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1  .TH PCREPATTERN 3  .TH PCREPATTERN 3 "07 November 2012" "PCRE 8.32"
2  .SH NAME  .SH NAME
3  PCRE - Perl-compatible regular expressions  PCRE - Perl-compatible regular expressions
4  .SH "PCRE REGULAR EXPRESSION DETAILS"  .SH "PCRE REGULAR EXPRESSION DETAILS"
# Line 21  published by O'Reilly, covers regular ex Line 21  published by O'Reilly, covers regular ex
21  description of PCRE's regular expressions is intended as reference material.  description of PCRE's regular expressions is intended as reference material.
22  .P  .P
23  The original operation of PCRE was on strings of one-byte characters. However,  The original operation of PCRE was on strings of one-byte characters. However,
24  there is now also support for UTF-8 character strings. To use this,  there is now also support for UTF-8 strings in the original library, an
25  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 an
26  \fBpcre_compile()\fP or \fBpcre_compile2()\fP with the PCRE_UTF8 option. There  extra library that supports 32-bit and UTF-32 character strings. To use these
27  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
28    strings you must either call the compiling function with the PCRE_UTF8,
29    PCRE_UTF16 or PCRE_UTF32 option, or the pattern must start with one of
30    these special sequences:
31  .sp  .sp
32    (*UTF8)    (*UTF8)
33      (*UTF16)
34      (*UTF32)
35  .sp  .sp
36  Starting a pattern with this sequence is equivalent to setting the PCRE_UTF8  Starting a pattern with such a sequence is equivalent to setting the relevant
37  option. This feature is not Perl-compatible. How setting UTF-8 mode affects  option. This feature is not Perl-compatible. How setting a UTF mode affects
38  pattern matching is mentioned in several places below. There is also a summary  pattern matching is mentioned in several places below. There is also a summary
39  of UTF-8 features in the  of features in the
 .\" HTML <a href="pcre.html#utf8support">  
 .\" </a>  
 section on UTF-8 support  
 .\"  
 in the main  
40  .\" HREF  .\" HREF
41  \fBpcre\fP  \fBpcreunicode\fP
42  .\"  .\"
43  page.  page.
44  .P  .P
45  Another special sequence that may appear at the start of a pattern or in  Another special sequence that may appear at the start of a pattern or in
46  combination with (*UTF8) is:  combination with (*UTF8) or (*UTF16) or (*UTF32) is:
47  .sp  .sp
48    (*UCP)    (*UCP)
49  .sp  .sp
# Line 52  such as \ed and \ew to use Unicode prope Line 52  such as \ed and \ew to use Unicode prope
52  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
53  table.  table.
54  .P  .P
55    If a pattern starts with (*NO_START_OPT), it has the same effect as setting the
56    PCRE_NO_START_OPTIMIZE option either at compile or matching time. There are
57    also some more of these special sequences that are concerned with the handling
58    of newlines; they are described below.
59    .P
60  The remainder of this document discusses the patterns that are supported by  The remainder of this document discusses the patterns that are supported by
61  PCRE when its main matching function, \fBpcre_exec()\fP, is used.  PCRE when one its main matching functions, \fBpcre_exec()\fP (8-bit) or
62  From release 6.0, PCRE offers a second matching function,  \fBpcre[16|32]_exec()\fP (16- or 32-bit), is used. PCRE also has alternative
63  \fBpcre_dfa_exec()\fP, which matches using a different algorithm that is not  matching functions, \fBpcre_dfa_exec()\fP and \fBpcre[16|32_dfa_exec()\fP,
64  Perl-compatible. Some of the features discussed below are not available when  which match using a different algorithm that is not Perl-compatible. Some of
65  \fBpcre_dfa_exec()\fP is used. The advantages and disadvantages of the  the features discussed below are not available when DFA matching is used. The
66  alternative function, and how it differs from the normal function, are  advantages and disadvantages of the alternative functions, and how they differ
67  discussed in the  from the normal functions, are discussed in the
68  .\" HREF  .\" HREF
69  \fBpcrematching\fP  \fBpcrematching\fP
70  .\"  .\"
71  page.  page.
72  .  .
73  .  .
