when B must follow.         when B must follow.
4085    
4086         When a pattern contains an unlimited repeat inside  a  subpattern  that         When  a  pattern  contains an unlimited repeat inside a subpattern that
4087         can  itself  be  repeated  an  unlimited number of times, the use of an         can itself be repeated an unlimited number of  times,  the  use  of  an
4088         atomic group is the only way to avoid some  failing  matches  taking  a         atomic  group  is  the  only way to avoid some failing matches taking a
4089         very long time indeed. The pattern         very long time indeed. The pattern
4090    
4091           (\D+|<\d+>)*[!?]           (\D+|<\d+>)*[!?]
4092    
4093         matches  an  unlimited number of substrings that either consist of non-         matches an unlimited number of substrings that either consist  of  non-
4094         digits, or digits enclosed in <>, followed by either ! or  ?.  When  it         digits,  or  digits  enclosed in <>, followed by either ! or ?. When it
4095         matches, it runs quickly. However, if it is applied to         matches, it runs quickly. However, if it is applied to
4096    
4097           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
4098    
4099         it  takes  a  long  time  before reporting failure. This is because the         it takes a long time before reporting  failure.  This  is  because  the
4100         string can be divided between the internal \D+ repeat and the  external         string  can be divided between the internal \D+ repeat and the external
4101         *  repeat  in  a  large  number of ways, and all have to be tried. (The         * repeat in a large number of ways, and all  have  to  be  tried.  (The
4102         example uses [!?] rather than a single character at  the  end,  because         example  uses  [!?]  rather than a single character at the end, because
4103         both  PCRE  and  Perl have an optimization that allows for fast failure         both PCRE and Perl have an optimization that allows  for  fast  failure
4104         when a single character is used. They remember the last single  charac-         when  a single character is used. They remember the last single charac-
4105         ter  that  is required for a match, and fail early if it is not present         ter that is required for a match, and fail early if it is  not  present
4106         in the string.) If the pattern is changed so that  it  uses  an  atomic         in  the  string.)  If  the pattern is changed so that it uses an atomic
4107         group, like this:         group, like this:
4108    
4109           ((?>\D+)|<\d+>)*[!?]           ((?>\D+)|<\d+>)*[!?]
4110    
4111         sequences  of non-digits cannot be broken, and failure happens quickly.         sequences of non-digits cannot be broken, and failure happens  quickly.
4112    
4113    
4114  BACK REFERENCES  BACK REFERENCES
4115    
4116         Outside a character class, a backslash followed by a digit greater than         Outside a character class, a backslash followed by a digit greater than
4117         0 (and possibly further digits) is a back reference to a capturing sub-         0 (and possibly further digits) is a back reference to a capturing sub-
4118         pattern earlier (that is, to its left) in the pattern,  provided  there         pattern  earlier  (that is, to its left) in the pattern, provided there
4119         have been that many previous capturing left parentheses.         have been that many previous capturing left parentheses.
4120    
4121         However, if the decimal number following the backslash is less than 10,         However, if the decimal number following the backslash is less than 10,
4122         it is always taken as a back reference, and causes  an  error  only  if         it  is  always  taken  as a back reference, and causes an error only if
4123         there  are  not that many capturing left parentheses in the entire pat-         there are not that many capturing left parentheses in the  entire  pat-
4124         tern. In other words, the parentheses that are referenced need  not  be         tern.  In  other words, the parentheses that are referenced need not be
4125         to  the left of the reference for numbers less than 10. A "forward back         to the left of the reference for numbers less than 10. A "forward  back
4126         reference" of this type can make sense when a  repetition  is  involved         reference"  of  this  type can make sense when a repetition is involved
4127         and  the  subpattern to the right has participated in an earlier itera-         and the subpattern to the right has participated in an  earlier  itera-
4128         tion.         tion.
4129    
4130         It is not possible to have a numerical "forward back  reference"  to  a         It  is  not  possible to have a numerical "forward back reference" to a
4131         subpattern  whose  number  is  10  or  more using this syntax because a         subpattern whose number is 10 or  more  using  this  syntax  because  a
4132         sequence such as \50 is interpreted as a character  defined  in  octal.         sequence  such  as  \50 is interpreted as a character defined in octal.
4133         See the subsection entitled "Non-printing characters" above for further         See the subsection entitled "Non-printing characters" above for further
4134         details of the handling of digits following a backslash.  There  is  no         details  of  the  handling of digits following a backslash. There is no
4135         such  problem  when named parentheses are used. A back reference to any         such problem when named parentheses are used. A back reference  to  any
4136         subpattern is possible using named parentheses (see below).         subpattern is possible using named parentheses (see below).
4137    
4138         Another way of avoiding the ambiguity inherent in  the  use  of  digits         Another  way  of  avoiding  the ambiguity inherent in the use of digits
4139         following a backslash is to use the \g escape sequence, which is a fea-         following a backslash is to use the \g escape sequence, which is a fea-
4140         ture introduced in Perl 5.10.  This  escape  must  be  followed  by  an         ture  introduced  in  Perl  5.10.  This  escape  must be followed by an
4141         unsigned  number  or  a negative number, optionally enclosed in braces.         unsigned number or a negative number, optionally  enclosed  in  braces.
4142         These examples are all identical:         These examples are all identical:
4143    
4144           (ring), \1           (ring), \1
4145           (ring), \g1           (ring), \g1
4146           (ring), \g{1}           (ring), \g{1}
4147    
4148         An unsigned number specifies an absolute reference without the  ambigu-         An  unsigned number specifies an absolute reference without the ambigu-
4149         ity that is present in the older syntax. It is also useful when literal         ity that is present in the older syntax. It is also useful when literal
4150         digits follow the reference. A negative number is a relative reference.         digits follow the reference. A negative number is a relative reference.
4151         Consider this example:         Consider this example:
# Line 4020  BACK REFERENCES Line 4153  BACK REFERENCES
4153           (abc(def)ghi)\g{-1}           (abc(def)ghi)\g{-1}
4154    
4155         The sequence \g{-1} is a reference to the most recently started captur-         The sequence \g{-1} is a reference to the most recently started captur-
4156         ing subpattern before \g, that is, is it equivalent to  \2.  Similarly,         ing  subpattern  before \g, that is, is it equivalent to \2. Similarly,
4157         \g{-2} would be equivalent to \1. The use of relative references can be         \g{-2} would be equivalent to \1. The use of relative references can be
4158         helpful in long patterns, and also in  patterns  that  are  created  by         helpful  in  long  patterns,  and  also in patterns that are created by
4159         joining together fragments that contain references within themselves.         joining together fragments that contain references within themselves.
4160    
4161         A  back  reference matches whatever actually matched the capturing sub-         A back reference matches whatever actually matched the  capturing  sub-
4162         pattern in the current subject string, rather  than  anything  matching         pattern  in  the  current subject string, rather than anything matching
4163         the subpattern itself (see "Subpatterns as subroutines" below for a way         the subpattern itself (see "Subpatterns as subroutines" below for a way
4164         of doing that). So the pattern         of doing that). So the pattern
4165    
4166           (sens|respons)e and \1ibility           (sens|respons)e and \1ibility
4167    
4168         matches "sense and sensibility" and "response and responsibility",  but         matches  "sense and sensibility" and "response and responsibility", but
4169         not  "sense and responsibility". If caseful matching is in force at the         not "sense and responsibility". If caseful matching is in force at  the
4170         time of the back reference, the case of letters is relevant. For  exam-         time  of the back reference, the case of letters is relevant. For exam-
4171         ple,         ple,
4172    
4173           ((?i)rah)\s+\1           ((?i)rah)\s+\1
4174    
4175         matches  "rah  rah"  and  "RAH RAH", but not "RAH rah", even though the         matches "rah rah" and "RAH RAH", but not "RAH  rah",  even  though  the
4176         original capturing subpattern is matched caselessly.         original capturing subpattern is matched caselessly.
