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revision 514 by ph10, Mon May 3 12:54:22 2010 UTC revision 630 by ph10, Fri Jul 22 10:00:10 2011 UTC
# Line 42  in the main Line 42  in the main
42  .\"  .\"
43  page.  page.
44  .P  .P
45    Another special sequence that may appear at the start of a pattern or in
46    combination with (*UTF8) is:
47    .sp
48      (*UCP)
49    .sp
50    This has the same effect as setting the PCRE_UCP option: it causes sequences
51    such as \ed and \ew to use Unicode properties to determine character types,
52    instead of recognizing only characters with codes less than 128 via a lookup
53    table.
54    .P
55    If a pattern starts with (*NO_START_OPT), it has the same effect as setting the
56    PCRE_NO_START_OPTIMIZE option either at compile or matching time. There are
57    also some more of these special sequences that are concerned with the handling
58    of newlines; they are described below.
59    .P
60  The remainder of this document discusses the patterns that are supported by  The remainder of this document discusses the patterns that are supported by
61  PCRE when its main matching function, \fBpcre_exec()\fP, is used.  PCRE when its main matching function, \fBpcre_exec()\fP, is used.
62  From release 6.0, PCRE offers a second matching function,  From release 6.0, PCRE offers a second matching function,
# Line 56  discussed in the Line 71  discussed in the
71  page.  page.
72  .  .
73  .  .
74    .\" HTML <a name="newlines"></a>
75  .SH "NEWLINE CONVENTIONS"  .SH "NEWLINE CONVENTIONS"
76  .rs  .rs
77  .sp  .sp
# Line 171  The following sections describe the use Line 187  The following sections describe the use
187  .rs  .rs
188  .sp  .sp
189  The backslash character has several uses. Firstly, if it is followed by a  The backslash character has several uses. Firstly, if it is followed by a
190  non-alphanumeric character, it takes away any special meaning that character  character that is not a number or a letter, it takes away any special meaning
191  may have. This use of backslash as an escape character applies both inside and  that character may have. This use of backslash as an escape character applies
192  outside character classes.  both inside and outside character classes.
193  .P  .P
194  For example, if you want to match a * character, you write \e* in the pattern.  For example, if you want to match a * character, you write \e* in the pattern.
195  This escaping action applies whether or not the following character would  This escaping action applies whether or not the following character would
# Line 181  otherwise be interpreted as a metacharac Line 197  otherwise be interpreted as a metacharac
197  non-alphanumeric with backslash to specify that it stands for itself. In  non-alphanumeric with backslash to specify that it stands for itself. In
198  particular, if you want to match a backslash, you write \e\e.  particular, if you want to match a backslash, you write \e\e.
199  .P  .P
200    In UTF-8 mode, only ASCII numbers and letters have any special meaning after a
201    backslash. All other characters (in particular, those whose codepoints are
202    greater than 127) are treated as literals.
203    .P
204  If a pattern is compiled with the PCRE_EXTENDED option, whitespace in the  If a pattern is compiled with the PCRE_EXTENDED option, whitespace in the
205  pattern (other than in a character class) and characters between a # outside  pattern (other than in a character class) and characters between a # outside
206  a character class and the next newline are ignored. An escaping backslash can  a character class and the next newline are ignored. An escaping backslash can
# Line 200  Perl, $ and @ cause variable interpolati Line 220  Perl, $ and @ cause variable interpolati
220    \eQabc\eE\e$\eQxyz\eE   abc$xyz        abc$xyz    \eQabc\eE\e$\eQxyz\eE   abc$xyz        abc$xyz
221  .sp  .sp
222  The \eQ...\eE sequence is recognized both inside and outside character classes.  The \eQ...\eE sequence is recognized both inside and outside character classes.
223    An isolated \eE that is not preceded by \eQ is ignored. If \eQ is not followed
224    by \eE later in the pattern, the literal interpretation continues to the end of
225    the pattern (that is, \eE is assumed at the end). If the isolated \eQ is inside
226    a character class, this causes an error, because the character class is not
227    terminated.
228  .  .
229  .  .
230  .\" HTML <a name="digitsafterbackslash"></a>  .\" HTML <a name="digitsafterbackslash"></a>
# Line 213  but when a pattern is being prepared by Line 238  but when a pattern is being prepared by
238  one of the following escape sequences than the binary character it represents:  one of the following escape sequences than the binary character it represents:
239  .sp  .sp
240    \ea        alarm, that is, the BEL character (hex 07)    \ea        alarm, that is, the BEL character (hex 07)
241    \ecx       "control-x", where x is any character    \ecx       "control-x", where x is any ASCII character
242    \ee        escape (hex 1B)    \ee        escape (hex 1B)
243    \ef        formfeed (hex 0C)    \ef        formfeed (hex 0C)
244    \en        linefeed (hex 0A)    \en        linefeed (hex 0A)
# Line 225  one of the following escape sequences th Line 250  one of the following escape sequences th
250  .sp  .sp
251  The precise effect of \ecx is as follows: if x is a lower case letter, it  The precise effect of \ecx is as follows: if x is a lower case letter, it
252  is converted to upper case. Then bit 6 of the character (hex 40) is inverted.  is converted to upper case. Then bit 6 of the character (hex 40) is inverted.
253  Thus \ecz becomes hex 1A, but \ec{ becomes hex 3B, while \ec; becomes hex  Thus \ecz becomes hex 1A (z is 7A), but \ec{ becomes hex 3B ({ is 7B), while
254  7B.  \ec; becomes hex 7B (; is 3B). If the byte following \ec has a value greater
255    than 127, a compile-time error occurs. This locks out non-ASCII characters in
256    both byte mode and UTF-8 mode. (When PCRE is compiled in EBCDIC mode, all byte
257    values are valid. A lower case letter is converted to upper case, and then the
258    0xc0 bits are flipped.)
259  .P  .P
260  After \ex, from zero to two hexadecimal digits are read (letters can be in  After \ex, from zero to two hexadecimal digits are read (letters can be in
261  upper or lower case). Any number of hexadecimal digits may appear between \ex{  upper or lower case). Any number of hexadecimal digits may appear between \ex{
# Line 340  subroutine Line 369  subroutine
369  call.  call.
370  .  .
