/[pcre]/code/trunk/doc/pcrepattern.3
ViewVC logotype

Diff of /code/trunk/doc/pcrepattern.3

Parent Directory Parent Directory | Revision Log Revision Log | View Patch Patch

revision 959 by ph10, Sat Apr 14 16:16:58 2012 UTC revision 1398 by ph10, Tue Nov 12 15:20:26 2013 UTC
# Line 1  Line 1 
1  .TH PCREPATTERN 3 "14 April 2012" "PCRE 8.31"  .TH PCREPATTERN 3 "12 November 2013" "PCRE 8.34"
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 20  have copious examples. Jeffrey Friedl's Line 20  have copious examples. Jeffrey Friedl's
20  published by O'Reilly, covers regular expressions in great detail. This  published by O'Reilly, covers regular expressions in great detail. This
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    This document discusses the patterns that are supported by PCRE when one its
24    main matching functions, \fBpcre_exec()\fP (8-bit) or \fBpcre[16|32]_exec()\fP
25    (16- or 32-bit), is used. PCRE also has alternative matching functions,
26    \fBpcre_dfa_exec()\fP and \fBpcre[16|32_dfa_exec()\fP, which match using a
27    different algorithm that is not Perl-compatible. Some of the features discussed
28    below are not available when DFA matching is used. The advantages and
29    disadvantages of the alternative functions, and how they differ from the normal
30    functions, are discussed in the
31    .\" HREF
32    \fBpcrematching\fP
33    .\"
34    page.
35    .
36    .
37    .SH "SPECIAL START-OF-PATTERN ITEMS"
38    .rs
39    .sp
40    A number of options that can be passed to \fBpcre_compile()\fP can also be set
41    by special items at the start of a pattern. These are not Perl-compatible, but
42    are provided to make these options accessible to pattern writers who are not
43    able to change the program that processes the pattern. Any number of these
44    items may appear, but they must all be together right at the start of the
45    pattern string, and the letters must be in upper case.
46    .
47    .
48    .SS "UTF support"
49    .rs
50    .sp
51  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,
52  there is now also support for UTF-8 strings in the original library, and a  there is now also support for UTF-8 strings in the original library, an
53  second library that supports 16-bit and UTF-16 character strings. To use these  extra library that supports 16-bit and UTF-16 character strings, and a
54    third library that supports 32-bit and UTF-32 character strings. To use these
55  features, PCRE must be built to include appropriate support. When using UTF  features, PCRE must be built to include appropriate support. When using UTF
56  strings you must either call the compiling function with the PCRE_UTF8 or  strings you must either call the compiling function with the PCRE_UTF8,
57  PCRE_UTF16 option, or the pattern must start with one of these special  PCRE_UTF16, or PCRE_UTF32 option, or the pattern must start with one of
58  sequences:  these special sequences:
59  .sp  .sp
60    (*UTF8)    (*UTF8)
61    (*UTF16)    (*UTF16)
62      (*UTF32)
63      (*UTF)
64  .sp  .sp
65    (*UTF) is a generic sequence that can be used with any of the libraries.
66  Starting a pattern with such a sequence is equivalent to setting the relevant  Starting a pattern with such a sequence is equivalent to setting the relevant
67  option. This feature is not Perl-compatible. How setting a UTF mode affects  option. How setting a UTF mode affects pattern matching is mentioned in several
68  pattern matching is mentioned in several places below. There is also a summary  places below. There is also a summary of features in the
 of features in the  
69  .\" HREF  .\" HREF
70  \fBpcreunicode\fP  \fBpcreunicode\fP
71  .\"  .\"
72  page.  page.
73  .P  .P
74  Another special sequence that may appear at the start of a pattern or in  Some applications that allow their users to supply patterns may wish to
75  combination with (*UTF8) or (*UTF16) is:  restrict them to non-UTF data for security reasons. If the PCRE_NEVER_UTF
76  .sp  option is set at compile time, (*UTF) etc. are not allowed, and their
77    (*UCP)  appearance causes an error.
78    .
79    .
80    .SS "Unicode property support"
81    .rs
82  .sp  .sp
83    Another special sequence that may appear at the start of a pattern is (*UCP).
84  This has the same effect as setting the PCRE_UCP option: it causes sequences  This has the same effect as setting the PCRE_UCP option: it causes sequences
85  such as \ed and \ew to use Unicode properties to determine character types,  such as \ed and \ew to use Unicode properties to determine character types,
86  instead of recognizing only characters with codes less than 128 via a lookup  instead of recognizing only characters with codes less than 128 via a lookup
87  table.  table.
88  .P  .
89    .
90    .SS "Disabling auto-possessification"
91    .rs
92    .sp
93    If a pattern starts with (*NO_AUTO_POSSESS), it has the same effect as setting
94    the PCRE_NO_AUTO_POSSESS option at compile time. This stops PCRE from making
95    quantifiers possessive when what follows cannot match the repeated item. For
96    example, by default a+b is treated as a++b. For more details, see the
97    .\" HREF
98    \fBpcreapi\fP
99    .\"
100    documentation.
101    .
102    .
103    .SS "Disabling start-up optimizations"
104    .rs
105    .sp
106  If a pattern starts with (*NO_START_OPT), it has the same effect as setting the  If a pattern starts with (*NO_START_OPT), it has the same effect as setting the
107  PCRE_NO_START_OPTIMIZE option either at compile or matching time. There are  PCRE_NO_START_OPTIMIZE option either at compile or matching time. This disables
108  also some more of these special sequences that are concerned with the handling  several optimizations for quickly reaching "no match" results. For more
109  of newlines; they are described below.  details, see the
 .P  
 The remainder of this document discusses the patterns that are supported by  
 PCRE when one its main matching functions, \fBpcre_exec()\fP (8-bit) or  
 \fBpcre16_exec()\fP (16-bit), is used. PCRE also has alternative matching  
 functions, \fBpcre_dfa_exec()\fP and \fBpcre16_dfa_exec()\fP, which match using  
 a different algorithm that is not Perl-compatible. Some of the features  
 discussed below are not available when DFA matching is used. The advantages and  
 disadvantages of the alternative functions, and how they differ from the normal  
 functions, are discussed in the  
110  .\" HREF  .\" HREF
111  \fBpcrematching\fP  \fBpcreapi\fP
112  .\"  .\"
113  page.  documentation.
114  .  .
115  .  .
116  .\" HTML <a name="newlines"></a>  .\" HTML <a name="newlines"></a>
117  .SH "NEWLINE CONVENTIONS"  .SS "Newline conventions"
118  .rs  .rs
119  .sp  .sp
120  PCRE supports five different conventions for indicating line breaks in  PCRE supports five different conventions for indicating line breaks in
# Line 103  example, on a Unix system where LF is th Line 147  example, on a Unix system where LF is th
147    (*CR)a.b    (*CR)a.b
148  .sp  .sp
149  changes the convention to CR. That pattern matches "a\enb" because LF is no  changes the convention to CR. That pattern matches "a\enb" because LF is no
150  longer a newline. Note that these special settings, which are not  longer a newline. If more than one of these settings is present, the last one
 Perl-compatible, are recognized only at the very start of a pattern, and that  
 they must be in upper case. If more than one of them is present, the last one  
151  is used.  is used.
152  .P  .P
153  The newline convention affects the interpretation of the dot metacharacter when  The newline convention affects where the circumflex and dollar assertions are
154  PCRE_DOTALL is not set, and also the behaviour of \eN. However, it does not  true. It also affects the interpretation of the dot metacharacter when
155  affect what the \eR escape sequence matches. By default, this is any Unicode  PCRE_DOTALL is not set, and the behaviour of \eN. However, it does not affect
156  newline sequence, for Perl compatibility. However, this can be changed; see the  what the \eR escape sequence matches. By default, this is any Unicode newline
157    sequence, for Perl compatibility. However, this can be changed; see the
158  description of \eR in the section entitled  description of \eR in the section entitled
159  .\" HTML <a href="#newlineseq">  .\" HTML <a href="#newlineseq">
160  .\" </a>  .\" </a>
# Line 121  below. A change of \eR setting can be co Line 164  below. A change of \eR setting can be co
164  convention.  convention.
165  .  .
166  .  .
167    .SS "Setting match and recursion limits"
168    .rs
169    .sp
170    The caller of \fBpcre_exec()\fP can set a limit on the number of times the
171    internal \fBmatch()\fP function is called and on the maximum depth of
172    recursive calls. These facilities are provided to catch runaway matches that
173    are provoked by patterns with huge matching trees (a typical example is a
174    pattern with nested unlimited repeats) and to avoid running out of system stack
175    by too much recursion. When one of these limits is reached, \fBpcre_exec()\fP
176    gives an error return. The limits can also be set by items at the start of the
177    pattern of the form
178    .sp
179      (*LIMIT_MATCH=d)
180      (*LIMIT_RECURSION=d)
181    .sp
182    where d is any number of decimal digits. However, the value of the setting must
183    be less than the value set (or defaulted) by the caller of \fBpcre_exec()\fP
184    for it to have any effect. In other words, the pattern writer can lower the
185    limits set by the programmer, but not raise them. If there is more than one
186    setting of one of these limits, the lower value is used.
187    .
188    .
189    .SH "EBCDIC CHARACTER CODES"
190    .rs
191    .sp
192    PCRE can be compiled to run in an environment that uses EBCDIC as its character
193    code rather than ASCII or Unicode (typically a mainframe system). In the
194    sections below, character code values are ASCII or Unicode; in an EBCDIC
195    environment these characters may have different code values, and there are no
196    code points greater than 255.
197    .
198    .
199  .SH "CHARACTERS AND METACHARACTERS"  .SH "CHARACTERS AND METACHARACTERS"
200  .rs  .rs
201  .sp  .sp
# Line 198  In a UTF mode, only ASCII numbers and le Line 273  In a UTF mode, only ASCII numbers and le
273  backslash. All other characters (in particular, those whose codepoints are  backslash. All other characters (in particular, those whose codepoints are
274  greater than 127) are treated as literals.  greater than 127) are treated as literals.
