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1  .TH PCREPATTERN 3  .TH PCREPATTERN 3 "26 April 2013" "PCRE 8.33"
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 character strings. To use this,  there is now also support for UTF-8 strings in the original library, an
53  PCRE must be built to include UTF-8 support, and you must call  extra library that supports 16-bit and UTF-16 character strings, and a
54  \fBpcre_compile()\fP or \fBpcre_compile2()\fP with the PCRE_UTF8 option. There  third library that supports 32-bit and UTF-32 character strings. To use these
55  is also a special sequence that can be given at the start of a pattern:  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,
57    PCRE_UTF16, or PCRE_UTF32 option, or the pattern must start with one of
58    these special sequences:
59  .sp  .sp
60    (*UTF8)    (*UTF8)
61  .sp    (*UTF16)
62  Starting a pattern with this sequence is equivalent to setting the PCRE_UTF8    (*UTF32)
63  option. This feature is not Perl-compatible. How setting UTF-8 mode affects    (*UTF)
64  pattern matching is mentioned in several places below. There is also a summary  .sp
65  of UTF-8 features in the  (*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
67    option. How setting a UTF mode affects pattern matching is mentioned in several
68    places below. There is also a summary 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) is:  restrict them to non-UTF data for security reasons. If the PCRE_NEVER_UTF
76    option is set at compile time, (*UTF) etc. are not allowed, and their
77    appearance causes an error.
78    .
79    .
80    .SS "Unicode property support"
81    .rs
82    .sp
83    Another special sequence that may appear at the start of a pattern is
84  .sp  .sp
85    (*UCP)    (*UCP)
86  .sp  .sp
# Line 46  This has the same effect as setting the Line 88  This has the same effect as setting the
88  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,
89  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
90  table.  table.
91  .P  .
92    .
93    .SS "Disabling start-up optimizations"
94    .rs
95    .sp
96  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
97  PCRE_NO_START_OPTIMIZE option either at compile or matching time. There are  PCRE_NO_START_OPTIMIZE option either at compile or matching time.
 also some more of these special sequences that are concerned with the handling  
 of newlines; they are described below.  
 .P  
 The remainder of this document discusses the patterns that are supported by  
 PCRE when its main matching function, \fBpcre_exec()\fP, is used.  
 From release 6.0, PCRE offers a second matching function,  
 \fBpcre_dfa_exec()\fP, which matches using a different algorithm that is not  
 Perl-compatible. Some of the features discussed below are not available when  
 \fBpcre_dfa_exec()\fP is used. The advantages and disadvantages of the  
 alternative function, and how it differs from the normal function, are  
 discussed in the  
 .\" HREF  
 \fBpcrematching\fP  
 .\"  
 page.  
98  .  .
99  .  .
100  .\" HTML <a name="newlines"></a>  .\" HTML <a name="newlines"></a>
101  .SH "NEWLINE CONVENTIONS"  .SS "Newline conventions"
102  .rs  .rs
103  .sp  .sp
104  PCRE supports five different conventions for indicating line breaks in  PCRE supports five different conventions for indicating line breaks in
# Line 94  string with one of the following five se Line 125  string with one of the following five se
125    (*ANYCRLF)   any of the three above    (*ANYCRLF)   any of the three above
126    (*ANY)       all Unicode newline sequences    (*ANY)       all Unicode newline sequences
127  .sp  .sp
128  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
129  \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  
130  .sp  .sp
131    (*CR)a.b    (*CR)a.b
132  .sp  .sp
133  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
134  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  
135  is used.  is used.
136  .P  .P
137  The newline convention affects the interpretation of the dot metacharacter when  The newline convention affects where the circumflex and dollar assertions are
138  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
139  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
140  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
141    sequence, for Perl compatibility. However, this can be changed; see the
142  description of \eR in the section entitled  description of \eR in the section entitled
143  .\" HTML <a href="#newlineseq">  .\" HTML <a href="#newlineseq">
144  .\" </a>  .\" </a>
# Line 119  below. A change of \eR setting can be co Line 148  below. A change of \eR setting can be co
148  convention.  convention.
149  .  .
150  .  .
151    .SS "Setting match and recursion limits"
152    .rs
153    .sp
154    The caller of \fBpcre_exec()\fP can set a limit on the number of times the
155    internal \fBmatch()\fP function is called and on the maximum depth of
156    recursive calls. These facilities are provided to catch runaway matches that
157    are provoked by patterns with huge matching trees (a typical example is a
158    pattern with nested unlimited repeats) and to avoid running out of system stack
159    by too much recursion. When one of these limits is reached, \fBpcre_exec()\fP
160    gives an error return. The limits can also be set by items at the start of the
161    pattern of the form
162    .sp
163      (*LIMIT_MATCH=d)
164      (*LIMIT_RECURSION=d)
165    .sp
166    where d is any number of decimal digits. However, the value of the setting must
167    be less than the value set by the caller of \fBpcre_exec()\fP for it to have
168    any effect. In other words, the pattern writer can lower the limit set by the
169    programmer, but not raise it. If there is more than one setting of one of these
170    limits, the lower value is used.
171    .
172    .
173    .SH "EBCDIC CHARACTER CODES"
174    .rs
175    .sp
176    PCRE can be compiled to run in an environment that uses EBCDIC as its character
177    code rather than ASCII or Unicode (typically a mainframe system). In the
178    sections below, character code values are ASCII or Unicode; in an EBCDIC
179    environment these characters may have different code values, and there are no
180    code points greater than 255.
181    .
182    .
183  .SH "CHARACTERS AND METACHARACTERS"  .SH "CHARACTERS AND METACHARACTERS"
184  .rs  .rs
185  .sp  .sp
# Line 130  corresponding characters in the subject. Line 191  corresponding characters in the subject.
191  .sp  .sp
192  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
193  caseless matching is specified (the PCRE_CASELESS option), letters are matched  caseless matching is specified (the PCRE_CASELESS option), letters are matched
194  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
195  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
196  always possible. For characters with higher values, the concept of case is  always possible. For characters with higher values, the concept of case is
197  supported if PCRE is compiled with Unicode property support, but not otherwise.  supported if PCRE is compiled with Unicode property support, but not otherwise.
198  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
199  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
200  UTF-8 support.  UTF support.
201  .P  .P
202  The power of regular expressions comes from the ability to include alternatives  The power of regular expressions comes from the ability to include alternatives
203  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 253  otherwise be interpreted as a metacharac
253  non-alphanumeric with backslash to specify that it stands for itself. In  non-alphanumeric with backslash to specify that it stands for itself. In
254  particular, if you want to match a backslash, you write \e\e.  particular, if you want to match a backslash, you write \e\e.
255  .P  .P
256  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
257  backslash. All other characters (in particular, those whose codepoints are  backslash. All other characters (in particular, those whose codepoints are
258  greater than 127) are treated as literals.  greater than 127) are treated as literals.
259  .P  .P
260  If a pattern is compiled with the PCRE_EXTENDED option, whitespace in the  If a pattern is compiled with the PCRE_EXTENDED option, white space in the
261  pattern (other than in a character class) and characters between a # outside  pattern (other than in a character class) and characters between a # outside
262  a character class and the next newline are ignored. An escaping backslash can  a character class and the next newline are ignored. An escaping backslash can
263  be used to include a whitespace or # character as part of the pattern.  be used to include a white space or # character as part of the pattern.