4177    
4178         There are several different ways of writing back  references  to  named         There  are  several  different ways of writing back references to named
4179         subpatterns.  The  .NET syntax \k{name} and the Perl syntax \k<name> or         subpatterns. The .NET syntax \k{name} and the Perl syntax  \k<name>  or
4180         \k'name' are supported, as is the Python syntax (?P=name). Perl  5.10's         \k'name'  are supported, as is the Python syntax (?P=name). Perl 5.10's
4181         unified back reference syntax, in which \g can be used for both numeric         unified back reference syntax, in which \g can be used for both numeric
4182         and named references, is also supported. We  could  rewrite  the  above         and  named  references,  is  also supported. We could rewrite the above
4183         example in any of the following ways:         example in any of the following ways:
4184    
4185           (?<p1>(?i)rah)\s+\k<p1>           (?<p1>(?i)rah)\s+\k<p1>
# Line 4054  BACK REFERENCES Line 4187  BACK REFERENCES
4187           (?P<p1>(?i)rah)\s+(?P=p1)           (?P<p1>(?i)rah)\s+(?P=p1)
4188           (?<p1>(?i)rah)\s+\g{p1}           (?<p1>(?i)rah)\s+\g{p1}
4189    
4190         A  subpattern  that  is  referenced  by  name may appear in the pattern         A subpattern that is referenced by  name  may  appear  in  the  pattern
4191         before or after the reference.         before or after the reference.
4192    
4193         There may be more than one back reference to the same subpattern. If  a         There  may be more than one back reference to the same subpattern. If a
4194         subpattern  has  not actually been used in a particular match, any back         subpattern has not actually been used in a particular match,  any  back
4195         references to it always fail. For example, the pattern         references to it always fail. For example, the pattern
4196    
4197           (a|(bc))\2           (a|(bc))\2
4198    
4199         always fails if it starts to match "a" rather than "bc". Because  there         always  fails if it starts to match "a" rather than "bc". Because there
4200         may  be  many  capturing parentheses in a pattern, all digits following         may be many capturing parentheses in a pattern,  all  digits  following
4201         the backslash are taken as part of a potential back  reference  number.         the  backslash  are taken as part of a potential back reference number.
4202         If the pattern continues with a digit character, some delimiter must be         If the pattern continues with a digit character, some delimiter must be
4203         used to terminate the back reference. If the  PCRE_EXTENDED  option  is         used  to  terminate  the back reference. If the PCRE_EXTENDED option is
4204         set,  this  can  be  whitespace.  Otherwise an empty comment (see "Com-         set, this can be whitespace.  Otherwise an  empty  comment  (see  "Com-
4205         ments" below) can be used.         ments" below) can be used.
4206    
4207         A back reference that occurs inside the parentheses to which it  refers         A  back reference that occurs inside the parentheses to which it refers
4208         fails  when  the subpattern is first used, so, for example, (a\1) never         fails when the subpattern is first used, so, for example,  (a\1)  never
4209         matches.  However, such references can be useful inside  repeated  sub-         matches.   However,  such references can be useful inside repeated sub-
4210         patterns. For example, the pattern         patterns. For example, the pattern
4211    
4212           (a|b\1)+           (a|b\1)+
4213    
4214         matches any number of "a"s and also "aba", "ababbaa" etc. At each iter-         matches any number of "a"s and also "aba", "ababbaa" etc. At each iter-
4215         ation of the subpattern,  the  back  reference  matches  the  character         ation  of  the  subpattern,  the  back  reference matches the character
4216         string  corresponding  to  the previous iteration. In order for this to         string corresponding to the previous iteration. In order  for  this  to
4217         work, the pattern must be such that the first iteration does  not  need         work,  the  pattern must be such that the first iteration does not need
4218         to  match the back reference. This can be done using alternation, as in         to match the back reference. This can be done using alternation, as  in
4219         the example above, or by a quantifier with a minimum of zero.         the example above, or by a quantifier with a minimum of zero.
4220    
4221    
4222  ASSERTIONS  ASSERTIONS
4223    
4224         An assertion is a test on the characters  following  or  preceding  the         An  assertion  is  a  test on the characters following or preceding the
4225         current  matching  point that does not actually consume any characters.         current matching point that does not actually consume  any  characters.
4226         The simple assertions coded as \b, \B, \A, \G, \Z,  \z,  ^  and  $  are         The  simple  assertions  coded  as  \b, \B, \A, \G, \Z, \z, ^ and $ are
4227         described above.         described above.
4228    
4229         More  complicated  assertions  are  coded as subpatterns. There are two         More complicated assertions are coded as  subpatterns.  There  are  two
4230         kinds: those that look ahead of the current  position  in  the  subject         kinds:  those  that  look  ahead of the current position in the subject
4231         string,  and  those  that  look  behind  it. An assertion subpattern is         string, and those that look  behind  it.  An  assertion  subpattern  is
4232         matched in the normal way, except that it does not  cause  the  current         matched  in  the  normal way, except that it does not cause the current
4233         matching position to be changed.         matching position to be changed.
4234    
4235         Assertion  subpatterns  are  not  capturing subpatterns, and may not be         Assertion subpatterns are not capturing subpatterns,  and  may  not  be
4236         repeated, because it makes no sense to assert the  same  thing  several         repeated,  because  it  makes no sense to assert the same thing several
4237         times.  If  any kind of assertion contains capturing subpatterns within         times. If any kind of assertion contains capturing  subpatterns  within
4238         it, these are counted for the purposes of numbering the capturing  sub-         it,  these are counted for the purposes of numbering the capturing sub-
4239         patterns in the whole pattern.  However, substring capturing is carried         patterns in the whole pattern.  However, substring capturing is carried
4240         out only for positive assertions, because it does not  make  sense  for         out  only  for  positive assertions, because it does not make sense for
4241         negative assertions.         negative assertions.
4242    
4243     Lookahead assertions     Lookahead assertions
# Line 4114  ASSERTIONS Line 4247  ASSERTIONS
4247    
4248           \w+(?=;)           \w+(?=;)
4249    
4250         matches a word followed by a semicolon, but does not include the  semi-         matches  a word followed by a semicolon, but does not include the semi-
4251         colon in the match, and         colon in the match, and
4252    
4253           foo(?!bar)           foo(?!bar)
4254    
4255         matches  any  occurrence  of  "foo" that is not followed by "bar". Note         matches any occurrence of "foo" that is not  followed  by  "bar".  Note
4256         that the apparently similar pattern         that the apparently similar pattern
4257    
4258           (?!foo)bar           (?!foo)bar
4259    
4260         does not find an occurrence of "bar"  that  is  preceded  by  something         does  not  find  an  occurrence  of "bar" that is preceded by something
4261         other  than "foo"; it finds any occurrence of "bar" whatsoever, because         other than "foo"; it finds any occurrence of "bar" whatsoever,  because
4262         the assertion (?!foo) is always true when the next three characters are         the assertion (?!foo) is always true when the next three characters are
4263         "bar". A lookbehind assertion is needed to achieve the other effect.         "bar". A lookbehind assertion is needed to achieve the other effect.
