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revision 456 by ph10, Fri Oct 2 08:53:31 2009 UTC revision 513 by ph10, Mon May 3 11:13:37 2010 UTC
# Line 21  published by O'Reilly, covers regular ex Line 21  published by O'Reilly, covers regular ex
21  description of PCRE's regular expressions is intended as reference material.  description of PCRE's regular expressions is intended as reference material.
22  .P  .P
23  The original operation of PCRE was on strings of one-byte characters. However,  The original operation of PCRE was on strings of one-byte characters. However,
24  there is now also support for UTF-8 character strings. To use this,  there is now also support for UTF-8 character strings. To use this,
25  PCRE must be built to include UTF-8 support, and you must call  PCRE must be built to include UTF-8 support, and you must call
26  \fBpcre_compile()\fP or \fBpcre_compile2()\fP with the PCRE_UTF8 option. There  \fBpcre_compile()\fP or \fBpcre_compile2()\fP with the PCRE_UTF8 option. There
27  is also a special sequence that can be given at the start of a pattern:  is also a special sequence that can be given at the start of a pattern:
# Line 83  string with one of the following five se Line 83  string with one of the following five se
83    (*ANYCRLF)   any of the three above    (*ANYCRLF)   any of the three above
84    (*ANY)       all Unicode newline sequences    (*ANY)       all Unicode newline sequences
85  .sp  .sp
86  These override the default and the options given to \fBpcre_compile()\fP or  These override the default and the options given to \fBpcre_compile()\fP or
87  \fBpcre_compile2()\fP. For example, on a Unix system where LF is the default  \fBpcre_compile2()\fP. For example, on a Unix system where LF is the default
88  newline sequence, the pattern  newline sequence, the pattern
89  .sp  .sp
# Line 217  one of the following escape sequences th Line 217  one of the following escape sequences th
217    \en        linefeed (hex 0A)    \en        linefeed (hex 0A)
218    \er        carriage return (hex 0D)    \er        carriage return (hex 0D)
219    \et        tab (hex 09)    \et        tab (hex 09)
220    \eddd      character with octal code ddd, or backreference    \eddd      character with octal code ddd, or back reference
221    \exhh      character with hex code hh    \exhh      character with hex code hh
222    \ex{hhh..} character with hex code hhh..    \ex{hhh..} character with hex code hhh..
223  .sp  .sp
# Line 295  zero, because no more than three octal d Line 295  zero, because no more than three octal d
295  .P  .P
296  All the sequences that define a single character value can be used both inside  All the sequences that define a single character value can be used both inside
297  and outside character classes. In addition, inside a character class, the  and outside character classes. In addition, inside a character class, the
298  sequence \eb is interpreted as the backspace character (hex 08), and the  sequence \eb is interpreted as the backspace character (hex 08). The sequences
299  sequences \eR and \eX are interpreted as the characters "R" and "X",  \eB, \eR, and \eX are not special inside a character class. Like any other
300  respectively. Outside a character class, these sequences have different  unrecognized escape sequences, they are treated as the literal characters "B",
301  meanings  "R", and "X" by default, but cause an error if the PCRE_EXTRA option is set.
302    Outside a character class, these sequences have different meanings
303  .\" HTML <a href="#uniextseq">  .\" HTML <a href="#uniextseq">
304  .\" </a>  .\" </a>
305  (see below).  (see below).
# Line 333  syntax for referencing a subpattern as a Line 334  syntax for referencing a subpattern as a
334  later.  later.
335  .\"  .\"
336  Note that \eg{...} (Perl syntax) and \eg<...> (Oniguruma syntax) are \fInot\fP  Note that \eg{...} (Perl syntax) and \eg<...> (Oniguruma syntax) are \fInot\fP
337  synonymous. The former is a back reference; the latter is a  synonymous. The former is a back reference; the latter is a
338  .\" HTML <a href="#subpatternsassubroutines">  .\" HTML <a href="#subpatternsassubroutines">
339  .\" </a>  .\" </a>
340  subroutine  subroutine
# Line 468  one of the following sequences: Line 469  one of the following sequences:
469    (*BSR_ANYCRLF)   CR, LF, or CRLF only    (*BSR_ANYCRLF)   CR, LF, or CRLF only
470    (*BSR_UNICODE)   any Unicode newline sequence    (*BSR_UNICODE)   any Unicode newline sequence
471  .sp  .sp
472  These override the default and the options given to \fBpcre_compile()\fP or  These override the default and the options given to \fBpcre_compile()\fP or
473  \fBpcre_compile2()\fP, but they can be overridden by options given to  \fBpcre_compile2()\fP, but they can be overridden by options given to
474  \fBpcre_exec()\fP or \fBpcre_dfa_exec()\fP. Note that these special settings,  \fBpcre_exec()\fP or \fBpcre_dfa_exec()\fP. Note that these special settings,
475  which are not Perl-compatible, are recognized only at the very start of a  which are not Perl-compatible, are recognized only at the very start of a
# Line 478  convention, for example, a pattern can s Line 479  convention, for example, a pattern can s
479  .sp  .sp
480    (*ANY)(*BSR_ANYCRLF)    (*ANY)(*BSR_ANYCRLF)
481  .sp  .sp
482  Inside a character class, \eR matches the letter "R".  Inside a character class, \eR is treated as an unrecognized escape sequence,
483    and so matches the letter "R" by default, but causes an error if PCRE_EXTRA is
484    set.
485  .  .
486  .  .