264  .P  .P
265  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
266  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 235  one of the following escape sequences th Line 296  one of the following escape sequences th
296    \ea        alarm, that is, the BEL character (hex 07)    \ea        alarm, that is, the BEL character (hex 07)
297    \ecx       "control-x", where x is any ASCII character    \ecx       "control-x", where x is any ASCII character
298    \ee        escape (hex 1B)    \ee        escape (hex 1B)
299    \ef        formfeed (hex 0C)    \ef        form feed (hex 0C)
300    \en        linefeed (hex 0A)    \en        linefeed (hex 0A)
301    \er        carriage return (hex 0D)    \er        carriage return (hex 0D)
302    \et        tab (hex 09)    \et        tab (hex 09)
303    \eddd      character with octal code ddd, or back reference    \eddd      character with octal code ddd, or back reference
304    \exhh      character with hex code hh    \exhh      character with hex code hh
305    \ex{hhh..} character with hex code hhh.. (non-JavaScript mode)    \ex{hhh..} character with hex code hhh.. (non-JavaScript mode)
306    \euhhhh    character with hex code hhhh (JavaScript mode only)    \euhhhh    character with hex code hhhh (JavaScript mode only)
307  .sp  .sp
308  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
309  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
310  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),
311  \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
312  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
313  both byte mode and UTF-8 mode. (When PCRE is compiled in EBCDIC mode, all byte  compile-time error occurs. This locks out non-ASCII characters in all modes.
314  values are valid. A lower case letter is converted to upper case, and then the  .P
315  0xc0 bits are flipped.)  The \ec facility was designed for use with ASCII characters, but with the
316    extension to Unicode it is even less useful than it once was. It is, however,
317    recognized when PCRE is compiled in EBCDIC mode, where data items are always
318    bytes. In this mode, all values are valid after \ec. If the next character is a
319    lower case letter, it is converted to upper case. Then the 0xc0 bits of the
320    byte are inverted. Thus \ecA becomes hex 01, as in ASCII (A is C1), but because
321    the EBCDIC letters are disjoint, \ecZ becomes hex 29 (Z is E9), and other
322    characters also generate different values.
323  .P  .P
324  By default, after \ex, from zero to two hexadecimal digits are read (letters  By default, after \ex, from zero to two hexadecimal digits are read (letters
325  can be in upper or lower case). Any number of hexadecimal digits may appear  can be in upper or lower case). Any number of hexadecimal digits may appear
326  between \ex{ and }, but the value of the character code must be less than 256  between \ex{ and }, but the character code is constrained as follows:
327  in non-UTF-8 mode, and less than 2**31 in UTF-8 mode. That is, the maximum  .sp
328  value in hexadecimal is 7FFFFFFF. Note that this is bigger than the largest    8-bit non-UTF mode    less than 0x100
329  Unicode code point, which is 10FFFF.    8-bit UTF-8 mode      less than 0x10ffff and a valid codepoint
330      16-bit non-UTF mode   less than 0x10000
331      16-bit UTF-16 mode    less than 0x10ffff and a valid codepoint
332      32-bit non-UTF mode   less than 0x80000000
333      32-bit UTF-32 mode    less than 0x10ffff and a valid codepoint
334    .sp
335    Invalid Unicode codepoints are the range 0xd800 to 0xdfff (the so-called
336    "surrogate" codepoints), and 0xffef.
337  .P  .P
338  If characters other than hexadecimal digits appear between \ex{ and }, or if  If characters other than hexadecimal digits appear between \ex{ and }, or if
339  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
340  initial \ex will be interpreted as a basic hexadecimal escape, with no  initial \ex will be interpreted as a basic hexadecimal escape, with no
341  following digits, giving a character whose value is zero.  following digits, giving a character whose value is zero.
342  .P  .P
343  If the PCRE_JAVASCRIPT_COMPAT option is set, the interpretation of \ex is  If the PCRE_JAVASCRIPT_COMPAT option is set, the interpretation of \ex is
344  as just described only when it is followed by two hexadecimal digits.  as just described only when it is followed by two hexadecimal digits.
345  Otherwise, it matches a literal "x" character. In JavaScript mode, support for  Otherwise, it matches a literal "x" character. In JavaScript mode, support for
346  code points greater than 256 is provided by \eu, which must be followed by  code points greater than 256 is provided by \eu, which must be followed by
347  four hexadecimal digits; otherwise it matches a literal "u" character.  four hexadecimal digits; otherwise it matches a literal "u" character.
348    Character codes specified by \eu in JavaScript mode are constrained in the same
349    was as those specified by \ex in non-JavaScript mode.
350  .P  .P
351  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
352  syntaxes for \ex (or by \eu in JavaScript mode). There is no difference in the  syntaxes for \ex (or by \eu in JavaScript mode). There is no difference in the
353  way they are handled. For example, \exdc is exactly the same as \ex{dc} (or  way they are handled. For example, \exdc is exactly the same as \ex{dc} (or
354  \eu00dc in JavaScript mode).  \eu00dc in JavaScript mode).
355  .P  .P
356  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
# Line 300  parenthesized subpatterns. Line 377  parenthesized subpatterns.
377  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
378  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
379  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
380  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
381  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.
382  to \e777 are permitted. For example:  For example:
383  .sp  .sp
384    \e040   is another way of writing a space    \e040   is another way of writing an ASCII space
385  .\" JOIN  .\" JOIN
386    \e40    is the same, provided there are fewer than 40    \e40    is the same, provided there are fewer than 40
387              previous capturing subpatterns              previous capturing subpatterns
# Line 319  to \e777 are permitted. For example: Line 396  to \e777 are permitted. For example:
396              character with octal code 113              character with octal code 113
397  .\" JOIN  .\" JOIN
398    \e377   might be a back reference, otherwise    \e377   might be a back reference, otherwise
399              the byte consisting entirely of 1 bits              the value 255 (decimal)
400  .\" JOIN  .\" JOIN
401    \e81    is either a back reference, or a binary zero    \e81    is either a back reference, or a binary zero
402              followed by the two characters "8" and "1"              followed by the two characters "8" and "1"
# Line 328  Note that octal values of 100 or greater Line 405  Note that octal values of 100 or greater
405  zero, because no more than three octal digits are ever read.  zero, because no more than three octal digits are ever read.
406  .P  .P
407  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
408  and outside character classes. In addition, inside a character class, the  and outside character classes. In addition, inside a character class, \eb is
409  sequence \eb is interpreted as the backspace character (hex 08). The sequences  interpreted as the backspace character (hex 08).
410  \eB, \eN, \eR, and \eX are not special inside a character class. Like any other  .P
411  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
412  "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
413  set. Outside a character class, these sequences have different meanings.  treated as the literal characters "B", "R", and "X" by default, but cause an
414    error if the PCRE_EXTRA option is set. Outside a character class, these
415    sequences have different meanings.
416  .  .
417  .  .
418  .SS "Unsupported escape sequences"  .SS "Unsupported escape sequences"
# Line 390  Another use of backslash is for specifyi Line 469  Another use of backslash is for specifyi
469  .sp  .sp
470    \ed     any decimal digit    \ed     any decimal digit
471    \eD     any character that is not a decimal digit    \eD     any character that is not a decimal digit
472    \eh     any horizontal whitespace character    \eh     any horizontal white space character
473    \eH     any character that is not a horizontal whitespace character    \eH     any character that is not a horizontal white space character
474    \es     any whitespace character    \es     any white space character
475    \eS     any character that is not a whitespace character    \eS     any character that is not a white space character
476    \ev     any vertical whitespace character    \ev     any vertical white space character
477    \eV     any character that is not a vertical whitespace character    \eV     any character that is not a vertical white space character
478    \ew     any "word" character    \ew     any "word" character
479    \eW     any "non-word" character    \eW     any "non-word" character
480  .sp  .sp
# Line 405  This is the same as Line 484  This is the same as
484  .\" </a>  .\" </a>
485  the "." metacharacter  the "." metacharacter
486  .\"  .\"
487  when PCRE_DOTALL is not set. Perl also uses \eN to match characters by name;  when PCRE_DOTALL is not set. Perl also uses \eN to match characters by name;
