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1  .TH PCREPATTERN 3  .TH PCREPATTERN 3 "14 April 2012" "PCRE 8.31"
2  .SH NAME  .SH NAME
3  PCRE - Perl-compatible regular expressions  PCRE - Perl-compatible regular expressions
4  .SH "PCRE REGULAR EXPRESSION DETAILS"  .SH "PCRE REGULAR EXPRESSION DETAILS"
# 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 strings in the original library, and a
25  PCRE must be built to include UTF-8 support, and you must call  second library that supports 16-bit and UTF-16 character strings. To use these
26  \fBpcre_compile()\fP or \fBpcre_compile2()\fP with the PCRE_UTF8 option. There  features, PCRE must be built to include appropriate support. When using UTF
27  is also a special sequence that can be given at the start of a pattern:  strings you must either call the compiling function with the PCRE_UTF8 or
28    PCRE_UTF16 option, or the pattern must start with one of these special
29    sequences:
30  .sp  .sp
31    (*UTF8)    (*UTF8)
32      (*UTF16)
33  .sp  .sp
34  Starting a pattern with this sequence is equivalent to setting the PCRE_UTF8  Starting a pattern with such a sequence is equivalent to setting the relevant
35  option. This feature is not Perl-compatible. How setting UTF-8 mode affects  option. This feature is not Perl-compatible. How setting a UTF mode affects
36  pattern matching is mentioned in several places below. There is also a summary  pattern matching is mentioned in several places below. There is also a summary
37  of UTF-8 features in the  of features in the
38  .\" HREF  .\" HREF
39  \fBpcreunicode\fP  \fBpcreunicode\fP
40  .\"  .\"
41  page.  page.
42  .P  .P
43  Another special sequence that may appear at the start of a pattern or in  Another special sequence that may appear at the start of a pattern or in
44  combination with (*UTF8) is:  combination with (*UTF8) or (*UTF16) is:
45  .sp  .sp
46    (*UCP)    (*UCP)
47  .sp  .sp
# Line 53  also some more of these special sequence Line 56  also some more of these special sequence
56  of newlines; they are described below.  of newlines; they are described below.
57  .P  .P
58  The remainder of this document discusses the patterns that are supported by  The remainder of this document discusses the patterns that are supported by
59  PCRE when its main matching function, \fBpcre_exec()\fP, is used.  PCRE when one its main matching functions, \fBpcre_exec()\fP (8-bit) or
60  From release 6.0, PCRE offers a second matching function,  \fBpcre16_exec()\fP (16-bit), is used. PCRE also has alternative matching
61  \fBpcre_dfa_exec()\fP, which matches using a different algorithm that is not  functions, \fBpcre_dfa_exec()\fP and \fBpcre16_dfa_exec()\fP, which match using
62  Perl-compatible. Some of the features discussed below are not available when  a different algorithm that is not Perl-compatible. Some of the features
63  \fBpcre_dfa_exec()\fP is used. The advantages and disadvantages of the  discussed below are not available when DFA matching is used. The advantages and
64  alternative function, and how it differs from the normal function, are  disadvantages of the alternative functions, and how they differ from the normal
65  discussed in the  functions, are discussed in the
66  .\" HREF  .\" HREF
67  \fBpcrematching\fP  \fBpcrematching\fP
68  .\"  .\"
# Line 94  string with one of the following five se Line 97  string with one of the following five se
97    (*ANYCRLF)   any of the three above    (*ANYCRLF)   any of the three above
98    (*ANY)       all Unicode newline sequences    (*ANY)       all Unicode newline sequences
99  .sp  .sp
100  These override the default and the options given to \fBpcre_compile()\fP or  These override the default and the options given to the compiling function. For
101  \fBpcre_compile2()\fP. For example, on a Unix system where LF is the default  example, on a Unix system where LF is the default newline sequence, the pattern
 newline sequence, the pattern  
102  .sp  .sp
103    (*CR)a.b    (*CR)a.b
104  .sp  .sp
# Line 130  corresponding characters in the subject. Line 132  corresponding characters in the subject.
132  .sp  .sp
133  matches a portion of a subject string that is identical to itself. When  matches a portion of a subject string that is identical to itself. When
134  caseless matching is specified (the PCRE_CASELESS option), letters are matched  caseless matching is specified (the PCRE_CASELESS option), letters are matched
135  independently of case. In UTF-8 mode, PCRE always understands the concept of  independently of case. In a UTF mode, PCRE always understands the concept of
136  case for characters whose values are less than 128, so caseless matching is  case for characters whose values are less than 128, so caseless matching is
137  always possible. For characters with higher values, the concept of case is  always possible. For characters with higher values, the concept of case is
138  supported if PCRE is compiled with Unicode property support, but not otherwise.  supported if PCRE is compiled with Unicode property support, but not otherwise.
139  If you want to use caseless matching for characters 128 and above, you must  If you want to use caseless matching for characters 128 and above, you must
140  ensure that PCRE is compiled with Unicode property support as well as with  ensure that PCRE is compiled with Unicode property support as well as with
141  UTF-8 support.  UTF support.
142  .P  .P
143  The power of regular expressions comes from the ability to include alternatives  The power of regular expressions comes from the ability to include alternatives
144  and repetitions in the pattern. These are encoded in the pattern by the use of  and repetitions in the pattern. These are encoded in the pattern by the use of
# Line 192  otherwise be interpreted as a metacharac Line 194  otherwise be interpreted as a metacharac
194  non-alphanumeric with backslash to specify that it stands for itself. In  non-alphanumeric with backslash to specify that it stands for itself. In
195  particular, if you want to match a backslash, you write \e\e.  particular, if you want to match a backslash, you write \e\e.
196  .P  .P
197  In UTF-8 mode, only ASCII numbers and letters have any special meaning after a  In a UTF mode, only ASCII numbers and letters have any special meaning after a
198  backslash. All other characters (in particular, those whose codepoints are  backslash. All other characters (in particular, those whose codepoints are
199  greater than 127) are treated as literals.  greater than 127) are treated as literals.
200  .P  .P
# Line 241  one of the following escape sequences th Line 243  one of the following escape sequences th
243    \et        tab (hex 09)    \et        tab (hex 09)
244    \eddd      character with octal code ddd, or back reference    \eddd      character with octal code ddd, or back reference
245    \exhh      character with hex code hh    \exhh      character with hex code hh
246    \ex{hhh..} character with hex code hhh..    \ex{hhh..} character with hex code hhh.. (non-JavaScript mode)
247      \euhhhh    character with hex code hhhh (JavaScript mode only)
248  .sp  .sp
249  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
250  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.