371  .  .
372    .\" HTML <a name="genericchartypes"></a>
373  .SS "Generic character types"  .SS "Generic character types"
374  .rs  .rs
375  .sp  .sp
# Line 356  Another use of backslash is for specifyi Line 386  Another use of backslash is for specifyi
386    \ew     any "word" character    \ew     any "word" character
387    \eW     any "non-word" character    \eW     any "non-word" character
388  .sp  .sp
389  There is also the single sequence \eN, which matches a non-newline character.  There is also the single sequence \eN, which matches a non-newline character.
390  This is the same as  This is the same as
391  .\" HTML <a href="#fullstopdot">  .\" HTML <a href="#fullstopdot">
392  .\" </a>  .\" </a>
393  the "." metacharacter  the "." metacharacter
394  .\"  .\"
395  when PCRE_DOTALL is not set.  when PCRE_DOTALL is not set.
396  .P  .P
397  Each pair of lower and upper case escape sequences partitions the complete set  Each pair of lower and upper case escape sequences partitions the complete set
398  of characters into two disjoint sets. Any given character matches one, and only  of characters into two disjoint sets. Any given character matches one, and only
399  one, of each pair.  one, of each pair. The sequences can appear both inside and outside character
 .P  
 These character type sequences can appear both inside and outside character  
400  classes. They each match one character of the appropriate type. If the current  classes. They each match one character of the appropriate type. If the current
401  matching point is at the end of the subject string, all of them fail, since  matching point is at the end of the subject string, all of them fail, because
402  there is no character to match.  there is no character to match.
403  .P  .P
404  For compatibility with Perl, \es does not match the VT character (code 11).  For compatibility with Perl, \es does not match the VT character (code 11).
# Line 379  are HT (9), LF (10), FF (12), CR (13), a Line 407  are HT (9), LF (10), FF (12), CR (13), a
407  included in a Perl script, \es may match the VT character. In PCRE, it never  included in a Perl script, \es may match the VT character. In PCRE, it never
408  does.  does.
409  .P  .P
410  In UTF-8 mode, characters with values greater than 128 never match \ed, \es, or  A "word" character is an underscore or any character that is a letter or digit.
411  \ew, and always match \eD, \eS, and \eW. This is true even when Unicode  By default, the definition of letters and digits is controlled by PCRE's
412  character property support is available. These sequences retain their original  low-valued character tables, and may vary if locale-specific matching is taking
413  meanings from before UTF-8 support was available, mainly for efficiency  place (see
414  reasons. Note that this also affects \eb, because it is defined in terms of \ew  .\" HTML <a href="pcreapi.html#localesupport">
415  and \eW.  .\" </a>
416  .P  "Locale support"
417  The sequences \eh, \eH, \ev, and \eV are Perl 5.10 features. In contrast to the  .\"
418  other sequences, these do match certain high-valued codepoints in UTF-8 mode.  in the
419  The horizontal space characters are:  .\" HREF
420    \fBpcreapi\fP
421    .\"
422    page). For example, in a French locale such as "fr_FR" in Unix-like systems,
423    or "french" in Windows, some character codes greater than 128 are used for
424    accented letters, and these are then matched by \ew. The use of locales with
425    Unicode is discouraged.
426    .P
427    By default, in UTF-8 mode, characters with values greater than 128 never match
428    \ed, \es, or \ew, and always match \eD, \eS, and \eW. These sequences retain
429    their original meanings from before UTF-8 support was available, mainly for
430    efficiency reasons. However, if PCRE is compiled with Unicode property support,
431    and the PCRE_UCP option is set, the behaviour is changed so that Unicode
432    properties are used to determine character types, as follows:
433    .sp
434      \ed  any character that \ep{Nd} matches (decimal digit)
435      \es  any character that \ep{Z} matches, plus HT, LF, FF, CR
436      \ew  any character that \ep{L} or \ep{N} matches, plus underscore
437    .sp
438    The upper case escapes match the inverse sets of characters. Note that \ed
439    matches only decimal digits, whereas \ew matches any Unicode digit, as well as
440    any Unicode letter, and underscore. Note also that PCRE_UCP affects \eb, and
441    \eB because they are defined in terms of \ew and \eW. Matching these sequences
442    is noticeably slower when PCRE_UCP is set.
443    .P
444    The sequences \eh, \eH, \ev, and \eV are features that were added to Perl at
445    release 5.10. In contrast to the other sequences, which match only ASCII
446    characters by default, these always match certain high-valued codepoints in
447    UTF-8 mode, whether or not PCRE_UCP is set. The horizontal space characters
448    are:
449  .sp  .sp
450    U+0009     Horizontal tab    U+0009     Horizontal tab
451    U+0020     Space    U+0020     Space
# Line 419  The vertical space characters are: Line 476  The vertical space characters are:
476    U+0085     Next line    U+0085     Next line
477    U+2028     Line separator    U+2028     Line separator
478    U+2029     Paragraph separator    U+2029     Paragraph separator
 .P  
 A "word" character is an underscore or any character less than 256 that is a  
 letter or digit. The definition of letters and digits is controlled by PCRE's  
 low-valued character tables, and may vary if locale-specific matching is taking  
 place (see  
 .\" HTML <a href="pcreapi.html#localesupport">  
 .\" </a>  
 "Locale support"  
 .\"  
 in the  
 .\" HREF  
 \fBpcreapi\fP  
 .\"  
 page). For example, in a French locale such as "fr_FR" in Unix-like systems,  
 or "french" in Windows, some character codes greater than 128 are used for  
 accented letters, and these are matched by \ew. The use of locales with Unicode  
 is discouraged.  
479  .  .
480  .  .