275  .P  .P
276  If a pattern is compiled with the PCRE_EXTENDED option, whitespace in the  If a pattern is compiled with the PCRE_EXTENDED option, most white space in the
277  pattern (other than in a character class) and characters between a # outside  pattern (other than in a character class), and characters between a # outside a
278  a character class and the next newline are ignored. An escaping backslash can  character class and the next newline, inclusive, are ignored. An escaping
279  be used to include a whitespace or # character as part of the pattern.  backslash can be used to include a white space or # character as part of the
280    pattern.
281  .P  .P
282  If you want to remove the special meaning from a sequence of characters, you  If you want to remove the special meaning from a sequence of characters, you
283  can do so by putting them between \eQ and \eE. This is different from Perl in  can do so by putting them between \eQ and \eE. This is different from Perl in
# Line 237  one of the following escape sequences th Line 313  one of the following escape sequences th
313    \ea        alarm, that is, the BEL character (hex 07)    \ea        alarm, that is, the BEL character (hex 07)
314    \ecx       "control-x", where x is any ASCII character    \ecx       "control-x", where x is any ASCII character
315    \ee        escape (hex 1B)    \ee        escape (hex 1B)
316    \ef        formfeed (hex 0C)    \ef        form feed (hex 0C)
317    \en        linefeed (hex 0A)    \en        linefeed (hex 0A)
318    \er        carriage return (hex 0D)    \er        carriage return (hex 0D)
319    \et        tab (hex 09)    \et        tab (hex 09)
320      \e0dd      character with octal code 0dd
321    \eddd      character with octal code ddd, or back reference    \eddd      character with octal code ddd, or back reference
322      \eo{ddd..} character with octal code ddd..
323    \exhh      character with hex code hh    \exhh      character with hex code hh
324    \ex{hhh..} character with hex code hhh.. (non-JavaScript mode)    \ex{hhh..} character with hex code hhh.. (non-JavaScript mode)
325    \euhhhh    character with hex code hhhh (JavaScript mode only)    \euhhhh    character with hex code hhhh (JavaScript mode only)
326  .sp  .sp
327  The precise effect of \ecx is as follows: if x is a lower case letter, it  The precise effect of \ecx on ASCII characters is as follows: if x is a lower
328  is converted to upper case. Then bit 6 of the character (hex 40) is inverted.  case letter, it is converted to upper case. Then bit 6 of the character (hex
329  Thus \ecz becomes hex 1A (z is 7A), but \ec{ becomes hex 3B ({ is 7B), while  40) is inverted. Thus \ecA to \ecZ become hex 01 to hex 1A (A is 41, Z is 5A),
330  \ec; becomes hex 7B (; is 3B). If the byte following \ec has a value greater  but \ec{ becomes hex 3B ({ is 7B), and \ec; becomes hex 7B (; is 3B). If the
331  than 127, a compile-time error occurs. This locks out non-ASCII characters in  data item (byte or 16-bit value) following \ec has a value greater than 127, a
332  all modes. (When PCRE is compiled in EBCDIC mode, all byte values are valid. A  compile-time error occurs. This locks out non-ASCII characters in all modes.
333  lower case letter is converted to upper case, and then the 0xc0 bits are  .P
334  flipped.)  The \ec facility was designed for use with ASCII characters, but with the
335  .P  extension to Unicode it is even less useful than it once was. It is, however,
336  By default, after \ex, from zero to two hexadecimal digits are read (letters  recognized when PCRE is compiled in EBCDIC mode, where data items are always
337  can be in upper or lower case). Any number of hexadecimal digits may appear  bytes. In this mode, all values are valid after \ec. If the next character is a
338  between \ex{ and }, but the character code is constrained as follows:  lower case letter, it is converted to upper case. Then the 0xc0 bits of the
339  .sp  byte are inverted. Thus \ecA becomes hex 01, as in ASCII (A is C1), but because
340    8-bit non-UTF mode    less than 0x100  the EBCDIC letters are disjoint, \ecZ becomes hex 29 (Z is E9), and other
341    8-bit UTF-8 mode      less than 0x10ffff and a valid codepoint  characters also generate different values.
   16-bit non-UTF mode   less than 0x10000  
   16-bit UTF-16 mode    less than 0x10ffff and a valid codepoint  
 .sp  
 Invalid Unicode codepoints are the range 0xd800 to 0xdfff (the so-called  
 "surrogate" codepoints).  
 .P  
 If characters other than hexadecimal digits appear between \ex{ and }, or if  
 there is no terminating }, this form of escape is not recognized. Instead, the  
 initial \ex will be interpreted as a basic hexadecimal escape, with no  
 following digits, giving a character whose value is zero.  
 .P  
 If the PCRE_JAVASCRIPT_COMPAT option is set, the interpretation of \ex is  
 as just described only when it is followed by two hexadecimal digits.  
 Otherwise, it matches a literal "x" character. In JavaScript mode, support for  
 code points greater than 256 is provided by \eu, which must be followed by  
 four hexadecimal digits; otherwise it matches a literal "u" character.  
 .P  
 Characters whose value is less than 256 can be defined by either of the two  
 syntaxes for \ex (or by \eu in JavaScript mode). There is no difference in the  
 way they are handled. For example, \exdc is exactly the same as \ex{dc} (or  
 \eu00dc in JavaScript mode).  
342  .P  .P
343  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
344  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 289  specifies two binary zeros followed by a Line 346  specifies two binary zeros followed by a
346  sure you supply two digits after the initial zero if the pattern character that  sure you supply two digits after the initial zero if the pattern character that
347  follows is itself an octal digit.  follows is itself an octal digit.
348  .P  .P
349  The handling of a backslash followed by a digit other than 0 is complicated.  The escape \eo must be followed by a sequence of octal digits, enclosed in
350  Outside a character class, PCRE reads it and any following digits as a decimal  braces. An error occurs if this is not the case. This escape is a recent
351  number. If the number is less than 10, or if there have been at least that many  addition to Perl; it provides way of specifying character code points as octal
352    numbers greater than 0777, and it also allows octal numbers and back references
353    to be unambiguously specified.
354    .P
355    For greater clarity and unambiguity, it is best to avoid following \e by a
356    digit greater than zero. Instead, use \eo{} or \ex{} to specify character
357    numbers, and \eg{} to specify back references. The following paragraphs
358    describe the old, ambiguous syntax.
359    .P
360    The handling of a backslash followed by a digit other than 0 is complicated,
361    and Perl has changed in recent releases, causing PCRE also to change. Outside a
362    character class, PCRE reads the digit and any following digits as a decimal
363    number. If the number is less than 8, or if there have been at least that many
364  previous capturing left parentheses in the expression, the entire sequence is  previous capturing left parentheses in the expression, the entire sequence is
365  taken as a \fIback reference\fP. A description of how this works is given  taken as a \fIback reference\fP. A description of how this works is given
366  .\" HTML <a href="#backreferences">  .\" HTML <a href="#backreferences">
# Line 304  following the discussion of Line 373  following the discussion of
373  parenthesized subpatterns.  parenthesized subpatterns.
374  .\"  .\"
375  .P  .P
376  Inside a character class, or if the decimal number is greater than 9 and there  Inside a character class, or if the decimal number following \e is greater than
377  have not been that many capturing subpatterns, PCRE re-reads up to three octal  7 and there have not been that many capturing subpatterns, PCRE handles \e8 and
378  digits following the backslash, and uses them to generate a data character. Any  \e9 as the literal characters "8" and "9", and otherwise re-reads up to three
379  subsequent digits stand for themselves. The value of the character is  octal digits following the backslash, using them to generate a data character.
380  constrained in the same way as characters specified in hexadecimal.  Any subsequent digits stand for themselves. For example:
 For example:  
381  .sp  .sp
382    \e040   is another way of writing a space    \e040   is another way of writing an ASCII space
383  .\" JOIN  .\" JOIN
384    \e40    is the same, provided there are fewer than 40    \e40    is the same, provided there are fewer than 40
385              previous capturing subpatterns              previous capturing subpatterns
# Line 328  For example: Line 396  For example:
396    \e377   might be a back reference, otherwise    \e377   might be a back reference, otherwise
397              the value 255 (decimal)              the value 255 (decimal)
398  .\" JOIN  .\" JOIN
399    \e81    is either a back reference, or a binary zero    \e81    is either a back reference, or the two
400              followed by the two characters "8" and "1"              characters "8" and "1"
401  .sp  .sp
402  Note that octal values of 100 or greater must not be introduced by a leading  Note that octal values of 100 or greater that are specified using this syntax
403  zero, because no more than three octal digits are ever read.  must not be introduced by a leading zero, because no more than three octal
404    digits are ever read.
405    .P
406    By default, after \ex that is not followed by {, from zero to two hexadecimal
407    digits are read (letters can be in upper or lower case). Any number of
408    hexadecimal digits may appear between \ex{ and }. If a character other than
409    a hexadecimal digit appears between \ex{ and }, or if there is no terminating
410    }, an error occurs.
411  .P  .P
412    If the PCRE_JAVASCRIPT_COMPAT option is set, the interpretation of \ex is
413    as just described only when it is followed by two hexadecimal digits.
414    Otherwise, it matches a literal "x" character. In JavaScript mode, support for
415    code points greater than 256 is provided by \eu, which must be followed by
416    four hexadecimal digits; otherwise it matches a literal "u" character.
417    .P
418    Characters whose value is less than 256 can be defined by either of the two
419    syntaxes for \ex (or by \eu in JavaScript mode). There is no difference in the
420    way they are handled. For example, \exdc is exactly the same as \ex{dc} (or
421    \eu00dc in JavaScript mode).
422    .
423    .