251  Thus \ecz becomes hex 1A (z is 7A), but \ec{ becomes hex 3B ({ is 7B), while  Thus \ecz becomes hex 1A (z is 7A), but \ec{ becomes hex 3B ({ is 7B), while
252  \ec; becomes hex 7B (; is 3B). If the byte following \ec has a value greater  \ec; becomes hex 7B (; is 3B). If the byte following \ec has a value greater
253  than 127, a compile-time error occurs. This locks out non-ASCII characters in  than 127, a compile-time error occurs. This locks out non-ASCII characters in
254  both byte mode and UTF-8 mode. (When PCRE is compiled in EBCDIC mode, all byte  all modes. (When PCRE is compiled in EBCDIC mode, all byte values are valid. A
255  values are valid. A lower case letter is converted to upper case, and then the  lower case letter is converted to upper case, and then the 0xc0 bits are
256  0xc0 bits are flipped.)  flipped.)
257  .P  .P
258  After \ex, from zero to two hexadecimal digits are read (letters can be in  By default, after \ex, from zero to two hexadecimal digits are read (letters
259  upper or lower case). Any number of hexadecimal digits may appear between \ex{  can be in upper or lower case). Any number of hexadecimal digits may appear
260  and }, but the value of the character code must be less than 256 in non-UTF-8  between \ex{ and }, but the character code is constrained as follows:
261  mode, and less than 2**31 in UTF-8 mode. That is, the maximum value in  .sp
262  hexadecimal is 7FFFFFFF. Note that this is bigger than the largest Unicode code    8-bit non-UTF mode    less than 0x100
263  point, which is 10FFFF.    8-bit UTF-8 mode      less than 0x10ffff and a valid codepoint
264      16-bit non-UTF mode   less than 0x10000
265      16-bit UTF-16 mode    less than 0x10ffff and a valid codepoint
266    .sp
267    Invalid Unicode codepoints are the range 0xd800 to 0xdfff (the so-called
268    "surrogate" codepoints).
269  .P  .P
270  If characters other than hexadecimal digits appear between \ex{ and }, or if  If characters other than hexadecimal digits appear between \ex{ and }, or if
271  there is no terminating }, this form of escape is not recognized. Instead, the  there is no terminating }, this form of escape is not recognized. Instead, the
272  initial \ex will be interpreted as a basic hexadecimal escape, with no  initial \ex will be interpreted as a basic hexadecimal escape, with no
273  following digits, giving a character whose value is zero.  following digits, giving a character whose value is zero.
274  .P  .P
275    If the PCRE_JAVASCRIPT_COMPAT option is set, the interpretation of \ex is
276    as just described only when it is followed by two hexadecimal digits.
277    Otherwise, it matches a literal "x" character. In JavaScript mode, support for
278    code points greater than 256 is provided by \eu, which must be followed by
279    four hexadecimal digits; otherwise it matches a literal "u" character.
280    .P
281  Characters whose value is less than 256 can be defined by either of the two  Characters whose value is less than 256 can be defined by either of the two
282  syntaxes for \ex. There is no difference in the way they are handled. For  syntaxes for \ex (or by \eu in JavaScript mode). There is no difference in the
283  example, \exdc is exactly the same as \ex{dc}.  way they are handled. For example, \exdc is exactly the same as \ex{dc} (or
284    \eu00dc in JavaScript mode).
285  .P  .P
286  After \e0 up to two further octal digits are read. If there are fewer than two  After \e0 up to two further octal digits are read. If there are fewer than two
287  digits, just those that are present are used. Thus the sequence \e0\ex\e07  digits, just those that are present are used. Thus the sequence \e0\ex\e07
# Line 292  parenthesized subpatterns. Line 307  parenthesized subpatterns.
307  Inside a character class, or if the decimal number is greater than 9 and there  Inside a character class, or if the decimal number is greater than 9 and there
308  have not been that many capturing subpatterns, PCRE re-reads up to three octal  have not been that many capturing subpatterns, PCRE re-reads up to three octal
309  digits following the backslash, and uses them to generate a data character. Any  digits following the backslash, and uses them to generate a data character. Any
310  subsequent digits stand for themselves. In non-UTF-8 mode, the value of a  subsequent digits stand for themselves. The value of the character is
311  character specified in octal must be less than \e400. In UTF-8 mode, values up  constrained in the same way as characters specified in hexadecimal.
312  to \e777 are permitted. For example:  For example:
313  .sp  .sp
314    \e040   is another way of writing a space    \e040   is another way of writing a space
315  .\" JOIN  .\" JOIN
# Line 311  to \e777 are permitted. For example: Line 326  to \e777 are permitted. For example:
326              character with octal code 113              character with octal code 113
327  .\" JOIN  .\" JOIN
328    \e377   might be a back reference, otherwise    \e377   might be a back reference, otherwise
329              the byte consisting entirely of 1 bits              the value 255 (decimal)
330  .\" JOIN  .\" JOIN
331    \e81    is either a back reference, or a binary zero    \e81    is either a back reference, or a binary zero
332              followed by the two characters "8" and "1"              followed by the two characters "8" and "1"
# Line 320  Note that octal values of 100 or greater Line 335  Note that octal values of 100 or greater
335  zero, because no more than three octal digits are ever read.  zero, because no more than three octal digits are ever read.
336  .P  .P
337  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
338  and outside character classes. In addition, inside a character class, the  and outside character classes. In addition, inside a character class, \eb is
339  sequence \eb is interpreted as the backspace character (hex 08). The sequences  interpreted as the backspace character (hex 08).
340  \eB, \eN, \eR, and \eX are not special inside a character class. Like any other  .P
341  unrecognized escape sequences, they are treated as the literal characters "B",  \eN is not allowed in a character class. \eB, \eR, and \eX are not special
342  "N", "R", and "X" by default, but cause an error if the PCRE_EXTRA option is  inside a character class. Like other unrecognized escape sequences, they are
343  set. Outside a character class, these sequences have different meanings.  treated as the literal characters "B", "R", and "X" by default, but cause an
344    error if the PCRE_EXTRA option is set. Outside a character class, these
345    sequences have different meanings.
346    .
347    .
348    .SS "Unsupported escape sequences"
349    .rs
350    .sp
351    In Perl, the sequences \el, \eL, \eu, and \eU are recognized by its string
352    handler and used to modify the case of following characters. By default, PCRE
353    does not support these escape sequences. However, if the PCRE_JAVASCRIPT_COMPAT
354    option is set, \eU matches a "U" character, and \eu can be used to define a
355    character by code point, as described in the previous section.
356  .  .
357  .  .