481  .\" HTML <a name="newlineseq"></a>  .\" HTML <a name="newlineseq"></a>
# Line 443  is discouraged. Line 483  is discouraged.
483  .rs  .rs
484  .sp  .sp
485  Outside a character class, by default, the escape sequence \eR matches any  Outside a character class, by default, the escape sequence \eR matches any
486  Unicode newline sequence. This is a Perl 5.10 feature. In non-UTF-8 mode \eR is  Unicode newline sequence. In non-UTF-8 mode \eR is equivalent to the following:
 equivalent to the following:  
487  .sp  .sp
488    (?>\er\en|\en|\ex0b|\ef|\er|\ex85)    (?>\er\en|\en|\ex0b|\ef|\er|\ex85)
489  .sp  .sp
# Line 481  These override the default and the optio Line 520  These override the default and the optio
520  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
521  pattern, and that they must be in upper case. If more than one of them is  pattern, and that they must be in upper case. If more than one of them is
522  present, the last one is used. They can be combined with a change of newline  present, the last one is used. They can be combined with a change of newline
523  convention, for example, a pattern can start with:  convention; for example, a pattern can start with:
524  .sp  .sp
525    (*ANY)(*BSR_ANYCRLF)    (*ANY)(*BSR_ANYCRLF)
526  .sp  .sp
527  Inside a character class, \eR is treated as an unrecognized escape sequence,  They can also be combined with the (*UTF8) or (*UCP) special sequences. Inside
528  and so matches the letter "R" by default, but causes an error if PCRE_EXTRA is  a character class, \eR is treated as an unrecognized escape sequence, and so
529  set.  matches the letter "R" by default, but causes an error if PCRE_EXTRA is set.
530  .  .
531  .  .
532  .\" HTML <a name="uniextseq"></a>  .\" HTML <a name="uniextseq"></a>
# Line 505  The extra escape sequences are: Line 544  The extra escape sequences are:
544    \eX       an extended Unicode sequence    \eX       an extended Unicode sequence
545  .sp  .sp
546  The property names represented by \fIxx\fP above are limited to the Unicode  The property names represented by \fIxx\fP above are limited to the Unicode
547  script names, the general category properties, and "Any", which matches any  script names, the general category properties, "Any", which matches any
548  character (including newline). Other properties such as "InMusicalSymbols" are  character (including newline), and some special PCRE properties (described
549  not currently supported by PCRE. Note that \eP{Any} does not match any  in the
550  characters, so always causes a match failure.  .\" HTML <a href="#extraprops">
551    .\" </a>
552    next section).
553    .\"
554    Other Perl properties such as "InMusicalSymbols" are not currently supported by
555    PCRE. Note that \eP{Any} does not match any characters, so always causes a
556    match failure.
557  .P  .P
558  Sets of Unicode characters are defined as belonging to certain scripts. A  Sets of Unicode characters are defined as belonging to certain scripts. A
559  character from one of these sets can be matched using a script name. For  character from one of these sets can be matched using a script name. For
# Line 613  Ugaritic, Line 658  Ugaritic,
658  Vai,  Vai,
659  Yi.  Yi.
660  .P  .P
661  Each character has exactly one general category property, specified by a  Each character has exactly one Unicode general category property, specified by
662  two-letter abbreviation. For compatibility with Perl, negation can be specified  a two-letter abbreviation. For compatibility with Perl, negation can be
663  by including a circumflex between the opening brace and the property name. For  specified by including a circumflex between the opening brace and the property
664  example, \ep{^Lu} is the same as \eP{Lu}.  name. For example, \ep{^Lu} is the same as \eP{Lu}.
665  .P  .P
666  If only one letter is specified with \ep or \eP, it includes all the general  If only one letter is specified with \ep or \eP, it includes all the general
667  category properties that start with that letter. In this case, in the absence  category properties that start with that letter. In this case, in the absence
# Line 712  Characters with the "mark" property are Line 757  Characters with the "mark" property are
757  preceding character. None of them have codepoints less than 256, so in  preceding character. None of them have codepoints less than 256, so in
758  non-UTF-8 mode \eX matches any one character.  non-UTF-8 mode \eX matches any one character.
759  .P  .P
760    Note that recent versions of Perl have changed \eX to match what Unicode calls
761    an "extended grapheme cluster", which has a more complicated definition.
762    .P
763  Matching characters by Unicode property is not fast, because PCRE has to search  Matching characters by Unicode property is not fast, because PCRE has to search
764  a structure that contains data for over fifteen thousand characters. That is  a structure that contains data for over fifteen thousand characters. That is
765  why the traditional escape sequences such as \ed and \ew do not use Unicode  why the traditional escape sequences such as \ed and \ew do not use Unicode
766  properties in PCRE.  properties in PCRE by default, though you can make them do so by setting the
767    PCRE_UCP option for \fBpcre_compile()\fP or by starting the pattern with
768    (*UCP).
769    .
770    .
771    .\" HTML <a name="extraprops"></a>
772    .SS PCRE's additional properties
773    .rs
774    .sp
775    As well as the standard Unicode properties described in the previous
776    section, PCRE supports four more that make it possible to convert traditional
777    escape sequences such as \ew and \es and POSIX character classes to use Unicode
778    properties. PCRE uses these non-standard, non-Perl properties internally when
779    PCRE_UCP is set. They are:
780    .sp
781      Xan   Any alphanumeric character
782      Xps   Any POSIX space character
783      Xsp   Any Perl space character
784      Xwd   Any Perl "word" character
785    .sp
786    Xan matches characters that have either the L (letter) or the N (number)
787    property. Xps matches the characters tab, linefeed, vertical tab, formfeed, or
788    carriage return, and any other character that has the Z (separator) property.
789    Xsp is the same as Xps, except that vertical tab is excluded. Xwd matches the
790    same characters as Xan, plus underscore.
791  .  .
792  .  .
793  .\" HTML <a name="resetmatchstart"></a>  .\" HTML <a name="resetmatchstart"></a>
794  .SS "Resetting the match start"  .SS "Resetting the match start"
795  .rs  .rs
796  .sp  .sp
797  The escape sequence \eK, which is a Perl 5.10 feature, causes any previously  The escape sequence \eK causes any previously matched characters not to be
798  matched characters not to be included in the final matched sequence. For  included in the final matched sequence. For example, the pattern:
 example, the pattern:  
799  .sp  .sp
800    foo\eKbar    foo\eKbar
801  .sp  .sp
# Line 775  The backslashed assertions are: Line 846  The backslashed assertions are:
846    \eG     matches at the first matching position in the subject    \eG     matches at the first matching position in the subject
847  .sp  .sp
848  Inside a character class, \eb has a different meaning; it matches the backspace  Inside a character class, \eb has a different meaning; it matches the backspace
849  character. If any other of these assertions appears in a character class, by  character. If any other of these assertions appears in a character class, by
850  default it matches the corresponding literal character (for example, \eB  default it matches the corresponding literal character (for example, \eB
851  matches the letter B). However, if the PCRE_EXTRA option is set, an "invalid  matches the letter B). However, if the PCRE_EXTRA option is set, an "invalid
852  escape sequence" error is generated instead.  escape sequence" error is generated instead.