487  .\" HTML <a name="uniextseq"></a>  .\" HTML <a name="uniextseq"></a>
# Line 513  Those that are not part of an identified Line 516  Those that are not part of an identified
516  .P  .P
517  Arabic,  Arabic,
518  Armenian,  Armenian,
519    Avestan,
520  Balinese,  Balinese,
521    Bamum,
522  Bengali,  Bengali,
523  Bopomofo,  Bopomofo,
524  Braille,  Braille,
525  Buginese,  Buginese,
526  Buhid,  Buhid,
527  Canadian_Aboriginal,  Canadian_Aboriginal,
528    Carian,
529    Cham,
530  Cherokee,  Cherokee,
531  Common,  Common,
532  Coptic,  Coptic,
# Line 528  Cypriot, Line 535  Cypriot,
535  Cyrillic,  Cyrillic,
536  Deseret,  Deseret,
537  Devanagari,  Devanagari,
538    Egyptian_Hieroglyphs,
539  Ethiopic,  Ethiopic,
540  Georgian,  Georgian,
541  Glagolitic,  Glagolitic,
# Line 540  Hangul, Line 548  Hangul,
548  Hanunoo,  Hanunoo,
549  Hebrew,  Hebrew,
550  Hiragana,  Hiragana,
551    Imperial_Aramaic,
552  Inherited,  Inherited,
553    Inscriptional_Pahlavi,
554    Inscriptional_Parthian,
555    Javanese,
556    Kaithi,
557  Kannada,  Kannada,
558  Katakana,  Katakana,
559    Kayah_Li,
560  Kharoshthi,  Kharoshthi,
561  Khmer,  Khmer,
562  Lao,  Lao,
563  Latin,  Latin,
564    Lepcha,
565  Limbu,  Limbu,
566  Linear_B,  Linear_B,
567    Lisu,
568    Lycian,
569    Lydian,
570  Malayalam,  Malayalam,
571    Meetei_Mayek,
572  Mongolian,  Mongolian,
573  Myanmar,  Myanmar,
574  New_Tai_Lue,  New_Tai_Lue,
# Line 557  Nko, Line 576  Nko,
576  Ogham,  Ogham,
577  Old_Italic,  Old_Italic,
578  Old_Persian,  Old_Persian,
579    Old_South_Arabian,
580    Old_Turkic,
581    Ol_Chiki,
582  Oriya,  Oriya,
583  Osmanya,  Osmanya,
584  Phags_Pa,  Phags_Pa,
585  Phoenician,  Phoenician,
586    Rejang,
587  Runic,  Runic,
588    Samaritan,
589    Saurashtra,
590  Shavian,  Shavian,
591  Sinhala,  Sinhala,
592    Sundanese,
593  Syloti_Nagri,  Syloti_Nagri,
594  Syriac,  Syriac,
595  Tagalog,  Tagalog,
596  Tagbanwa,  Tagbanwa,
597  Tai_Le,  Tai_Le,
598    Tai_Tham,
599    Tai_Viet,
600  Tamil,  Tamil,
601  Telugu,  Telugu,
602  Thaana,  Thaana,
# Line 576  Thai, Line 604  Thai,
604  Tibetan,  Tibetan,
605  Tifinagh,  Tifinagh,
606  Ugaritic,  Ugaritic,
607    Vai,
608  Yi.  Yi.
609  .P  .P
610  Each character has exactly one general category property, specified by a  Each character has exactly one general category property, specified by a
# Line 711  For example, when the pattern Line 740  For example, when the pattern
740    (foo)\eKbar    (foo)\eKbar
741  .sp  .sp
742  matches "foobar", the first substring is still set to "foo".  matches "foobar", the first substring is still set to "foo".
743    .P
744    Perl documents that the use of \eK within assertions is "not well defined". In
745    PCRE, \eK is acted upon when it occurs inside positive assertions, but is
746    ignored in negative assertions.
747  .  .
748  .  .
749  .\" HTML <a name="smallassertions"></a>  .\" HTML <a name="smallassertions"></a>
# Line 735  The backslashed assertions are: Line 768  The backslashed assertions are:
768    \ez     matches only at the end of the subject    \ez     matches only at the end of the subject
769    \eG     matches at the first matching position in the subject    \eG     matches at the first matching position in the subject
770  .sp  .sp
771  These assertions may not appear in character classes (but note that \eb has a  Inside a character class, \eb has a different meaning; it matches the backspace
772  different meaning, namely the backspace character, inside a character class).  character. If any other of these assertions appears in a character class, by
773    default it matches the corresponding literal character (for example, \eB
774    matches the letter B). However, if the PCRE_EXTRA option is set, an "invalid
775    escape sequence" error is generated instead.
776  .P  .P
777  A word boundary is a position in the subject string where the current character  A word boundary is a position in the subject string where the current character
778  and the previous character do not both match \ew or \eW (i.e. one matches  and the previous character do not both match \ew or \eW (i.e. one matches
779  \ew and the other matches \eW), or the start or end of the string if the  \ew and the other matches \eW), or the start or end of the string if the
780  first or last character matches \ew, respectively. Neither PCRE nor Perl has a  first or last character matches \ew, respectively. Neither PCRE nor Perl has a
781  separte "start of word" or "end of word" metasequence. However, whatever  separte "start of word" or "end of word" metasequence. However, whatever
782  follows \eb normally determines which it is. For example, the fragment  follows \eb normally determines which it is. For example, the fragment
783  \eba matches "a" at the start of a word.  \eba matches "a" at the start of a word.
784  .P  .P
785  The \eA, \eZ, and \ez assertions differ from the traditional circumflex and  The \eA, \eZ, and \ez assertions differ from the traditional circumflex and
# Line 876  the lookbehind. Line 912  the lookbehind.
912  .rs  .rs
913  .sp  .sp
914  An opening square bracket introduces a character class, terminated by a closing  An opening square bracket introduces a character class, terminated by a closing
915  square bracket. A closing square bracket on its own is not special by default.  square bracket. A closing square bracket on its own is not special by default.
916  However, if the PCRE_JAVASCRIPT_COMPAT option is set, a lone closing square  However, if the PCRE_JAVASCRIPT_COMPAT option is set, a lone closing square
917  bracket causes a compile-time error. If a closing square bracket is required as  bracket causes a compile-time error. If a closing square bracket is required as
918  a member of the class, it should be the first data character in the class  a member of the class, it should be the first data character in the class
919  (after an initial circumflex, if present) or escaped with a backslash.  (after an initial circumflex, if present) or escaped with a backslash.
# Line 1163  stored. Line 1199  stored.
1199    / ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x    / ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x
1200    # 1            2         2  3        2     3     4    # 1            2         2  3        2     3     4
1201  .sp  .sp
1202  A backreference to a numbered subpattern uses the most recent value that is set  A back reference to a numbered subpattern uses the most recent value that is
1203  for that number by any subpattern. The following pattern matches "abcabc" or  set for that number by any subpattern. The following pattern matches "abcabc"
1204  "defdef":  or "defdef":
1205  .sp  .sp
1206    /(?|(abc)|(def))\1/    /(?|(abc)|(def))\e1/
1207  .sp  .sp
1208  In contrast, a recursive or "subroutine" call to a numbered subpattern always  In contrast, a recursive or "subroutine" call to a numbered subpattern always
1209  refers to the first one in the pattern with the given number. The following  refers to the first one in the pattern with the given number. The following
1210  pattern matches "abcabc" or "defabc":  pattern matches "abcabc" or "defabc":
1211  .sp  .sp
1212    /(?|(abc)|(def))(?1)/    /(?|(abc)|(def))(?1)/
1213  .sp  .sp
1214    If a
1215    .\" HTML <a href="#conditions">
1216    .\" </a>
1217    condition test
1218    .\"
1219    for a subpattern's having matched refers to a non-unique number, the test is
1220    true if any of the subpatterns of that number have matched.