358  .SS "Absolute and relative back references"  .SS "Absolute and relative back references"
# Line 387  This is the same as Line 414  This is the same as
414  .\" </a>  .\" </a>
415  the "." metacharacter  the "." metacharacter
416  .\"  .\"
417  when PCRE_DOTALL is not set.  when PCRE_DOTALL is not set. Perl also uses \eN to match characters by name;
418    PCRE does not support this.
419  .P  .P
420  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
421  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
# Line 419  or "french" in Windows, some character c Line 447  or "french" in Windows, some character c
447  accented letters, and these are then matched by \ew. The use of locales with  accented letters, and these are then matched by \ew. The use of locales with
448  Unicode is discouraged.  Unicode is discouraged.
449  .P  .P
450  By default, in UTF-8 mode, characters with values greater than 128 never match  By default, in a UTF mode, characters with values greater than 128 never match
451  \ed, \es, or \ew, and always match \eD, \eS, and \eW. These sequences retain  \ed, \es, or \ew, and always match \eD, \eS, and \eW. These sequences retain
452  their original meanings from before UTF-8 support was available, mainly for  their original meanings from before UTF support was available, mainly for
453  efficiency reasons. However, if PCRE is compiled with Unicode property support,  efficiency reasons. However, if PCRE is compiled with Unicode property support,
454  and the PCRE_UCP option is set, the behaviour is changed so that Unicode  and the PCRE_UCP option is set, the behaviour is changed so that Unicode
455  properties are used to determine character types, as follows:  properties are used to determine character types, as follows:
# Line 438  is noticeably slower when PCRE_UCP is se Line 466  is noticeably slower when PCRE_UCP is se
466  .P  .P
467  The sequences \eh, \eH, \ev, and \eV are features that were added to Perl at  The sequences \eh, \eH, \ev, and \eV are features that were added to Perl at
468  release 5.10. In contrast to the other sequences, which match only ASCII  release 5.10. In contrast to the other sequences, which match only ASCII
469  characters by default, these always match certain high-valued codepoints in  characters by default, these always match certain high-valued codepoints,
470  UTF-8 mode, whether or not PCRE_UCP is set. The horizontal space characters  whether or not PCRE_UCP is set. The horizontal space characters are:
 are:  
471  .sp  .sp
472    U+0009     Horizontal tab    U+0009     Horizontal tab
473    U+0020     Space    U+0020     Space
# Line 471  The vertical space characters are: Line 498  The vertical space characters are:
498    U+0085     Next line    U+0085     Next line
499    U+2028     Line separator    U+2028     Line separator
500    U+2029     Paragraph separator    U+2029     Paragraph separator
501    .sp
502    In 8-bit, non-UTF-8 mode, only the characters with codepoints less than 256 are
503    relevant.
504  .  .
505  .  .
506  .\" HTML <a name="newlineseq"></a>  .\" HTML <a name="newlineseq"></a>
# Line 478  The vertical space characters are: Line 508  The vertical space characters are:
508  .rs  .rs
509  .sp  .sp
510  Outside a character class, by default, the escape sequence \eR matches any  Outside a character class, by default, the escape sequence \eR matches any
511  Unicode newline sequence. In non-UTF-8 mode \eR is equivalent to the following:  Unicode newline sequence. In 8-bit non-UTF-8 mode \eR is equivalent to the
512    following:
513  .sp  .sp
514    (?>\er\en|\en|\ex0b|\ef|\er|\ex85)    (?>\er\en|\en|\ex0b|\ef|\er|\ex85)
515  .sp  .sp
# Line 493  U+000B), FF (formfeed, U+000C), CR (carr Line 524  U+000B), FF (formfeed, U+000C), CR (carr
524  line, U+0085). The two-character sequence is treated as a single unit that  line, U+0085). The two-character sequence is treated as a single unit that
525  cannot be split.  cannot be split.
526  .P  .P
527  In UTF-8 mode, two additional characters whose codepoints are greater than 255  In other modes, two additional characters whose codepoints are greater than 255
528  are added: LS (line separator, U+2028) and PS (paragraph separator, U+2029).  are added: LS (line separator, U+2028) and PS (paragraph separator, U+2029).
529  Unicode character property support is not needed for these characters to be  Unicode character property support is not needed for these characters to be
530  recognized.  recognized.
# Line 509  one of the following sequences: Line 540  one of the following sequences:
540    (*BSR_ANYCRLF)   CR, LF, or CRLF only    (*BSR_ANYCRLF)   CR, LF, or CRLF only
541    (*BSR_UNICODE)   any Unicode newline sequence    (*BSR_UNICODE)   any Unicode newline sequence
542  .sp  .sp
543  These override the default and the options given to \fBpcre_compile()\fP or  These override the default and the options given to the compiling function, but
544  \fBpcre_compile2()\fP, but they can be overridden by options given to  they can themselves be overridden by options given to a matching function. Note
545  \fBpcre_exec()\fP or \fBpcre_dfa_exec()\fP. Note that these special settings,  that these special settings, which are not Perl-compatible, are recognized only
546  which are not Perl-compatible, are recognized only at the very start of a  at the very start of a pattern, and that they must be in upper case. If more
547  pattern, and that they must be in upper case. If more than one of them is  than one of them is present, the last one is used. They can be combined with a
548  present, the last one is used. They can be combined with a change of newline  change of newline convention; for example, a pattern can start with:
 convention; for example, a pattern can start with:  
549  .sp  .sp
550    (*ANY)(*BSR_ANYCRLF)    (*ANY)(*BSR_ANYCRLF)
551  .sp  .sp
552  They can also be combined with the (*UTF8) or (*UCP) special sequences. Inside  They can also be combined with the (*UTF8), (*UTF16), or (*UCP) special
553  a character class, \eR is treated as an unrecognized escape sequence, and so  sequences. Inside a character class, \eR is treated as an unrecognized escape
554  matches the letter "R" by default, but causes an error if PCRE_EXTRA is set.  sequence, and so matches the letter "R" by default, but causes an error if
555    PCRE_EXTRA is set.
556  .  .
557  .  .
558  .\" HTML <a name="uniextseq"></a>  .\" HTML <a name="uniextseq"></a>
# Line 530  matches the letter "R" by default, but c Line 561  matches the letter "R" by default, but c
561  .sp  .sp
562  When PCRE is built with Unicode character property support, three additional  When PCRE is built with Unicode character property support, three additional
563  escape sequences that match characters with specific properties are available.  escape sequences that match characters with specific properties are available.
564  When not in UTF-8 mode, these sequences are of course limited to testing  When in 8-bit non-UTF-8 mode, these sequences are of course limited to testing
565  characters whose codepoints are less than 256, but they do work in this mode.  characters whose codepoints are less than 256, but they do work in this mode.
566  The extra escape sequences are:  The extra escape sequences are:
567  .sp  .sp
# Line 565  Armenian, Line 596  Armenian,
596  Avestan,  Avestan,
597  Balinese,  Balinese,
598  Bamum,  Bamum,
599    Batak,
600  Bengali,  Bengali,
601  Bopomofo,  Bopomofo,
602    Brahmi,
603  Braille,  Braille,
604  Buginese,  Buginese,
605  Buhid,  Buhid,
606  Canadian_Aboriginal,  Canadian_Aboriginal,
607  Carian,  Carian,
608    Chakma,
609  Cham,  Cham,
610  Cherokee,  Cherokee,
611  Common,  Common,
# Line 614  Lisu, Line 648  Lisu,
648  Lycian,  Lycian,
649  Lydian,  Lydian,
650  Malayalam,  Malayalam,
651    Mandaic,
652  Meetei_Mayek,  Meetei_Mayek,
653    Meroitic_Cursive,
654    Meroitic_Hieroglyphs,
655    Miao,
656  Mongolian,  Mongolian,
657  Myanmar,  Myanmar,
658  New_Tai_Lue,  New_Tai_Lue,
# Line 633  Rejang, Line 671  Rejang,
671  Runic,  Runic,
672  Samaritan,  Samaritan,
673  Saurashtra,  Saurashtra,
674    Sharada,
675  Shavian,  Shavian,
676  Sinhala,  Sinhala,
677    Sora_Sompeng,
678  Sundanese,  Sundanese,
679  Syloti_Nagri,  Syloti_Nagri,
680  Syriac,  Syriac,
# Line 643  Tagbanwa, Line 683  Tagbanwa,
683  Tai_Le,  Tai_Le,
684  Tai_Tham,  Tai_Tham,
685  Tai_Viet,  Tai_Viet,
686    Takri,
687  Tamil,  Tamil,
688  Telugu,  Telugu,
689  Thaana,  Thaana,
# Line 717  the Lu, Ll, or Lt property, in other wor Line 758  the Lu, Ll, or Lt property, in other wor
758  a modifier or "other".  a modifier or "other".