424    .SS "Constraints on character values"
425    .rs
426    .sp
427    Characters that are specified using octal or hexadecimal numbers are
428    limited to certain values, as follows:
429    .sp
430      8-bit non-UTF mode    less than 0x100
431      8-bit UTF-8 mode      less than 0x10ffff and a valid codepoint
432      16-bit non-UTF mode   less than 0x10000
433      16-bit UTF-16 mode    less than 0x10ffff and a valid codepoint
434      32-bit non-UTF mode   less than 0x100000000
435      32-bit UTF-32 mode    less than 0x10ffff and a valid codepoint
436    .sp
437    Invalid Unicode codepoints are the range 0xd800 to 0xdfff (the so-called
438    "surrogate" codepoints), and 0xffef.
439    .
440    .
441    .SS "Escape sequences in character classes"
442    .rs
443    .sp
444  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
445  and outside character classes. In addition, inside a character class, \eb is  and outside character classes. In addition, inside a character class, \eb is
446  interpreted as the backspace character (hex 08).  interpreted as the backspace character (hex 08).
# Line 399  Another use of backslash is for specifyi Line 506  Another use of backslash is for specifyi
506  .sp  .sp
507    \ed     any decimal digit    \ed     any decimal digit
508    \eD     any character that is not a decimal digit    \eD     any character that is not a decimal digit
509    \eh     any horizontal whitespace character    \eh     any horizontal white space character
510    \eH     any character that is not a horizontal whitespace character    \eH     any character that is not a horizontal white space character
511    \es     any whitespace character    \es     any white space character
512    \eS     any character that is not a whitespace character    \eS     any character that is not a white space character
513    \ev     any vertical whitespace character    \ev     any vertical white space character
514    \eV     any character that is not a vertical whitespace character    \eV     any character that is not a vertical white space character
515    \ew     any "word" character    \ew     any "word" character
516    \eW     any "non-word" character    \eW     any "non-word" character
517  .sp  .sp
# Line 424  classes. They each match one character o Line 531  classes. They each match one character o
531  matching point is at the end of the subject string, all of them fail, because  matching point is at the end of the subject string, all of them fail, because
532  there is no character to match.  there is no character to match.
533  .P  .P
534  For compatibility with Perl, \es does not match the VT character (code 11).  For compatibility with Perl, \es did not used to match the VT character (code
535  This makes it different from the the POSIX "space" class. The \es characters  11), which made it different from the the POSIX "space" class. However, Perl
536  are HT (9), LF (10), FF (12), CR (13), and space (32). If "use locale;" is  added VT at release 5.18, and PCRE followed suit at release 8.34. The \es
537  included in a Perl script, \es may match the VT character. In PCRE, it never  characters are now HT (9), LF (10), VT (11), FF (12), CR (13), and space (32).
 does.  
538  .P  .P
539  A "word" character is an underscore or any character that is a letter or digit.  A "word" character is an underscore or any character that is a letter or digit.
540  By default, the definition of letters and digits is controlled by PCRE's  By default, the definition of letters and digits is controlled by PCRE's
# Line 454  efficiency reasons. However, if PCRE is Line 560  efficiency reasons. However, if PCRE is
560  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
561  properties are used to determine character types, as follows:  properties are used to determine character types, as follows:
562  .sp  .sp
563    \ed  any character that \ep{Nd} matches (decimal digit)    \ed  any character that matches \ep{Nd} (decimal digit)
564    \es  any character that \ep{Z} matches, plus HT, LF, FF, CR    \es  any character that matches \ep{Z} or \eh or \ev
565    \ew  any character that \ep{L} or \ep{N} matches, plus underscore    \ew  any character that matches \ep{L} or \ep{N}, plus underscore
566  .sp  .sp
567  The upper case escapes match the inverse sets of characters. Note that \ed  The upper case escapes match the inverse sets of characters. Note that \ed
568  matches only decimal digits, whereas \ew matches any Unicode digit, as well as  matches only decimal digits, whereas \ew matches any Unicode digit, as well as
# Line 469  release 5.10. In contrast to the other s Line 575  release 5.10. In contrast to the other s
575  characters by default, these always match certain high-valued codepoints,  characters by default, these always match certain high-valued codepoints,
576  whether or not PCRE_UCP is set. The horizontal space characters are:  whether or not PCRE_UCP is set. The horizontal space characters are:
577  .sp  .sp
578    U+0009     Horizontal tab    U+0009     Horizontal tab (HT)
579    U+0020     Space    U+0020     Space
580    U+00A0     Non-break space    U+00A0     Non-break space
581    U+1680     Ogham space mark    U+1680     Ogham space mark
# Line 491  whether or not PCRE_UCP is set. The hori Line 597  whether or not PCRE_UCP is set. The hori
597  .sp  .sp
598  The vertical space characters are:  The vertical space characters are:
599  .sp  .sp
600    U+000A     Linefeed    U+000A     Linefeed (LF)
601    U+000B     Vertical tab    U+000B     Vertical tab (VT)
602    U+000C     Formfeed    U+000C     Form feed (FF)
603    U+000D     Carriage return    U+000D     Carriage return (CR)
604    U+0085     Next line    U+0085     Next line (NEL)
605    U+2028     Line separator    U+2028     Line separator
606    U+2029     Paragraph separator    U+2029     Paragraph separator
607  .sp  .sp
# Line 520  below. Line 626  below.
626  .\"  .\"
627  This particular group matches either the two-character sequence CR followed by  This particular group matches either the two-character sequence CR followed by
628  LF, or one of the single characters LF (linefeed, U+000A), VT (vertical tab,  LF, or one of the single characters LF (linefeed, U+000A), VT (vertical tab,
629  U+000B), FF (formfeed, U+000C), CR (carriage return, U+000D), or NEL (next  U+000B), FF (form feed, U+000C), CR (carriage return, U+000D), or NEL (next
630  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
631  cannot be split.  cannot be split.
632  .P  .P
# Line 549  change of newline convention; for exampl Line 655  change of newline convention; for exampl
655  .sp  .sp
656    (*ANY)(*BSR_ANYCRLF)    (*ANY)(*BSR_ANYCRLF)
657  .sp  .sp
658  They can also be combined with the (*UTF8), (*UTF16), or (*UCP) special  They can also be combined with the (*UTF8), (*UTF16), (*UTF32), (*UTF) or
659  sequences. Inside a character class, \eR is treated as an unrecognized escape  (*UCP) special sequences. Inside a character class, \eR is treated as an
660  sequence, and so matches the letter "R" by default, but causes an error if  unrecognized escape sequence, and so matches the letter "R" by default, but
661  PCRE_EXTRA is set.  causes an error if PCRE_EXTRA is set.
662  .  .
663  .  .
664  .\" HTML <a name="uniextseq"></a>  .\" HTML <a name="uniextseq"></a>
# Line 567  The extra escape sequences are: Line 673  The extra escape sequences are:
673  .sp  .sp
674    \ep{\fIxx\fP}   a character with the \fIxx\fP property    \ep{\fIxx\fP}   a character with the \fIxx\fP property
675    \eP{\fIxx\fP}   a character without the \fIxx\fP property    \eP{\fIxx\fP}   a character without the \fIxx\fP property
676    \eX       an extended Unicode sequence    \eX       a Unicode extended grapheme cluster
677  .sp  .sp
678  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
679  script names, the general category properties, "Any", which matches any  script names, the general category properties, "Any", which matches any
# Line 760  a modifier or "other". Line 866  a modifier or "other".
866  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
867  U+DFFF. Such characters are not valid in Unicode strings and so  U+DFFF. Such characters are not valid in Unicode strings and so
868  cannot be tested by PCRE, unless UTF validity checking has been turned off  cannot be tested by PCRE, unless UTF validity checking has been turned off
869  (see the discussion of PCRE_NO_UTF8_CHECK and PCRE_NO_UTF16_CHECK in the  (see the discussion of PCRE_NO_UTF8_CHECK, PCRE_NO_UTF16_CHECK and
870    PCRE_NO_UTF32_CHECK in the
871  .\" HREF  .\" HREF
872  \fBpcreapi\fP  \fBpcreapi\fP
873  .\"  .\"
# Line 775  Instead, this property is assumed for an Line 882  Instead, this property is assumed for an
882  Unicode table.  Unicode table.
883  .P  .P
884  Specifying caseless matching does not affect these escape sequences. For  Specifying caseless matching does not affect these escape sequences. For
885  example, \ep{Lu} always matches only upper case letters.  example, \ep{Lu} always matches only upper case letters. This is different from
886    the behaviour of current versions of Perl.
887  .P  .P
888  The \eX escape matches any number of Unicode characters that form an extended  Matching characters by Unicode property is not fast, because PCRE has to do a
889  Unicode sequence. \eX is equivalent to  multistage table lookup in order to find a character's property. That is why
890  .sp  the traditional escape sequences such as \ed and \ew do not use Unicode
891    (?>\ePM\epM*)  properties in PCRE by default, though you can make them do so by setting the
892    PCRE_UCP option or by starting the pattern with (*UCP).
893    .
894    .
895    .SS Extended grapheme clusters
896    .rs
897  .sp  .sp
898  That is, it matches a character without the "mark" property, followed by zero  The \eX escape matches any number of Unicode characters that form an "extended
899  or more characters with the "mark" property, and treats the sequence as an  grapheme cluster", and treats the sequence as an atomic group
 atomic group  
900  .\" HTML <a href="#atomicgroup">  .\" HTML <a href="#atomicgroup">
901  .\" </a>  .\" </a>
902  (see below).  (see below).
903  .\"  .\"
904  Characters with the "mark" property are typically accents that affect the  Up to and including release 8.31, PCRE matched an earlier, simpler definition
905  preceding character. None of them have codepoints less than 256, so in  that was equivalent to
906  8-bit non-UTF-8 mode \eX matches any one character.  .sp
907  .P    (?>\ePM\epM*)
908  Note that recent versions of Perl have changed \eX to match what Unicode calls  .sp
909  an "extended grapheme cluster", which has a more complicated definition.  That is, it matched a character without the "mark" property, followed by zero
910  .P  or more characters with the "mark" property. Characters with the "mark"
911  Matching characters by Unicode property is not fast, because PCRE has to search  property are typically non-spacing accents that affect the preceding character.