# Line 783  escape sequence" error is generated inst Line 854  escape sequence" error is generated inst
854  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
855  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
856  \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
857  first or last character matches \ew, respectively. Neither PCRE nor Perl has a  first or last character matches \ew, respectively. In UTF-8 mode, the meanings
858  separte "start of word" or "end of word" metasequence. However, whatever  of \ew and \eW can be changed by setting the PCRE_UCP option. When this is
859  follows \eb normally determines which it is. For example, the fragment  done, it also affects \eb and \eB. Neither PCRE nor Perl has a separate "start
860  \eba matches "a" at the start of a word.  of word" or "end of word" metasequence. However, whatever follows \eb normally
861    determines which it is. For example, the fragment \eba matches "a" at the start
862    of a word.
863  .P  .P
864  The \eA, \eZ, and \ez assertions differ from the traditional circumflex and  The \eA, \eZ, and \ez assertions differ from the traditional circumflex and
865  dollar (described in the next section) in that they only ever match at the very  dollar (described in the next section) in that they only ever match at the very
# Line 894  The handling of dot is entirely independ Line 967  The handling of dot is entirely independ
967  dollar, the only relationship being that they both involve newlines. Dot has no  dollar, the only relationship being that they both involve newlines. Dot has no
968  special meaning in a character class.  special meaning in a character class.
969  .P  .P
970  The escape sequence \eN always behaves as a dot does when PCRE_DOTALL is not  The escape sequence \eN behaves like a dot, except that it is not affected by
971  set. In other words, it matches any one character except one that signifies the  the PCRE_DOTALL option. In other words, it matches any character except one
972  end of a line.  that signifies the end of a line.
973  .  .
974  .  .
975  .SH "MATCHING A SINGLE BYTE"  .SH "MATCHING A SINGLE BYTE"
# Line 905  end of a line. Line 978  end of a line.
978  Outside a character class, the escape sequence \eC matches any one byte, both  Outside a character class, the escape sequence \eC matches any one byte, both
979  in and out of UTF-8 mode. Unlike a dot, it always matches any line-ending  in and out of UTF-8 mode. Unlike a dot, it always matches any line-ending
980  characters. The feature is provided in Perl in order to match individual bytes  characters. The feature is provided in Perl in order to match individual bytes
981  in UTF-8 mode. Because it breaks up UTF-8 characters into individual bytes,  in UTF-8 mode. Because it breaks up UTF-8 characters into individual bytes, the
982  what remains in the string may be a malformed UTF-8 string. For this reason,  rest of the string may start with a malformed UTF-8 character. For this reason,
983  the \eC escape sequence is best avoided.  the \eC escape sequence is best avoided.
984  .P  .P
985  PCRE does not allow \eC to appear in lookbehind assertions  PCRE does not allow \eC to appear in lookbehind assertions
# Line 991  characters in both cases. In UTF-8 mode, Line 1064  characters in both cases. In UTF-8 mode,
1064  characters with values greater than 128 only when it is compiled with Unicode  characters with values greater than 128 only when it is compiled with Unicode
1065  property support.  property support.
1066  .P  .P
1067  The character types \ed, \eD, \ep, \eP, \es, \eS, \ew, and \eW may also appear  The character escape sequences \ed, \eD, \eh, \eH, \ep, \eP, \es, \eS, \ev,
1068  in a character class, and add the characters that they match to the class. For  \eV, \ew, and \eW may appear in a character class, and add the characters that
1069  example, [\edABCDEF] matches any hexadecimal digit. A circumflex can  they match to the class. For example, [\edABCDEF] matches any hexadecimal
1070  conveniently be used with the upper case character types to specify a more  digit. In UTF-8 mode, the PCRE_UCP option affects the meanings of \ed, \es, \ew
1071  restricted set of characters than the matching lower case type. For example,  and their upper case partners, just as it does when they appear outside a
1072  the class [^\eW_] matches any letter or digit, but not underscore.  character class, as described in the section entitled
1073    .\" HTML <a href="#genericchartypes">
1074    .\" </a>
1075    "Generic character types"
1076    .\"
1077    above. The escape sequence \eb has a different meaning inside a character
1078    class; it matches the backspace character. The sequences \eB, \eN, \eR, and \eX
1079    are not special inside a character class. Like any other unrecognized escape
1080    sequences, they are treated as the literal characters "B", "N", "R", and "X" by
1081    default, but cause an error if the PCRE_EXTRA option is set.
1082    .P
1083    A circumflex can conveniently be used with the upper case character types to
1084    specify a more restricted set of characters than the matching lower case type.
1085    For example, the class [^\eW_] matches any letter or digit, but not underscore,
1086    whereas [\ew] includes underscore. A positive character class should be read as
1087    "something OR something OR ..." and a negative class as "NOT something AND NOT
1088    something AND NOT ...".
1089  .P  .P
1090  The only metacharacters that are recognized in character classes are backslash,  The only metacharacters that are recognized in character classes are backslash,
1091  hyphen (only where it can be interpreted as specifying a range), circumflex  hyphen (only where it can be interpreted as specifying a range), circumflex
# Line 1016  this notation. For example, Line 1105  this notation. For example,
1105    [01[:alpha:]%]    [01[:alpha:]%]
1106  .sp  .sp
1107  matches "0", "1", any alphabetic character, or "%". The supported class names  matches "0", "1", any alphabetic character, or "%". The supported class names
1108  are  are:
1109  .sp  .sp
1110    alnum    letters and digits    alnum    letters and digits
1111    alpha    letters    alpha    letters
# Line 1027  are Line 1116  are
1116    graph    printing characters, excluding space    graph    printing characters, excluding space
1117    lower    lower case letters    lower    lower case letters
1118    print    printing characters, including space    print    printing characters, including space
1119    punct    printing characters, excluding letters and digits    punct    printing characters, excluding letters and digits and space
1120    space    white space (not quite the same as \es)    space    white space (not quite the same as \es)
1121    upper    upper case letters    upper    upper case letters
1122    word     "word" characters (same as \ew)    word     "word" characters (same as \ew)
# Line 1048  matches "1", "2", or any non-digit. PCRE Line 1137  matches "1", "2", or any non-digit. PCRE
1137  syntax [.ch.] and [=ch=] where "ch" is a "collating element", but these are not  syntax [.ch.] and [=ch=] where "ch" is a "collating element", but these are not
1138  supported, and an error is given if they are encountered.  supported, and an error is given if they are encountered.