488  PCRE does not support this.  PCRE does not support this.
489  .P  .P
490  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
# Line 438  or "french" in Windows, some character c Line 517  or "french" in Windows, some character c
517  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
518  Unicode is discouraged.  Unicode is discouraged.
519  .P  .P
520  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
521  \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
522  their original meanings from before UTF-8 support was available, mainly for  their original meanings from before UTF support was available, mainly for
523  efficiency reasons. However, if PCRE is compiled with Unicode property support,  efficiency reasons. However, if PCRE is compiled with Unicode property support,
524  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
525  properties are used to determine character types, as follows:  properties are used to determine character types, as follows:
# Line 457  is noticeably slower when PCRE_UCP is se Line 536  is noticeably slower when PCRE_UCP is se
536  .P  .P
537  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
538  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
539  characters by default, these always match certain high-valued codepoints in  characters by default, these always match certain high-valued codepoints,
540  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:  
541  .sp  .sp
542    U+0009     Horizontal tab    U+0009     Horizontal tab (HT)
543    U+0020     Space    U+0020     Space
544    U+00A0     Non-break space    U+00A0     Non-break space
545    U+1680     Ogham space mark    U+1680     Ogham space mark
# Line 483  are: Line 561  are:
561  .sp  .sp
562  The vertical space characters are:  The vertical space characters are:
563  .sp  .sp
564    U+000A     Linefeed    U+000A     Linefeed (LF)
565    U+000B     Vertical tab    U+000B     Vertical tab (VT)
566    U+000C     Formfeed    U+000C     Form feed (FF)
567    U+000D     Carriage return    U+000D     Carriage return (CR)
568    U+0085     Next line    U+0085     Next line (NEL)
569    U+2028     Line separator    U+2028     Line separator
570    U+2029     Paragraph separator    U+2029     Paragraph separator
571    .sp
572    In 8-bit, non-UTF-8 mode, only the characters with codepoints less than 256 are
573    relevant.
574  .  .
575  .  .
576  .\" HTML <a name="newlineseq"></a>  .\" HTML <a name="newlineseq"></a>
# Line 497  The vertical space characters are: Line 578  The vertical space characters are:
578  .rs  .rs
579  .sp  .sp
580  Outside a character class, by default, the escape sequence \eR matches any  Outside a character class, by default, the escape sequence \eR matches any
581  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
582    following:
583  .sp  .sp
584    (?>\er\en|\en|\ex0b|\ef|\er|\ex85)    (?>\er\en|\en|\ex0b|\ef|\er|\ex85)
585  .sp  .sp
# Line 508  below. Line 590  below.
590  .\"  .\"
591  This particular group matches either the two-character sequence CR followed by  This particular group matches either the two-character sequence CR followed by
592  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,
593  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
594  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
595  cannot be split.  cannot be split.
596  .P  .P
597  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
598  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).
599  Unicode character property support is not needed for these characters to be  Unicode character property support is not needed for these characters to be
600  recognized.  recognized.
# Line 528  one of the following sequences: Line 610  one of the following sequences:
610    (*BSR_ANYCRLF)   CR, LF, or CRLF only    (*BSR_ANYCRLF)   CR, LF, or CRLF only
611    (*BSR_UNICODE)   any Unicode newline sequence    (*BSR_UNICODE)   any Unicode newline sequence
612  .sp  .sp
613  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
614  \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
615  \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
616  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
617  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
618  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:  
619  .sp  .sp
620    (*ANY)(*BSR_ANYCRLF)    (*ANY)(*BSR_ANYCRLF)
621  .sp  .sp
622  They can also be combined with the (*UTF8) or (*UCP) special sequences. Inside  They can also be combined with the (*UTF8), (*UTF16), (*UTF32), (*UTF) or
623  a character class, \eR is treated as an unrecognized escape sequence, and so  (*UCP) special sequences. Inside a character class, \eR is treated as an
624  matches the letter "R" by default, but causes an error if PCRE_EXTRA is set.  unrecognized escape sequence, and so matches the letter "R" by default, but
625    causes an error if PCRE_EXTRA is set.
626  .  .
627  .  .
628  .\" HTML <a name="uniextseq"></a>  .\" HTML <a name="uniextseq"></a>
# Line 549  matches the letter "R" by default, but c Line 631  matches the letter "R" by default, but c
631  .sp  .sp
632  When PCRE is built with Unicode character property support, three additional  When PCRE is built with Unicode character property support, three additional
633  escape sequences that match characters with specific properties are available.  escape sequences that match characters with specific properties are available.
634  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
635  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.
636  The extra escape sequences are:  The extra escape sequences are:
637  .sp  .sp
638    \ep{\fIxx\fP}   a character with the \fIxx\fP property    \ep{\fIxx\fP}   a character with the \fIxx\fP property
639    \eP{\fIxx\fP}   a character without the \fIxx\fP property    \eP{\fIxx\fP}   a character without the \fIxx\fP property
640    \eX       an extended Unicode sequence    \eX       a Unicode extended grapheme cluster
641  .sp  .sp
642  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
643  script names, the general category properties, "Any", which matches any  script names, the general category properties, "Any", which matches any
# Line 584  Armenian, Line 666  Armenian,
666  Avestan,  Avestan,
667  Balinese,  Balinese,
668  Bamum,  Bamum,
669    Batak,
670  Bengali,  Bengali,
671  Bopomofo,  Bopomofo,
672    Brahmi,
673  Braille,  Braille,
674  Buginese,  Buginese,
675  Buhid,  Buhid,
676  Canadian_Aboriginal,  Canadian_Aboriginal,
677  Carian,  Carian,
678    Chakma,
679  Cham,  Cham,
680  Cherokee,  Cherokee,
681  Common,  Common,
# Line 633  Lisu, Line 718  Lisu,
718  Lycian,  Lycian,
719  Lydian,  Lydian,
720  Malayalam,  Malayalam,
721    Mandaic,
722  Meetei_Mayek,  Meetei_Mayek,
723    Meroitic_Cursive,
724    Meroitic_Hieroglyphs,
725    Miao,
726  Mongolian,  Mongolian,
727  Myanmar,  Myanmar,
728  New_Tai_Lue,  New_Tai_Lue,
# Line 652  Rejang, Line 741  Rejang,
741  Runic,  Runic,
742  Samaritan,  Samaritan,
743  Saurashtra,  Saurashtra,
744    Sharada,
745  Shavian,  Shavian,
746  Sinhala,  Sinhala,
747    Sora_Sompeng,
748  Sundanese,  Sundanese,
749  Syloti_Nagri,  Syloti_Nagri,
750  Syriac,  Syriac,
# Line 662  Tagbanwa, Line 753  Tagbanwa,
753  Tai_Le,  Tai_Le,
754  Tai_Tham,  Tai_Tham,
755  Tai_Viet,  Tai_Viet,
756    Takri,
757  Tamil,  Tamil,
758  Telugu,  Telugu,
759  Thaana,  Thaana,
# Line 736  the Lu, Ll, or Lt property, in other wor Line 828  the Lu, Ll, or Lt property, in other wor
828  a modifier or "other".  a modifier or "other".
829  .P  .P
830  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
831  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
832  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
833  (see the discussion of PCRE_NO_UTF8_CHECK in the  (see the discussion of PCRE_NO_UTF8_CHECK, PCRE_NO_UTF16_CHECK and
834    PCRE_NO_UTF32_CHECK in the
835  .\" HREF  .\" HREF
836  \fBpcreapi\fP  \fBpcreapi\fP
837  .\"  .\"
# Line 753  Instead, this property is assumed for an Line 846  Instead, this property is assumed for an
846  Unicode table.  Unicode table.
847  .P  .P
848  Specifying caseless matching does not affect these escape sequences. For  Specifying caseless matching does not affect these escape sequences. For
849  example, \ep{Lu} always matches only upper case letters.  example, \ep{Lu} always matches only upper case letters. This is different from
850    the behaviour of current versions of Perl.
851  .P  .P
852  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
853  Unicode sequence. \eX is equivalent to  multistage table lookup in order to find a character's property. That is why
854  .sp  the traditional escape sequences such as \ed and \ew do not use Unicode
855    (?>\ePM\epM*)  properties in PCRE by default, though you can make them do so by setting the
856    PCRE_UCP option or by starting the pattern with (*UCP).
857    .
858    .