4264    
4265         If you want to force a matching failure at some point in a pattern, the         If you want to force a matching failure at some point in a pattern, the
4266         most convenient way to do it is  with  (?!)  because  an  empty  string         most  convenient  way  to  do  it  is with (?!) because an empty string
4267         always  matches, so an assertion that requires there not to be an empty         always matches, so an assertion that requires there not to be an  empty
4268         string must always fail.         string must always fail.
4269    
4270     Lookbehind assertions     Lookbehind assertions
4271    
4272         Lookbehind assertions start with (?<= for positive assertions and  (?<!         Lookbehind  assertions start with (?<= for positive assertions and (?<!
4273         for negative assertions. For example,         for negative assertions. For example,
4274    
4275           (?<!foo)bar           (?<!foo)bar
4276    
4277         does  find  an  occurrence  of "bar" that is not preceded by "foo". The         does find an occurrence of "bar" that is not  preceded  by  "foo".  The
4278         contents of a lookbehind assertion are restricted  such  that  all  the         contents  of  a  lookbehind  assertion are restricted such that all the
4279         strings it matches must have a fixed length. However, if there are sev-         strings it matches must have a fixed length. However, if there are sev-
4280         eral top-level alternatives, they do not all  have  to  have  the  same         eral  top-level  alternatives,  they  do  not all have to have the same
4281         fixed length. Thus         fixed length. Thus
4282    
4283           (?<=bullock|donkey)           (?<=bullock|donkey)
# Line 4153  ASSERTIONS Line 4286  ASSERTIONS
4286    
4287           (?<!dogs?|cats?)           (?<!dogs?|cats?)
4288    
4289         causes  an  error at compile time. Branches that match different length         causes an error at compile time. Branches that match  different  length
4290         strings are permitted only at the top level of a lookbehind  assertion.         strings  are permitted only at the top level of a lookbehind assertion.
4291         This  is  an  extension  compared  with  Perl (at least for 5.8), which         This is an extension compared with  Perl  (at  least  for  5.8),  which
4292         requires all branches to match the same length of string. An  assertion         requires  all branches to match the same length of string. An assertion
4293         such as         such as
4294    
4295           (?<=ab(c|de))           (?<=ab(c|de))
4296    
4297         is  not  permitted,  because  its single top-level branch can match two         is not permitted, because its single top-level  branch  can  match  two
4298         different lengths, but it is acceptable if rewritten to  use  two  top-         different  lengths,  but  it is acceptable if rewritten to use two top-
4299         level branches:         level branches:
4300    
4301           (?<=abc|abde)           (?<=abc|abde)
4302    
4303         In some cases, the Perl 5.10 escape sequence \K (see above) can be used         In some cases, the Perl 5.10 escape sequence \K (see above) can be used
4304         instead of a lookbehind assertion; this is not restricted to  a  fixed-         instead  of  a lookbehind assertion; this is not restricted to a fixed-
4305         length.         length.
4306    
4307         The  implementation  of lookbehind assertions is, for each alternative,         The implementation of lookbehind assertions is, for  each  alternative,
4308         to temporarily move the current position back by the fixed  length  and         to  temporarily  move the current position back by the fixed length and
4309         then try to match. If there are insufficient characters before the cur-         then try to match. If there are insufficient characters before the cur-
4310         rent position, the assertion fails.         rent position, the assertion fails.
4311    
4312         PCRE does not allow the \C escape (which matches a single byte in UTF-8         PCRE does not allow the \C escape (which matches a single byte in UTF-8
4313         mode)  to appear in lookbehind assertions, because it makes it impossi-         mode) to appear in lookbehind assertions, because it makes it  impossi-
4314         ble to calculate the length of the lookbehind. The \X and  \R  escapes,         ble  to  calculate the length of the lookbehind. The \X and \R escapes,
4315         which can match different numbers of bytes, are also not permitted.         which can match different numbers of bytes, are also not permitted.
4316    
4317         Possessive  quantifiers  can  be  used  in  conjunction with lookbehind         Possessive quantifiers can  be  used  in  conjunction  with  lookbehind
4318         assertions to specify efficient matching at  the  end  of  the  subject         assertions  to  specify  efficient  matching  at the end of the subject
4319         string. Consider a simple pattern such as         string. Consider a simple pattern such as
4320    
4321           abcd$           abcd$
4322    
4323         when  applied  to  a  long string that does not match. Because matching         when applied to a long string that does  not  match.  Because  matching
4324         proceeds from left to right, PCRE will look for each "a" in the subject         proceeds from left to right, PCRE will look for each "a" in the subject
4325         and  then  see  if what follows matches the rest of the pattern. If the         and then see if what follows matches the rest of the  pattern.  If  the
4326         pattern is specified as         pattern is specified as
4327    
4328           ^.*abcd$           ^.*abcd$
4329    
4330         the initial .* matches the entire string at first, but when this  fails         the  initial .* matches the entire string at first, but when this fails
4331         (because there is no following "a"), it backtracks to match all but the         (because there is no following "a"), it backtracks to match all but the
4332         last character, then all but the last two characters, and so  on.  Once         last  character,  then all but the last two characters, and so on. Once
4333         again  the search for "a" covers the entire string, from right to left,         again the search for "a" covers the entire string, from right to  left,
4334         so we are no better off. However, if the pattern is written as         so we are no better off. However, if the pattern is written as
4335    
4336           ^.*+(?<=abcd)           ^.*+(?<=abcd)
4337    
4338         there can be no backtracking for the .*+ item; it can  match  only  the         there  can  be  no backtracking for the .*+ item; it can match only the
4339         entire  string.  The subsequent lookbehind assertion does a single test         entire string. The subsequent lookbehind assertion does a  single  test
4340         on the last four characters. If it fails, the match fails  immediately.         on  the last four characters. If it fails, the match fails immediately.
4341         For  long  strings, this approach makes a significant difference to the         For long strings, this approach makes a significant difference  to  the
4342         processing time.         processing time.
4343    
4344     Using multiple assertions     Using multiple assertions
# Line 4214  ASSERTIONS Line 4347  ASSERTIONS
4347    
4348           (?<=\d{3})(?<!999)foo           (?<=\d{3})(?<!999)foo
4349    
4350         matches "foo" preceded by three digits that are not "999". Notice  that         matches  "foo" preceded by three digits that are not "999". Notice that
4351         each  of  the  assertions is applied independently at the same point in         each of the assertions is applied independently at the  same  point  in
4352         the subject string. First there is a  check  that  the  previous  three         the  subject  string.  First  there  is a check that the previous three
4353         characters  are  all  digits,  and  then there is a check that the same         characters are all digits, and then there is  a  check  that  the  same
4354         three characters are not "999".  This pattern does not match "foo" pre-         three characters are not "999".  This pattern does not match "foo" pre-
4355         ceded  by  six  characters,  the first of which are digits and the last         ceded by six characters, the first of which are  digits  and  the  last
4356         three of which are not "999". For example, it  doesn't  match  "123abc-         three  of  which  are not "999". For example, it doesn't match "123abc-
4357         foo". A pattern to do that is         foo". A pattern to do that is
4358    
4359           (?<=\d{3}...)(?<!999)foo           (?<=\d{3}...)(?<!999)foo
4360    
4361         This  time  the  first assertion looks at the preceding six characters,         This time the first assertion looks at the  preceding  six  characters,
4362         checking that the first three are digits, and then the second assertion         checking that the first three are digits, and then the second assertion
4363         checks that the preceding three characters are not "999".         checks that the preceding three characters are not "999".