759  .P  .P
760  The Cs (Surrogate) property applies only to characters in the range U+D800 to  The Cs (Surrogate) property applies only to characters in the range U+D800 to
761  U+DFFF. Such characters are not valid in UTF-8 strings (see RFC 3629) and so  U+DFFF. Such characters are not valid in Unicode strings and so
762  cannot be tested by PCRE, unless UTF-8 validity checking has been turned off  cannot be tested by PCRE, unless UTF validity checking has been turned off
763  (see the discussion of PCRE_NO_UTF8_CHECK in the  (see the discussion of PCRE_NO_UTF8_CHECK and PCRE_NO_UTF16_CHECK in the
764  .\" HREF  .\" HREF
765  \fBpcreapi\fP  \fBpcreapi\fP
766  .\"  .\"
# Line 750  atomic group Line 791  atomic group
791  .\"  .\"
792  Characters with the "mark" property are typically accents that affect the  Characters with the "mark" property are typically accents that affect the
793  preceding character. None of them have codepoints less than 256, so in  preceding character. None of them have codepoints less than 256, so in
794  non-UTF-8 mode \eX matches any one character.  8-bit non-UTF-8 mode \eX matches any one character.
795  .P  .P
796  Note that recent versions of Perl have changed \eX to match what Unicode calls  Note that recent versions of Perl have changed \eX to match what Unicode calls
797  an "extended grapheme cluster", which has a more complicated definition.  an "extended grapheme cluster", which has a more complicated definition.
# Line 759  Matching characters by Unicode property Line 800  Matching characters by Unicode property
800  a structure that contains data for over fifteen thousand characters. That is  a structure that contains data for over fifteen thousand characters. That is
801  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
802  properties in PCRE by default, though you can make them do so by setting the  properties in PCRE by default, though you can make them do so by setting the
803  PCRE_UCP option for \fBpcre_compile()\fP or by starting the pattern with  PCRE_UCP option or by starting the pattern with (*UCP).
 (*UCP).  
804  .  .
805  .  .
806  .\" HTML <a name="extraprops"></a>  .\" HTML <a name="extraprops"></a>
# Line 849  escape sequence" error is generated inst Line 889  escape sequence" error is generated inst
889  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
890  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
891  \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
892  first or last character matches \ew, respectively. In UTF-8 mode, the meanings  first or last character matches \ew, respectively. In a UTF mode, the meanings
893  of \ew and \eW can be changed by setting the PCRE_UCP option. When this is  of \ew and \eW can be changed by setting the PCRE_UCP option. When this is
894  done, it also affects \eb and \eB. Neither PCRE nor Perl has a separate "start  done, it also affects \eb and \eB. Neither PCRE nor Perl has a separate "start
895  of word" or "end of word" metasequence. However, whatever follows \eb normally  of word" or "end of word" metasequence. However, whatever follows \eb normally
# Line 944  end of the subject in both modes, and if Line 984  end of the subject in both modes, and if
984  .sp  .sp
985  Outside a character class, a dot in the pattern matches any one character in  Outside a character class, a dot in the pattern matches any one character in
986  the subject string except (by default) a character that signifies the end of a  the subject string except (by default) a character that signifies the end of a
987  line. In UTF-8 mode, the matched character may be more than one byte long.  line.
988  .P  .P
989  When a line ending is defined as a single character, dot never matches that  When a line ending is defined as a single character, dot never matches that
990  character; when the two-character sequence CRLF is used, dot does not match CR  character; when the two-character sequence CRLF is used, dot does not match CR
# Line 964  special meaning in a character class. Line 1004  special meaning in a character class.
1004  .P  .P
1005  The escape sequence \eN behaves like a dot, except that it is not affected by  The escape sequence \eN behaves like a dot, except that it is not affected by
1006  the PCRE_DOTALL option. In other words, it matches any character except one  the PCRE_DOTALL option. In other words, it matches any character except one
1007  that signifies the end of a line.  that signifies the end of a line. Perl also uses \eN to match characters by
1008    name; PCRE does not support this.
1009  .  .
1010  .  .
1011  .SH "MATCHING A SINGLE BYTE"  .SH "MATCHING A SINGLE DATA UNIT"
1012  .rs  .rs
1013  .sp  .sp
1014  Outside a character class, the escape sequence \eC matches any one byte, both  Outside a character class, the escape sequence \eC matches any one data unit,
1015  in and out of UTF-8 mode. Unlike a dot, it always matches line-ending  whether or not a UTF mode is set. In the 8-bit library, one data unit is one
1016  characters. The feature is provided in Perl in order to match individual bytes  byte; in the 16-bit library it is a 16-bit unit. Unlike a dot, \eC always
1017  in UTF-8 mode, but it is unclear how it can usefully be used. Because \eC  matches line-ending characters. The feature is provided in Perl in order to
1018  breaks up characters into individual bytes, matching one byte with \eC in UTF-8  match individual bytes in UTF-8 mode, but it is unclear how it can usefully be
1019  mode means that the rest of the string may start with a malformed UTF-8  used. Because \eC breaks up characters into individual data units, matching one
1020  character. This has undefined results, because PCRE assumes that it is dealing  unit with \eC in a UTF mode means that the rest of the string may start with a
1021  with valid UTF-8 strings (and by default it checks this at the start of  malformed UTF character. This has undefined results, because PCRE assumes that
1022  processing unless the PCRE_NO_UTF8_CHECK option is used).  it is dealing with valid UTF strings (and by default it checks this at the
1023    start of processing unless the PCRE_NO_UTF8_CHECK or PCRE_NO_UTF16_CHECK option
1024    is used).
1025  .P  .P
1026  PCRE does not allow \eC to appear in lookbehind assertions  PCRE does not allow \eC to appear in lookbehind assertions
1027  .\" HTML <a href="#lookbehind">  .\" HTML <a href="#lookbehind">
1028  .\" </a>  .\" </a>
1029  (described below),  (described below)
1030  .\"  .\"
1031  because in UTF-8 mode this would make it impossible to calculate the length of  in a UTF mode, because this would make it impossible to calculate the length of
1032  the lookbehind.  the lookbehind.