859    .SS Extended grapheme clusters
860    .rs
861  .sp  .sp
862  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
863  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  
864  .\" HTML <a href="#atomicgroup">  .\" HTML <a href="#atomicgroup">
865  .\" </a>  .\" </a>
866  (see below).  (see below).
867  .\"  .\"
868  Characters with the "mark" property are typically accents that affect the  Up to and including release 8.31, PCRE matched an earlier, simpler definition
869  preceding character. None of them have codepoints less than 256, so in  that was equivalent to
870  non-UTF-8 mode \eX matches any one character.  .sp
871  .P    (?>\ePM\epM*)
872  Note that recent versions of Perl have changed \eX to match what Unicode calls  .sp
873  an "extended grapheme cluster", which has a more complicated definition.  That is, it matched a character without the "mark" property, followed by zero
874  .P  or more characters with the "mark" property. Characters with the "mark"
875  Matching characters by Unicode property is not fast, because PCRE has to search  property are typically non-spacing accents that affect the preceding character.
876  a structure that contains data for over fifteen thousand characters. That is  .P
877  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
878  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
879  PCRE_UCP option for \fBpcre_compile()\fP or by starting the pattern with  property, and creating rules that use these properties to define the boundaries
880  (*UCP).  of extended grapheme clusters. In releases of PCRE later than 8.31, \eX matches
881    one of these clusters.
882    .P
883    \eX always matches at least one character. Then it decides whether to add
884    additional characters according to the following rules for ending a cluster:
885    .P
886    1. End at the end of the subject string.
887    .P
888    2. Do not end between CR and LF; otherwise end after any control character.
889    .P
890    3. Do not break Hangul (a Korean script) syllable sequences. Hangul characters
891    are of five types: L, V, T, LV, and LVT. An L character may be followed by an
892    L, V, LV, or LVT character; an LV or V character may be followed by a V or T
893    character; an LVT or T character may be follwed only by a T character.
894    .P
895    4. Do not end before extending characters or spacing marks. Characters with
896    the "mark" property always have the "extend" grapheme breaking property.
897    .P
898    5. Do not end after prepend characters.
899    .P
900    6. Otherwise, end the cluster.
901  .  .
902  .  .
903  .\" HTML <a name="extraprops"></a>  .\" HTML <a name="extraprops"></a>
904  .SS PCRE's additional properties  .SS PCRE's additional properties
905  .rs  .rs
906  .sp  .sp
907  As well as the standard Unicode properties described in the previous  As well as the standard Unicode properties described above, PCRE supports four
908  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
909  escape sequences such as \ew and \es and POSIX character classes to use Unicode  and \es and POSIX character classes to use Unicode properties. PCRE uses these
910  properties. PCRE uses these non-standard, non-Perl properties internally when  non-standard, non-Perl properties internally when PCRE_UCP is set. However,
911  PCRE_UCP is set. They are:  they may also be used explicitly. These properties are:
912  .sp  .sp
913    Xan   Any alphanumeric character    Xan   Any alphanumeric character
914    Xps   Any POSIX space character    Xps   Any POSIX space character
# Line 798  PCRE_UCP is set. They are: Line 916  PCRE_UCP is set. They are:
916    Xwd   Any Perl "word" character    Xwd   Any Perl "word" character
917  .sp  .sp
918  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)
919  property. Xps matches the characters tab, linefeed, vertical tab, formfeed, or  property. Xps matches the characters tab, linefeed, vertical tab, form feed, or
920  carriage return, and any other character that has the Z (separator) property.  carriage return, and any other character that has the Z (separator) property.
921  Xsp is the same as Xps, except that vertical tab is excluded. Xwd matches the  Xsp is the same as Xps, except that vertical tab is excluded. Xwd matches the
922  same characters as Xan, plus underscore.  same characters as Xan, plus underscore.
923    .P
924    There is another non-standard property, Xuc, which matches any character that
925    can be represented by a Universal Character Name in C++ and other programming
926    languages. These are the characters $, @, ` (grave accent), and all characters
927    with Unicode code points greater than or equal to U+00A0, except for the
928    surrogates U+D800 to U+DFFF. Note that most base (ASCII) characters are
929    excluded. (Universal Character Names are of the form \euHHHH or \eUHHHHHHHH
930    where H is a hexadecimal digit. Note that the Xuc property does not match these
931    sequences but the characters that they represent.)
932  .  .
933  .  .
934  .\" HTML <a name="resetmatchstart"></a>  .\" HTML <a name="resetmatchstart"></a>
# Line 868  escape sequence" error is generated inst Line 995  escape sequence" error is generated inst
995  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
996  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
997  \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
998  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
999  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
1000  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
1001  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 907  regular expression. Line 1034  regular expression.
1034  .SH "CIRCUMFLEX AND DOLLAR"  .SH "CIRCUMFLEX AND DOLLAR"
1035  .rs  .rs
1036  .sp  .sp
1037    The circumflex and dollar metacharacters are zero-width assertions. That is,
1038    they test for a particular condition being true without consuming any
1039    characters from the subject string.
1040    .P
1041  Outside a character class, in the default matching mode, the circumflex  Outside a character class, in the default matching mode, the circumflex
1042  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
1043  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
1044  \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
1045  option is unset. Inside a character class, circumflex has an entirely different  option is unset. Inside a character class, circumflex has an entirely different
1046  meaning  meaning
# Line 926  constrained to match only at the start o Line 1057  constrained to match only at the start o
1057  "anchored" pattern. (There are also other constructs that can cause a pattern  "anchored" pattern. (There are also other constructs that can cause a pattern
1058  to be anchored.)  to be anchored.)
1059  .P  .P
1060  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
1061  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
1062  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
1063  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
1064  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
1065  character class.  branch in which it appears. Dollar has no special meaning in a character class.
1066  .P  .P
1067  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
1068  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 963  end of the subject in both modes, and if Line 1094  end of the subject in both modes, and if
1094  .sp  .sp
1095  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
1096  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
1097  line. In UTF-8 mode, the matched character may be more than one byte long.  line.
1098  .P  .P
1099  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
1100  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 987  that signifies the end of a line. Perl a Line 1118  that signifies the end of a line. Perl a
1118  name; PCRE does not support this.  name; PCRE does not support this.
1119  .  .
1120  .  .
1121  .SH "MATCHING A SINGLE BYTE"  .SH "MATCHING A SINGLE DATA UNIT"
1122  .rs  .rs
1123  .sp  .sp
1124  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,
1125  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
1126  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; in the 32-bit library it is
1127  in UTF-8 mode, but it is unclear how it can usefully be used. Because \eC  a 32-bit unit. Unlike a dot, \eC always
1128  breaks up characters into individual bytes, matching one byte with \eC in UTF-8  matches line-ending characters. The feature is provided in Perl in order to
1129  mode means that the rest of the string may start with a malformed UTF-8  match individual bytes in UTF-8 mode, but it is unclear how it can usefully be
1130  character. This has undefined results, because PCRE assumes that it is dealing  used. Because \eC breaks up characters into individual data units, matching one
1131  with valid UTF-8 strings (and by default it checks this at the start of  unit with \eC in a UTF mode means that the rest of the string may start with a
1132  processing unless the PCRE_NO_UTF8_CHECK option is used).  malformed UTF character. This has undefined results, because PCRE assumes that
1133    it is dealing with valid UTF strings (and by default it checks this at the
1134    start of processing unless the PCRE_NO_UTF8_CHECK, PCRE_NO_UTF16_CHECK or
1135    PCRE_NO_UTF32_CHECK option is used).
1136  .P  .P
1137  PCRE does not allow \eC to appear in lookbehind assertions  PCRE does not allow \eC to appear in lookbehind assertions
1138  .\" HTML <a href="#lookbehind">  .\" HTML <a href="#lookbehind">
1139  .\" </a>  .\" </a>
1140  (described below),  (described below)
1141  .\"  .\"
1142  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
1143  the lookbehind.  the lookbehind.