4364    
# Line 4233  ASSERTIONS Line 4366  ASSERTIONS
4366    
4367           (?<=(?<!foo)bar)baz           (?<=(?<!foo)bar)baz
4368    
4369         matches  an occurrence of "baz" that is preceded by "bar" which in turn         matches an occurrence of "baz" that is preceded by "bar" which in  turn
4370         is not preceded by "foo", while         is not preceded by "foo", while
4371    
4372           (?<=\d{3}(?!999)...)foo           (?<=\d{3}(?!999)...)foo
4373    
4374         is another pattern that matches "foo" preceded by three digits and  any         is  another pattern that matches "foo" preceded by three digits and any
4375         three characters that are not "999".         three characters that are not "999".
4376    
4377    
4378  CONDITIONAL SUBPATTERNS  CONDITIONAL SUBPATTERNS
4379    
4380         It  is possible to cause the matching process to obey a subpattern con-         It is possible to cause the matching process to obey a subpattern  con-
4381         ditionally or to choose between two alternative subpatterns,  depending         ditionally  or to choose between two alternative subpatterns, depending
4382         on  the result of an assertion, or whether a previous capturing subpat-         on the result of an assertion, or whether a previous capturing  subpat-
4383         tern matched or not. The two possible forms of  conditional  subpattern         tern  matched  or not. The two possible forms of conditional subpattern
4384         are         are
4385    
4386           (?(condition)yes-pattern)           (?(condition)yes-pattern)
4387           (?(condition)yes-pattern|no-pattern)           (?(condition)yes-pattern|no-pattern)
4388    
4389         If  the  condition is satisfied, the yes-pattern is used; otherwise the         If the condition is satisfied, the yes-pattern is used;  otherwise  the
4390         no-pattern (if present) is used. If there are more  than  two  alterna-         no-pattern  (if  present)  is used. If there are more than two alterna-
4391         tives in the subpattern, a compile-time error occurs.         tives in the subpattern, a compile-time error occurs.
4392    
4393         There  are  four  kinds of condition: references to subpatterns, refer-         There are four kinds of condition: references  to  subpatterns,  refer-
4394         ences to recursion, a pseudo-condition called DEFINE, and assertions.         ences to recursion, a pseudo-condition called DEFINE, and assertions.
4395    
4396     Checking for a used subpattern by number     Checking for a used subpattern by number
4397    
4398         If the text between the parentheses consists of a sequence  of  digits,         If  the  text between the parentheses consists of a sequence of digits,
4399         the  condition  is  true if the capturing subpattern of that number has         the condition is true if the capturing subpattern of  that  number  has
4400         previously matched. An alternative notation is to  precede  the  digits         previously  matched.  An  alternative notation is to precede the digits
4401         with a plus or minus sign. In this case, the subpattern number is rela-         with a plus or minus sign. In this case, the subpattern number is rela-
4402         tive rather than absolute.  The most recently opened parentheses can be         tive rather than absolute.  The most recently opened parentheses can be
4403         referenced  by  (?(-1),  the  next most recent by (?(-2), and so on. In         referenced by (?(-1), the next most recent by (?(-2),  and  so  on.  In
4404         looping constructs it can also make sense to refer to subsequent groups         looping constructs it can also make sense to refer to subsequent groups
4405         with constructs such as (?(+2).         with constructs such as (?(+2).
4406    
4407         Consider  the  following  pattern, which contains non-significant white         Consider the following pattern, which  contains  non-significant  white
4408         space to make it more readable (assume the PCRE_EXTENDED option) and to         space to make it more readable (assume the PCRE_EXTENDED option) and to
4409         divide it into three parts for ease of discussion:         divide it into three parts for ease of discussion:
4410    
4411           ( \( )?    [^()]+    (?(1) \) )           ( \( )?    [^()]+    (?(1) \) )
4412    
4413         The  first  part  matches  an optional opening parenthesis, and if that         The first part matches an optional opening  parenthesis,  and  if  that
4414         character is present, sets it as the first captured substring. The sec-         character is present, sets it as the first captured substring. The sec-
4415         ond  part  matches one or more characters that are not parentheses. The         ond part matches one or more characters that are not  parentheses.  The
4416         third part is a conditional subpattern that tests whether the first set         third part is a conditional subpattern that tests whether the first set
4417         of parentheses matched or not. If they did, that is, if subject started         of parentheses matched or not. If they did, that is, if subject started
4418         with an opening parenthesis, the condition is true, and so the yes-pat-         with an opening parenthesis, the condition is true, and so the yes-pat-
4419         tern  is  executed  and  a  closing parenthesis is required. Otherwise,         tern is executed and a  closing  parenthesis  is  required.  Otherwise,
4420         since no-pattern is not present, the  subpattern  matches  nothing.  In         since  no-pattern  is  not  present, the subpattern matches nothing. In
4421         other  words,  this  pattern  matches  a  sequence  of non-parentheses,         other words,  this  pattern  matches  a  sequence  of  non-parentheses,
4422         optionally enclosed in parentheses.         optionally enclosed in parentheses.
4423    
4424         If you were embedding this pattern in a larger one,  you  could  use  a         If  you  were  embedding  this pattern in a larger one, you could use a
4425         relative reference:         relative reference:
4426    
4427           ...other stuff... ( \( )?    [^()]+    (?(-1) \) ) ...           ...other stuff... ( \( )?    [^()]+    (?(-1) \) ) ...
4428    
4429         This  makes  the  fragment independent of the parentheses in the larger         This makes the fragment independent of the parentheses  in  the  larger
4430         pattern.         pattern.
4431    
4432     Checking for a used subpattern by name     Checking for a used subpattern by name
4433    
4434         Perl uses the syntax (?(<name>)...) or (?('name')...)  to  test  for  a         Perl  uses  the  syntax  (?(<name>)...) or (?('name')...) to test for a
4435         used  subpattern  by  name.  For compatibility with earlier versions of         used subpattern by name. For compatibility  with  earlier  versions  of
4436         PCRE, which had this facility before Perl, the syntax  (?(name)...)  is         PCRE,  which  had this facility before Perl, the syntax (?(name)...) is
4437         also  recognized. However, there is a possible ambiguity with this syn-         also recognized. However, there is a possible ambiguity with this  syn-
4438         tax, because subpattern names may  consist  entirely  of  digits.  PCRE         tax,  because  subpattern  names  may  consist entirely of digits. PCRE
4439         looks  first for a named subpattern; if it cannot find one and the name         looks first for a named subpattern; if it cannot find one and the  name
4440         consists entirely of digits, PCRE looks for a subpattern of  that  num-         consists  entirely  of digits, PCRE looks for a subpattern of that num-
4441         ber,  which must be greater than zero. Using subpattern names that con-         ber, which must be greater than zero. Using subpattern names that  con-
4442         sist entirely of digits is not recommended.         sist entirely of digits is not recommended.