1139  .P  .P
1140  In UTF-8 mode, characters with values greater than 128 do not match any of  By default, in UTF-8 mode, characters with values greater than 128 do not match
1141  the POSIX character classes.  any of the POSIX character classes. However, if the PCRE_UCP option is passed
1142    to \fBpcre_compile()\fP, some of the classes are changed so that Unicode
1143    character properties are used. This is achieved by replacing the POSIX classes
1144    by other sequences, as follows:
1145    .sp
1146      [:alnum:]  becomes  \ep{Xan}
1147      [:alpha:]  becomes  \ep{L}
1148      [:blank:]  becomes  \eh
1149      [:digit:]  becomes  \ep{Nd}
1150      [:lower:]  becomes  \ep{Ll}
1151      [:space:]  becomes  \ep{Xps}
1152      [:upper:]  becomes  \ep{Lu}
1153      [:word:]   becomes  \ep{Xwd}
1154    .sp
1155    Negated versions, such as [:^alpha:] use \eP instead of \ep. The other POSIX
1156    classes are unchanged, and match only characters with code points less than
1157    128.
1158  .  .
1159  .  .
1160  .SH "VERTICAL BAR"  .SH "VERTICAL BAR"
# Line 1103  extracts it into the global options (and Line 1208  extracts it into the global options (and
1208  extracted by the \fBpcre_fullinfo()\fP function).  extracted by the \fBpcre_fullinfo()\fP function).
1209  .P  .P
1210  An option change within a subpattern (see below for a description of  An option change within a subpattern (see below for a description of
1211  subpatterns) affects only that part of the current pattern that follows it, so  subpatterns) affects only that part of the subpattern that follows it, so
1212  .sp  .sp
1213    (a(?i)b)c    (a(?i)b)c
1214  .sp  .sp
# Line 1128  section entitled Line 1233  section entitled
1233  .\" </a>  .\" </a>
1234  "Newline sequences"  "Newline sequences"
1235  .\"  .\"
1236  above. There is also the (*UTF8) leading sequence that can be used to set UTF-8  above. There are also the (*UTF8) and (*UCP) leading sequences that can be used
1237  mode; this is equivalent to setting the PCRE_UTF8 option.  to set UTF-8 and Unicode property modes; they are equivalent to setting the
1238    PCRE_UTF8 and the PCRE_UCP options, respectively.
1239  .  .
1240  .  .
1241  .\" HTML <a name="subpattern"></a>  .\" HTML <a name="subpattern"></a>
# Line 1143  Turning part of a pattern into a subpatt Line 1249  Turning part of a pattern into a subpatt
1249  .sp  .sp
1250    cat(aract|erpillar|)    cat(aract|erpillar|)
1251  .sp  .sp
1252  matches one of the words "cat", "cataract", or "caterpillar". Without the  matches "cataract", "caterpillar", or "cat". Without the parentheses, it would
1253  parentheses, it would match "cataract", "erpillar" or an empty string.  match "cataract", "erpillar" or an empty string.
1254  .sp  .sp
1255  2. It sets up the subpattern as a capturing subpattern. This means that, when  2. It sets up the subpattern as a capturing subpattern. This means that, when
1256  the whole pattern matches, that portion of the subject string that matched the  the whole pattern matches, that portion of the subject string that matched the
1257  subpattern is passed back to the caller via the \fIovector\fP argument of  subpattern is passed back to the caller via the \fIovector\fP argument of
1258  \fBpcre_exec()\fP. Opening parentheses are counted from left to right (starting  \fBpcre_exec()\fP. Opening parentheses are counted from left to right (starting
1259  from 1) to obtain numbers for the capturing subpatterns.  from 1) to obtain numbers for the capturing subpatterns. For example, if the
1260  .P  string "the red king" is matched against the pattern
 For example, if the string "the red king" is matched against the pattern  
1261  .sp  .sp
1262    the ((red|white) (king|queen))    the ((red|white) (king|queen))
1263  .sp  .sp
# Line 1201  at captured substring number one, whiche Line 1306  at captured substring number one, whiche
1306  is useful when you want to capture part, but not all, of one of a number of  is useful when you want to capture part, but not all, of one of a number of
1307  alternatives. Inside a (?| group, parentheses are numbered as usual, but the  alternatives. Inside a (?| group, parentheses are numbered as usual, but the
1308  number is reset at the start of each branch. The numbers of any capturing  number is reset at the start of each branch. The numbers of any capturing
1309  buffers that follow the subpattern start after the highest number used in any  parentheses that follow the subpattern start after the highest number used in
1310  branch. The following example is taken from the Perl documentation.  any branch. The following example is taken from the Perl documentation. The
1311  The numbers underneath show in which buffer the captured content will be  numbers underneath show in which buffer the captured content will be stored.
 stored.  
1312  .sp  .sp
1313    # before  ---------------branch-reset----------- after    # before  ---------------branch-reset----------- after
1314    / ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x    / ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x
# Line 1331  items: Line 1435  items:
1435    the \eC escape sequence    the \eC escape sequence
1436    the \eX escape sequence (in UTF-8 mode with Unicode properties)    the \eX escape sequence (in UTF-8 mode with Unicode properties)
1437    the \eR escape sequence    the \eR escape sequence
1438    an escape such as \ed that matches a single character    an escape such as \ed or \epL that matches a single character
1439    a character class    a character class
1440    a back reference (see next section)    a back reference (see next section)
1441    a parenthesized subpattern (unless it is an assertion)    a parenthesized subpattern (unless it is an assertion)
# Line 1373  subpatterns that are referenced as Line 1477  subpatterns that are referenced as
1477  .\" </a>  .\" </a>
1478  subroutines  subroutines
1479  .\"  .\"
1480  from elsewhere in the pattern. Items other than subpatterns that have a {0}  from elsewhere in the pattern (but see also the section entitled
1481  quantifier are omitted from the compiled pattern.  .\" HTML <a href="#subdefine">
1482    .\" </a>
1483    "Defining subpatterns for use by reference only"
1484    .\"
1485    below). Items other than subpatterns that have a {0} quantifier are omitted
1486    from the compiled pattern.