1144  .P  .P
1145  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
1146  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
1147  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
1148  (ignore white space and line breaks):  could be used with a UTF-8 string (ignore white space and line breaks):
1149  .sp  .sp
1150    (?| (?=[\ex00-\ex7f])(\eC) |    (?| (?=[\ex00-\ex7f])(\eC) |
1151        (?=[\ex80-\ex{7ff}])(\eC)(\eC) |        (?=[\ex80-\ex{7ff}])(\eC)(\eC) |
# Line 1041  bracket causes a compile-time error. If Line 1175  bracket causes a compile-time error. If
1175  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
1176  (after an initial circumflex, if present) or escaped with a backslash.  (after an initial circumflex, if present) or escaped with a backslash.
1177  .P  .P
1178  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
1179  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
1180  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
1181  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
1182  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
1183  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
1184  backslash.  backslash.
1185  .P  .P
1186  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 1057  circumflex is not an assertion; it still Line 1191  circumflex is not an assertion; it still
1191  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
1192  string.  string.
1193  .P  .P
1194  In UTF-8 mode, characters with values greater than 255 can be included in a  In UTF-8 (UTF-16, UTF-32) mode, characters with values greater than 255 (0xffff)
1195  class as a literal string of bytes, or by using the \ex{ escaping mechanism.  can be included in a class as a literal string of data units, or by using the
1196    \ex{ escaping mechanism.
1197  .P  .P
1198  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
1199  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
1200  "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
1201  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
1202  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
1203  always possible. For characters with higher values, the concept of case is  always possible. For characters with higher values, the concept of case is
1204  supported if PCRE is compiled with Unicode property support, but not otherwise.  supported if PCRE is compiled with Unicode property support, but not otherwise.
1205  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
1206  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
1207  with UTF-8 support.  well as with UTF support.
1208  .P  .P
1209  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
1210  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 1091  followed by two other characters. The oc Line 1226  followed by two other characters. The oc
1226  "]" can also be used to end a range.  "]" can also be used to end a range.
1227  .P  .P
1228  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
1229  used for characters specified numerically, for example [\e000-\e037]. In UTF-8  used for characters specified numerically, for example [\e000-\e037]. Ranges
1230  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}].  
1231  .P  .P
1232  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
1233  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
1234  [][\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
1235  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
1236  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
1237  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
1238  property support.  property support.
1239  .P  .P
1240  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,
1241  \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
1242  they match to the class. For example, [\edABCDEF] matches any hexadecimal  they match to the class. For example, [\edABCDEF] matches any hexadecimal
1243  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
1244  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
1245  character class, as described in the section entitled  character class, as described in the section entitled
1246  .\" HTML <a href="#genericchartypes">  .\" HTML <a href="#genericchartypes">
# Line 1176  matches "1", "2", or any non-digit. PCRE Line 1310  matches "1", "2", or any non-digit. PCRE
1310  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
1311  supported, and an error is given if they are encountered.  supported, and an error is given if they are encountered.
1312  .P  .P
1313  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
1314  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
1315  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
1316  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 1264  option settings happen at compile time. Line 1398  option settings happen at compile time.
1398  behaviour otherwise.  behaviour otherwise.
1399  .P  .P
1400  \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
1401  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
1402  pattern can contain special leading sequences such as (*CRLF) to override what  the pattern can contain special leading sequences such as (*CRLF) to override
1403  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
1404  section entitled  the section entitled
1405  .\" HTML <a href="#newlineseq">  .\" HTML <a href="#newlineseq">
1406  .\" </a>  .\" </a>
1407  "Newline sequences"  "Newline sequences"
1408  .\"  .\"
1409  above. There are also the (*UTF8) and (*UCP) leading sequences that can be used  above. There are also the (*UTF8), (*UTF16),(*UTF32), and (*UCP) leading
1410  to set UTF-8 and Unicode property modes; they are equivalent to setting the  sequences that can be used to set UTF and Unicode property modes; they are
1411  PCRE_UTF8 and the PCRE_UCP options, respectively.  equivalent to setting the PCRE_UTF8, PCRE_UTF16, PCRE_UTF32 and the PCRE_UCP
1412    options, respectively. The (*UTF) sequence is a generic version that can be
1413    used with any of the libraries. However, the application can set the
1414    PCRE_NEVER_UTF option, which locks out the use of the (*UTF) sequences.
1415  .  .
1416  .  .
1417  .\" HTML <a name="subpattern"></a>  .\" HTML <a name="subpattern"></a>
# Line 1293  match "cataract", "erpillar" or an empty Line 1430  match "cataract", "erpillar" or an empty
1430  .sp  .sp
1431  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
1432  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
1433  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
1434  \fBpcre_exec()\fP. Opening parentheses are counted from left to right (starting  matching function. (This applies only to the traditional matching functions;
1435  from 1) to obtain numbers for the capturing subpatterns. For example, if the  the DFA matching functions do not support capturing.)
1436  string "the red king" is matched against the pattern  .P
1437    Opening parentheses are counted from left to right (starting from 1) to obtain
1438    numbers for the capturing subpatterns. For example, if the string "the red
1439    king" is matched against the pattern
1440  .sp  .sp
1441    the ((red|white) (king|queen))    the ((red|white) (king|queen))
1442  .sp  .sp
# Line 1472  items: Line 1612  items:
1612    a literal data character    a literal data character
1613    the dot metacharacter    the dot metacharacter
1614    the \eC escape sequence    the \eC escape sequence
1615    the \eX escape sequence (in UTF-8 mode with Unicode properties)    the \eX escape sequence
1616    the \eR escape sequence    the \eR escape sequence
1617    an escape such as \ed or \epL that matches a single character    an escape such as \ed or \epL that matches a single character
1618    a character class    a character class
# Line 1503  where a quantifier is not allowed, or on Line 1643  where a quantifier is not allowed, or on
1643  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
1644  quantifier, but a literal string of four characters.  quantifier, but a literal string of four characters.
1645  .P  .P
1646  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
1647  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
1648  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,
1649  support is available, \eX{3} matches three Unicode extended sequences, each of  \eX{3} matches three Unicode extended grapheme clusters, each of which may be
1650  which may be several bytes long (and they may be of different lengths).  several data units long (and they may be of different lengths).
1651  .P  .P
1652  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
1653  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 1593  In cases where it is known that the subj Line 1733  In cases where it is known that the subj
1733  worth setting PCRE_DOTALL in order to obtain this optimization, or  worth setting PCRE_DOTALL in order to obtain this optimization, or
1734  alternatively using ^ to indicate anchoring explicitly.  alternatively using ^ to indicate anchoring explicitly.
1735  .P  .P
1736  However, there is one situation where the optimization cannot be used. When .*  However, there are some cases where the optimization cannot be used. When .*
1737  is inside capturing parentheses that are the subject of a back reference  is inside capturing parentheses that are the subject of a back reference
1738  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
1739  succeeds. Consider, for example:  succeeds. Consider, for example:
# Line 1603  succeeds. Consider, for example: Line 1743  succeeds. Consider, for example:
1743  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
1744  this reason, such a pattern is not implicitly anchored.  this reason, such a pattern is not implicitly anchored.
1745  .P  .P
1746    Another case where implicit anchoring is not applied is when the leading .* is
1747    inside an atomic group. Once again, a match at the start may fail where a later
1748    one succeeds. Consider this pattern:
1749    .sp
1750      (?>.*?a)b
1751    .sp
1752    It matches "ab" in the subject "aab". The use of the backtracking control verbs
1753    (*PRUNE) and (*SKIP) also disable this optimization.
1754    .P
1755  When a capturing subpattern is repeated, the value captured is the substring  When a capturing subpattern is repeated, the value captured is the substring
1756  that matched the final iteration. For example, after  that matched the final iteration. For example, after
1757  .sp  .sp
# Line 1817  Because there may be many capturing pare Line 1966  Because there may be many capturing pare
1966  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.