1221  .P  .P
1222  An alternative approach to using the "branch reset" feature is to use  An alternative approach to using this "branch reset" feature is to use
1223  duplicate named subpatterns, as described in the next section.  duplicate named subpatterns, as described in the next section.
1224  .  .
1225  .  .
# Line 1189  if an expression is modified, the number Line 1232  if an expression is modified, the number
1232  difficulty, PCRE supports the naming of subpatterns. This feature was not  difficulty, PCRE supports the naming of subpatterns. This feature was not
1233  added to Perl until release 5.10. Python had the feature earlier, and PCRE  added to Perl until release 5.10. Python had the feature earlier, and PCRE
1234  introduced it at release 4.0, using the Python syntax. PCRE now supports both  introduced it at release 4.0, using the Python syntax. PCRE now supports both
1235  the Perl and the Python syntax.  the Perl and the Python syntax. Perl allows identically numbered subpatterns to
1236    have different names, but PCRE does not.
1237  .P  .P
1238  In PCRE, a subpattern can be named in one of three ways: (?<name>...) or  In PCRE, a subpattern can be named in one of three ways: (?<name>...) or
1239  (?'name'...) as in Perl, or (?P<name>...) as in Python. References to capturing  (?'name'...) as in Perl, or (?P<name>...) as in Python. References to capturing
1240  parentheses from other parts of the pattern, such as  parentheses from other parts of the pattern, such as
1241  .\" HTML <a href="#backreferences">  .\" HTML <a href="#backreferences">
1242  .\" </a>  .\" </a>
1243  backreferences,  back references,
1244  .\"  .\"
1245  .\" HTML <a href="#recursion">  .\" HTML <a href="#recursion">
1246  .\" </a>  .\" </a>
# Line 1216  extracting the name-to-number translatio Line 1260  extracting the name-to-number translatio
1260  is also a convenience function for extracting a captured substring by name.  is also a convenience function for extracting a captured substring by name.
1261  .P  .P
1262  By default, a name must be unique within a pattern, but it is possible to relax  By default, a name must be unique within a pattern, but it is possible to relax
1263  this constraint by setting the PCRE_DUPNAMES option at compile time. This can  this constraint by setting the PCRE_DUPNAMES option at compile time. (Duplicate
1264  be useful for patterns where only one instance of the named parentheses can  names are also always permitted for subpatterns with the same number, set up as
1265  match. Suppose you want to match the name of a weekday, either as a 3-letter  described in the previous section.) Duplicate names can be useful for patterns
1266  abbreviation or as the full name, and in both cases you want to extract the  where only one instance of the named parentheses can match. Suppose you want to
1267  abbreviation. This pattern (ignoring the line breaks) does the job:  match the name of a weekday, either as a 3-letter abbreviation or as the full
1268    name, and in both cases you want to extract the abbreviation. This pattern
1269    (ignoring the line breaks) does the job:
1270  .sp  .sp
1271    (?<DN>Mon|Fri|Sun)(?:day)?|    (?<DN>Mon|Fri|Sun)(?:day)?|
1272    (?<DN>Tue)(?:sday)?|    (?<DN>Tue)(?:sday)?|
# Line 1234  subpattern, as described in the previous Line 1280  subpattern, as described in the previous
1280  .P  .P
1281  The convenience function for extracting the data by name returns the substring  The convenience function for extracting the data by name returns the substring
1282  for the first (and in this example, the only) subpattern of that name that  for the first (and in this example, the only) subpattern of that name that
1283  matched. This saves searching to find which numbered subpattern it was. If you  matched. This saves searching to find which numbered subpattern it was.
1284  make a reference to a non-unique named subpattern from elsewhere in the  .P
1285  pattern, the one that corresponds to the lowest number is used. For further  If you make a back reference to a non-unique named subpattern from elsewhere in
1286  details of the interfaces for handling named subpatterns, see the  the pattern, the one that corresponds to the first occurrence of the name is
1287    used. In the absence of duplicate numbers (see the previous section) this is
1288    the one with the lowest number. If you use a named reference in a condition
1289    test (see the
1290    .\"
1291    .\" HTML <a href="#conditions">
1292    .\" </a>
1293    section about conditions
1294    .\"
1295    below), either to check whether a subpattern has matched, or to check for
1296    recursion, all subpatterns with the same name are tested. If the condition is
1297    true for any one of them, the overall condition is true. This is the same
1298    behaviour as testing by number. For further details of the interfaces for
1299    handling named subpatterns, see the
1300  .\" HREF  .\" HREF
1301  \fBpcreapi\fP  \fBpcreapi\fP
1302  .\"  .\"
1303  documentation.  documentation.
1304  .P  .P
1305  \fBWarning:\fP You cannot use different names to distinguish between two  \fBWarning:\fP You cannot use different names to distinguish between two
1306  subpatterns with the same number (see the previous section) because PCRE uses  subpatterns with the same number because PCRE uses only the numbers when
1307  only the numbers when matching.  matching. For this reason, an error is given at compile time if different names
1308    are given to subpatterns with the same number. However, you can give the same
1309    name to subpatterns with the same number, even when PCRE_DUPNAMES is not set.
1310  .  .
1311  .  .
1312  .SH REPETITION  .SH REPETITION
# Line 1263  items: Line 1324  items:
1324    a character class    a character class
1325    a back reference (see next section)    a back reference (see next section)
1326    a parenthesized subpattern (unless it is an assertion)    a parenthesized subpattern (unless it is an assertion)
1327    a recursive or "subroutine" call to a subpattern    a recursive or "subroutine" call to a subpattern
1328  .sp  .sp
1329  The general repetition quantifier specifies a minimum and maximum number of  The general repetition quantifier specifies a minimum and maximum number of
1330  permitted matches, by giving the two numbers in curly brackets (braces),  permitted matches, by giving the two numbers in curly brackets (braces),
# Line 1374  worth setting PCRE_DOTALL in order to ob Line 1435  worth setting PCRE_DOTALL in order to ob
1435  alternatively using ^ to indicate anchoring explicitly.  alternatively using ^ to indicate anchoring explicitly.