74    .SH "EBCDIC CHARACTER CODES"
75    .rs
76    .sp
77    PCRE can be compiled to run in an environment that uses EBCDIC as its character
78    code rather than ASCII or Unicode (typically a mainframe system). In the
79    sections below, character code values are ASCII or Unicode; in an EBCDIC
80    environment these characters may have different code values, and there are no
81    code points greater than 255.
82    .
83    .
84    .\" HTML <a name="newlines"></a>
85  .SH "NEWLINE CONVENTIONS"  .SH "NEWLINE CONVENTIONS"
86  .rs  .rs
87  .sp  .sp
# Line 93  string with one of the following five se Line 109  string with one of the following five se
109    (*ANYCRLF)   any of the three above    (*ANYCRLF)   any of the three above
110    (*ANY)       all Unicode newline sequences    (*ANY)       all Unicode newline sequences
111  .sp  .sp
112  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
113  \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  
114  .sp  .sp
115    (*CR)a.b    (*CR)a.b
116  .sp  .sp
# Line 105  Perl-compatible, are recognized only at Line 120  Perl-compatible, are recognized only at
120  they must be in upper case. If more than one of them is present, the last one  they must be in upper case. If more than one of them is present, the last one
121  is used.  is used.
122  .P  .P
123  The newline convention affects the interpretation of the dot metacharacter when  The newline convention affects where the circumflex and dollar assertions are
124  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
125  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
126  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
127    sequence, for Perl compatibility. However, this can be changed; see the
128  description of \eR in the section entitled  description of \eR in the section entitled
129  .\" HTML <a href="#newlineseq">  .\" HTML <a href="#newlineseq">
130  .\" </a>  .\" </a>
# Line 129  corresponding characters in the subject. Line 145  corresponding characters in the subject.
145  .sp  .sp
146  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
147  caseless matching is specified (the PCRE_CASELESS option), letters are matched  caseless matching is specified (the PCRE_CASELESS option), letters are matched
148  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
149  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
150  always possible. For characters with higher values, the concept of case is  always possible. For characters with higher values, the concept of case is
151  supported if PCRE is compiled with Unicode property support, but not otherwise.  supported if PCRE is compiled with Unicode property support, but not otherwise.
152  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
153  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
154  UTF-8 support.  UTF support.
155  .P  .P
156  The power of regular expressions comes from the ability to include alternatives  The power of regular expressions comes from the ability to include alternatives
157  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 181  The following sections describe the use Line 197  The following sections describe the use
197  .rs  .rs
198  .sp  .sp
199  The backslash character has several uses. Firstly, if it is followed by a  The backslash character has several uses. Firstly, if it is followed by a
200  non-alphanumeric character, it takes away any special meaning that character  character that is not a number or a letter, it takes away any special meaning
201  may have. This use of backslash as an escape character applies both inside and  that character may have. This use of backslash as an escape character applies
202  outside character classes.  both inside and outside character classes.
203  .P  .P
204  For example, if you want to match a * character, you write \e* in the pattern.  For example, if you want to match a * character, you write \e* in the pattern.
205  This escaping action applies whether or not the following character would  This escaping action applies whether or not the following character would
# Line 191  otherwise be interpreted as a metacharac Line 207  otherwise be interpreted as a metacharac
207  non-alphanumeric with backslash to specify that it stands for itself. In  non-alphanumeric with backslash to specify that it stands for itself. In
208  particular, if you want to match a backslash, you write \e\e.  particular, if you want to match a backslash, you write \e\e.
209  .P  .P
210  If a pattern is compiled with the PCRE_EXTENDED option, whitespace in the  In a UTF mode, only ASCII numbers and letters have any special meaning after a
211    backslash. All other characters (in particular, those whose codepoints are
212    greater than 127) are treated as literals.
213    .P
214    If a pattern is compiled with the PCRE_EXTENDED option, white space in the
215  pattern (other than in a character class) and characters between a # outside  pattern (other than in a character class) and characters between a # outside
216  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
217  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.
218  .P  .P
219  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
220  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 210  Perl, $ and @ cause variable interpolati Line 230  Perl, $ and @ cause variable interpolati
230    \eQabc\eE\e$\eQxyz\eE   abc$xyz        abc$xyz    \eQabc\eE\e$\eQxyz\eE   abc$xyz        abc$xyz
231  .sp  .sp
232  The \eQ...\eE sequence is recognized both inside and outside character classes.  The \eQ...\eE sequence is recognized both inside and outside character classes.