1967  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
1968  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
1969  whitespace. Otherwise, the \eg{ syntax or an empty comment (see  white space. Otherwise, the \eg{ syntax or an empty comment (see
1970  .\" HTML <a href="#comments">  .\" HTML <a href="#comments">
1971  .\" </a>  .\" </a>
1972  "Comments"  "Comments"
# Line 1871  except that it does not cause the curren Line 2020  except that it does not cause the curren
2020  Assertion subpatterns are not capturing subpatterns. If such an assertion  Assertion subpatterns are not capturing subpatterns. If such an assertion
2021  contains capturing subpatterns within it, these are counted for the purposes of  contains capturing subpatterns within it, these are counted for the purposes of
2022  numbering the capturing subpatterns in the whole pattern. However, substring  numbering the capturing subpatterns in the whole pattern. However, substring
2023  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
2024  sense for negative assertions.  always, does do capturing in negative assertions.)
2025  .P  .P
2026  For compatibility with Perl, assertion subpatterns may be repeated; though  For compatibility with Perl, assertion subpatterns may be repeated; though
2027  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 1970  temporarily move the current position ba Line 2119  temporarily move the current position ba
2119  match. If there are insufficient characters before the current position, the  match. If there are insufficient characters before the current position, the
2120  assertion fails.  assertion fails.
2121  .P  .P
2122  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
2123  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
2124  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
2125  different numbers of bytes, are also not permitted.  escapes, which can match different numbers of data units, are also not
2126    permitted.
2127  .P  .P
2128  .\" HTML <a href="#subpatternsassubroutines">  .\" HTML <a href="#subpatternsassubroutines">
2129  .\" </a>  .\" </a>
# Line 2173  subroutines that can be referenced from Line 2323  subroutines that can be referenced from
2323  subroutines  subroutines
2324  .\"  .\"
2325  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
2326  "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
2327  breaks):  breaks):
2328  .sp  .sp
2329    (?(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 2220  closing parenthesis. Nested parentheses Line 2370  closing parenthesis. Nested parentheses
2370  option is set, an unescaped # character also introduces a comment, which in  option is set, an unescaped # character also introduces a comment, which in
2371  this case continues to immediately after the next newline character or  this case continues to immediately after the next newline character or
2372  character sequence in the pattern. Which characters are interpreted as newlines  character sequence in the pattern. Which characters are interpreted as newlines
2373  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
2374  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
2375  .\" HTML <a href="#newlines">  .\" HTML <a href="#newlines">
2376  .\" </a>  .\" </a>
# Line 2522  same pair of parentheses when there is a Line 2672  same pair of parentheses when there is a
2672  .P  .P
2673  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
2674  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
2675  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
2676    (8-bit library) or \fIpcre[16|32]_callout\fP (16-bit or 32-bit library).
2677  By default, this variable contains NULL, which disables all calling out.  By default, this variable contains NULL, which disables all calling out.
2678  .P  .P
2679  Within a regular expression, (?C) indicates the points at which the external  Within a regular expression, (?C) indicates the points at which the external
# Line 2532  For example, this pattern has two callou Line 2683  For example, this pattern has two callou
2683  .sp  .sp
2684    (?C1)abc(?C2)def    (?C1)abc(?C2)def
2685  .sp  .sp
2686  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
2687  automatically installed before each item in the pattern. They are all numbered  automatically installed before each item in the pattern. They are all numbered
2688  255.  255. If there is a conditional group in the pattern whose condition is an
2689  .P  assertion, an additional callout is inserted just before the condition. An
2690  During matching, when PCRE reaches a callout point (and \fIpcre_callout\fP is  explicit callout may also be set at this position, as in this example:
2691  set), the external function is called. It is provided with the number of the  .sp
2692  callout, the position in the pattern, and, optionally, one item of data    (?(?C9)(?=a)abc|def)
2693  originally supplied by the caller of \fBpcre_exec()\fP. The callout function  .sp
2694  may cause matching to proceed, to backtrack, or to fail altogether. A complete  Note that this applies only to assertion conditions, not to other types of
2695  description of the interface to the callout function is given in the  condition.
2696    .P
2697    During matching, when PCRE reaches a callout point, the external function is
2698    called. It is provided with the number of the callout, the position in the
2699    pattern, and, optionally, one item of data originally supplied by the caller of
2700    the matching function. The callout function may cause matching to proceed, to
2701    backtrack, or to fail altogether. A complete description of the interface to
2702    the callout function is given in the
2703  .\" HREF  .\" HREF
2704  \fBpcrecallout\fP  \fBpcrecallout\fP
2705  .\"  .\"
# Line 2553  documentation. Line 2711  documentation.
2711  .rs  .rs
2712  .sp  .sp
2713  Perl 5.10 introduced a number of "Special Backtracking Control Verbs", which  Perl 5.10 introduced a number of "Special Backtracking Control Verbs", which
2714  are described in the Perl documentation as "experimental and subject to change  are still described in the Perl documentation as "experimental and subject to
2715  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
2716  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
2717  remarks apply to the PCRE features described in this section.  remarks apply to the PCRE features described in this section.
2718  .P  .P
 Since these verbs are specifically related to backtracking, most of them can be  
 used only when the pattern is to be matched using \fBpcre_exec()\fP, which uses  
 a backtracking algorithm. With the exception of (*FAIL), which behaves like a  
 failing negative assertion, they cause an error if encountered by  
 \fBpcre_dfa_exec()\fP.  
 .P  
 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: a *MARK that is encountered in a positive assertion \fIis\fP passed  
 back (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.  
 .P  
2719  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
2720  parenthesis followed by an asterisk. They are generally of the form  parenthesis followed by an asterisk. They are generally of the form
2721  (*VERB) or (*VERB:NAME). Some may take either form, with differing behaviour,  (*VERB) or (*VERB:NAME). Some may take either form, possibly behaving
2722  depending on whether or not an argument is present. A name is any sequence of  differently depending on whether or not a name is present. A name is any
2723  characters that does not include a closing parenthesis. If the name is empty,  sequence of characters that does not include a closing parenthesis. The maximum
2724  that is, if the closing parenthesis immediately follows the colon, the effect  length of name is 255 in the 8-bit library and 65535 in the 16-bit and 32-bit
2725  is as if the colon were not there. Any number of these verbs may occur in a  libraries. If the name is empty, that is, if the closing parenthesis
2726  pattern.  immediately follows the colon, the effect is as if the colon were not there.
2727    Any number of these verbs may occur in a pattern.
2728  .P  .P
2729    Since these verbs are specifically related to backtracking, most of them can be
2730    used only when the pattern is to be matched using one of the traditional
2731    matching functions, because these use a backtracking algorithm. With the
2732    exception of (*FAIL), which behaves like a failing negative assertion, the
2733    backtracking control verbs cause an error if encountered by a DFA matching
2734    function.
2735    .P
2736    The behaviour of these verbs in
2737    .\" HTML <a href="#btrepeat">
2738    .\" </a>
2739    repeated groups,
2740    .\"
2741    .\" HTML <a href="#btassert">
2742    .\" </a>
2743    assertions,
2744    .\"
2745    and in
2746    .\" HTML <a href="#btsub">
2747    .\" </a>
2748    subpatterns called as subroutines
2749    .\"
2750    (whether or not recursively) is documented below.
2751    .
2752    .
2753    .\" HTML <a name="nooptimize"></a>
2754    .SS "Optimizations that affect backtracking verbs"
2755    .rs
2756    .sp
2757  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
2758  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
2759  minimum length of matching subject, or that a particular character must be  minimum length of matching subject, or that a particular character must be
2760  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
2761  included backtracking verbs will not, of course, be processed. You can suppress  included backtracking verbs will not, of course, be processed. You can suppress
2762  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
2763  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
2764  pattern with (*NO_START_OPT).  pattern with (*NO_START_OPT). There is more discussion of this option in the
2765    section entitled
2766    .\" HTML <a href="pcreapi.html#execoptions">
2767    .\" </a>
2768    "Option bits for \fBpcre_exec()\fP"
2769    .\"
2770    in the
2771    .\" HREF
2772    \fBpcreapi\fP
2773    .\"
2774    documentation.