1436  .P  .P
1437  However, there is one situation where the optimization cannot be used. When .*  However, there is one situation where the optimization cannot be used. When .*
1438  is inside capturing parentheses that are the subject of a backreference  is inside capturing parentheses that are the subject of a back reference
1439  elsewhere in the pattern, a match at the start may fail where a later one  elsewhere in the pattern, a match at the start may fail where a later one
1440  succeeds. Consider, for example:  succeeds. Consider, for example:
1441  .sp  .sp
# Line 1589  references to it always fail by default. Line 1650  references to it always fail by default.
1650  .sp  .sp
1651    (a|(bc))\e2    (a|(bc))\e2
1652  .sp  .sp
1653  always fails if it starts to match "a" rather than "bc". However, if the  always fails if it starts to match "a" rather than "bc". However, if the
1654  PCRE_JAVASCRIPT_COMPAT option is set at compile time, a back reference to an  PCRE_JAVASCRIPT_COMPAT option is set at compile time, a back reference to an
1655  unset value matches an empty string.  unset value matches an empty string.
1656  .P  .P
1657  Because there may be many capturing parentheses in a pattern, all digits  Because there may be many capturing parentheses in a pattern, all digits
# Line 1603  whitespace. Otherwise, the \eg{ syntax o Line 1664  whitespace. Otherwise, the \eg{ syntax o
1664  "Comments"  "Comments"
1665  .\"  .\"
1666  below) can be used.  below) can be used.
1667  .P  .
1668    .SS "Recursive back references"
1669    .rs
1670    .sp
1671  A back reference that occurs inside the parentheses to which it refers fails  A back reference that occurs inside the parentheses to which it refers fails
1672  when the subpattern is first used, so, for example, (a\e1) never matches.  when the subpattern is first used, so, for example, (a\e1) never matches.
1673  However, such references can be useful inside repeated subpatterns. For  However, such references can be useful inside repeated subpatterns. For
# Line 1617  to the previous iteration. In order for Line 1681  to the previous iteration. In order for
1681  that the first iteration does not need to match the back reference. This can be  that the first iteration does not need to match the back reference. This can be
1682  done using alternation, as in the example above, or by a quantifier with a  done using alternation, as in the example above, or by a quantifier with a
1683  minimum of zero.  minimum of zero.
1684    .P
1685    Back references of this type cause the group that they reference to be treated
1686    as an
1687    .\" HTML <a href="#atomicgroup">
1688    .\" </a>
1689    atomic group.
1690    .\"
1691    Once the whole group has been matched, a subsequent matching failure cannot
1692    cause backtracking into the middle of the group.
1693  .  .
1694  .  .
1695  .\" HTML <a name="bigassertions"></a>  .\" HTML <a name="bigassertions"></a>
# Line 1712  In some cases, the Perl 5.10 escape sequ Line 1785  In some cases, the Perl 5.10 escape sequ
1785  .\" </a>  .\" </a>
1786  (see above)  (see above)
1787  .\"  .\"
1788  can be used instead of a lookbehind assertion to get round the fixed-length  can be used instead of a lookbehind assertion to get round the fixed-length
1789  restriction.  restriction.
1790  .P  .P
1791  The implementation of lookbehind assertions is, for each alternative, to  The implementation of lookbehind assertions is, for each alternative, to
# Line 1730  different numbers of bytes, are also not Line 1803  different numbers of bytes, are also not
1803  "Subroutine"  "Subroutine"
1804  .\"  .\"
1805  calls (see below) such as (?2) or (?&X) are permitted in lookbehinds, as long  calls (see below) such as (?2) or (?&X) are permitted in lookbehinds, as long
1806  as the subpattern matches a fixed-length string.  as the subpattern matches a fixed-length string.
1807  .\" HTML <a href="#recursion">  .\" HTML <a href="#recursion">
1808  .\" </a>  .\" </a>
1809  Recursion,  Recursion,
# Line 1803  characters that are not "999". Line 1876  characters that are not "999".
1876  .sp  .sp
1877  It is possible to cause the matching process to obey a subpattern  It is possible to cause the matching process to obey a subpattern
1878  conditionally or to choose between two alternative subpatterns, depending on  conditionally or to choose between two alternative subpatterns, depending on
1879  the result of an assertion, or whether a specific capturing subpattern has  the result of an assertion, or whether a specific capturing subpattern has
1880  already been matched. The two possible forms of conditional subpattern are:  already been matched. The two possible forms of conditional subpattern are:
1881  .sp  .sp
1882    (?(condition)yes-pattern)    (?(condition)yes-pattern)
# Line 1821  recursion, a pseudo-condition called DEF Line 1894  recursion, a pseudo-condition called DEF
1894  .sp  .sp
1895  If the text between the parentheses consists of a sequence of digits, the  If the text between the parentheses consists of a sequence of digits, the
1896  condition is true if a capturing subpattern of that number has previously  condition is true if a capturing subpattern of that number has previously
1897  matched. If there is more than one capturing subpattern with the same number  matched. If there is more than one capturing subpattern with the same number
1898  (see the earlier  (see the earlier
1899  .\"  .\"
1900  .\" HTML <a href="#recursion">  .\" HTML <a href="#recursion">
1901  .\" </a>  .\" </a>
# Line 1874  Rewriting the above example to use a nam Line 1947  Rewriting the above example to use a nam
1947  .sp  .sp
1948    (?<OPEN> \e( )?    [^()]+    (?(<OPEN>) \e) )    (?<OPEN> \e( )?    [^()]+    (?(<OPEN>) \e) )
1949  .sp  .sp
1950    If the name used in a condition of this kind is a duplicate, the test is
1951    applied to all subpatterns of the same name, and is true if any one of them has
1952    matched.
1953  .  .
1954  .SS "Checking for pattern recursion"  .SS "Checking for pattern recursion"
1955  .rs  .rs
# Line 1887  letter R, for example: Line 1963  letter R, for example:
1963  .sp  .sp
1964  the condition is true if the most recent recursion is into a subpattern whose  the condition is true if the most recent recursion is into a subpattern whose
1965  number or name is given. This condition does not check the entire recursion  number or name is given. This condition does not check the entire recursion
1966  stack.  stack. If the name used in a condition of this kind is a duplicate, the test is
1967    applied to all subpatterns of the same name, and is true if any one of them is
1968    the most recent recursion.
1969  .P  .P
1970  At "top level", all these recursion test conditions are false.  At "top level", all these recursion test conditions are false.
1971  .\" HTML <a href="#recursion">  .\" HTML <a href="#recursion">
1972  .\" </a>  .\" </a>
1973  Recursive patterns  The syntax for recursive patterns
1974  .\"  .\"
1975  are described below.  is described below.
1976  .  .