912  a structure that contains data for over fifteen thousand characters. That is  .P
913  why the traditional escape sequences such as \ed and \ew do not use Unicode  This simple definition was extended in Unicode to include more complicated
914  properties in PCRE by default, though you can make them do so by setting the  kinds of composite character by giving each character a grapheme breaking
915  PCRE_UCP option or by starting the pattern with (*UCP).  property, and creating rules that use these properties to define the boundaries
916    of extended grapheme clusters. In releases of PCRE later than 8.31, \eX matches
917    one of these clusters.
918    .P
919    \eX always matches at least one character. Then it decides whether to add
920    additional characters according to the following rules for ending a cluster:
921    .P
922    1. End at the end of the subject string.
923    .P
924    2. Do not end between CR and LF; otherwise end after any control character.
925    .P
926    3. Do not break Hangul (a Korean script) syllable sequences. Hangul characters
927    are of five types: L, V, T, LV, and LVT. An L character may be followed by an
928    L, V, LV, or LVT character; an LV or V character may be followed by a V or T
929    character; an LVT or T character may be follwed only by a T character.
930    .P
931    4. Do not end before extending characters or spacing marks. Characters with
932    the "mark" property always have the "extend" grapheme breaking property.
933    .P
934    5. Do not end after prepend characters.
935    .P
936    6. Otherwise, end the cluster.
937  .  .
938  .  .
939  .\" HTML <a name="extraprops"></a>  .\" HTML <a name="extraprops"></a>
940  .SS PCRE's additional properties  .SS PCRE's additional properties
941  .rs  .rs
942  .sp  .sp
943  As well as the standard Unicode properties described in the previous  As well as the standard Unicode properties described above, PCRE supports four
944  section, PCRE supports four more that make it possible to convert traditional  more that make it possible to convert traditional escape sequences such as \ew
945  escape sequences such as \ew and \es and POSIX character classes to use Unicode  and \es to use Unicode properties. PCRE uses these non-standard, non-Perl
946  properties. PCRE uses these non-standard, non-Perl properties internally when  properties internally when PCRE_UCP is set. However, they may also be used
947  PCRE_UCP is set. They are:  explicitly. These properties are:
948  .sp  .sp
949    Xan   Any alphanumeric character    Xan   Any alphanumeric character
950    Xps   Any POSIX space character    Xps   Any POSIX space character
# Line 819  PCRE_UCP is set. They are: Line 952  PCRE_UCP is set. They are:
952    Xwd   Any Perl "word" character    Xwd   Any Perl "word" character
953  .sp  .sp
954  Xan matches characters that have either the L (letter) or the N (number)  Xan matches characters that have either the L (letter) or the N (number)
955  property. Xps matches the characters tab, linefeed, vertical tab, formfeed, or  property. Xps matches the characters tab, linefeed, vertical tab, form feed, or
956  carriage return, and any other character that has the Z (separator) property.  carriage return, and any other character that has the Z (separator) property.
957  Xsp is the same as Xps, except that vertical tab is excluded. Xwd matches the  Xsp is the same as Xps; it used to exclude vertical tab, for Perl
958  same characters as Xan, plus underscore.  compatibility, but Perl changed, and so PCRE followed at release 8.34. Xwd
959    matches the same characters as Xan, plus underscore.
960    .P
961    There is another non-standard property, Xuc, which matches any character that
962    can be represented by a Universal Character Name in C++ and other programming
963    languages. These are the characters $, @, ` (grave accent), and all characters
964    with Unicode code points greater than or equal to U+00A0, except for the
965    surrogates U+D800 to U+DFFF. Note that most base (ASCII) characters are
966    excluded. (Universal Character Names are of the form \euHHHH or \eUHHHHHHHH
967    where H is a hexadecimal digit. Note that the Xuc property does not match these
968    sequences but the characters that they represent.)
969  .  .
970  .  .
971  .\" HTML <a name="resetmatchstart"></a>  .\" HTML <a name="resetmatchstart"></a>
# Line 928  regular expression. Line 1071  regular expression.
1071  .SH "CIRCUMFLEX AND DOLLAR"  .SH "CIRCUMFLEX AND DOLLAR"
1072  .rs  .rs
1073  .sp  .sp
1074    The circumflex and dollar metacharacters are zero-width assertions. That is,
1075    they test for a particular condition being true without consuming any
1076    characters from the subject string.
1077    .P
1078  Outside a character class, in the default matching mode, the circumflex  Outside a character class, in the default matching mode, the circumflex
1079  character is an assertion that is true only if the current matching point is  character is an assertion that is true only if the current matching point is at
1080  at the start of the subject string. If the \fIstartoffset\fP argument of  the start of the subject string. If the \fIstartoffset\fP argument of
1081  \fBpcre_exec()\fP is non-zero, circumflex can never match if the PCRE_MULTILINE  \fBpcre_exec()\fP is non-zero, circumflex can never match if the PCRE_MULTILINE
1082  option is unset. Inside a character class, circumflex has an entirely different  option is unset. Inside a character class, circumflex has an entirely different
1083  meaning  meaning
# Line 947  constrained to match only at the start o Line 1094  constrained to match only at the start o
1094  "anchored" pattern. (There are also other constructs that can cause a pattern  "anchored" pattern. (There are also other constructs that can cause a pattern
1095  to be anchored.)  to be anchored.)
1096  .P  .P
1097  A dollar character is an assertion that is true only if the current matching  The dollar character is an assertion that is true only if the current matching
1098  point is at the end of the subject string, or immediately before a newline  point is at the end of the subject string, or immediately before a newline at
1099  at the end of the string (by default). Dollar need not be the last character of  the end of the string (by default). Note, however, that it does not actually
1100  the pattern if a number of alternatives are involved, but it should be the last  match the newline. Dollar need not be the last character of the pattern if a
1101  item in any branch in which it appears. Dollar has no special meaning in a  number of alternatives are involved, but it should be the last item in any
1102  character class.  branch in which it appears. Dollar has no special meaning in a character class.
1103  .P  .P
1104  The meaning of dollar can be changed so that it matches only at the very end of  The meaning of dollar can be changed so that it matches only at the very end of
1105  the string, by setting the PCRE_DOLLAR_ENDONLY option at compile time. This  the string, by setting the PCRE_DOLLAR_ENDONLY option at compile time. This
# Line 1013  name; PCRE does not support this. Line 1160  name; PCRE does not support this.
1160  .sp  .sp
1161  Outside a character class, the escape sequence \eC matches any one data unit,  Outside a character class, the escape sequence \eC matches any one data unit,
1162  whether or not a UTF mode is set. In the 8-bit library, one data unit is one  whether or not a UTF mode is set. In the 8-bit library, one data unit is one
1163  byte; in the 16-bit library it is a 16-bit unit. Unlike a dot, \eC always  byte; in the 16-bit library it is a 16-bit unit; in the 32-bit library it is
1164    a 32-bit unit. Unlike a dot, \eC always
1165  matches line-ending characters. The feature is provided in Perl in order to  matches line-ending characters. The feature is provided in Perl in order to
1166  match individual bytes in UTF-8 mode, but it is unclear how it can usefully be  match individual bytes in UTF-8 mode, but it is unclear how it can usefully be
1167  used. Because \eC breaks up characters into individual data units, matching one  used. Because \eC breaks up characters into individual data units, matching one
1168  unit with \eC in a UTF mode means that the rest of the string may start with a  unit with \eC in a UTF mode means that the rest of the string may start with a
1169  malformed UTF character. This has undefined results, because PCRE assumes that  malformed UTF character. This has undefined results, because PCRE assumes that
1170  it is dealing with valid UTF strings (and by default it checks this at the  it is dealing with valid UTF strings (and by default it checks this at the
1171  start of processing unless the PCRE_NO_UTF8_CHECK or PCRE_NO_UTF16_CHECK option  start of processing unless the PCRE_NO_UTF8_CHECK, PCRE_NO_UTF16_CHECK or
1172  is used).  PCRE_NO_UTF32_CHECK option is used).
1173  .P  .P
1174  PCRE does not allow \eC to appear in lookbehind assertions  PCRE does not allow \eC to appear in lookbehind assertions
1175  .\" HTML <a href="#lookbehind">  .\" HTML <a href="#lookbehind">
# Line 1080  circumflex is not an assertion; it still Line 1228  circumflex is not an assertion; it still
1228  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
1229  string.  string.
1230  .P  .P
1231  In UTF-8 (UTF-16) mode, characters with values greater than 255 (0xffff) can be  In UTF-8 (UTF-16, UTF-32) mode, characters with values greater than 255 (0xffff)
1232  included in a class as a literal string of data units, or by using the \ex{  can be included in a class as a literal string of data units, or by using the
1233  escaping mechanism.  \ex{ escaping mechanism.
1234  .P  .P
1235  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
1236  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
# Line 1104  The minus (hyphen) character can be used Line 1252  The minus (hyphen) character can be used
1252  character class. For example, [d-m] matches any letter between d and m,  character class. For example, [d-m] matches any letter between d and m,
1253  inclusive. If a minus character is required in a class, it must be escaped with  inclusive. If a minus character is required in a class, it must be escaped with
1254  a backslash or appear in a position where it cannot be interpreted as  a backslash or appear in a position where it cannot be interpreted as
1255  indicating a range, typically as the first or last character in the class.  indicating a range, typically as the first or last character in the class, or
1256    immediately after a range. For example, [b-d-z] matches letters in the range b
1257    to d, a hyphen character, or z.
1258  .P  .P
1259  It is not possible to have the literal character "]" as the end character of a  It is not possible to have the literal character "]" as the end character of a
1260  range. A pattern such as [W-]46] is interpreted as a class of two characters  range. A pattern such as [W-]46] is interpreted as a class of two characters
# Line 1114  the end of range, so [W-\e]46] is interp Line 1264  the end of range, so [W-\e]46] is interp
1264  followed by two other characters. The octal or hexadecimal representation of  followed by two other characters. The octal or hexadecimal representation of
1265  "]" can also be used to end a range.  "]" can also be used to end a range.