2775    .P
2776    Experiments with Perl suggest that it too has similar optimizations, sometimes
2777    leading to anomalous results.
2778  .  .
2779  .  .
2780  .SS "Verbs that act immediately"  .SS "Verbs that act immediately"
# Line 2602  followed by a name. Line 2788  followed by a name.
2788  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
2789  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
2790  subroutine, only that subpattern is ended successfully. Matching then continues  subroutine, only that subpattern is ended successfully. Matching then continues
2791  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
2792  far is captured. For example:  assertion succeeds; in a negative assertion, the assertion fails.
2793    .P
2794    If (*ACCEPT) is inside capturing parentheses, the data so far is captured. For
2795    example:
2796  .sp  .sp
2797    A((?:A|B(*ACCEPT)|C)D)    A((?:A|B(*ACCEPT)|C)D)
2798  .sp  .sp
# Line 2636  starting point (see (*SKIP) below). Line 2825  starting point (see (*SKIP) below).
2825  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
2826  (*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.
2827  .P  .P
2828  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:NAME),
2829  to the caller via the \fIpcre_extra\fP data structure, as described in the  (*PRUNE:NAME), or (*THEN:NAME) on the matching path is passed back to the
2830    caller as described in the section entitled
2831  .\" HTML <a href="pcreapi.html#extradata">  .\" HTML <a href="pcreapi.html#extradata">
2832  .\" </a>  .\" </a>
2833  section on \fIpcre_extra\fP  "Extra data for \fBpcre_exec()\fP"
2834  .\"  .\"
2835  in the  in the
2836  .\" HREF  .\" HREF
2837  \fBpcreapi\fP  \fBpcreapi\fP
2838  .\"  .\"
2839  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
2840  \fBpcretest\fP output, where the /K modifier requests the retrieval and  modifier requests the retrieval and outputting of (*MARK) data:
 outputting of (*MARK) data:  
2841  .sp  .sp
2842    /X(*MARK:A)Y|X(*MARK:B)Z/K      re> /X(*MARK:A)Y|X(*MARK:B)Z/K
2843    XY    data> XY
2844     0: XY     0: XY
2845    MK: A    MK: A
2846    XZ    XZ
# Line 2663  indicates which of the two alternatives Line 2852  indicates which of the two alternatives
2852  of obtaining this information than putting each alternative in its own  of obtaining this information than putting each alternative in its own
2853  capturing parentheses.  capturing parentheses.
2854  .P  .P
2855  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
2856  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
2857  assertions.  happen for negative assertions or failing positive assertions.
2858  .P  .P
2859  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 last encountered name in the
2860  pattern involves (*MARK). However, unless (*MARK) used in conjunction with  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  
 .sp  
 There are three potential starting points for this match (starting with X,  
 starting with P, and with an empty string). If the pattern is anchored, the  
 result is different:  
2861  .sp  .sp
2862    /^X(*MARK:A)Y|^X(*MARK:B)Z/K      re> /X(*MARK:A)Y|X(*MARK:B)Z/K
2863    XP    data> XP
2864    No match, mark = B    No match, mark = B
2865  .sp  .sp
2866  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
2867  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
2868  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
2869  .P  (*MARK) item, but nevertheless do not reset it.
2870  Note that similar anomalies (though different in detail) exist in Perl, no  .P
2871  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
2872  unanchored pattern is not recommended, unless (*COMMIT) is involved.  probably set the PCRE_NO_START_OPTIMIZE option
2873    .\" HTML <a href="#nooptimize">
2874    .\" </a>
2875    (see above)
2876    .\"
2877    to ensure that the match is always attempted.
2878  .  .
2879  .  .
2880  .SS "Verbs that act after backtracking"  .SS "Verbs that act after backtracking"
# Line 2700  unanchored pattern is not recommended, u Line 2883  unanchored pattern is not recommended, u
2883  The following verbs do nothing when they are encountered. Matching continues  The following verbs do nothing when they are encountered. Matching continues
2884  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
2885  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
2886  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
2887  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
2888  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
2889  "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
2890  above, that this localization also applies in subroutine calls and assertions.)  or assertion. (Remember also, as stated above, that this localization also
2891    applies in subroutine calls.)
2892  .P  .P
2893  These verbs differ in exactly what kind of failure occurs when backtracking  These verbs differ in exactly what kind of failure occurs when backtracking
2894  reaches them.  reaches them. The behaviour described below is what happens when the verb is
2895    not in a subroutine or an assertion. Subsequent sections cover these special
2896    cases.
2897  .sp  .sp
2898    (*COMMIT)    (*COMMIT)
2899  .sp  .sp
2900  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
2901  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
2902  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
2903  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
2904  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
2905    committed to finding a match at the current starting point, or not at all. For
2906    example:
2907  .sp  .sp
2908    a+(*COMMIT)b    a+(*COMMIT)b
2909  .sp  .sp
# Line 2724  dynamic anchor, or "I've started, so I m Line 2912  dynamic anchor, or "I've started, so I m
2912  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
2913  match failure.  match failure.
2914  .P  .P
2915    If there is more than one backtracking verb in a pattern, a different one that
2916    follows (*COMMIT) may be triggered first, so merely passing (*COMMIT) during a
2917    match does not always guarantee that a match must be at this starting point.
2918    .P
2919  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,
2920  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
2921  \fBpcretest\fP example:  \fBpcretest\fP example:
2922  .sp  .sp
2923    /(*COMMIT)abc/      re> /(*COMMIT)abc/
2924    xyzabc    data> xyzabc
2925     0: abc     0: abc
2926    xyzabc\eY    xyzabc\eY
2927    No match    No match
# Line 2743  starting points. Line 2935  starting points.
2935    (*PRUNE) or (*PRUNE:NAME)    (*PRUNE) or (*PRUNE:NAME)
2936  .sp  .sp
2937  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
2938  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
2939  unanchored, the normal "bumpalong" advance to the next starting character then  it. If the pattern is unanchored, the normal "bumpalong" advance to the next
2940  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
2941  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
2942  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
2943  (*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
2944  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
2945  The behaviour of (*PRUNE:NAME) is the same as (*MARK:NAME)(*PRUNE) when the  expressed in any other way. In an anchored pattern (*PRUNE) has the same effect
2946  match fails completely; the name is passed back if this is the final attempt.  as (*COMMIT).
2947  (*PRUNE:NAME) does not pass back a name if the match succeeds. In an anchored  .P
2948  pattern (*PRUNE) has the same effect as (*COMMIT).  The behaviour of (*PRUNE:NAME) is the not the same as (*MARK:NAME)(*PRUNE).
2949    It is like (*MARK:NAME) in that the name is remembered for passing back to the
2950    caller. However, (*SKIP:NAME) searches only for names set with (*MARK).
2951  .sp  .sp
2952    (*SKIP)    (*SKIP)
2953  .sp  .sp
# Line 2774  instead of skipping on to "c". Line 2968  instead of skipping on to "c".
2968  .sp  .sp
2969    (*SKIP:NAME)    (*SKIP:NAME)
2970  .sp  .sp
2971  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
2972  following pattern fails to match, the previous path through the pattern is  triggered, the previous path through the pattern is searched for the most
2973  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
2974  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
2975  (*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
2976  matching name is found, normal "bumpalong" of one character happens (that is,  (*SKIP) is ignored.
2977  the (*SKIP) is ignored).  .P
2978    Note that (*SKIP:NAME) searches only for names set by (*MARK:NAME). It ignores
2979    names that are set by (*PRUNE:NAME) or (*THEN:NAME).