4443    
4444         Rewriting the above example to use a named subpattern gives this:         Rewriting the above example to use a named subpattern gives this:
# Line 4316  CONDITIONAL SUBPATTERNS Line 4449  CONDITIONAL SUBPATTERNS
4449     Checking for pattern recursion     Checking for pattern recursion
4450    
4451         If the condition is the string (R), and there is no subpattern with the         If the condition is the string (R), and there is no subpattern with the
4452         name  R, the condition is true if a recursive call to the whole pattern         name R, the condition is true if a recursive call to the whole  pattern
4453         or any subpattern has been made. If digits or a name preceded by amper-         or any subpattern has been made. If digits or a name preceded by amper-
4454         sand follow the letter R, for example:         sand follow the letter R, for example:
4455    
4456           (?(R3)...) or (?(R&name)...)           (?(R3)...) or (?(R&name)...)
4457    
4458         the  condition is true if the most recent recursion is into the subpat-         the condition is true if the most recent recursion is into the  subpat-
4459         tern whose number or name is given. This condition does not  check  the         tern  whose  number or name is given. This condition does not check the
4460         entire recursion stack.         entire recursion stack.
4461    
4462         At  "top  level", all these recursion test conditions are false. Recur-         At "top level", all these recursion test conditions are  false.  Recur-
4463         sive patterns are described below.         sive patterns are described below.
4464    
4465     Defining subpatterns for use by reference only     Defining subpatterns for use by reference only
4466    
4467         If the condition is the string (DEFINE), and  there  is  no  subpattern         If  the  condition  is  the string (DEFINE), and there is no subpattern
4468         with  the  name  DEFINE,  the  condition is always false. In this case,         with the name DEFINE, the condition is  always  false.  In  this  case,
4469         there may be only one alternative  in  the  subpattern.  It  is  always         there  may  be  only  one  alternative  in the subpattern. It is always
4470         skipped  if  control  reaches  this  point  in the pattern; the idea of         skipped if control reaches this point  in  the  pattern;  the  idea  of
4471         DEFINE is that it can be used to define "subroutines" that can be  ref-         DEFINE  is that it can be used to define "subroutines" that can be ref-
4472         erenced  from elsewhere. (The use of "subroutines" is described below.)         erenced from elsewhere. (The use of "subroutines" is described  below.)
4473         For example, a pattern to match an IPv4 address could be  written  like         For  example,  a pattern to match an IPv4 address could be written like
4474         this (ignore whitespace and line breaks):         this (ignore whitespace and line breaks):
4475    
4476           (?(DEFINE) (?<byte> 2[0-4]\d | 25[0-5] | 1\d\d | [1-9]?\d) )           (?(DEFINE) (?<byte> 2[0-4]\d | 25[0-5] | 1\d\d | [1-9]?\d) )
4477           \b (?&byte) (\.(?&byte)){3} \b           \b (?&byte) (\.(?&byte)){3} \b
4478    
4479         The  first part of the pattern is a DEFINE group inside which a another         The first part of the pattern is a DEFINE group inside which a  another
4480         group named "byte" is defined. This matches an individual component  of         group  named "byte" is defined. This matches an individual component of
4481         an  IPv4  address  (a number less than 256). When matching takes place,         an IPv4 address (a number less than 256). When  matching  takes  place,
4482         this part of the pattern is skipped because DEFINE acts  like  a  false         this  part  of  the pattern is skipped because DEFINE acts like a false
4483         condition.         condition.
4484    
4485         The rest of the pattern uses references to the named group to match the         The rest of the pattern uses references to the named group to match the
4486         four dot-separated components of an IPv4 address, insisting on  a  word         four  dot-separated  components of an IPv4 address, insisting on a word
4487         boundary at each end.         boundary at each end.
4488    
4489     Assertion conditions     Assertion conditions
4490    
4491         If  the  condition  is  not  in any of the above formats, it must be an         If the condition is not in any of the above  formats,  it  must  be  an
4492         assertion.  This may be a positive or negative lookahead or  lookbehind         assertion.   This may be a positive or negative lookahead or lookbehind
4493         assertion.  Consider  this  pattern,  again  containing non-significant         assertion. Consider  this  pattern,  again  containing  non-significant
4494         white space, and with the two alternatives on the second line:         white space, and with the two alternatives on the second line:
4495    
4496           (?(?=[^a-z]*[a-z])           (?(?=[^a-z]*[a-z])
4497           \d{2}-[a-z]{3}-\d{2}  |  \d{2}-\d{2}-\d{2} )           \d{2}-[a-z]{3}-\d{2}  |  \d{2}-\d{2}-\d{2} )
4498    
4499         The condition  is  a  positive  lookahead  assertion  that  matches  an         The  condition  is  a  positive  lookahead  assertion  that  matches an
4500         optional  sequence of non-letters followed by a letter. In other words,         optional sequence of non-letters followed by a letter. In other  words,
4501         it tests for the presence of at least one letter in the subject.  If  a         it  tests  for the presence of at least one letter in the subject. If a
4502         letter  is found, the subject is matched against the first alternative;         letter is found, the subject is matched against the first  alternative;
4503         otherwise it is  matched  against  the  second.  This  pattern  matches         otherwise  it  is  matched  against  the  second.  This pattern matches
4504         strings  in  one  of the two forms dd-aaa-dd or dd-dd-dd, where aaa are         strings in one of the two forms dd-aaa-dd or dd-dd-dd,  where  aaa  are
4505         letters and dd are digits.         letters and dd are digits.
4506    
4507    
4508  COMMENTS  COMMENTS
4509    
4510         The sequence (?# marks the start of a comment that continues up to  the         The  sequence (?# marks the start of a comment that continues up to the
4511         next  closing  parenthesis.  Nested  parentheses are not permitted. The         next closing parenthesis. Nested parentheses  are  not  permitted.  The
4512         characters that make up a comment play no part in the pattern  matching         characters  that make up a comment play no part in the pattern matching
4513         at all.         at all.
4514    
4515         If  the PCRE_EXTENDED option is set, an unescaped # character outside a         If the PCRE_EXTENDED option is set, an unescaped # character outside  a
4516         character class introduces a  comment  that  continues  to  immediately         character  class  introduces  a  comment  that continues to immediately
4517         after the next newline in the pattern.         after the next newline in the pattern.
4518    
4519    
4520  RECURSIVE PATTERNS  RECURSIVE PATTERNS
4521    
4522         Consider  the problem of matching a string in parentheses, allowing for         Consider the problem of matching a string in parentheses, allowing  for
4523         unlimited nested parentheses. Without the use of  recursion,  the  best         unlimited  nested  parentheses.  Without the use of recursion, the best
4524         that  can  be  done  is  to use a pattern that matches up to some fixed         that can be done is to use a pattern that  matches  up  to  some  fixed
4525         depth of nesting. It is not possible to  handle  an  arbitrary  nesting         depth  of  nesting.  It  is not possible to handle an arbitrary nesting
4526         depth.         depth.