1487  .P  .P
1488  For convenience, the three most common quantifiers have single-character  For convenience, the three most common quantifiers have single-character
1489  abbreviations:  abbreviations:
# Line 1599  no such problem when named parentheses a Line 1708  no such problem when named parentheses a
1708  subpattern is possible using named parentheses (see below).  subpattern is possible using named parentheses (see below).
1709  .P  .P
1710  Another way of avoiding the ambiguity inherent in the use of digits following a  Another way of avoiding the ambiguity inherent in the use of digits following a
1711  backslash is to use the \eg escape sequence, which is a feature introduced in  backslash is to use the \eg escape sequence. This escape must be followed by an
1712  Perl 5.10. This escape must be followed by an unsigned number or a negative  unsigned number or a negative number, optionally enclosed in braces. These
1713  number, optionally enclosed in braces. These examples are all identical:  examples are all identical:
1714  .sp  .sp
1715    (ring), \e1    (ring), \e1
1716    (ring), \eg1    (ring), \eg1
# Line 1615  example: Line 1724  example:
1724    (abc(def)ghi)\eg{-1}    (abc(def)ghi)\eg{-1}
1725  .sp  .sp
1726  The sequence \eg{-1} is a reference to the most recently started capturing  The sequence \eg{-1} is a reference to the most recently started capturing
1727  subpattern before \eg, that is, is it equivalent to \e2. Similarly, \eg{-2}  subpattern before \eg, that is, is it equivalent to \e2 in this example.
1728  would be equivalent to \e1. The use of relative references can be helpful in  Similarly, \eg{-2} would be equivalent to \e1. The use of relative references
1729  long patterns, and also in patterns that are created by joining together  can be helpful in long patterns, and also in patterns that are created by
1730  fragments that contain references within themselves.  joining together fragments that contain references within themselves.
1731  .P  .P
1732  A back reference matches whatever actually matched the capturing subpattern in  A back reference matches whatever actually matched the capturing subpattern in
1733  the current subject string, rather than anything matching the subpattern  the current subject string, rather than anything matching the subpattern
# Line 1754  lookbehind assertion is needed to achiev Line 1863  lookbehind assertion is needed to achiev
1863  If you want to force a matching failure at some point in a pattern, the most  If you want to force a matching failure at some point in a pattern, the most
1864  convenient way to do it is with (?!) because an empty string always matches, so  convenient way to do it is with (?!) because an empty string always matches, so
1865  an assertion that requires there not to be an empty string must always fail.  an assertion that requires there not to be an empty string must always fail.
1866  The Perl 5.10 backtracking control verb (*FAIL) or (*F) is essentially a  The backtracking control verb (*FAIL) or (*F) is a synonym for (?!).
 synonym for (?!).  
1867  .  .
1868  .  .
1869  .\" HTML <a name="lookbehind"></a>  .\" HTML <a name="lookbehind"></a>
# Line 1780  is permitted, but Line 1888  is permitted, but
1888  .sp  .sp
1889  causes an error at compile time. Branches that match different length strings  causes an error at compile time. Branches that match different length strings
1890  are permitted only at the top level of a lookbehind assertion. This is an  are permitted only at the top level of a lookbehind assertion. This is an
1891  extension compared with Perl (5.8 and 5.10), which requires all branches to  extension compared with Perl, which requires all branches to match the same
1892  match the same length of string. An assertion such as  length of string. An assertion such as
1893  .sp  .sp
1894    (?<=ab(c|de))    (?<=ab(c|de))
1895  .sp  .sp
# Line 1791  branches: Line 1899  branches:
1899  .sp  .sp
1900    (?<=abc|abde)    (?<=abc|abde)
1901  .sp  .sp
1902  In some cases, the Perl 5.10 escape sequence \eK  In some cases, the escape sequence \eK
1903  .\" HTML <a href="#resetmatchstart">  .\" HTML <a href="#resetmatchstart">
1904  .\" </a>  .\" </a>
1905  (see above)  (see above)
# Line 1895  already been matched. The two possible f Line 2003  already been matched. The two possible f
2003  .sp  .sp
2004  If the condition is satisfied, the yes-pattern is used; otherwise the  If the condition is satisfied, the yes-pattern is used; otherwise the
2005  no-pattern (if present) is used. If there are more than two alternatives in the  no-pattern (if present) is used. If there are more than two alternatives in the
2006  subpattern, a compile-time error occurs.  subpattern, a compile-time error occurs. Each of the two alternatives may
2007    itself contain nested subpatterns of any form, including conditional
2008    subpatterns; the restriction to two alternatives applies only at the level of
2009    the condition. This pattern fragment is an example where the alternatives are
2010    complex:
2011    .sp
2012      (?(1) (A|B|C) | (D | (?(2)E|F) | E) )
2013    .sp
2014  .P  .P
2015  There are four kinds of condition: references to subpatterns, references to  There are four kinds of condition: references to subpatterns, references to
2016  recursion, a pseudo-condition called DEFINE, and assertions.  recursion, a pseudo-condition called DEFINE, and assertions.
# Line 1912  matched. If there is more than one captu Line 2027  matched. If there is more than one captu
2027  .\" </a>  .\" </a>
2028  section about duplicate subpattern numbers),  section about duplicate subpattern numbers),
2029  .\"  .\"
2030  the condition is true if any of them have been set. An alternative notation is  the condition is true if any of them have matched. An alternative notation is
2031  to precede the digits with a plus or minus sign. In this case, the subpattern  to precede the digits with a plus or minus sign. In this case, the subpattern
2032  number is relative rather than absolute. The most recently opened parentheses  number is relative rather than absolute. The most recently opened parentheses
2033  can be referenced by (?(-1), the next most recent by (?(-2), and so on. In  can be referenced by (?(-1), the next most recent by (?(-2), and so on. Inside
2034  looping constructs it can also make sense to refer to subsequent groups with  loops it can also make sense to refer to subsequent groups. The next
2035  constructs such as (?(+2).  parentheses to be opened can be referenced as (?(+1), and so on. (The value
2036    zero in any of these forms is not used; it provokes a compile-time error.)