1033  .P  .P
1034  In general, the \eC escape sequence is best avoided in UTF-8 mode. However, one  In general, the \eC escape sequence is best avoided. However, one
1035  way of using it that avoids the problem of malformed UTF-8 characters is to  way of using it that avoids the problem of malformed UTF characters is to use a
1036  use a lookahead to check the length of the next character, as in this pattern  lookahead to check the length of the next character, as in this pattern, which
1037  (ignore white space and line breaks):  could be used with a UTF-8 string (ignore white space and line breaks):
1038  .sp  .sp
1039    (?| (?=[\ex00-\ex7f])(\eC) |    (?| (?=[\ex00-\ex7f])(\eC) |
1040        (?=[\ex80-\ex{7ff}])(\eC)(\eC) |        (?=[\ex80-\ex{7ff}])(\eC)(\eC) |
# Line 1021  bracket causes a compile-time error. If Line 1064  bracket causes a compile-time error. If
1064  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
1065  (after an initial circumflex, if present) or escaped with a backslash.  (after an initial circumflex, if present) or escaped with a backslash.
1066  .P  .P
1067  A character class matches a single character in the subject. In UTF-8 mode, the  A character class matches a single character in the subject. In a UTF mode, the
1068  character may be more than one byte long. A matched character must be in the  character may be more than one data unit long. A matched character must be in
1069  set of characters defined by the class, unless the first character in the class  the set of characters defined by the class, unless the first character in the
1070  definition is a circumflex, in which case the subject character must not be in  class definition is a circumflex, in which case the subject character must not
1071  the set defined by the class. If a circumflex is actually required as a member  be in the set defined by the class. If a circumflex is actually required as a
1072  of the class, ensure it is not the first character, or escape it with a  member of the class, ensure it is not the first character, or escape it with a
1073  backslash.  backslash.
1074  .P  .P
1075  For example, the character class [aeiou] matches any lower case vowel, while  For example, the character class [aeiou] matches any lower case vowel, while
# Line 1037  circumflex is not an assertion; it still Line 1080  circumflex is not an assertion; it still
1080  string, and therefore it fails if the current pointer is at the end of the  string, and therefore it fails if the current pointer is at the end of the
1081  string.  string.
1082  .P  .P
1083  In UTF-8 mode, characters with values greater than 255 can be included in a  In UTF-8 (UTF-16) mode, characters with values greater than 255 (0xffff) can be
1084  class as a literal string of bytes, or by using the \ex{ escaping mechanism.  included in a class as a literal string of data units, or by using the \ex{
1085    escaping mechanism.
1086  .P  .P
1087  When caseless matching is set, any letters in a class represent both their  When caseless matching is set, any letters in a class represent both their
1088  upper case and lower case versions, so for example, a caseless [aeiou] matches  upper case and lower case versions, so for example, a caseless [aeiou] matches
1089  "A" as well as "a", and a caseless [^aeiou] does not match "A", whereas a  "A" as well as "a", and a caseless [^aeiou] does not match "A", whereas a
1090  caseful version would. In UTF-8 mode, PCRE always understands the concept of  caseful version would. In a UTF mode, PCRE always understands the concept of
1091  case for characters whose values are less than 128, so caseless matching is  case for characters whose values are less than 128, so caseless matching is
1092  always possible. For characters with higher values, the concept of case is  always possible. For characters with higher values, the concept of case is
1093  supported if PCRE is compiled with Unicode property support, but not otherwise.  supported if PCRE is compiled with Unicode property support, but not otherwise.
1094  If you want to use caseless matching in UTF8-mode for characters 128 and above,  If you want to use caseless matching in a UTF mode for characters 128 and
1095  you must ensure that PCRE is compiled with Unicode property support as well as  above, you must ensure that PCRE is compiled with Unicode property support as
1096  with UTF-8 support.  well as with UTF support.
1097  .P  .P
1098  Characters that might indicate line breaks are never treated in any special way  Characters that might indicate line breaks are never treated in any special way
1099  when matching character classes, whatever line-ending sequence is in use, and  when matching character classes, whatever line-ending sequence is in use, and
# Line 1071  followed by two other characters. The oc Line 1115  followed by two other characters. The oc
1115  "]" can also be used to end a range.  "]" can also be used to end a range.
1116  .P  .P
1117  Ranges operate in the collating sequence of character values. They can also be  Ranges operate in the collating sequence of character values. They can also be
1118  used for characters specified numerically, for example [\e000-\e037]. In UTF-8  used for characters specified numerically, for example [\e000-\e037]. Ranges
1119  mode, ranges can include characters whose values are greater than 255, for  can include any characters that are valid for the current mode.
 example [\ex{100}-\ex{2ff}].  
1120  .P  .P
1121  If a range that includes letters is used when caseless matching is set, it  If a range that includes letters is used when caseless matching is set, it
1122  matches the letters in either case. For example, [W-c] is equivalent to  matches the letters in either case. For example, [W-c] is equivalent to
1123  [][\e\e^_`wxyzabc], matched caselessly, and in non-UTF-8 mode, if character  [][\e\e^_`wxyzabc], matched caselessly, and in a non-UTF mode, if character
1124  tables for a French locale are in use, [\exc8-\excb] matches accented E  tables for a French locale are in use, [\exc8-\excb] matches accented E
1125  characters in both cases. In UTF-8 mode, PCRE supports the concept of case for  characters in both cases. In UTF modes, PCRE supports the concept of case for
1126  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
1127  property support.  property support.
1128  .P  .P
1129  The character escape sequences \ed, \eD, \eh, \eH, \ep, \eP, \es, \eS, \ev,  The character escape sequences \ed, \eD, \eh, \eH, \ep, \eP, \es, \eS, \ev,
1130  \eV, \ew, and \eW may appear in a character class, and add the characters that  \eV, \ew, and \eW may appear in a character class, and add the characters that
1131  they match to the class. For example, [\edABCDEF] matches any hexadecimal  they match to the class. For example, [\edABCDEF] matches any hexadecimal
1132  digit. In UTF-8 mode, the PCRE_UCP option affects the meanings of \ed, \es, \ew  digit. In UTF modes, the PCRE_UCP option affects the meanings of \ed, \es, \ew
1133  and their upper case partners, just as it does when they appear outside a  and their upper case partners, just as it does when they appear outside a
1134  character class, as described in the section entitled  character class, as described in the section entitled
1135  .\" HTML <a href="#genericchartypes">  .\" HTML <a href="#genericchartypes">
# Line 1156  matches "1", "2", or any non-digit. PCRE Line 1199  matches "1", "2", or any non-digit. PCRE
1199  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
1200  supported, and an error is given if they are encountered.  supported, and an error is given if they are encountered.