1977  .SS "Defining subpatterns for use by reference only"  .SS "Defining subpatterns for use by reference only"
1978  .rs  .rs
# Line 1903  If the condition is the string (DEFINE), Line 1981  If the condition is the string (DEFINE),
1981  name DEFINE, the condition is always false. In this case, there may be only one  name DEFINE, the condition is always false. In this case, there may be only one
1982  alternative in the subpattern. It is always skipped if control reaches this  alternative in the subpattern. It is always skipped if control reaches this
1983  point in the pattern; the idea of DEFINE is that it can be used to define  point in the pattern; the idea of DEFINE is that it can be used to define
1984  "subroutines" that can be referenced from elsewhere. (The use of  "subroutines" that can be referenced from elsewhere. (The use of
1985  .\" HTML <a href="#subpatternsassubroutines">  .\" HTML <a href="#subpatternsassubroutines">
1986  .\" </a>  .\" </a>
1987  "subroutines"  "subroutines"
# Line 1980  this kind of recursion was subsequently Line 2058  this kind of recursion was subsequently
2058  .P  .P
2059  A special item that consists of (? followed by a number greater than zero and a  A special item that consists of (? followed by a number greater than zero and a
2060  closing parenthesis is a recursive call of the subpattern of the given number,  closing parenthesis is a recursive call of the subpattern of the given number,
2061  provided that it occurs inside that subpattern. (If not, it is a  provided that it occurs inside that subpattern. (If not, it is a
2062  .\" HTML <a href="#subpatternsassubroutines">  .\" HTML <a href="#subpatternsassubroutines">
2063  .\" </a>  .\" </a>
2064  "subroutine"  "subroutine"
# Line 1996  PCRE_EXTENDED option is set so that whit Line 2074  PCRE_EXTENDED option is set so that whit
2074  First it matches an opening parenthesis. Then it matches any number of  First it matches an opening parenthesis. Then it matches any number of
2075  substrings which can either be a sequence of non-parentheses, or a recursive  substrings which can either be a sequence of non-parentheses, or a recursive
2076  match of the pattern itself (that is, a correctly parenthesized substring).  match of the pattern itself (that is, a correctly parenthesized substring).
2077  Finally there is a closing parenthesis. Note the use of a possessive quantifier  Finally there is a closing parenthesis. Note the use of a possessive quantifier
2078  to avoid backtracking into sequences of non-parentheses.  to avoid backtracking into sequences of non-parentheses.
2079  .P  .P
2080  If this were part of a larger pattern, you would not want to recurse the entire  If this were part of a larger pattern, you would not want to recurse the entire
# Line 2044  the match runs for a very long time inde Line 2122  the match runs for a very long time inde
2122  ways the + and * repeats can carve up the subject, and all have to be tested  ways the + and * repeats can carve up the subject, and all have to be tested
2123  before failure can be reported.  before failure can be reported.
2124  .P  .P
2125  At the end of a match, the values set for any capturing subpatterns are those  At the end of a match, the values of capturing parentheses are those from
2126  from the outermost level of the recursion at which the subpattern value is set.  the outermost level. If you want to obtain intermediate values, a callout
2127  If you want to obtain intermediate values, a callout function can be used (see  function can be used (see below and the
 below and the  
2128  .\" HREF  .\" HREF
2129  \fBpcrecallout\fP  \fBpcrecallout\fP
2130  .\"  .\"
# Line 2055  documentation). If the pattern above is Line 2132  documentation). If the pattern above is
2132  .sp  .sp
2133    (ab(cd)ef)    (ab(cd)ef)
2134  .sp  .sp
2135  the value for the capturing parentheses is "ef", which is the last value taken  the value for the inner capturing parentheses (numbered 2) is "ef", which is
2136  on at the top level. If additional parentheses are added, giving  the last value taken on at the top level. If a capturing subpattern is not
2137  .sp  matched at the top level, its final value is unset, even if it is (temporarily)
2138    \e( ( ( [^()]++ | (?R) )* ) \e)  set at a deeper level.
2139       ^                        ^  .P
2140       ^                        ^  If there are more than 15 capturing parentheses in a pattern, PCRE has to
2141  .sp  obtain extra memory to store data during a recursion, which it does by using
2142  the string they capture is "ab(cd)ef", the contents of the top level  \fBpcre_malloc\fP, freeing it via \fBpcre_free\fP afterwards. If no memory can
2143  parentheses. If there are more than 15 capturing parentheses in a pattern, PCRE  be obtained, the match fails with the PCRE_ERROR_NOMEMORY error.
 has to obtain extra memory to store data during a recursion, which it does by  
 using \fBpcre_malloc\fP, freeing it via \fBpcre_free\fP afterwards. If no  
 memory can be obtained, the match fails with the PCRE_ERROR_NOMEMORY error.  
2144  .P  .P
2145  Do not confuse the (?R) item with the condition (R), which tests for recursion.  Do not confuse the (?R) item with the condition (R), which tests for recursion.
2146  Consider this pattern, which matches text in angle brackets, allowing for  Consider this pattern, which matches text in angle brackets, allowing for
# Line 2087  is the actual recursive call. Line 2161  is the actual recursive call.
2161  In PCRE (like Python, but unlike Perl), a recursive subpattern call is always  In PCRE (like Python, but unlike Perl), a recursive subpattern call is always
2162  treated as an atomic group. That is, once it has matched some of the subject  treated as an atomic group. That is, once it has matched some of the subject
2163  string, it is never re-entered, even if it contains untried alternatives and  string, it is never re-entered, even if it contains untried alternatives and
2164  there is a subsequent matching failure. This can be illustrated by the  there is a subsequent matching failure. This can be illustrated by the
2165  following pattern, which purports to match a palindromic string that contains  following pattern, which purports to match a palindromic string that contains
2166  an odd number of characters (for example, "a", "aba", "abcba", "abcdcba"):  an odd number of characters (for example, "a", "aba", "abcba", "abcdcba"):
2167  .sp  .sp
2168    ^(.|(.)(?1)\e2)$    ^(.|(.)(?1)\e2)$
2169  .sp  .sp
2170  The idea is that it either matches a single character, or two identical  The idea is that it either matches a single character, or two identical
2171  characters surrounding a sub-palindrome. In Perl, this pattern works; in PCRE  characters surrounding a sub-palindrome. In Perl, this pattern works; in PCRE
2172  it does not if the pattern is longer than three characters. Consider the  it does not if the pattern is longer than three characters. Consider the
2173  subject string "abcba":  subject string "abcba":
2174  .P  .P
2175  At the top level, the first character is matched, but as it is not at the end  At the top level, the first character is matched, but as it is not at the end
2176  of the string, the first alternative fails; the second alternative is taken  of the string, the first alternative fails; the second alternative is taken
2177  and the recursion kicks in. The recursive call to subpattern 1 successfully  and the recursion kicks in. The recursive call to subpattern 1 successfully
2178  matches the next character ("b"). (Note that the beginning and end of line  matches the next character ("b"). (Note that the beginning and end of line
2179  tests are not part of the recursion).  tests are not part of the recursion).