1266  .P  .P
1267    An error is generated if a POSIX character class (see below) or an escape
1268    sequence other than one that defines a single character appears at a point
1269    where a range ending character is expected. For example, [z-\exff] is valid,
1270    but [A-\ed] and [A-[:digit:]] are not.
1271    .P
1272  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
1273  used for characters specified numerically, for example [\e000-\e037]. Ranges  used for characters specified numerically, for example [\e000-\e037]. Ranges
1274  can include any characters that are valid for the current mode.  can include any characters that are valid for the current mode.
# Line 1179  are: Line 1334  are:
1334    lower    lower case letters    lower    lower case letters
1335    print    printing characters, including space    print    printing characters, including space
1336    punct    printing characters, excluding letters and digits and space    punct    printing characters, excluding letters and digits and space
1337    space    white space (not quite the same as \es)    space    white space (the same as \es from PCRE 8.34)
1338    upper    upper case letters    upper    upper case letters
1339    word     "word" characters (same as \ew)    word     "word" characters (same as \ew)
1340    xdigit   hexadecimal digits    xdigit   hexadecimal digits
1341  .sp  .sp
1342  The "space" characters are HT (9), LF (10), VT (11), FF (12), CR (13), and  The "space" characters are HT (9), LF (10), VT (11), FF (12), CR (13), and
1343  space (32). Notice that this list includes the VT character (code 11). This  space (32). "Space" used to be different to \es, which did not include VT, for
1344  makes "space" different to \es, which does not include VT (for Perl  Perl compatibility. However, Perl changed at release 5.18, and PCRE followed at
1345  compatibility).  release 8.34. "Space" and \es now match the same set of characters.
1346  .P  .P
1347  The name "word" is a Perl extension, and "blank" is a GNU extension from Perl  The name "word" is a Perl extension, and "blank" is a GNU extension from Perl
1348  5.8. Another Perl extension is negation, which is indicated by a ^ character  5.8. Another Perl extension is negation, which is indicated by a ^ character
# Line 1202  supported, and an error is given if they Line 1357  supported, and an error is given if they
1357  By default, in UTF modes, characters with values greater than 128 do not match  By default, in UTF modes, characters with values greater than 128 do not match
1358  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
1359  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
1360  character properties are used. This is achieved by replacing the POSIX classes  character properties are used. This is achieved by replacing certain POSIX
1361  by other sequences, as follows:  classes by other sequences, as follows:
1362  .sp  .sp
1363    [:alnum:]  becomes  \ep{Xan}    [:alnum:]  becomes  \ep{Xan}
1364    [:alpha:]  becomes  \ep{L}    [:alpha:]  becomes  \ep{L}
# Line 1214  by other sequences, as follows: Line 1369  by other sequences, as follows:
1369    [:upper:]  becomes  \ep{Lu}    [:upper:]  becomes  \ep{Lu}
1370    [:word:]   becomes  \ep{Xwd}    [:word:]   becomes  \ep{Xwd}
1371  .sp  .sp
1372  Negated versions, such as [:^alpha:] use \eP instead of \ep. The other POSIX  Negated versions, such as [:^alpha:] use \eP instead of \ep. Three other POSIX
1373  classes are unchanged, and match only characters with code points less than  classes are handled specially in UCP mode:
1374  128.  .TP 10
1375    [:graph:]
1376    This matches characters that have glyphs that mark the page when printed. In
1377    Unicode property terms, it matches all characters with the L, M, N, P, S, or Cf
1378    properties, except for:
1379    .sp
1380      U+061C           Arabic Letter Mark
1381      U+180E           Mongolian Vowel Separator
1382      U+2066 - U+2069  Various "isolate"s
1383    .sp
1384    .TP 10
1385    [:print:]
1386    This matches the same characters as [:graph:] plus space characters that are
1387    not controls, that is, characters with the Zs property.
1388    .TP 10
1389    [:punct:]
1390    This matches all characters that have the Unicode P (punctuation) property,
1391    plus those characters whose code points are less than 128 that have the S
1392    (Symbol) property.
1393    .P
1394    The other POSIX classes are unchanged, and match only characters with code
1395    points less than 128.
1396  .  .
1397  .  .
1398  .SH "VERTICAL BAR"  .SH "VERTICAL BAR"
# Line 1295  the section entitled Line 1471  the section entitled
1471  .\" </a>  .\" </a>
1472  "Newline sequences"  "Newline sequences"
1473  .\"  .\"
1474  above. There are also the (*UTF8), (*UTF16), and (*UCP) leading sequences that  above. There are also the (*UTF8), (*UTF16),(*UTF32), and (*UCP) leading
1475  can be used to set UTF and Unicode property modes; they are equivalent to  sequences that can be used to set UTF and Unicode property modes; they are
1476  setting the PCRE_UTF8, PCRE_UTF16, and the PCRE_UCP options, respectively.  equivalent to setting the PCRE_UTF8, PCRE_UTF16, PCRE_UTF32 and the PCRE_UCP
1477    options, respectively. The (*UTF) sequence is a generic version that can be
1478    used with any of the libraries. However, the application can set the
1479    PCRE_NEVER_UTF option, which locks out the use of the (*UTF) sequences.
1480  .  .
1481  .  .
1482  .\" HTML <a name="subpattern"></a>  .\" HTML <a name="subpattern"></a>
# Line 1433  conditions, Line 1612  conditions,
1612  .\"  .\"
1613  can be made by name as well as by number.  can be made by name as well as by number.
1614  .P  .P
1615  Names consist of up to 32 alphanumeric characters and underscores. Named  Names consist of up to 32 alphanumeric characters and underscores, but must
1616  capturing parentheses are still allocated numbers as well as names, exactly as  start with a non-digit. Named capturing parentheses are still allocated numbers
1617  if the names were not present. The PCRE API provides function calls for  as well as names, exactly as if the names were not present. The PCRE API
1618  extracting the name-to-number translation table from a compiled pattern. There  provides function calls for extracting the name-to-number translation table
1619  is also a convenience function for extracting a captured substring by name.  from a compiled pattern. There is also a convenience function for extracting a
1620    captured substring by name.
1621  .P  .P
1622  By default, a name must be unique within a pattern, but it is possible to relax  By default, a name must be unique within a pattern, but it is possible to relax
1623  this constraint by setting the PCRE_DUPNAMES option at compile time. (Duplicate  this constraint by setting the PCRE_DUPNAMES option at compile time. (Duplicate
# Line 1463  for the first (and in this example, the Line 1643  for the first (and in this example, the
1643  matched. This saves searching to find which numbered subpattern it was.  matched. This saves searching to find which numbered subpattern it was.
1644  .P  .P
1645  If you make a back reference to a non-unique named subpattern from elsewhere in  If you make a back reference to a non-unique named subpattern from elsewhere in
1646  the pattern, the one that corresponds to the first occurrence of the name is  the pattern, the subpatterns to which the name refers are checked in the order
1647  used. In the absence of duplicate numbers (see the previous section) this is  in which they appear in the overall pattern. The first one that is set is used
1648  the one with the lowest number. If you use a named reference in a condition  for the reference. For example, this pattern matches both "foofoo" and
1649    "barbar" but not "foobar" or "barfoo":
1650    .sp
1651      (?:(?<n>foo)|(?<n>bar))\k<n>
1652    .sp
1653    .P
1654    If you make a subroutine call to a non-unique named subpattern, the one that
1655    corresponds to the first occurrence of the name is used. In the absence of
1656    duplicate numbers (see the previous section) this is the one with the lowest
1657    number.
1658    .P
1659    If you use a named reference in a condition
1660  test (see the  test (see the
1661  .\"  .\"
1662  .\" HTML <a href="#conditions">  .\" HTML <a href="#conditions">
# Line 1485  documentation. Line 1676  documentation.
1676  \fBWarning:\fP You cannot use different names to distinguish between two  \fBWarning:\fP You cannot use different names to distinguish between two
1677  subpatterns with the same number because PCRE uses only the numbers when  subpatterns with the same number because PCRE uses only the numbers when
1678  matching. For this reason, an error is given at compile time if different names  matching. For this reason, an error is given at compile time if different names
1679  are given to subpatterns with the same number. However, you can give the same  are given to subpatterns with the same number. However, you can always give the
1680  name to subpatterns with the same number, even when PCRE_DUPNAMES is not set.  same name to subpatterns with the same number, even when PCRE_DUPNAMES is not
1681    set.
1682  .  .
1683  .  .
1684  .SH REPETITION  .SH REPETITION
# Line 1532  quantifier, but a literal string of four Line 1724  quantifier, but a literal string of four
1724  In UTF modes, quantifiers apply to characters rather than to individual data  In UTF modes, quantifiers apply to characters rather than to individual data
1725  units. Thus, for example, \ex{100}{2} matches two characters, each of  units. Thus, for example, \ex{100}{2} matches two characters, each of
1726  which is represented by a two-byte sequence in a UTF-8 string. Similarly,  which is represented by a two-byte sequence in a UTF-8 string. Similarly,
1727  \eX{3} matches three Unicode extended sequences, each of which may be several  \eX{3} matches three Unicode extended grapheme clusters, each of which may be
1728  data units long (and they may be of different lengths).  several data units long (and they may be of different lengths).
1729  .P  .P
1730  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
1731  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 1619  In cases where it is known that the subj Line 1811  In cases where it is known that the subj
1811  worth setting PCRE_DOTALL in order to obtain this optimization, or  worth setting PCRE_DOTALL in order to obtain this optimization, or
1812  alternatively using ^ to indicate anchoring explicitly.  alternatively using ^ to indicate anchoring explicitly.