1201  .P  .P
1202  By default, in UTF-8 mode, characters with values greater than 128 do not match  By default, in UTF modes, characters with values greater than 128 do not match
1203  any of the POSIX character classes. However, if the PCRE_UCP option is passed  any of the POSIX character classes. However, if the PCRE_UCP option is passed
1204  to \fBpcre_compile()\fP, some of the classes are changed so that Unicode  to \fBpcre_compile()\fP, some of the classes are changed so that Unicode
1205  character properties are used. This is achieved by replacing the POSIX classes  character properties are used. This is achieved by replacing the POSIX classes
# Line 1244  option settings happen at compile time. Line 1287  option settings happen at compile time.
1287  behaviour otherwise.  behaviour otherwise.
1288  .P  .P
1289  \fBNote:\fP There are other PCRE-specific options that can be set by the  \fBNote:\fP There are other PCRE-specific options that can be set by the
1290  application when the compile or match functions are called. In some cases the  application when the compiling or matching functions are called. In some cases
1291  pattern can contain special leading sequences such as (*CRLF) to override what  the pattern can contain special leading sequences such as (*CRLF) to override
1292  the application has set or what has been defaulted. Details are given in the  what the application has set or what has been defaulted. Details are given in
1293  section entitled  the section entitled
1294  .\" HTML <a href="#newlineseq">  .\" HTML <a href="#newlineseq">
1295  .\" </a>  .\" </a>
1296  "Newline sequences"  "Newline sequences"
1297  .\"  .\"
1298  above. There are also the (*UTF8) and (*UCP) leading sequences that can be used  above. There are also the (*UTF8), (*UTF16), and (*UCP) leading sequences that
1299  to set UTF-8 and Unicode property modes; they are equivalent to setting the  can be used to set UTF and Unicode property modes; they are equivalent to
1300  PCRE_UTF8 and the PCRE_UCP options, respectively.  setting the PCRE_UTF8, PCRE_UTF16, and the PCRE_UCP options, respectively.
1301  .  .
1302  .  .
1303  .\" HTML <a name="subpattern"></a>  .\" HTML <a name="subpattern"></a>
# Line 1273  match "cataract", "erpillar" or an empty Line 1316  match "cataract", "erpillar" or an empty
1316  .sp  .sp
1317  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
1318  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
1319  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 the
1320  \fBpcre_exec()\fP. Opening parentheses are counted from left to right (starting  matching function. (This applies only to the traditional matching functions;
1321  from 1) to obtain numbers for the capturing subpatterns. For example, if the  the DFA matching functions do not support capturing.)
1322  string "the red king" is matched against the pattern  .P
1323    Opening parentheses are counted from left to right (starting from 1) to obtain
1324    numbers for the capturing subpatterns. For example, if the string "the red
1325    king" is matched against the pattern
1326  .sp  .sp
1327    the ((red|white) (king|queen))    the ((red|white) (king|queen))
1328  .sp  .sp
# Line 1452  items: Line 1498  items:
1498    a literal data character    a literal data character
1499    the dot metacharacter    the dot metacharacter
1500    the \eC escape sequence    the \eC escape sequence
1501    the \eX escape sequence (in UTF-8 mode with Unicode properties)    the \eX escape sequence
1502    the \eR escape sequence    the \eR escape sequence
1503    an escape such as \ed or \epL that matches a single character    an escape such as \ed or \epL that matches a single character
1504    a character class    a character class
# Line 1483  where a quantifier is not allowed, or on Line 1529  where a quantifier is not allowed, or on
1529  quantifier, is taken as a literal character. For example, {,6} is not a  quantifier, is taken as a literal character. For example, {,6} is not a
1530  quantifier, but a literal string of four characters.  quantifier, but a literal string of four characters.
1531  .P  .P
1532  In UTF-8 mode, quantifiers apply to UTF-8 characters rather than to individual  In UTF modes, quantifiers apply to characters rather than to individual data
1533  bytes. Thus, for example, \ex{100}{2} matches two UTF-8 characters, each of  units. Thus, for example, \ex{100}{2} matches two characters, each of
1534  which is represented by a two-byte sequence. Similarly, when Unicode property  which is represented by a two-byte sequence in a UTF-8 string. Similarly,
1535  support is available, \eX{3} matches three Unicode extended sequences, each of  \eX{3} matches three Unicode extended sequences, each of which may be several
1536  which may be several bytes long (and they may be of different lengths).  data units long (and they may be of different lengths).
1537  .P  .P
1538  The quantifier {0} is permitted, causing the expression to behave as if the  The quantifier {0} is permitted, causing the expression to behave as if the
1539  previous item and the quantifier were not present. This may be useful for  previous item and the quantifier were not present. This may be useful for
# Line 1950  temporarily move the current position ba Line 1996  temporarily move the current position ba
1996  match. If there are insufficient characters before the current position, the  match. If there are insufficient characters before the current position, the
1997  assertion fails.  assertion fails.
1998  .P  .P
1999  PCRE does not allow the \eC escape (which matches a single byte in UTF-8 mode)  In a UTF mode, PCRE does not allow the \eC escape (which matches a single data
2000  to appear in lookbehind assertions, because it makes it impossible to calculate  unit even in a UTF mode) to appear in lookbehind assertions, because it makes
2001  the length of the lookbehind. The \eX and \eR escapes, which can match  it impossible to calculate the length of the lookbehind. The \eX and \eR
2002  different numbers of bytes, are also not permitted.  escapes, which can match different numbers of data units, are also not
2003    permitted.
2004  .P  .P
2005  .\" HTML <a href="#subpatternsassubroutines">  .\" HTML <a href="#subpatternsassubroutines">
2006  .\" </a>  .\" </a>
# Line 2200  closing parenthesis. Nested parentheses Line 2247  closing parenthesis. Nested parentheses
2247  option is set, an unescaped # character also introduces a comment, which in  option is set, an unescaped # character also introduces a comment, which in
2248  this case continues to immediately after the next newline character or  this case continues to immediately after the next newline character or
2249  character sequence in the pattern. Which characters are interpreted as newlines  character sequence in the pattern. Which characters are interpreted as newlines
2250  is controlled by the options passed to \fBpcre_compile()\fP or by a special  is controlled by the options passed to a compiling function or by a special
2251  sequence at the start of the pattern, as described in the section entitled  sequence at the start of the pattern, as described in the section entitled
2252  .\" HTML <a href="#newlines">  .\" HTML <a href="#newlines">
2253  .\" </a>  .\" </a>
# Line 2502  same pair of parentheses when there is a Line 2549  same pair of parentheses when there is a
2549  .P  .P
2550  PCRE provides a similar feature, but of course it cannot obey arbitrary Perl  PCRE provides a similar feature, but of course it cannot obey arbitrary Perl
2551  code. The feature is called "callout". The caller of PCRE provides an external  code. The feature is called "callout". The caller of PCRE provides an external
2552  function by putting its entry point in the global variable \fIpcre_callout\fP.  function by putting its entry point in the global variable \fIpcre_callout\fP
2553  By default, this variable contains NULL, which disables all calling out.  (8-bit library) or \fIpcre16_callout\fP (16-bit library). By default, this
2554    variable contains NULL, which disables all calling out.