4527    
4528         For some time, Perl has provided a facility that allows regular expres-         For some time, Perl has provided a facility that allows regular expres-
4529         sions to recurse (amongst other things). It does this by  interpolating         sions  to recurse (amongst other things). It does this by interpolating
4530         Perl  code in the expression at run time, and the code can refer to the         Perl code in the expression at run time, and the code can refer to  the
4531         expression itself. A Perl pattern using code interpolation to solve the         expression itself. A Perl pattern using code interpolation to solve the
4532         parentheses problem can be created like this:         parentheses problem can be created like this:
4533    
# Line 4404  RECURSIVE PATTERNS Line 4537  RECURSIVE PATTERNS
4537         refers recursively to the pattern in which it appears.         refers recursively to the pattern in which it appears.
4538    
4539         Obviously, PCRE cannot support the interpolation of Perl code. Instead,         Obviously, PCRE cannot support the interpolation of Perl code. Instead,
4540         it  supports  special  syntax  for recursion of the entire pattern, and         it supports special syntax for recursion of  the  entire  pattern,  and
4541         also for individual subpattern recursion.  After  its  introduction  in         also  for  individual  subpattern  recursion. After its introduction in
4542         PCRE  and  Python,  this  kind of recursion was introduced into Perl at         PCRE and Python, this kind of recursion was  introduced  into  Perl  at
4543         release 5.10.         release 5.10.
4544    
4545         A special item that consists of (? followed by a  number  greater  than         A  special  item  that consists of (? followed by a number greater than
4546         zero and a closing parenthesis is a recursive call of the subpattern of         zero and a closing parenthesis is a recursive call of the subpattern of
4547         the given number, provided that it occurs inside that  subpattern.  (If         the  given  number, provided that it occurs inside that subpattern. (If
4548         not,  it  is  a  "subroutine" call, which is described in the next sec-         not, it is a "subroutine" call, which is described  in  the  next  sec-
4549         tion.) The special item (?R) or (?0) is a recursive call of the  entire         tion.)  The special item (?R) or (?0) is a recursive call of the entire
4550         regular expression.         regular expression.
4551    
4552         In  PCRE (like Python, but unlike Perl), a recursive subpattern call is         In PCRE (like Python, but unlike Perl), a recursive subpattern call  is
4553         always treated as an atomic group. That is, once it has matched some of         always treated as an atomic group. That is, once it has matched some of
4554         the subject string, it is never re-entered, even if it contains untried         the subject string, it is never re-entered, even if it contains untried
4555         alternatives and there is a subsequent matching failure.         alternatives and there is a subsequent matching failure.
4556    
4557         This PCRE pattern solves the nested  parentheses  problem  (assume  the         This  PCRE  pattern  solves  the nested parentheses problem (assume the
4558         PCRE_EXTENDED option is set so that white space is ignored):         PCRE_EXTENDED option is set so that white space is ignored):
4559    
4560           \( ( (?>[^()]+) | (?R) )* \)           \( ( (?>[^()]+) | (?R) )* \)
4561    
4562         First  it matches an opening parenthesis. Then it matches any number of         First it matches an opening parenthesis. Then it matches any number  of
4563         substrings which can either be a  sequence  of  non-parentheses,  or  a         substrings  which  can  either  be  a sequence of non-parentheses, or a
4564         recursive  match  of the pattern itself (that is, a correctly parenthe-         recursive match of the pattern itself (that is, a  correctly  parenthe-
4565         sized substring).  Finally there is a closing parenthesis.         sized substring).  Finally there is a closing parenthesis.
4566    
4567         If this were part of a larger pattern, you would not  want  to  recurse         If  this  were  part of a larger pattern, you would not want to recurse
4568         the entire pattern, so instead you could use this:         the entire pattern, so instead you could use this:
4569    
4570           ( \( ( (?>[^()]+) | (?1) )* \) )           ( \( ( (?>[^()]+) | (?1) )* \) )
4571    
4572         We  have  put the pattern into parentheses, and caused the recursion to         We have put the pattern into parentheses, and caused the  recursion  to
4573         refer to them instead of the whole pattern.         refer to them instead of the whole pattern.
4574    
4575         In a larger pattern,  keeping  track  of  parenthesis  numbers  can  be         In  a  larger  pattern,  keeping  track  of  parenthesis numbers can be
4576         tricky.  This is made easier by the use of relative references. (A Perl         tricky. This is made easier by the use of relative references. (A  Perl
4577         5.10 feature.)  Instead of (?1) in the  pattern  above  you  can  write         5.10  feature.)   Instead  of  (?1)  in the pattern above you can write
4578         (?-2) to refer to the second most recently opened parentheses preceding         (?-2) to refer to the second most recently opened parentheses preceding
4579         the recursion. In other  words,  a  negative  number  counts  capturing         the  recursion.  In  other  words,  a  negative number counts capturing
4580         parentheses leftwards from the point at which it is encountered.         parentheses leftwards from the point at which it is encountered.
4581    
4582         It  is  also  possible  to refer to subsequently opened parentheses, by         It is also possible to refer to  subsequently  opened  parentheses,  by
4583         writing references such as (?+2). However, these  cannot  be  recursive         writing  references  such  as (?+2). However, these cannot be recursive
4584         because  the  reference  is  not inside the parentheses that are refer-         because the reference is not inside the  parentheses  that  are  refer-
4585         enced. They are always "subroutine" calls, as  described  in  the  next         enced.  They  are  always  "subroutine" calls, as described in the next
4586         section.         section.
4587    
4588         An  alternative  approach is to use named parentheses instead. The Perl         An alternative approach is to use named parentheses instead.  The  Perl
4589         syntax for this is (?&name); PCRE's earlier syntax  (?P>name)  is  also         syntax  for  this  is (?&name); PCRE's earlier syntax (?P>name) is also
4590         supported. We could rewrite the above example as follows:         supported. We could rewrite the above example as follows:
4591    
4592           (?<pn> \( ( (?>[^()]+) | (?&pn) )* \) )           (?<pn> \( ( (?>[^()]+) | (?&pn) )* \) )
4593    
4594         If  there  is more than one subpattern with the same name, the earliest         If there is more than one subpattern with the same name,  the  earliest
4595         one is used.         one is used.
4596    
4597         This particular example pattern that we have been looking  at  contains         This  particular  example pattern that we have been looking at contains
4598         nested  unlimited repeats, and so the use of atomic grouping for match-         nested unlimited repeats, and so the use of atomic grouping for  match-
4599         ing strings of non-parentheses is important when applying  the  pattern         ing  strings  of non-parentheses is important when applying the pattern
4600         to strings that do not match. For example, when this pattern is applied         to strings that do not match. For example, when this pattern is applied
4601         to         to
4602    
4603           (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa()           (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa()
4604    
4605         it yields "no match" quickly. However, if atomic grouping is not  used,         it  yields "no match" quickly. However, if atomic grouping is not used,
4606         the  match  runs  for a very long time indeed because there are so many         the match runs for a very long time indeed because there  are  so  many
4607         different ways the + and * repeats can carve up the  subject,  and  all         different  ways  the  + and * repeats can carve up the subject, and all
4608         have to be tested before failure can be reported.         have to be tested before failure can be reported.