2037  .P  .P
2038  Consider the following pattern, which contains non-significant white space to  Consider the following pattern, which contains non-significant white space to
2039  make it more readable (assume the PCRE_EXTENDED option) and to divide it into  make it more readable (assume the PCRE_EXTENDED option) and to divide it into
# Line 1928  three parts for ease of discussion: Line 2044  three parts for ease of discussion:
2044  The first part matches an optional opening parenthesis, and if that  The first part matches an optional opening parenthesis, and if that
2045  character is present, sets it as the first captured substring. The second part  character is present, sets it as the first captured substring. The second part
2046  matches one or more characters that are not parentheses. The third part is a  matches one or more characters that are not parentheses. The third part is a
2047  conditional subpattern that tests whether the first set of parentheses matched  conditional subpattern that tests whether or not the first set of parentheses
2048  or not. If they did, that is, if subject started with an opening parenthesis,  matched. If they did, that is, if subject started with an opening parenthesis,
2049  the condition is true, and so the yes-pattern is executed and a closing  the condition is true, and so the yes-pattern is executed and a closing
2050  parenthesis is required. Otherwise, since no-pattern is not present, the  parenthesis is required. Otherwise, since no-pattern is not present, the
2051  subpattern matches nothing. In other words, this pattern matches a sequence of  subpattern matches nothing. In other words, this pattern matches a sequence of
# Line 1985  The syntax for recursive patterns Line 2101  The syntax for recursive patterns
2101  .\"  .\"
2102  is described below.  is described below.
2103  .  .
2104    .\" HTML <a name="subdefine"></a>
2105  .SS "Defining subpatterns for use by reference only"  .SS "Defining subpatterns for use by reference only"
2106  .rs  .rs
2107  .sp  .sp
# Line 1997  point in the pattern; the idea of DEFINE Line 2114  point in the pattern; the idea of DEFINE
2114  .\" </a>  .\" </a>
2115  "subroutines"  "subroutines"
2116  .\"  .\"
2117  is described below.) For example, a pattern to match an IPv4 address could be  is described below.) For example, a pattern to match an IPv4 address such as
2118  written like this (ignore whitespace and line breaks):  "192.168.23.245" could be written like this (ignore whitespace and line
2119    breaks):
2120  .sp  .sp
2121    (?(DEFINE) (?<byte> 2[0-4]\ed | 25[0-5] | 1\ed\ed | [1-9]?\ed) )    (?(DEFINE) (?<byte> 2[0-4]\ed | 25[0-5] | 1\ed\ed | [1-9]?\ed) )
2122    \eb (?&byte) (\e.(?&byte)){3} \eb    \eb (?&byte) (\e.(?&byte)){3} \eb
# Line 2033  dd-aaa-dd or dd-dd-dd, where aaa are let Line 2151  dd-aaa-dd or dd-dd-dd, where aaa are let
2151  .SH COMMENTS  .SH COMMENTS
2152  .rs  .rs
2153  .sp  .sp
2154  The sequence (?# marks the start of a comment that continues up to the next  There are two ways of including comments in patterns that are processed by
2155  closing parenthesis. Nested parentheses are not permitted. The characters  PCRE. In both cases, the start of the comment must not be in a character class,
2156  that make up a comment play no part in the pattern matching at all.  nor in the middle of any other sequence of related characters such as (?: or a
2157    subpattern name or number. The characters that make up a comment play no part
2158    in the pattern matching.
2159  .P  .P
2160  If the PCRE_EXTENDED option is set, an unescaped # character outside a  The sequence (?# marks the start of a comment that continues up to the next
2161  character class introduces a comment that continues to immediately after the  closing parenthesis. Nested parentheses are not permitted. If the PCRE_EXTENDED
2162  next newline in the pattern.  option is set, an unescaped # character also introduces a comment, which in
2163    this case continues to immediately after the next newline character or
2164    character sequence in the pattern. Which characters are interpreted as newlines
2165    is controlled by the options passed to \fBpcre_compile()\fP or by a special
2166    sequence at the start of the pattern, as described in the section entitled
2167    .\" HTML <a href="#newlines">
2168    .\" </a>
2169    "Newline conventions"
2170    .\"
2171    above. Note that the end of this type of comment is a literal newline sequence
2172    in the pattern; escape sequences that happen to represent a newline do not
2173    count. For example, consider this pattern when PCRE_EXTENDED is set, and the
2174    default newline convention is in force:
2175    .sp
2176      abc #comment \en still comment
2177    .sp
2178    On encountering the # character, \fBpcre_compile()\fP skips along, looking for
2179    a newline in the pattern. The sequence \en is still literal at this stage, so
2180    it does not terminate the comment. Only an actual character with the code value
2181    0x0a (the default newline) does so.
2182  .  .
2183  .  .
2184  .\" HTML <a name="recursion"></a>  .\" HTML <a name="recursion"></a>
# Line 2097  We have put the pattern into parentheses Line 2236  We have put the pattern into parentheses
2236  them instead of the whole pattern.  them instead of the whole pattern.
2237  .P  .P
2238  In a larger pattern, keeping track of parenthesis numbers can be tricky. This  In a larger pattern, keeping track of parenthesis numbers can be tricky. This
2239  is made easier by the use of relative references (a Perl 5.10 feature).  is made easier by the use of relative references. Instead of (?1) in the
2240  Instead of (?1) in the pattern above you can write (?-2) to refer to the second  pattern above you can write (?-2) to refer to the second most recently opened
2241  most recently opened parentheses preceding the recursion. In other words, a  parentheses preceding the recursion. In other words, a negative number counts
2242  negative number counts capturing parentheses leftwards from the point at which  capturing parentheses leftwards from the point at which it is encountered.
 it is encountered.  