1813  .P  .P
1814  However, there is one situation where the optimization cannot be used. When .*  However, there are some cases where the optimization cannot be used. When .*
1815  is inside capturing parentheses that are the subject of a back reference  is inside capturing parentheses that are the subject of a back reference
1816  elsewhere in the pattern, a match at the start may fail where a later one  elsewhere in the pattern, a match at the start may fail where a later one
1817  succeeds. Consider, for example:  succeeds. Consider, for example:
# Line 1629  succeeds. Consider, for example: Line 1821  succeeds. Consider, for example:
1821  If the subject is "xyz123abc123" the match point is the fourth character. For  If the subject is "xyz123abc123" the match point is the fourth character. For
1822  this reason, such a pattern is not implicitly anchored.  this reason, such a pattern is not implicitly anchored.
1823  .P  .P
1824    Another case where implicit anchoring is not applied is when the leading .* is
1825    inside an atomic group. Once again, a match at the start may fail where a later
1826    one succeeds. Consider this pattern:
1827    .sp
1828      (?>.*?a)b
1829    .sp
1830    It matches "ab" in the subject "aab". The use of the backtracking control verbs
1831    (*PRUNE) and (*SKIP) also disable this optimization.
1832    .P
1833  When a capturing subpattern is repeated, the value captured is the substring  When a capturing subpattern is repeated, the value captured is the substring
1834  that matched the final iteration. For example, after  that matched the final iteration. For example, after
1835  .sp  .sp
# Line 1843  Because there may be many capturing pare Line 2044  Because there may be many capturing pare
2044  following a backslash are taken as part of a potential back reference number.  following a backslash are taken as part of a potential back reference number.
2045  If the pattern continues with a digit character, some delimiter must be used to  If the pattern continues with a digit character, some delimiter must be used to
2046  terminate the back reference. If the PCRE_EXTENDED option is set, this can be  terminate the back reference. If the PCRE_EXTENDED option is set, this can be
2047  whitespace. Otherwise, the \eg{ syntax or an empty comment (see  white space. Otherwise, the \eg{ syntax or an empty comment (see
2048  .\" HTML <a href="#comments">  .\" HTML <a href="#comments">
2049  .\" </a>  .\" </a>
2050  "Comments"  "Comments"
# Line 1897  except that it does not cause the curren Line 2098  except that it does not cause the curren
2098  Assertion subpatterns are not capturing subpatterns. If such an assertion  Assertion subpatterns are not capturing subpatterns. If such an assertion
2099  contains capturing subpatterns within it, these are counted for the purposes of  contains capturing subpatterns within it, these are counted for the purposes of
2100  numbering the capturing subpatterns in the whole pattern. However, substring  numbering the capturing subpatterns in the whole pattern. However, substring
2101  capturing is carried out only for positive assertions, because it does not make  capturing is carried out only for positive assertions. (Perl sometimes, but not
2102  sense for negative assertions.  always, does do capturing in negative assertions.)
2103  .P  .P
2104  For compatibility with Perl, assertion subpatterns may be repeated; though  For compatibility with Perl, assertion subpatterns may be repeated; though
2105  it makes no sense to assert the same thing several times, the side effect of  it makes no sense to assert the same thing several times, the side effect of
# Line 2148  This makes the fragment independent of t Line 2349  This makes the fragment independent of t
2349  .sp  .sp
2350  Perl uses the syntax (?(<name>)...) or (?('name')...) to test for a used  Perl uses the syntax (?(<name>)...) or (?('name')...) to test for a used
2351  subpattern by name. For compatibility with earlier versions of PCRE, which had  subpattern by name. For compatibility with earlier versions of PCRE, which had
2352  this facility before Perl, the syntax (?(name)...) is also recognized. However,  this facility before Perl, the syntax (?(name)...) is also recognized.
 there is a possible ambiguity with this syntax, because subpattern names may  
 consist entirely of digits. PCRE looks first for a named subpattern; if it  
 cannot find one and the name consists entirely of digits, PCRE looks for a  
 subpattern of that number, which must be greater than zero. Using subpattern  
 names that consist entirely of digits is not recommended.  
2353  .P  .P
2354  Rewriting the above example to use a named subpattern gives this:  Rewriting the above example to use a named subpattern gives this:
2355  .sp  .sp
# Line 2200  subroutines that can be referenced from Line 2396  subroutines that can be referenced from
2396  subroutines  subroutines
2397  .\"  .\"
2398  is described below.) For example, a pattern to match an IPv4 address such as  is described below.) For example, a pattern to match an IPv4 address such as
2399  "192.168.23.245" could be written like this (ignore whitespace and line  "192.168.23.245" could be written like this (ignore white space and line
2400  breaks):  breaks):
2401  .sp  .sp
2402    (?(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) )
# Line 2550  same pair of parentheses when there is a Line 2746  same pair of parentheses when there is a
2746  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
2747  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
2748  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
2749  (8-bit library) or \fIpcre16_callout\fP (16-bit library). By default, this  (8-bit library) or \fIpcre[16|32]_callout\fP (16-bit or 32-bit library).
2750  variable contains NULL, which disables all calling out.  By default, this variable contains NULL, which disables all calling out.
2751  .P  .P
2752  Within a regular expression, (?C) indicates the points at which the external  Within a regular expression, (?C) indicates the points at which the external
2753  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 2562  For example, this pattern has two callou Line 2758  For example, this pattern has two callou
2758  .sp  .sp
2759  If the PCRE_AUTO_CALLOUT flag is passed to a compiling function, callouts are  If the PCRE_AUTO_CALLOUT flag is passed to a compiling function, callouts are
2760  automatically installed before each item in the pattern. They are all numbered  automatically installed before each item in the pattern. They are all numbered
2761  255.  255. If there is a conditional group in the pattern whose condition is an
2762    assertion, an additional callout is inserted just before the condition. An
2763    explicit callout may also be set at this position, as in this example:
2764    .sp
2765      (?(?C9)(?=a)abc|def)
2766    .sp
2767    Note that this applies only to assertion conditions, not to other types of
2768    condition.
2769  .P  .P
2770  During matching, when PCRE reaches a callout point, the external function is  During matching, when PCRE reaches a callout point, the external function is
2771  called. It is provided with the number of the callout, the position in the  called. It is provided with the number of the callout, the position in the
2772  pattern, and, optionally, one item of data originally supplied by the caller of  pattern, and, optionally, one item of data originally supplied by the caller of
2773  the matching function. The callout function may cause matching to proceed, to  the matching function. The callout function may cause matching to proceed, to
2774  backtrack, or to fail altogether. A complete description of the interface to  backtrack, or to fail altogether.
2775  the callout function is given in the  .P
2776    By default, PCRE implements a number of optimizations at compile time and
2777    matching time, and one side-effect is that sometimes callouts are skipped. If
2778    you need all possible callouts to happen, you need to set options that disable
2779    the relevant optimizations. More details, and a complete description of the
2780    interface to the callout function, are given in the
2781  .\" HREF  .\" HREF
2782  \fBpcrecallout\fP  \fBpcrecallout\fP
2783  .\"  .\"
# Line 2581  documentation. Line 2789  documentation.
2789  .rs  .rs
2790  .sp  .sp
2791  Perl 5.10 introduced a number of "Special Backtracking Control Verbs", which  Perl 5.10 introduced a number of "Special Backtracking Control Verbs", which
2792  are described in the Perl documentation as "experimental and subject to change  are still described in the Perl documentation as "experimental and subject to
2793  or removal in a future version of Perl". It goes on to say: "Their usage in  change or removal in a future version of Perl". It goes on to say: "Their usage
2794  production code should be noted to avoid problems during upgrades." The same  in production code should be noted to avoid problems during upgrades." The same
2795  remarks apply to the PCRE features described in this section.  remarks apply to the PCRE features described in this section.
2796  .P  .P
2797    The new verbs make use of what was previously invalid syntax: an opening
2798    parenthesis followed by an asterisk. They are generally of the form
2799    (*VERB) or (*VERB:NAME). Some may take either form, possibly behaving
2800    differently depending on whether or not a name is present. A name is any
2801    sequence of characters that does not include a closing parenthesis. The maximum
2802    length of name is 255 in the 8-bit library and 65535 in the 16-bit and 32-bit
2803    libraries. If the name is empty, that is, if the closing parenthesis
2804    immediately follows the colon, the effect is as if the colon were not there.
2805    Any number of these verbs may occur in a pattern.
2806    .P
2807  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
2808  used only when the pattern is to be matched using one of the traditional  used only when the pattern is to be matched using one of the traditional
2809  matching functions, which use a backtracking algorithm. With the exception of  matching functions, because these use a backtracking algorithm. With the
2810  (*FAIL), which behaves like a failing negative assertion, they cause an error  exception of (*FAIL), which behaves like a failing negative assertion, the
2811  if encountered by a DFA matching function.  backtracking control verbs cause an error if encountered by a DFA matching
2812  .P  function.
 If any of these verbs are used in an assertion or in a subpattern that is  
 called as a subroutine (whether or not recursively), their effect is confined  
 to that subpattern; it does not extend to the surrounding pattern, with one  
 exception: the name from a *(MARK), (*PRUNE), or (*THEN) that is encountered in  
 a successful positive assertion \fIis\fP passed back when a match succeeds  
 (compare capturing parentheses in assertions). Note that such subpatterns are  
 processed as anchored at the point where they are tested. Note also that Perl's  
 treatment of subroutines is different in some cases.  
2813  .P  .P
2814  The new verbs make use of what was previously invalid syntax: an opening  The behaviour of these verbs in
2815  parenthesis followed by an asterisk. They are generally of the form  .\" HTML <a href="#btrepeat">
2816  (*VERB) or (*VERB:NAME). Some may take either form, with differing behaviour,  .\" </a>
2817  depending on whether or not an argument is present. A name is any sequence of  repeated groups,
2818  characters that does not include a closing parenthesis. If the name is empty,  .\"
2819  that is, if the closing parenthesis immediately follows the colon, the effect  .\" HTML <a href="#btassert">
2820  is as if the colon were not there. Any number of these verbs may occur in a  .\" </a>
2821  pattern.  assertions,
2822    .\"
2823    and in
2824    .\" HTML <a href="#btsub">
2825    .\" </a>
2826    subpatterns called as subroutines
2827    .\"
2828    (whether or not recursively) is documented below.