2180  .P  .P
2181  Back at the top level, the next character ("c") is compared with what  Back at the top level, the next character ("c") is compared with what
2182  subpattern 2 matched, which was "a". This fails. Because the recursion is  subpattern 2 matched, which was "a". This fails. Because the recursion is
2183  treated as an atomic group, there are now no backtracking points, and so the  treated as an atomic group, there are now no backtracking points, and so the
2184  entire match fails. (Perl is able, at this point, to re-enter the recursion and  entire match fails. (Perl is able, at this point, to re-enter the recursion and
2185  try the second alternative.) However, if the pattern is written with the  try the second alternative.) However, if the pattern is written with the
# Line 2113  alternatives in the other order, things Line 2187  alternatives in the other order, things
2187  .sp  .sp
2188    ^((.)(?1)\e2|.)$    ^((.)(?1)\e2|.)$
2189  .sp  .sp
2190  This time, the recursing alternative is tried first, and continues to recurse  This time, the recursing alternative is tried first, and continues to recurse
2191  until it runs out of characters, at which point the recursion fails. But this  until it runs out of characters, at which point the recursion fails. But this
2192  time we do have another alternative to try at the higher level. That is the big  time we do have another alternative to try at the higher level. That is the big
2193  difference: in the previous case the remaining alternative is at a deeper  difference: in the previous case the remaining alternative is at a deeper
2194  recursion level, which PCRE cannot use.  recursion level, which PCRE cannot use.
2195  .P  .P
2196  To change the pattern so that matches all palindromic strings, not just those  To change the pattern so that matches all palindromic strings, not just those
2197  with an odd number of characters, it is tempting to change the pattern to this:  with an odd number of characters, it is tempting to change the pattern to this:
2198  .sp  .sp
2199    ^((.)(?1)\e2|.?)$    ^((.)(?1)\e2|.?)$
2200  .sp  .sp
2201  Again, this works in Perl, but not in PCRE, and for the same reason. When a  Again, this works in Perl, but not in PCRE, and for the same reason. When a
2202  deeper recursion has matched a single character, it cannot be entered again in  deeper recursion has matched a single character, it cannot be entered again in
2203  order to match an empty string. The solution is to separate the two cases, and  order to match an empty string. The solution is to separate the two cases, and
2204  write out the odd and even cases as alternatives at the higher level:  write out the odd and even cases as alternatives at the higher level:
2205  .sp  .sp
2206    ^(?:((.)(?1)\e2|)|((.)(?3)\e4|.))    ^(?:((.)(?1)\e2|)|((.)(?3)\e4|.))
2207  .sp  .sp
2208  If you want to match typical palindromic phrases, the pattern has to ignore all  If you want to match typical palindromic phrases, the pattern has to ignore all
2209  non-word characters, which can be done like this:  non-word characters, which can be done like this:
2210  .sp  .sp
2211    ^\eW*+(?:((.)\eW*+(?1)\eW*+\e2|)|((.)\eW*+(?3)\eW*+\4|\eW*+.\eW*+))\eW*+$    ^\eW*+(?:((.)\eW*+(?1)\eW*+\e2|)|((.)\eW*+(?3)\eW*+\e4|\eW*+.\eW*+))\eW*+$
2212  .sp  .sp
2213  If run with the PCRE_CASELESS option, this pattern matches phrases such as "A  If run with the PCRE_CASELESS option, this pattern matches phrases such as "A
2214  man, a plan, a canal: Panama!" and it works well in both PCRE and Perl. Note  man, a plan, a canal: Panama!" and it works well in both PCRE and Perl. Note
2215  the use of the possessive quantifier *+ to avoid backtracking into sequences of  the use of the possessive quantifier *+ to avoid backtracking into sequences of
2216  non-word characters. Without this, PCRE takes a great deal longer (ten times or  non-word characters. Without this, PCRE takes a great deal longer (ten times or
2217  more) to match typical phrases, and Perl takes so long that you think it has  more) to match typical phrases, and Perl takes so long that you think it has
2218  gone into a loop.  gone into a loop.
# Line 2177  matches "sense and sensibility" and "res Line 2251  matches "sense and sensibility" and "res
2251  is used, it does match "sense and responsibility" as well as the other two  is used, it does match "sense and responsibility" as well as the other two
2252  strings. Another example is given in the discussion of DEFINE above.  strings. Another example is given in the discussion of DEFINE above.
2253  .P  .P
2254  Like recursive subpatterns, a "subroutine" call is always treated as an atomic  Like recursive subpatterns, a subroutine call is always treated as an atomic
2255  group. That is, once it has matched some of the subject string, it is never  group. That is, once it has matched some of the subject string, it is never
2256  re-entered, even if it contains untried alternatives and there is a subsequent  re-entered, even if it contains untried alternatives and there is a subsequent
2257  matching failure.  matching failure. Any capturing parentheses that are set during the subroutine
2258    call revert to their previous values afterwards.
2259  .P  .P
2260  When a subpattern is used as a subroutine, processing options such as  When a subpattern is used as a subroutine, processing options such as
2261  case-independence are fixed when the subpattern is defined. They cannot be  case-independence are fixed when the subpattern is defined. They cannot be
# Line 2249  description of the interface to the call Line 2324  description of the interface to the call
2324  documentation.  documentation.
2325  .  .
2326  .  .
2327    .\" HTML <a name="backtrackcontrol"></a>
2328  .SH "BACKTRACKING CONTROL"  .SH "BACKTRACKING CONTROL"
2329  .rs  .rs
2330  .sp  .sp
# Line 2264  a backtracking algorithm. With the excep Line 2340  a backtracking algorithm. With the excep
2340  failing negative assertion, they cause an error if encountered by  failing negative assertion, they cause an error if encountered by
2341  \fBpcre_dfa_exec()\fP.  \fBpcre_dfa_exec()\fP.
2342  .P  .P
2343  If any of these verbs are used in an assertion subpattern, their effect is  If any of these verbs are used in an assertion or subroutine subpattern
2344  confined to that subpattern; it does not extend to the surrounding pattern.  (including recursive subpatterns), their effect is confined to that subpattern;
2345  Note that assertion subpatterns are processed as anchored at the point where  it does not extend to the surrounding pattern. Note that such subpatterns are
2346  they are tested.  processed as anchored at the point where they are tested.