2555  .P  .P
2556  Within a regular expression, (?C) indicates the points at which the external  Within a regular expression, (?C) indicates the points at which the external
2557  function is to be called. If you want to identify different callout points, you  function is to be called. If you want to identify different callout points, you
# Line 2512  For example, this pattern has two callou Line 2560  For example, this pattern has two callou
2560  .sp  .sp
2561    (?C1)abc(?C2)def    (?C1)abc(?C2)def
2562  .sp  .sp
2563  If the PCRE_AUTO_CALLOUT flag is passed to \fBpcre_compile()\fP, callouts are  If the PCRE_AUTO_CALLOUT flag is passed to a compiling function, callouts are
2564  automatically installed before each item in the pattern. They are all numbered  automatically installed before each item in the pattern. They are all numbered
2565  255.  255.
2566  .P  .P
2567  During matching, when PCRE reaches a callout point (and \fIpcre_callout\fP is  During matching, when PCRE reaches a callout point, the external function is
2568  set), the external function is called. It is provided with the number of the  called. It is provided with the number of the callout, the position in the
2569  callout, the position in the pattern, and, optionally, one item of data  pattern, and, optionally, one item of data originally supplied by the caller of
2570  originally supplied by the caller of \fBpcre_exec()\fP. The callout function  the matching function. The callout function may cause matching to proceed, to
2571  may cause matching to proceed, to backtrack, or to fail altogether. A complete  backtrack, or to fail altogether. A complete description of the interface to
2572  description of the interface to the callout function is given in the  the callout function is given in the
2573  .\" HREF  .\" HREF
2574  \fBpcrecallout\fP  \fBpcrecallout\fP
2575  .\"  .\"
# Line 2539  production code should be noted to avoid Line 2587  production code should be noted to avoid
2587  remarks apply to the PCRE features described in this section.  remarks apply to the PCRE features described in this section.
2588  .P  .P
2589  Since these verbs are specifically related to backtracking, most of them can be  Since these verbs are specifically related to backtracking, most of them can be
2590  used only when the pattern is to be matched using \fBpcre_exec()\fP, which uses  used only when the pattern is to be matched using one of the traditional
2591  a backtracking algorithm. With the exception of (*FAIL), which behaves like a  matching functions, which use a backtracking algorithm. With the exception of
2592  failing negative assertion, they cause an error if encountered by  (*FAIL), which behaves like a failing negative assertion, they cause an error
2593  \fBpcre_dfa_exec()\fP.  if encountered by a DFA matching function.
2594  .P  .P
2595  If any of these verbs are used in an assertion or in a subpattern that is  If any of these verbs are used in an assertion or in a subpattern that is
2596  called as a subroutine (whether or not recursively), their effect is confined  called as a subroutine (whether or not recursively), their effect is confined
2597  to that subpattern; it does not extend to the surrounding pattern, with one  to that subpattern; it does not extend to the surrounding pattern, with one
2598  exception: a *MARK that is encountered in a positive assertion \fIis\fP passed  exception: the name from a *(MARK), (*PRUNE), or (*THEN) that is encountered in
2599  back (compare capturing parentheses in assertions). Note that such subpatterns  a successful positive assertion \fIis\fP passed back when a match succeeds
2600  are processed as anchored at the point where they are tested. Note also that  (compare capturing parentheses in assertions). Note that such subpatterns are
2601  Perl's treatment of subroutines is different in some cases.  processed as anchored at the point where they are tested. Note also that Perl's
2602    treatment of subroutines is different in some cases.
2603  .P  .P
2604  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
2605  parenthesis followed by an asterisk. They are generally of the form  parenthesis followed by an asterisk. They are generally of the form
# Line 2560  characters that does not include a closi Line 2609  characters that does not include a closi
2609  that is, if the closing parenthesis immediately follows the colon, the effect  that is, if the closing parenthesis immediately follows the colon, the effect
2610  is as if the colon were not there. Any number of these verbs may occur in a  is as if the colon were not there. Any number of these verbs may occur in a
2611  pattern.  pattern.
2612  .P  .
2613    .
2614    .\" HTML <a name="nooptimize"></a>
2615    .SS "Optimizations that affect backtracking verbs"
2616    .rs
2617    .sp
2618  PCRE contains some optimizations that are used to speed up matching by running  PCRE contains some optimizations that are used to speed up matching by running
2619  some checks at the start of each match attempt. For example, it may know the  some checks at the start of each match attempt. For example, it may know the
2620  minimum length of matching subject, or that a particular character must be  minimum length of matching subject, or that a particular character must be
# Line 2568  present. When one of these optimizations Line 2622  present. When one of these optimizations
2622  included backtracking verbs will not, of course, be processed. You can suppress  included backtracking verbs will not, of course, be processed. You can suppress
2623  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
2624  when calling \fBpcre_compile()\fP or \fBpcre_exec()\fP, or by starting the  when calling \fBpcre_compile()\fP or \fBpcre_exec()\fP, or by starting the
2625  pattern with (*NO_START_OPT).  pattern with (*NO_START_OPT). There is more discussion of this option in the
2626    section entitled
2627    .\" HTML <a href="pcreapi.html#execoptions">
2628    .\" </a>
2629    "Option bits for \fBpcre_exec()\fP"
2630    .\"
2631    in the
2632    .\" HREF
2633    \fBpcreapi\fP
2634    .\"
2635    documentation.
2636    .P
2637    Experiments with Perl suggest that it too has similar optimizations, sometimes
2638    leading to anomalous results.
2639  .  .
2640  .  .
2641  .SS "Verbs that act immediately"  .SS "Verbs that act immediately"
# Line 2616  starting point (see (*SKIP) below). Line 2683  starting point (see (*SKIP) below).
2683  A name is always required with this verb. There may be as many instances of  A name is always required with this verb. There may be as many instances of
2684  (*MARK) as you like in a pattern, and their names do not have to be unique.  (*MARK) as you like in a pattern, and their names do not have to be unique.
2685  .P  .P
2686  When a match succeeds, the name of the last-encountered (*MARK) is passed back  When a match succeeds, the name of the last-encountered (*MARK) on the matching
2687  to the caller via the \fIpcre_extra\fP data structure, as described in the  path is passed back to the caller as described in the section entitled
2688  .\" HTML <a href="pcreapi.html#extradata">  .\" HTML <a href="pcreapi.html#extradata">
2689  .\" </a>  .\" </a>
2690  section on \fIpcre_extra\fP  "Extra data for \fBpcre_exec()\fP"
2691  .\"  .\"
2692  in the  in the
2693  .\" HREF  .\" HREF
2694  \fBpcreapi\fP  \fBpcreapi\fP
2695  .\"  .\"
2696  documentation. No data is returned for a partial match. Here is an example of  documentation. Here is an example of \fBpcretest\fP output, where the /K
2697  \fBpcretest\fP output, where the /K modifier requests the retrieval and  modifier requests the retrieval and outputting of (*MARK) data:
 outputting of (*MARK) data:  
2698  .sp  .sp
2699    /X(*MARK:A)Y|X(*MARK:B)Z/K      re> /X(*MARK:A)Y|X(*MARK:B)Z/K
2700    XY    data> XY
2701     0: XY     0: XY
2702    MK: A    MK: A
2703    XZ    XZ
# Line 2647  If (*MARK) is encountered in a positive Line 2713  If (*MARK) is encountered in a positive
2713  passed back if it is the last-encountered. This does not happen for negative  passed back if it is the last-encountered. This does not happen for negative
2714  assertions.  assertions.