2829  .  .
2830  .  .
2831  .\" HTML <a name="nooptimize"></a>  .\" HTML <a name="nooptimize"></a>
# Line 2618  pattern. Line 2835  pattern.
2835  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
2836  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
2837  minimum length of matching subject, or that a particular character must be  minimum length of matching subject, or that a particular character must be
2838  present. When one of these optimizations suppresses the running of a match, any  present. When one of these optimizations bypasses the running of a match, any
2839  included backtracking verbs will not, of course, be processed. You can suppress  included backtracking verbs will not, of course, be processed. You can suppress
2840  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
2841  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
# Line 2632  in the Line 2849  in the
2849  .\" HREF  .\" HREF
2850  \fBpcreapi\fP  \fBpcreapi\fP
2851  .\"  .\"
2852  documentation.  documentation.
2853  .P  .P
2854  Experiments with Perl suggest that it too has similar optimizations, sometimes  Experiments with Perl suggest that it too has similar optimizations, sometimes
2855  leading to anomalous results.  leading to anomalous results.
# Line 2649  followed by a name. Line 2866  followed by a name.
2866  This verb causes the match to end successfully, skipping the remainder of the  This verb causes the match to end successfully, skipping the remainder of the
2867  pattern. However, when it is inside a subpattern that is called as a  pattern. However, when it is inside a subpattern that is called as a
2868  subroutine, only that subpattern is ended successfully. Matching then continues  subroutine, only that subpattern is ended successfully. Matching then continues
2869  at the outer level. If (*ACCEPT) is inside capturing parentheses, the data so  at the outer level. If (*ACCEPT) in triggered in a positive assertion, the
2870  far is captured. For example:  assertion succeeds; in a negative assertion, the assertion fails.
2871    .P
2872    If (*ACCEPT) is inside capturing parentheses, the data so far is captured. For
2873    example:
2874  .sp  .sp
2875    A((?:A|B(*ACCEPT)|C)D)    A((?:A|B(*ACCEPT)|C)D)
2876  .sp  .sp
# Line 2683  starting point (see (*SKIP) below). Line 2903  starting point (see (*SKIP) below).
2903  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
2904  (*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.
2905  .P  .P
2906  When a match succeeds, the name of the last-encountered (*MARK) on the matching  When a match succeeds, the name of the last-encountered (*MARK:NAME),
2907  path is passed back to the caller as described in the section entitled  (*PRUNE:NAME), or (*THEN:NAME) on the matching path is passed back to the
2908    caller as described in the section entitled
2909  .\" HTML <a href="pcreapi.html#extradata">  .\" HTML <a href="pcreapi.html#extradata">
2910  .\" </a>  .\" </a>
2911  "Extra data for \fBpcre_exec()\fP"  "Extra data for \fBpcre_exec()\fP"
# Line 2709  indicates which of the two alternatives Line 2930  indicates which of the two alternatives
2930  of obtaining this information than putting each alternative in its own  of obtaining this information than putting each alternative in its own
2931  capturing parentheses.  capturing parentheses.
2932  .P  .P
2933  If (*MARK) is encountered in a positive assertion, its name is recorded and  If a verb with a name is encountered in a positive assertion that is true, the
2934  passed back if it is the last-encountered. This does not happen for negative  name is recorded and passed back if it is the last-encountered. This does not
2935  assertions.  happen for negative assertions or failing positive assertions.
2936  .P  .P
2937  After a partial match or a failed match, the name of the last encountered  After a partial match or a failed match, the last encountered name in the
2938  (*MARK) in the entire match process is returned. For example:  entire match process is returned. For example:
2939  .sp  .sp
2940      re> /X(*MARK:A)Y|X(*MARK:B)Z/K      re> /X(*MARK:A)Y|X(*MARK:B)Z/K
2941    data> XP    data> XP
# Line 2726  attempts starting at "P" and then with a Line 2947  attempts starting at "P" and then with a
2947  (*MARK) item, but nevertheless do not reset it.  (*MARK) item, but nevertheless do not reset it.
2948  .P  .P
2949  If you are interested in (*MARK) values after failed matches, you should  If you are interested in (*MARK) values after failed matches, you should
2950  probably set the PCRE_NO_START_OPTIMIZE option  probably set the PCRE_NO_START_OPTIMIZE option
2951  .\" HTML <a href="#nooptimize">  .\" HTML <a href="#nooptimize">
2952  .\" </a>  .\" </a>
2953  (see above)  (see above)
2954  .\"  .\"
2955  to ensure that the match is always attempted.  to ensure that the match is always attempted.
2956  .  .
# Line 2740  to ensure that the match is always attem Line 2961  to ensure that the match is always attem
2961  The following verbs do nothing when they are encountered. Matching continues  The following verbs do nothing when they are encountered. Matching continues
2962  with what follows, but if there is no subsequent match, causing a backtrack to  with what follows, but if there is no subsequent match, causing a backtrack to
2963  the verb, a failure is forced. That is, backtracking cannot pass to the left of  the verb, a failure is forced. That is, backtracking cannot pass to the left of
2964  the verb. However, when one of these verbs appears inside an atomic group, its  the verb. However, when one of these verbs appears inside an atomic group or an
2965  effect is confined to that group, because once the group has been matched,  assertion that is true, its effect is confined to that group, because once the
2966  there is never any backtracking into it. In this situation, backtracking can  group has been matched, there is never any backtracking into it. In this
2967  "jump back" to the left of the entire atomic group. (Remember also, as stated  situation, backtracking can "jump back" to the left of the entire atomic group
2968  above, that this localization also applies in subroutine calls and assertions.)  or assertion. (Remember also, as stated above, that this localization also
2969    applies in subroutine calls.)
2970  .P  .P
2971  These verbs differ in exactly what kind of failure occurs when backtracking  These verbs differ in exactly what kind of failure occurs when backtracking
2972  reaches them.  reaches them. The behaviour described below is what happens when the verb is
2973    not in a subroutine or an assertion. Subsequent sections cover these special
2974    cases.
2975  .sp  .sp
2976    (*COMMIT)    (*COMMIT)
2977  .sp  .sp
2978  This verb, which may not be followed by a name, causes the whole match to fail  This verb, which may not be followed by a name, causes the whole match to fail
2979  outright if the rest of the pattern does not match. Even if the pattern is  outright if there is a later matching failure that causes backtracking to reach
2980  unanchored, no further attempts to find a match by advancing the starting point  it. Even if the pattern is unanchored, no further attempts to find a match by
2981  take place. Once (*COMMIT) has been passed, \fBpcre_exec()\fP is committed to  advancing the starting point take place. If (*COMMIT) is the only backtracking
2982  finding a match at the current starting point, or not at all. For example:  verb that is encountered, once it has been passed \fBpcre_exec()\fP is
2983    committed to finding a match at the current starting point, or not at all. For
2984    example:
2985  .sp  .sp
2986    a+(*COMMIT)b    a+(*COMMIT)b
2987  .sp  .sp
# Line 2764  dynamic anchor, or "I've started, so I m Line 2990  dynamic anchor, or "I've started, so I m
2990  recently passed (*MARK) in the path is passed back when (*COMMIT) forces a  recently passed (*MARK) in the path is passed back when (*COMMIT) forces a
2991  match failure.  match failure.
2992  .P  .P
2993    If there is more than one backtracking verb in a pattern, a different one that
2994    follows (*COMMIT) may be triggered first, so merely passing (*COMMIT) during a
2995    match does not always guarantee that a match must be at this starting point.
2996    .P
2997  Note that (*COMMIT) at the start of a pattern is not the same as an anchor,  Note that (*COMMIT) at the start of a pattern is not the same as an anchor,
2998  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
2999  \fBpcretest\fP example:  \fBpcretest\fP example:
# Line 2783  starting points. Line 3013  starting points.
3013    (*PRUNE) or (*PRUNE:NAME)    (*PRUNE) or (*PRUNE:NAME)
3014  .sp  .sp
3015  This verb causes the match to fail at the current starting position in the  This verb causes the match to fail at the current starting position in the
3016  subject if the rest of the pattern does not match. If the pattern is  subject if there is a later matching failure that causes backtracking to reach
3017  unanchored, the normal "bumpalong" advance to the next starting character then  it. If the pattern is unanchored, the normal "bumpalong" advance to the next
3018  happens. Backtracking can occur as usual to the left of (*PRUNE), before it is  starting character then happens. Backtracking can occur as usual to the left of
3019  reached, or when matching to the right of (*PRUNE), but if there is no match to  (*PRUNE), before it is reached, or when matching to the right of (*PRUNE), but
3020  the right, backtracking cannot cross (*PRUNE). In simple cases, the use of  if there is no match to the right, backtracking cannot cross (*PRUNE). In
3021  (*PRUNE) is just an alternative to an atomic group or possessive quantifier,  simple cases, the use of (*PRUNE) is just an alternative to an atomic group or
3022  but there are some uses of (*PRUNE) that cannot be expressed in any other way.  possessive quantifier, but there are some uses of (*PRUNE) that cannot be
3023  The behaviour of (*PRUNE:NAME) is the same as (*MARK:NAME)(*PRUNE). In an  expressed in any other way. In an anchored pattern (*PRUNE) has the same effect
3024  anchored pattern (*PRUNE) has the same effect as (*COMMIT).  as (*COMMIT).
3025    .P
3026    The behaviour of (*PRUNE:NAME) is the not the same as (*MARK:NAME)(*PRUNE).
3027    It is like (*MARK:NAME) in that the name is remembered for passing back to the
3028    caller. However, (*SKIP:NAME) searches only for names set with (*MARK).