2347  .P  .P
2348  The new verbs make use of what was previously invalid syntax: an opening  The new verbs make use of what was previously invalid syntax: an opening
2349  parenthesis followed by an asterisk. In Perl, they are generally of the form  parenthesis followed by an asterisk. They are generally of the form
2350  (*VERB:ARG) but PCRE does not support the use of arguments, so its general  (*VERB) or (*VERB:NAME). Some may take either form, with differing behaviour,
2351  form is just (*VERB). Any number of these verbs may occur in a pattern. There  depending on whether or not an argument is present. An name is a sequence of
2352  are two kinds:  letters, digits, and underscores. If the name is empty, that is, if the closing
2353    parenthesis immediately follows the colon, the effect is as if the colon were
2354    not there. Any number of these verbs may occur in a pattern.
2355    .P
2356    PCRE contains some optimizations that are used to speed up matching by running
2357    some checks at the start of each match attempt. For example, it may know the
2358    minimum length of matching subject, or that a particular character must be
2359    present. When one of these optimizations suppresses the running of a match, any
2360    included backtracking verbs will not, of course, be processed. You can suppress
2361    the start-of-match optimizations by setting the PCRE_NO_START_OPTIMIZE option
2362    when calling \fBpcre_exec()\fP.
2363    .
2364  .  .
2365  .SS "Verbs that act immediately"  .SS "Verbs that act immediately"
2366  .rs  .rs
2367  .sp  .sp
2368  The following verbs act as soon as they are encountered:  The following verbs act as soon as they are encountered. They may not be
2369    followed by a name.
2370  .sp  .sp
2371     (*ACCEPT)     (*ACCEPT)
2372  .sp  .sp
# Line 2289  captured. (This feature was added to PCR Line 2377  captured. (This feature was added to PCR
2377  .sp  .sp
2378    A((?:A|B(*ACCEPT)|C)D)    A((?:A|B(*ACCEPT)|C)D)
2379  .sp  .sp
2380  This matches "AB", "AAD", or "ACD"; when it matches "AB", "B" is captured by  This matches "AB", "AAD", or "ACD"; when it matches "AB", "B" is captured by
2381  the outer parentheses.  the outer parentheses.
2382  .sp  .sp
2383    (*FAIL) or (*F)    (*FAIL) or (*F)
# Line 2305  callout feature, as for example in this Line 2393  callout feature, as for example in this
2393  A match with the string "aaaa" always fails, but the callout is taken before  A match with the string "aaaa" always fails, but the callout is taken before
2394  each backtrack happens (in this example, 10 times).  each backtrack happens (in this example, 10 times).
2395  .  .
2396    .
2397    .SS "Recording which path was taken"
2398    .rs
2399    .sp
2400    There is one verb whose main purpose is to track how a match was arrived at,
2401    though it also has a secondary use in conjunction with advancing the match
2402    starting point (see (*SKIP) below).
2403    .sp
2404      (*MARK:NAME) or (*:NAME)
2405    .sp
2406    A name is always required with this verb. There may be as many instances of
2407    (*MARK) as you like in a pattern, and their names do not have to be unique.
2408    .P
2409    When a match succeeds, the name of the last-encountered (*MARK) is passed back
2410    to the caller via the \fIpcre_extra\fP data structure, as described in the
2411    .\" HTML <a href="pcreapi.html#extradata">
2412    .\" </a>
2413    section on \fIpcre_extra\fP
2414    .\"
2415    in the
2416    .\" HREF
2417    \fBpcreapi\fP
2418    .\"
2419    documentation. No data is returned for a partial match. Here is an example of
2420    \fBpcretest\fP output, where the /K modifier requests the retrieval and
2421    outputting of (*MARK) data:
2422    .sp
2423      /X(*MARK:A)Y|X(*MARK:B)Z/K
2424      XY
2425       0: XY
2426      MK: A
2427      XZ
2428       0: XZ
2429      MK: B
2430    .sp
2431    The (*MARK) name is tagged with "MK:" in this output, and in this example it
2432    indicates which of the two alternatives matched. This is a more efficient way
2433    of obtaining this information than putting each alternative in its own
2434    capturing parentheses.
2435    .P
2436    A name may also be returned after a failed match if the final path through the
2437    pattern involves (*MARK). However, unless (*MARK) used in conjunction with
2438    (*COMMIT), this is unlikely to happen for an unanchored pattern because, as the
2439    starting point for matching is advanced, the final check is often with an empty
2440    string, causing a failure before (*MARK) is reached. For example:
2441    .sp
2442      /X(*MARK:A)Y|X(*MARK:B)Z/K
2443      XP
2444      No match
2445    .sp
2446    There are three potential starting points for this match (starting with X,
2447    starting with P, and with an empty string). If the pattern is anchored, the
2448    result is different:
2449    .sp
2450      /^X(*MARK:A)Y|^X(*MARK:B)Z/K
2451      XP
2452      No match, mark = B
2453    .sp
2454    PCRE's start-of-match optimizations can also interfere with this. For example,
2455    if, as a result of a call to \fBpcre_study()\fP, it knows the minimum
2456    subject length for a match, a shorter subject will not be scanned at all.
2457    .P
2458    Note that similar anomalies (though different in detail) exist in Perl, no
2459    doubt for the same reasons. The use of (*MARK) data after a failed match of an
2460    unanchored pattern is not recommended, unless (*COMMIT) is involved.
2461    .
2462    .
2463  .SS "Verbs that act after backtracking"  .SS "Verbs that act after backtracking"
2464  .rs  .rs
2465  .sp  .sp
2466  The following verbs do nothing when they are encountered. Matching continues  The following verbs do nothing when they are encountered. Matching continues
2467  with what follows, but if there is no subsequent match, a failure is forced.  with what follows, but if there is no subsequent match, causing a backtrack to
2468  The verbs differ in exactly what kind of failure occurs.  the verb, a failure is forced. That is, backtracking cannot pass to the left of
2469    the verb. However, when one of these verbs appears inside an atomic group, its
2470    effect is confined to that group, because once the group has been matched,
2471    there is never any backtracking into it. In this situation, backtracking can
2472    "jump back" to the left of the entire atomic group. (Remember also, as stated
2473    above, that this localization also applies in subroutine calls and assertions.)
2474    .P
2475    These verbs differ in exactly what kind of failure occurs when backtracking
2476    reaches them.