2980  .sp  .sp
2981    (*THEN) or (*THEN:NAME)    (*THEN) or (*THEN:NAME)
2982  .sp  .sp
2983  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
2984  pattern does not match. That is, it cancels pending backtracking, but only  reaches it. That is, it cancels any further backtracking within the current
2985  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
2986  be used for a pattern-based if-then-else block:  pattern-based if-then-else block:
2987  .sp  .sp
2988    ( COND1 (*THEN) FOO | COND2 (*THEN) BAR | COND3 (*THEN) BAZ ) ...    ( COND1 (*THEN) FOO | COND2 (*THEN) BAR | COND3 (*THEN) BAZ ) ...
2989  .sp  .sp
2990  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
2991  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
2992  second alternative and tries COND2, without backtracking into COND1. The  second alternative and tries COND2, without backtracking into COND1. If that
2993  behaviour of (*THEN:NAME) is exactly the same as (*MARK:NAME)(*THEN) if the  succeeds and BAR fails, COND3 is tried. If subsequently BAZ fails, there are no
2994  overall match fails. If (*THEN) is not inside an alternation, it acts like  more alternatives, so there is a backtrack to whatever came before the entire
2995  (*PRUNE).  group. If (*THEN) is not inside an alternation, it acts like (*PRUNE).
2996    .P
2997    The behaviour of (*THEN:NAME) is the not the same as (*MARK:NAME)(*THEN).
2998    It is like (*MARK:NAME) in that the name is remembered for passing back to the
2999    caller. However, (*SKIP:NAME) searches only for names set with (*MARK).
3000  .P  .P
3001  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
3002  the enclosing alternative; it is not a nested alternation with only one  enclosing alternative; it is not a nested alternation with only one
3003  alternative. The effect of (*THEN) extends beyond such a subpattern to the  alternative. The effect of (*THEN) extends beyond such a subpattern to the
3004  enclosing alternative. Consider this pattern, where A, B, etc. are complex  enclosing alternative. Consider this pattern, where A, B, etc. are complex
3005  pattern fragments that do not contain any | characters at this level:  pattern fragments that do not contain any | characters at this level:
# Line 2818  in C, matching moves to (*FAIL), which c Line 3018  in C, matching moves to (*FAIL), which c
3018  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
3019  backtrack into A.  backtrack into A.
3020  .P  .P
3021  Note also that a conditional subpattern is not considered as having two  Note that a conditional subpattern is not considered as having two
3022  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
3023  a conditional subpattern has a different meaning. Ignoring white space,  a conditional subpattern has a different meaning. Ignoring white space,
3024  consider:  consider:
# Line 2840  starting position, but allowing an advan Line 3040  starting position, but allowing an advan
3040  unanchored pattern). (*SKIP) is similar, except that the advance may be more  unanchored pattern). (*SKIP) is similar, except that the advance may be more
3041  than one character. (*COMMIT) is the strongest, causing the entire match to  than one character. (*COMMIT) is the strongest, causing the entire match to
3042  fail.  fail.
3043    .
3044    .
3045    .SS "More than one backtracking verb"
3046    .rs
3047    .sp
3048    If more than one backtracking verb is present in a pattern, the one that is
3049    backtracked onto first acts. For example, consider this pattern, where A, B,
3050    etc. are complex pattern fragments:
3051    .sp
3052      (A(*COMMIT)B(*THEN)C|ABD)
3053    .sp
3054    If A matches but B fails, the backtrack to (*COMMIT) causes the entire match to
3055    fail. However, if A and B match, but C fails, the backtrack to (*THEN) causes
3056    the next alternative (ABD) to be tried. This behaviour is consistent, but is
3057    not always the same as Perl's. It means that if two or more backtracking verbs
3058    appear in succession, all the the last of them has no effect. Consider this
3059    example:
3060    .sp
3061      ...(*COMMIT)(*PRUNE)...
3062    .sp
3063    If there is a matching failure to the right, backtracking onto (*PRUNE) cases
3064    it to be triggered, and its action is taken. There can never be a backtrack
3065    onto (*COMMIT).
3066    .
3067    .
3068    .\" HTML <a name="btrepeat"></a>
3069    .SS "Backtracking verbs in repeated groups"
3070    .rs
3071    .sp
3072    PCRE differs from Perl in its handling of backtracking verbs in repeated
3073    groups. For example, consider:
3074    .sp
3075      /(a(*COMMIT)b)+ac/
3076    .sp
3077    If the subject is "abac", Perl matches, but PCRE fails because the (*COMMIT) in
3078    the second repeat of the group acts.
3079    .
3080    .
3081    .\" HTML <a name="btassert"></a>
3082    .SS "Backtracking verbs in assertions"
3083    .rs
3084    .sp
3085    (*FAIL) in an assertion has its normal effect: it forces an immediate backtrack.
3086    .P
3087    (*ACCEPT) in a positive assertion causes the assertion to succeed without any
3088    further processing. In a negative assertion, (*ACCEPT) causes the assertion to
3089    fail without any further processing.
3090    .P
3091    The other backtracking verbs are not treated specially if they appear in a
3092    positive assertion. In particular, (*THEN) skips to the next alternative in the
3093    innermost enclosing group that has alternations, whether or not this is within
3094    the assertion.
3095    .P
3096    Negative assertions are, however, different, in order to ensure that changing a
3097    positive assertion into a negative assertion changes its result. Backtracking
3098    into (*COMMIT), (*SKIP), or (*PRUNE) causes a negative assertion to be true,
3099    without considering any further alternative branches in the assertion.
3100    Backtracking into (*THEN) causes it to skip to the next enclosing alternative
3101    within the assertion (the normal behaviour), but if the assertion does not have
3102    such an alternative, (*THEN) behaves like (*PRUNE).
3103    .
3104    .
3105    .\" HTML <a name="btsub"></a>
3106    .SS "Backtracking verbs in subroutines"
3107    .rs
3108    .sp
3109    These behaviours occur whether or not the subpattern is called recursively.
3110    Perl's treatment of subroutines is different in some cases.
3111    .P
3112    (*FAIL) in a subpattern called as a subroutine has its normal effect: it forces
3113    an immediate backtrack.
3114  .P  .P
3115  If more than one such verb is present in a pattern, the "strongest" one wins.  (*ACCEPT) in a subpattern called as a subroutine causes the subroutine match to
3116  For example, consider this pattern, where A, B, etc. are complex pattern  succeed without any further processing. Matching then continues after the
3117  fragments:  subroutine call.
3118  .sp  .P
3119    (A(*COMMIT)B(*THEN)C|D)  (*COMMIT), (*SKIP), and (*PRUNE) in a subpattern called as a subroutine cause
3120  .sp  the subroutine match to fail.
3121  Once A has matched, PCRE is committed to this match, at the current starting  .P
3122  position. If subsequently B matches, but C does not, the normal (*THEN) action  (*THEN) skips to the next alternative in the innermost enclosing group within
3123  of trying the next alternative (that is, D) does not happen because (*COMMIT)  the subpattern that has alternatives. If there is no such group within the
3124  overrides.  subpattern, (*THEN) causes the subroutine match to fail.
3125  .  .
3126  .  .
3127  .SH "SEE ALSO"  .SH "SEE ALSO"
3128  .rs  .rs
3129  .sp  .sp
3130  \fBpcreapi\fP(3), \fBpcrecallout\fP(3), \fBpcrematching\fP(3),  \fBpcreapi\fP(3), \fBpcrecallout\fP(3), \fBpcrematching\fP(3),
3131  \fBpcresyntax\fP(3), \fBpcre\fP(3).  \fBpcresyntax\fP(3), \fBpcre\fP(3), \fBpcre16(3)\fP, \fBpcre32(3)\fP.
3132  .  .
3133  .  .
3134  .SH AUTHOR  .SH AUTHOR
# Line 2874  Cambridge CB2 3QH, England. Line 3145  Cambridge CB2 3QH, England.
3145  .rs  .rs
3146  .sp  .sp
3147  .nf  .nf
3148  Last updated: 14 November 2011  Last updated: 26 April 2013
3149  Copyright (c) 1997-2011 University of Cambridge.  Copyright (c) 1997-2013 University of Cambridge.
3150  .fi  .fi

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