3029  .sp  .sp
3030    (*SKIP)    (*SKIP)
3031  .sp  .sp
# Line 2812  instead of skipping on to "c". Line 3046  instead of skipping on to "c".
3046  .sp  .sp
3047    (*SKIP:NAME)    (*SKIP:NAME)
3048  .sp  .sp
3049  When (*SKIP) has an associated name, its behaviour is modified. If the  When (*SKIP) has an associated name, its behaviour is modified. When it is
3050  following pattern fails to match, the previous path through the pattern is  triggered, the previous path through the pattern is searched for the most
3051  searched for the most recent (*MARK) that has the same name. If one is found,  recent (*MARK) that has the same name. If one is found, the "bumpalong" advance
3052  the "bumpalong" advance is to the subject position that corresponds to that  is to the subject position that corresponds to that (*MARK) instead of to where
3053  (*MARK) instead of to where (*SKIP) was encountered. If no (*MARK) with a  (*SKIP) was encountered. If no (*MARK) with a matching name is found, the
3054  matching name is found, the (*SKIP) is ignored.  (*SKIP) is ignored.
3055    .P
3056    Note that (*SKIP:NAME) searches only for names set by (*MARK:NAME). It ignores
3057    names that are set by (*PRUNE:NAME) or (*THEN:NAME).
3058  .sp  .sp
3059    (*THEN) or (*THEN:NAME)    (*THEN) or (*THEN:NAME)
3060  .sp  .sp
3061  This verb causes a skip to the next innermost alternative if the rest of the  This verb causes a skip to the next innermost alternative when backtracking
3062  pattern does not match. That is, it cancels pending backtracking, but only  reaches it. That is, it cancels any further backtracking within the current
3063  within the current alternative. Its name comes from the observation that it can  alternative. Its name comes from the observation that it can be used for a
3064  be used for a pattern-based if-then-else block:  pattern-based if-then-else block:
3065  .sp  .sp
3066    ( COND1 (*THEN) FOO | COND2 (*THEN) BAR | COND3 (*THEN) BAZ ) ...    ( COND1 (*THEN) FOO | COND2 (*THEN) BAR | COND3 (*THEN) BAZ ) ...
3067  .sp  .sp
3068  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
3069  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
3070  second alternative and tries COND2, without backtracking into COND1. The  second alternative and tries COND2, without backtracking into COND1. If that
3071  behaviour of (*THEN:NAME) is exactly the same as (*MARK:NAME)(*THEN).  succeeds and BAR fails, COND3 is tried. If subsequently BAZ fails, there are no
3072  If (*THEN) is not inside an alternation, it acts like (*PRUNE).  more alternatives, so there is a backtrack to whatever came before the entire
3073    group. If (*THEN) is not inside an alternation, it acts like (*PRUNE).
3074    .P
3075    The behaviour of (*THEN:NAME) is the not the same as (*MARK:NAME)(*THEN).
3076    It is like (*MARK:NAME) in that the name is remembered for passing back to the
3077    caller. However, (*SKIP:NAME) searches only for names set with (*MARK).
3078  .P  .P
3079  Note that a subpattern that does not contain a | character is just a part of  A subpattern that does not contain a | character is just a part of the
3080  the enclosing alternative; it is not a nested alternation with only one  enclosing alternative; it is not a nested alternation with only one
3081  alternative. The effect of (*THEN) extends beyond such a subpattern to the  alternative. The effect of (*THEN) extends beyond such a subpattern to the
3082  enclosing alternative. Consider this pattern, where A, B, etc. are complex  enclosing alternative. Consider this pattern, where A, B, etc. are complex
3083  pattern fragments that do not contain any | characters at this level:  pattern fragments that do not contain any | characters at this level:
# Line 2854  in C, matching moves to (*FAIL), which c Line 3096  in C, matching moves to (*FAIL), which c
3096  because there are no more alternatives to try. In this case, matching does now  because there are no more alternatives to try. In this case, matching does now
3097  backtrack into A.  backtrack into A.
3098  .P  .P
3099  Note also that a conditional subpattern is not considered as having two  Note that a conditional subpattern is not considered as having two
3100  alternatives, because only one is ever used. In other words, the | character in  alternatives, because only one is ever used. In other words, the | character in
3101  a conditional subpattern has a different meaning. Ignoring white space,  a conditional subpattern has a different meaning. Ignoring white space,
3102  consider:  consider:
# Line 2876  starting position, but allowing an advan Line 3118  starting position, but allowing an advan
3118  unanchored pattern). (*SKIP) is similar, except that the advance may be more  unanchored pattern). (*SKIP) is similar, except that the advance may be more
3119  than one character. (*COMMIT) is the strongest, causing the entire match to  than one character. (*COMMIT) is the strongest, causing the entire match to
3120  fail.  fail.
3121    .
3122    .
3123    .SS "More than one backtracking verb"
3124    .rs
3125    .sp
3126    If more than one backtracking verb is present in a pattern, the one that is
3127    backtracked onto first acts. For example, consider this pattern, where A, B,
3128    etc. are complex pattern fragments:
3129    .sp
3130      (A(*COMMIT)B(*THEN)C|ABD)
3131    .sp
3132    If A matches but B fails, the backtrack to (*COMMIT) causes the entire match to
3133    fail. However, if A and B match, but C fails, the backtrack to (*THEN) causes
3134    the next alternative (ABD) to be tried. This behaviour is consistent, but is
3135    not always the same as Perl's. It means that if two or more backtracking verbs
3136    appear in succession, all the the last of them has no effect. Consider this
3137    example:
3138    .sp
3139      ...(*COMMIT)(*PRUNE)...
3140    .sp
3141    If there is a matching failure to the right, backtracking onto (*PRUNE) causes
3142    it to be triggered, and its action is taken. There can never be a backtrack
3143    onto (*COMMIT).
3144    .
3145    .
3146    .\" HTML <a name="btrepeat"></a>
3147    .SS "Backtracking verbs in repeated groups"
3148    .rs
3149    .sp
3150    PCRE differs from Perl in its handling of backtracking verbs in repeated
3151    groups. For example, consider:
3152    .sp
3153      /(a(*COMMIT)b)+ac/
3154    .sp
3155    If the subject is "abac", Perl matches, but PCRE fails because the (*COMMIT) in
3156    the second repeat of the group acts.
3157    .
3158    .
3159    .\" HTML <a name="btassert"></a>
3160    .SS "Backtracking verbs in assertions"
3161    .rs
3162    .sp
3163    (*FAIL) in an assertion has its normal effect: it forces an immediate backtrack.
3164    .P
3165    (*ACCEPT) in a positive assertion causes the assertion to succeed without any
3166    further processing. In a negative assertion, (*ACCEPT) causes the assertion to
3167    fail without any further processing.
3168    .P
3169    The other backtracking verbs are not treated specially if they appear in a
3170    positive assertion. In particular, (*THEN) skips to the next alternative in the
3171    innermost enclosing group that has alternations, whether or not this is within
3172    the assertion.
3173    .P
3174    Negative assertions are, however, different, in order to ensure that changing a
3175    positive assertion into a negative assertion changes its result. Backtracking
3176    into (*COMMIT), (*SKIP), or (*PRUNE) causes a negative assertion to be true,
3177    without considering any further alternative branches in the assertion.
3178    Backtracking into (*THEN) causes it to skip to the next enclosing alternative
3179    within the assertion (the normal behaviour), but if the assertion does not have
3180    such an alternative, (*THEN) behaves like (*PRUNE).
3181    .
3182    .
3183    .\" HTML <a name="btsub"></a>
3184    .SS "Backtracking verbs in subroutines"
3185    .rs
3186    .sp
3187    These behaviours occur whether or not the subpattern is called recursively.
3188    Perl's treatment of subroutines is different in some cases.
3189    .P
3190    (*FAIL) in a subpattern called as a subroutine has its normal effect: it forces
3191    an immediate backtrack.
3192    .P
3193    (*ACCEPT) in a subpattern called as a subroutine causes the subroutine match to
3194    succeed without any further processing. Matching then continues after the
3195    subroutine call.
3196    .P
3197    (*COMMIT), (*SKIP), and (*PRUNE) in a subpattern called as a subroutine cause
3198    the subroutine match to fail.
3199  .P  .P
3200  If more than one such verb is present in a pattern, the "strongest" one wins.  (*THEN) skips to the next alternative in the innermost enclosing group within
3201  For example, consider this pattern, where A, B, etc. are complex pattern  the subpattern that has alternatives. If there is no such group within the
3202  fragments:  subpattern, (*THEN) causes the subroutine match to fail.
 .sp  
   (A(*COMMIT)B(*THEN)C|D)  
 .sp  
 Once A has matched, PCRE is committed to this match, at the current starting  
 position. If subsequently B matches, but C does not, the normal (*THEN) action  
 of trying the next alternative (that is, D) does not happen because (*COMMIT)  
 overrides.  
3203  .  .
3204  .  .
3205  .SH "SEE ALSO"  .SH "SEE ALSO"
3206  .rs  .rs
3207  .sp  .sp
3208  \fBpcreapi\fP(3), \fBpcrecallout\fP(3), \fBpcrematching\fP(3),  \fBpcreapi\fP(3), \fBpcrecallout\fP(3), \fBpcrematching\fP(3),
3209  \fBpcresyntax\fP(3), \fBpcre\fP(3), \fBpcre16(3)\fP.  \fBpcresyntax\fP(3), \fBpcre\fP(3), \fBpcre16(3)\fP, \fBpcre32(3)\fP.
3210  .  .
3211  .  .
3212  .SH AUTHOR  .SH AUTHOR
# Line 2910  Cambridge CB2 3QH, England. Line 3223  Cambridge CB2 3QH, England.
3223  .rs  .rs
3224  .sp  .sp
3225  .nf  .nf
3226  Last updated: 14 April 2012  Last updated: 12 November 2013
3227  Copyright (c) 1997-2012 University of Cambridge.  Copyright (c) 1997-2013 University of Cambridge.
3228  .fi  .fi

Legend:
Removed from v.959  
changed lines
  Added in v.1398

  ViewVC Help
Powered by ViewVC 1.1.5