4609    
4610         At the end of a match, the values set for any capturing subpatterns are         At the end of a match, the values set for any capturing subpatterns are
4611         those from the outermost level of the recursion at which the subpattern         those from the outermost level of the recursion at which the subpattern
4612         value  is  set.   If  you want to obtain intermediate values, a callout         value is set.  If you want to obtain  intermediate  values,  a  callout
4613         function can be used (see below and the pcrecallout documentation).  If         function  can be used (see below and the pcrecallout documentation). If
4614         the pattern above is matched against         the pattern above is matched against
4615    
4616           (ab(cd)ef)           (ab(cd)ef)
4617    
4618         the  value  for  the  capturing  parentheses is "ef", which is the last         the value for the capturing parentheses is  "ef",  which  is  the  last
4619         value taken on at the top level. If additional parentheses  are  added,         value  taken  on at the top level. If additional parentheses are added,
4620         giving         giving
4621    
4622           \( ( ( (?>[^()]+) | (?R) )* ) \)           \( ( ( (?>[^()]+) | (?R) )* ) \)
4623              ^                        ^              ^                        ^
4624              ^                        ^              ^                        ^
4625    
4626         the  string  they  capture is "ab(cd)ef", the contents of the top level         the string they capture is "ab(cd)ef", the contents of  the  top  level
4627         parentheses. If there are more than 15 capturing parentheses in a  pat-         parentheses.  If there are more than 15 capturing parentheses in a pat-
4628         tern, PCRE has to obtain extra memory to store data during a recursion,         tern, PCRE has to obtain extra memory to store data during a recursion,
4629         which it does by using pcre_malloc, freeing  it  via  pcre_free  after-         which  it  does  by  using pcre_malloc, freeing it via pcre_free after-
4630         wards.  If  no  memory  can  be  obtained,  the  match  fails  with the         wards. If  no  memory  can  be  obtained,  the  match  fails  with  the
4631         PCRE_ERROR_NOMEMORY error.         PCRE_ERROR_NOMEMORY error.
4632    
4633         Do not confuse the (?R) item with the condition (R),  which  tests  for         Do  not  confuse  the (?R) item with the condition (R), which tests for
4634         recursion.   Consider  this pattern, which matches text in angle brack-         recursion.  Consider this pattern, which matches text in  angle  brack-
4635         ets, allowing for arbitrary nesting. Only digits are allowed in  nested         ets,  allowing for arbitrary nesting. Only digits are allowed in nested
4636         brackets  (that is, when recursing), whereas any characters are permit-         brackets (that is, when recursing), whereas any characters are  permit-
4637         ted at the outer level.         ted at the outer level.
4638    
4639           < (?: (?(R) \d++  | [^<>]*+) | (?R)) * >           < (?: (?(R) \d++  | [^<>]*+) | (?R)) * >
4640    
4641         In this pattern, (?(R) is the start of a conditional  subpattern,  with         In  this  pattern, (?(R) is the start of a conditional subpattern, with
4642         two  different  alternatives for the recursive and non-recursive cases.         two different alternatives for the recursive and  non-recursive  cases.
4643         The (?R) item is the actual recursive call.         The (?R) item is the actual recursive call.
4644    
4645    
4646  SUBPATTERNS AS SUBROUTINES  SUBPATTERNS AS SUBROUTINES
4647    
4648         If the syntax for a recursive subpattern reference (either by number or         If the syntax for a recursive subpattern reference (either by number or
4649         by  name)  is used outside the parentheses to which it refers, it oper-         by name) is used outside the parentheses to which it refers,  it  oper-
4650         ates like a subroutine in a programming language. The "called"  subpat-         ates  like a subroutine in a programming language. The "called" subpat-
4651         tern may be defined before or after the reference. A numbered reference         tern may be defined before or after the reference. A numbered reference
4652         can be absolute or relative, as in these examples:         can be absolute or relative, as in these examples:
4653    
# Line 4526  SUBPATTERNS AS SUBROUTINES Line 4659  SUBPATTERNS AS SUBROUTINES
4659    
4660           (sens|respons)e and \1ibility           (sens|respons)e and \1ibility
4661    
4662         matches "sense and sensibility" and "response and responsibility",  but         matches  "sense and sensibility" and "response and responsibility", but
4663         not "sense and responsibility". If instead the pattern         not "sense and responsibility". If instead the pattern
4664    
4665           (sens|respons)e and (?1)ibility           (sens|respons)e and (?1)ibility
4666    
4667         is  used, it does match "sense and responsibility" as well as the other         is used, it does match "sense and responsibility" as well as the  other
4668         two strings. Another example is  given  in  the  discussion  of  DEFINE         two  strings.  Another  example  is  given  in the discussion of DEFINE
4669         above.         above.
4670    
4671         Like recursive subpatterns, a "subroutine" call is always treated as an         Like recursive subpatterns, a "subroutine" call is always treated as an
4672         atomic group. That is, once it has matched some of the subject  string,         atomic  group. That is, once it has matched some of the subject string,
4673         it  is  never  re-entered, even if it contains untried alternatives and         it is never re-entered, even if it contains  untried  alternatives  and
4674         there is a subsequent matching failure.         there is a subsequent matching failure.
4675    
4676         When a subpattern is used as a subroutine, processing options  such  as         When  a  subpattern is used as a subroutine, processing options such as
4677         case-independence are fixed when the subpattern is defined. They cannot         case-independence are fixed when the subpattern is defined. They cannot
4678         be changed for different calls. For example, consider this pattern:         be changed for different calls. For example, consider this pattern:
4679    
4680           (abc)(?i:(?-1))           (abc)(?i:(?-1))
4681    
4682         It matches "abcabc". It does not match "abcABC" because the  change  of         It  matches  "abcabc". It does not match "abcABC" because the change of
4683         processing option does not affect the called subpattern.         processing option does not affect the called subpattern.
4684    
4685    
4686  CALLOUTS  CALLOUTS
4687    
4688         Perl has a feature whereby using the sequence (?{...}) causes arbitrary         Perl has a feature whereby using the sequence (?{...}) causes arbitrary
4689         Perl code to be obeyed in the middle of matching a regular  expression.         Perl  code to be obeyed in the middle of matching a regular expression.
4690         This makes it possible, amongst other things, to extract different sub-         This makes it possible, amongst other things, to extract different sub-
4691         strings that match the same pair of parentheses when there is a repeti-         strings that match the same pair of parentheses when there is a repeti-
4692         tion.         tion.
4693    
4694         PCRE provides a similar feature, but of course it cannot obey arbitrary         PCRE provides a similar feature, but of course it cannot obey arbitrary
4695         Perl code. The feature is called "callout". The caller of PCRE provides         Perl code. The feature is called "callout". The caller of PCRE provides
4696         an  external function by putting its entry point in the global variable         an external function by putting its entry point in the global  variable
4697         pcre_callout.  By default, this variable contains NULL, which  disables         pcre_callout.   By default, this variable contains NULL, which disables
4698         all calling out.         all calling out.
4699    
4700         Within  a  regular  expression,  (?C) indicates the points at which the         Within a regular expression, (?C) indicates the  points  at  which  the
4701         external function is to be called. If you want  to  identify  different         external  function  is  to be called. If you want to identify different
4702         callout  points, you can put a number less than 256 after the letter C.         callout points, you can put a number less than 256 after the letter  C.