2477  .sp  .sp
2478    (*COMMIT)    (*COMMIT)
2479  .sp  .sp
2480  This verb causes the whole match to fail outright if the rest of the pattern  This verb, which may not be followed by a name, causes the whole match to fail
2481  does not match. Even if the pattern is unanchored, no further attempts to find  outright if the rest of the pattern does not match. Even if the pattern is
2482  a match by advancing the starting point take place. Once (*COMMIT) has been  unanchored, no further attempts to find a match by advancing the starting point
2483  passed, \fBpcre_exec()\fP is committed to finding a match at the current  take place. Once (*COMMIT) has been passed, \fBpcre_exec()\fP is committed to
2484  starting point, or not at all. For example:  finding a match at the current starting point, or not at all. For example:
2485  .sp  .sp
2486    a+(*COMMIT)b    a+(*COMMIT)b
2487  .sp  .sp
2488  This matches "xxaab" but not "aacaab". It can be thought of as a kind of  This matches "xxaab" but not "aacaab". It can be thought of as a kind of
2489  dynamic anchor, or "I've started, so I must finish."  dynamic anchor, or "I've started, so I must finish." The name of the most
2490  .sp  recently passed (*MARK) in the path is passed back when (*COMMIT) forces a
2491    (*PRUNE)  match failure.
2492  .sp  .P
2493  This verb causes the match to fail at the current position if the rest of the  Note that (*COMMIT) at the start of a pattern is not the same as an anchor,
2494  pattern does not match. If the pattern is unanchored, the normal "bumpalong"  unless PCRE's start-of-match optimizations are turned off, as shown in this
2495  advance to the next starting character then happens. Backtracking can occur as  \fBpcretest\fP example:
2496  usual to the left of (*PRUNE), or when matching to the right of (*PRUNE), but  .sp
2497  if there is no match to the right, backtracking cannot cross (*PRUNE).    /(*COMMIT)abc/
2498  In simple cases, the use of (*PRUNE) is just an alternative to an atomic    xyzabc
2499  group or possessive quantifier, but there are some uses of (*PRUNE) that cannot     0: abc
2500  be expressed in any other way.    xyzabc\eY
2501      No match
2502    .sp
2503    PCRE knows that any match must start with "a", so the optimization skips along
2504    the subject to "a" before running the first match attempt, which succeeds. When
2505    the optimization is disabled by the \eY escape in the second subject, the match
2506    starts at "x" and so the (*COMMIT) causes it to fail without trying any other
2507    starting points.
2508    .sp
2509      (*PRUNE) or (*PRUNE:NAME)
2510    .sp
2511    This verb causes the match to fail at the current starting position in the
2512    subject if the rest of the pattern does not match. If the pattern is
2513    unanchored, the normal "bumpalong" advance to the next starting character then
2514    happens. Backtracking can occur as usual to the left of (*PRUNE), before it is
2515    reached, or when matching to the right of (*PRUNE), but if there is no match to
2516    the right, backtracking cannot cross (*PRUNE). In simple cases, the use of
2517    (*PRUNE) is just an alternative to an atomic group or possessive quantifier,
2518    but there are some uses of (*PRUNE) that cannot be expressed in any other way.
2519    The behaviour of (*PRUNE:NAME) is the same as (*MARK:NAME)(*PRUNE) when the
2520    match fails completely; the name is passed back if this is the final attempt.
2521    (*PRUNE:NAME) does not pass back a name if the match succeeds. In an anchored
2522    pattern (*PRUNE) has the same effect as (*COMMIT).
2523  .sp  .sp
2524    (*SKIP)    (*SKIP)
2525  .sp  .sp
2526  This verb is like (*PRUNE), except that if the pattern is unanchored, the  This verb, when given without a name, is like (*PRUNE), except that if the
2527  "bumpalong" advance is not to the next character, but to the position in the  pattern is unanchored, the "bumpalong" advance is not to the next character,
2528  subject where (*SKIP) was encountered. (*SKIP) signifies that whatever text  but to the position in the subject where (*SKIP) was encountered. (*SKIP)
2529  was matched leading up to it cannot be part of a successful match. Consider:  signifies that whatever text was matched leading up to it cannot be part of a
2530    successful match. Consider:
2531  .sp  .sp
2532    a+(*SKIP)b    a+(*SKIP)b
2533  .sp  .sp
# Line 2352  effect as this example; although it woul Line 2538  effect as this example; although it woul
2538  first match attempt, the second attempt would start at the second character  first match attempt, the second attempt would start at the second character
2539  instead of skipping on to "c".  instead of skipping on to "c".
2540  .sp  .sp
2541    (*THEN)    (*SKIP:NAME)
2542    .sp
2543    When (*SKIP) has an associated name, its behaviour is modified. If the
2544    following pattern fails to match, the previous path through the pattern is
2545    searched for the most recent (*MARK) that has the same name. If one is found,
2546    the "bumpalong" advance is to the subject position that corresponds to that
2547    (*MARK) instead of to where (*SKIP) was encountered. If no (*MARK) with a
2548    matching name is found, normal "bumpalong" of one character happens (the
2549    (*SKIP) is ignored).
2550    .sp
2551      (*THEN) or (*THEN:NAME)
2552  .sp  .sp
2553  This verb causes a skip to the next alternation if the rest of the pattern does  This verb causes a skip to the next alternation if the rest of the pattern does
2554  not match. That is, it cancels pending backtracking, but only within the  not match. That is, it cancels pending backtracking, but only within the
# Line 2363  for a pattern-based if-then-else block: Line 2559  for a pattern-based if-then-else block:
2559  .sp  .sp
2560  If the COND1 pattern matches, FOO is tried (and possibly further items after  If the COND1 pattern matches, FOO is tried (and possibly further items after
2561  the end of the group if FOO succeeds); on failure the matcher skips to the  the end of the group if FOO succeeds); on failure the matcher skips to the
2562  second alternative and tries COND2, without backtracking into COND1. If (*THEN)  second alternative and tries COND2, without backtracking into COND1. The
2563  is used outside of any alternation, it acts exactly like (*PRUNE).  behaviour of (*THEN:NAME) is exactly the same as (*MARK:NAME)(*THEN) if the
2564    overall match fails. If (*THEN) is not directly inside an alternation, it acts
2565    like (*PRUNE).
2566  .  .
2567  .  .
2568  .SH "SEE ALSO"  .SH "SEE ALSO"
2569  .rs  .rs
2570  .sp  .sp
2571  \fBpcreapi\fP(3), \fBpcrecallout\fP(3), \fBpcrematching\fP(3),  \fBpcreapi\fP(3), \fBpcrecallout\fP(3), \fBpcrematching\fP(3),
2572  \fBpcresyntax\fP(3), \fBpcre\fP(3).  \fBpcresyntax\fP(3), \fBpcre\fP(3).
2573  .  .
2574  .  .
# Line 2388  Cambridge CB2 3QH, England. Line 2586  Cambridge CB2 3QH, England.
2586  .rs  .rs
2587  .sp  .sp
2588  .nf  .nf
2589  Last updated: 30 September 2009  Last updated: 03 May 2010
2590  Copyright (c) 1997-2009 University of Cambridge.  Copyright (c) 1997-2010 University of Cambridge.
2591  .fi  .fi

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