2715  .P  .P
2716  A name may also be returned after a failed match if the final path through the  After a partial match or a failed match, the name of the last encountered
2717  pattern involves (*MARK). However, unless (*MARK) used in conjunction with  (*MARK) in the entire match process is returned. For example:
 (*COMMIT), this is unlikely to happen for an unanchored pattern because, as the  
 starting point for matching is advanced, the final check is often with an empty  
 string, causing a failure before (*MARK) is reached. For example:  
 .sp  
   /X(*MARK:A)Y|X(*MARK:B)Z/K  
   XP  
   No match  
2718  .sp  .sp
2719  There are three potential starting points for this match (starting with X,      re> /X(*MARK:A)Y|X(*MARK:B)Z/K
2720  starting with P, and with an empty string). If the pattern is anchored, the    data> XP
 result is different:  
 .sp  
   /^X(*MARK:A)Y|^X(*MARK:B)Z/K  
   XP  
2721    No match, mark = B    No match, mark = B
2722  .sp  .sp
2723  PCRE's start-of-match optimizations can also interfere with this. For example,  Note that in this unanchored example the mark is retained from the match
2724  if, as a result of a call to \fBpcre_study()\fP, it knows the minimum  attempt that started at the letter "X" in the subject. Subsequent match
2725  subject length for a match, a shorter subject will not be scanned at all.  attempts starting at "P" and then with an empty string do not get as far as the
2726  .P  (*MARK) item, but nevertheless do not reset it.
2727  Note that similar anomalies (though different in detail) exist in Perl, no  .P
2728  doubt for the same reasons. The use of (*MARK) data after a failed match of an  If you are interested in (*MARK) values after failed matches, you should
2729  unanchored pattern is not recommended, unless (*COMMIT) is involved.  probably set the PCRE_NO_START_OPTIMIZE option
2730    .\" HTML <a href="#nooptimize">
2731    .\" </a>
2732    (see above)
2733    .\"
2734    to ensure that the match is always attempted.
2735  .  .
2736  .  .
2737  .SS "Verbs that act after backtracking"  .SS "Verbs that act after backtracking"
# Line 2708  Note that (*COMMIT) at the start of a pa Line 2768  Note that (*COMMIT) at the start of a pa
2768  unless PCRE's start-of-match optimizations are turned off, as shown in this  unless PCRE's start-of-match optimizations are turned off, as shown in this
2769  \fBpcretest\fP example:  \fBpcretest\fP example:
2770  .sp  .sp
2771    /(*COMMIT)abc/      re> /(*COMMIT)abc/
2772    xyzabc    data> xyzabc
2773     0: abc     0: abc
2774    xyzabc\eY    xyzabc\eY
2775    No match    No match
# Line 2730  reached, or when matching to the right o Line 2790  reached, or when matching to the right o
2790  the right, backtracking cannot cross (*PRUNE). In simple cases, the use of  the right, backtracking cannot cross (*PRUNE). In simple cases, the use of
2791  (*PRUNE) is just an alternative to an atomic group or possessive quantifier,  (*PRUNE) is just an alternative to an atomic group or possessive quantifier,
2792  but there are some uses of (*PRUNE) that cannot be expressed in any other way.  but there are some uses of (*PRUNE) that cannot be expressed in any other way.
2793  The behaviour of (*PRUNE:NAME) is the same as (*MARK:NAME)(*PRUNE) when the  The behaviour of (*PRUNE:NAME) is the same as (*MARK:NAME)(*PRUNE). In an
2794  match fails completely; the name is passed back if this is the final attempt.  anchored pattern (*PRUNE) has the same effect as (*COMMIT).
 (*PRUNE:NAME) does not pass back a name if the match succeeds. In an anchored  
 pattern (*PRUNE) has the same effect as (*COMMIT).  
2795  .sp  .sp
2796    (*SKIP)    (*SKIP)
2797  .sp  .sp
# Line 2759  following pattern fails to match, the pr Line 2817  following pattern fails to match, the pr
2817  searched for the most recent (*MARK) that has the same name. If one is found,  searched for the most recent (*MARK) that has the same name. If one is found,
2818  the "bumpalong" advance is to the subject position that corresponds to that  the "bumpalong" advance is to the subject position that corresponds to that
2819  (*MARK) instead of to where (*SKIP) was encountered. If no (*MARK) with a  (*MARK) instead of to where (*SKIP) was encountered. If no (*MARK) with a
2820  matching name is found, normal "bumpalong" of one character happens (that is,  matching name is found, the (*SKIP) is ignored.
 the (*SKIP) is ignored).  
2821  .sp  .sp
2822    (*THEN) or (*THEN:NAME)    (*THEN) or (*THEN:NAME)
2823  .sp  .sp
# Line 2774  be used for a pattern-based if-then-else Line 2831  be used for a pattern-based if-then-else
2831  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
2832  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
2833  second alternative and tries COND2, without backtracking into COND1. The  second alternative and tries COND2, without backtracking into COND1. The
2834  behaviour of (*THEN:NAME) is exactly the same as (*MARK:NAME)(*THEN) if the  behaviour of (*THEN:NAME) is exactly the same as (*MARK:NAME)(*THEN).
2835  overall match fails. If (*THEN) is not inside an alternation, it acts like  If (*THEN) is not inside an alternation, it acts like (*PRUNE).
 (*PRUNE).  
2836  .P  .P
2837  Note that a subpattern that does not contain a | character is just a part of  Note that a subpattern that does not contain a | character is just a part of
2838  the enclosing alternative; it is not a nested alternation with only one  the enclosing alternative; it is not a nested alternation with only one
# Line 2837  overrides. Line 2893  overrides.
2893  .rs  .rs
2894  .sp  .sp
2895  \fBpcreapi\fP(3), \fBpcrecallout\fP(3), \fBpcrematching\fP(3),  \fBpcreapi\fP(3), \fBpcrecallout\fP(3), \fBpcrematching\fP(3),
2896  \fBpcresyntax\fP(3), \fBpcre\fP(3).  \fBpcresyntax\fP(3), \fBpcre\fP(3), \fBpcre16(3)\fP.
2897  .  .
2898  .  .
2899  .SH AUTHOR  .SH AUTHOR
# Line 2854  Cambridge CB2 3QH, England. Line 2910  Cambridge CB2 3QH, England.
2910  .rs  .rs
2911  .sp  .sp
2912  .nf  .nf
2913  Last updated: 19 October 2011  Last updated: 14 April 2012
2914  Copyright (c) 1997-2011 University of Cambridge.  Copyright (c) 1997-2012 University of Cambridge.
2915  .fi  .fi

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