4703         The default value is zero.  For example, this pattern has  two  callout         The  default  value is zero.  For example, this pattern has two callout
4704         points:         points:
4705    
4706           (?C1)abc(?C2)def           (?C1)abc(?C2)def
4707    
4708         If the PCRE_AUTO_CALLOUT flag is passed to pcre_compile(), callouts are         If the PCRE_AUTO_CALLOUT flag is passed to pcre_compile(), callouts are
4709         automatically installed before each item in the pattern. They  are  all         automatically  installed  before each item in the pattern. They are all
4710         numbered 255.         numbered 255.
4711    
4712         During matching, when PCRE reaches a callout point (and pcre_callout is         During matching, when PCRE reaches a callout point (and pcre_callout is
4713         set), the external function is called. It is provided with  the  number         set),  the  external function is called. It is provided with the number
4714         of  the callout, the position in the pattern, and, optionally, one item         of the callout, the position in the pattern, and, optionally, one  item
4715         of data originally supplied by the caller of pcre_exec().  The  callout         of  data  originally supplied by the caller of pcre_exec(). The callout
4716         function  may cause matching to proceed, to backtrack, or to fail alto-         function may cause matching to proceed, to backtrack, or to fail  alto-
4717         gether. A complete description of the interface to the callout function         gether. A complete description of the interface to the callout function
4718         is given in the pcrecallout documentation.         is given in the pcrecallout documentation.
4719    
4720    
4721  BACTRACKING CONTROL  BACTRACKING CONTROL
4722    
4723         Perl  5.10 introduced a number of "Special Backtracking Control Verbs",         Perl 5.10 introduced a number of "Special Backtracking Control  Verbs",
4724         which are described in the Perl documentation as "experimental and sub-         which are described in the Perl documentation as "experimental and sub-
4725         ject  to  change or removal in a future version of Perl". It goes on to         ject to change or removal in a future version of Perl". It goes  on  to
4726         say: "Their usage in production code should be noted to avoid  problems         say:  "Their usage in production code should be noted to avoid problems
4727         during upgrades." The same remarks apply to the PCRE features described         during upgrades." The same remarks apply to the PCRE features described
4728         in this section.         in this section.
4729    
4730         Since these verbs are specifically related to backtracking, they can be         Since these verbs are specifically related to backtracking, they can be
4731         used  only  when  the pattern is to be matched using pcre_exec(), which         used only when the pattern is to be matched  using  pcre_exec(),  which
4732         uses a backtracking algorithm. They cause an error  if  encountered  by         uses  a  backtracking  algorithm. They cause an error if encountered by
4733         pcre_dfa_exec().         pcre_dfa_exec().
4734    
4735         The  new verbs make use of what was previously invalid syntax: an open-         The new verbs make use of what was previously invalid syntax: an  open-
4736         ing parenthesis followed by an asterisk. In Perl, they are generally of         ing parenthesis followed by an asterisk. In Perl, they are generally of
4737         the form (*VERB:ARG) but PCRE does not support the use of arguments, so         the form (*VERB:ARG) but PCRE does not support the use of arguments, so
4738         its general form is just (*VERB). Any number of these verbs  may  occur         its  general  form is just (*VERB). Any number of these verbs may occur
4739         in a pattern. There are two kinds:         in a pattern. There are two kinds:
4740    
4741     Verbs that act immediately     Verbs that act immediately
# Line 4611  BACTRACKING CONTROL Line 4744  BACTRACKING CONTROL
4744    
4745            (*ACCEPT)            (*ACCEPT)
4746    
4747         This  verb causes the match to end successfully, skipping the remainder         This verb causes the match to end successfully, skipping the  remainder
4748         of the pattern. When inside a recursion, only the innermost pattern  is         of  the pattern. When inside a recursion, only the innermost pattern is
4749         ended  immediately.  PCRE  differs  from  Perl  in  what happens if the         ended immediately. PCRE differs  from  Perl  in  what  happens  if  the
4750         (*ACCEPT) is inside capturing parentheses. In Perl, the data so far  is         (*ACCEPT)  is inside capturing parentheses. In Perl, the data so far is
4751         captured: in PCRE no data is captured. For example:         captured: in PCRE no data is captured. For example:
4752    
4753           A(A|B(*ACCEPT)|C)D           A(A|B(*ACCEPT)|C)D
4754    
4755         This  matches  "AB", "AAD", or "ACD", but when it matches "AB", no data         This matches "AB", "AAD", or "ACD", but when it matches "AB",  no  data
4756         is captured.         is captured.
4757    
4758           (*FAIL) or (*F)           (*FAIL) or (*F)
4759    
4760         This verb causes the match to fail, forcing backtracking to  occur.  It         This  verb  causes the match to fail, forcing backtracking to occur. It
4761         is  equivalent to (?!) but easier to read. The Perl documentation notes         is equivalent to (?!) but easier to read. The Perl documentation  notes
4762         that it is probably useful only when combined  with  (?{})  or  (??{}).         that  it  is  probably  useful only when combined with (?{}) or (??{}).
4763         Those  are,  of course, Perl features that are not present in PCRE. The         Those are, of course, Perl features that are not present in  PCRE.  The
4764         nearest equivalent is the callout feature, as for example in this  pat-         nearest  equivalent is the callout feature, as for example in this pat-
4765         tern:         tern:
4766    
4767           a+(?C)(*FAIL)           a+(?C)(*FAIL)
4768    
4769         A  match  with the string "aaaa" always fails, but the callout is taken         A match with the string "aaaa" always fails, but the callout  is  taken
4770         before each backtrack happens (in this example, 10 times).         before each backtrack happens (in this example, 10 times).
4771    
4772     Verbs that act after backtracking     Verbs that act after backtracking
4773    
4774         The following verbs do nothing when they are encountered. Matching con-         The following verbs do nothing when they are encountered. Matching con-
4775         tinues  with what follows, but if there is no subsequent match, a fail-         tinues with what follows, but if there is no subsequent match, a  fail-
4776         ure is forced.  The verbs  differ  in  exactly  what  kind  of  failure         ure  is  forced.   The  verbs  differ  in  exactly what kind of failure
4777         occurs.         occurs.
4778    
4779           (*COMMIT)           (*COMMIT)
4780    
4781         This  verb  causes  the whole match to fail outright if the rest of the         This verb causes the whole match to fail outright if the  rest  of  the
4782         pattern does not match. Even if the pattern is unanchored,  no  further         pattern  does  not match. Even if the pattern is unanchored, no further
4783         attempts  to find a match by advancing the start point take place. Once         attempts to find a match by advancing the start point take place.  Once
4784         (*COMMIT) has been passed, pcre_exec() is committed to finding a  match         (*COMMIT)  has been passed, pcre_exec() is committed to finding a match
4785         at the current starting point, or not at all. For example:         at the current starting point, or not at all. For example:
4786    
4787           a+(*COMMIT)b           a+(*COMMIT)b
4788    
4789         This  matches  "xxaab" but not "aacaab". It can be thought of as a kind         This matches "xxaab" but not "aacaab". It can be thought of as  a  kind
4790         of dynamic anchor, or "I've started, so I must finish."         of dynamic anchor, or "I've started, so I must finish."
4791    
4792           (*PRUNE)           (*PRUNE)
4793    
4794         This verb causes the match to fail at the current position if the  rest         This  verb causes the match to fail at the current position