2243  .P  .P
2244  It is also possible to refer to subsequently opened parentheses, by writing  It is also possible to refer to subsequently opened parentheses, by writing
2245  references such as (?+2). However, these cannot be recursive because the  references such as (?+2). However, these cannot be recursive because the
# Line 2204  time we do have another alternative to t Line 2342  time we do have another alternative to t
2342  difference: in the previous case the remaining alternative is at a deeper  difference: in the previous case the remaining alternative is at a deeper
2343  recursion level, which PCRE cannot use.  recursion level, which PCRE cannot use.
2344  .P  .P
2345  To change the pattern so that matches all palindromic strings, not just those  To change the pattern so that it matches all palindromic strings, not just
2346  with an odd number of characters, it is tempting to change the pattern to this:  those with an odd number of characters, it is tempting to change the pattern to
2347    this:
2348  .sp  .sp
2349    ^((.)(?1)\e2|.?)$    ^((.)(?1)\e2|.?)$
2350  .sp  .sp
# Line 2353  failing negative assertion, they cause a Line 2492  failing negative assertion, they cause a
2492  .P  .P
2493  If any of these verbs are used in an assertion or subroutine subpattern  If any of these verbs are used in an assertion or subroutine subpattern
2494  (including recursive subpatterns), their effect is confined to that subpattern;  (including recursive subpatterns), their effect is confined to that subpattern;
2495  it does not extend to the surrounding pattern. Note that such subpatterns are  it does not extend to the surrounding pattern, with one exception: a *MARK that
2496  processed as anchored at the point where they are tested.  is encountered in a positive assertion \fIis\fP passed back (compare capturing
2497    parentheses in assertions). Note that such subpatterns are processed as
2498    anchored at the point where they are tested.
2499  .P  .P
2500  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
2501  parenthesis followed by an asterisk. They are generally of the form  parenthesis followed by an asterisk. They are generally of the form
# Line 2370  minimum length of matching subject, or t Line 2511  minimum length of matching subject, or t
2511  present. When one of these optimizations suppresses the running of a match, any  present. When one of these optimizations suppresses the running of a match, any
2512  included backtracking verbs will not, of course, be processed. You can suppress  included backtracking verbs will not, of course, be processed. You can suppress
2513  the start-of-match optimizations by setting the PCRE_NO_START_OPTIMIZE option  the start-of-match optimizations by setting the PCRE_NO_START_OPTIMIZE option
2514  when calling \fBpcre_exec()\fP.  when calling \fBpcre_compile()\fP or \fBpcre_exec()\fP, or by starting the
2515    pattern with (*NO_START_OPT).
2516  .  .
2517  .  .
2518  .SS "Verbs that act immediately"  .SS "Verbs that act immediately"
# Line 2444  indicates which of the two alternatives Line 2586  indicates which of the two alternatives
2586  of obtaining this information than putting each alternative in its own  of obtaining this information than putting each alternative in its own
2587  capturing parentheses.  capturing parentheses.
2588  .P  .P
2589    If (*MARK) is encountered in a positive assertion, its name is recorded and
2590    passed back if it is the last-encountered. This does not happen for negative
2591    assetions.
2592    .P
2593  A name may also be returned after a failed match if the final path through the  A name may also be returned after a failed match if the final path through the
2594  pattern involves (*MARK). However, unless (*MARK) used in conjunction with  pattern involves (*MARK). However, unless (*MARK) used in conjunction with
2595  (*COMMIT), this is unlikely to happen for an unanchored pattern because, as the  (*COMMIT), this is unlikely to happen for an unanchored pattern because, as the
# Line 2561  matching name is found, normal "bumpalon Line 2707  matching name is found, normal "bumpalon
2707  .sp  .sp
2708    (*THEN) or (*THEN:NAME)    (*THEN) or (*THEN:NAME)
2709  .sp  .sp
2710  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 in the innermost enclosing
2711  not match. That is, it cancels pending backtracking, but only within the  group if the rest of the pattern does not match. That is, it cancels pending
2712  current alternation. Its name comes from the observation that it can be used  backtracking, but only within the current alternation. Its name comes from the
2713  for a pattern-based if-then-else block:  observation that it can be used for a pattern-based if-then-else block:
2714  .sp  .sp
2715    ( COND1 (*THEN) FOO | COND2 (*THEN) BAR | COND3 (*THEN) BAZ ) ...    ( COND1 (*THEN) FOO | COND2 (*THEN) BAR | COND3 (*THEN) BAZ ) ...
2716  .sp  .sp
# Line 2575  behaviour of (*THEN:NAME) is exactly the Line 2721  behaviour of (*THEN:NAME) is exactly the
2721  overall match fails. If (*THEN) is not directly inside an alternation, it acts  overall match fails. If (*THEN) is not directly inside an alternation, it acts
2722  like (*PRUNE).  like (*PRUNE).
2723  .  .
2724    .P
2725    The above verbs provide four different "strengths" of control when subsequent
2726    matching fails. (*THEN) is the weakest, carrying on the match at the next
2727    alternation. (*PRUNE) comes next, failing the match at the current starting
2728    position, but allowing an advance to the next character (for an unanchored
2729    pattern). (*SKIP) is similar, except that the advance may be more than one
2730    character. (*COMMIT) is the strongest, causing the entire match to fail.
2731    .P
2732    If more than one is present in a pattern, the "stongest" one wins. For example,
2733    consider this pattern, where A, B, etc. are complex pattern fragments:
2734    .sp
2735      (A(*COMMIT)B(*THEN)C|D)
2736    .sp
2737    Once A has matched, PCRE is committed to this match, at the current starting
2738    position. If subsequently B matches, but C does not, the normal (*THEN) action
2739    of trying the next alternation (that is, D) does not happen because (*COMMIT)
2740    overrides.
2741    .
2742  .  .
2743  .SH "SEE ALSO"  .SH "SEE ALSO"
2744  .rs  .rs
# Line 2597  Cambridge CB2 3QH, England. Line 2761  Cambridge CB2 3QH, England.
2761  .rs  .rs
2762  .sp  .sp
2763  .nf  .nf
2764  Last updated: 03 May 2010  Last updated: 22 July 2011
2765  Copyright (c) 1997-2010 University of Cambridge.  Copyright (c) 1997-2011 University of Cambridge.
2766  .fi  .fi

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