233  An isolated \eE that is not preceded by \eQ is ignored.  An isolated \eE that is not preceded by \eQ is ignored. If \eQ is not followed
234    by \eE later in the pattern, the literal interpretation continues to the end of
235    the pattern (that is, \eE is assumed at the end). If the isolated \eQ is inside
236    a character class, this causes an error, because the character class is not
237    terminated.
238  .  .
239  .  .
240  .\" HTML <a name="digitsafterbackslash"></a>  .\" HTML <a name="digitsafterbackslash"></a>
# Line 224  but when a pattern is being prepared by Line 248  but when a pattern is being prepared by
248  one of the following escape sequences than the binary character it represents:  one of the following escape sequences than the binary character it represents:
249  .sp  .sp
250    \ea        alarm, that is, the BEL character (hex 07)    \ea        alarm, that is, the BEL character (hex 07)
251    \ecx       "control-x", where x is any character    \ecx       "control-x", where x is any ASCII character
252    \ee        escape (hex 1B)    \ee        escape (hex 1B)
253    \ef        formfeed (hex 0C)    \ef        form feed (hex 0C)
254    \en        linefeed (hex 0A)    \en        linefeed (hex 0A)
255    \er        carriage return (hex 0D)    \er        carriage return (hex 0D)
256    \et        tab (hex 09)    \et        tab (hex 09)
257    \eddd      character with octal code ddd, or back reference    \eddd      character with octal code ddd, or back reference
258    \exhh      character with hex code hh    \exhh      character with hex code hh
259    \ex{hhh..} character with hex code hhh..    \ex{hhh..} character with hex code hhh.. (non-JavaScript mode)
260      \euhhhh    character with hex code hhhh (JavaScript mode only)
261    .sp
262    The precise effect of \ecx on ASCII characters is as follows: if x is a lower
263    case letter, it is converted to upper case. Then bit 6 of the character (hex
264    40) is inverted. Thus \ecA to \ecZ become hex 01 to hex 1A (A is 41, Z is 5A),
265    but \ec{ becomes hex 3B ({ is 7B), and \ec; becomes hex 7B (; is 3B). If the
266    data item (byte or 16-bit value) following \ec has a value greater than 127, a
267    compile-time error occurs. This locks out non-ASCII characters in all modes.
268    .P
269    The \ec facility was designed for use with ASCII characters, but with the
270    extension to Unicode it is even less useful than it once was. It is, however,
271    recognized when PCRE is compiled in EBCDIC mode, where data items are always
272    bytes. In this mode, all values are valid after \ec. If the next character is a
273    lower case letter, it is converted to upper case. Then the 0xc0 bits of the
274    byte are inverted. Thus \ecA becomes hex 01, as in ASCII (A is C1), but because
275    the EBCDIC letters are disjoint, \ecZ becomes hex 29 (Z is E9), and other
276    characters also generate different values.
277    .P
278    By default, after \ex, from zero to two hexadecimal digits are read (letters
279    can be in upper or lower case). Any number of hexadecimal digits may appear
280    between \ex{ and }, but the character code is constrained as follows:
281    .sp
282      8-bit non-UTF mode    less than 0x100
283      8-bit UTF-8 mode      less than 0x10ffff and a valid codepoint
284      16-bit non-UTF mode   less than 0x10000
285      16-bit UTF-16 mode    less than 0x10ffff and a valid codepoint
286      32-bit non-UTF mode   less than 0x80000000
287      32-bit UTF-32 mode    less than 0x10ffff and a valid codepoint
288  .sp  .sp
289  The precise effect of \ecx is as follows: if x is a lower case letter, it  Invalid Unicode codepoints are the range 0xd800 to 0xdfff (the so-called
290  is converted to upper case. Then bit 6 of the character (hex 40) is inverted.  "surrogate" codepoints), and 0xffef.
 Thus \ecz becomes hex 1A, but \ec{ becomes hex 3B, while \ec; becomes hex  
 7B.  
 .P  
 After \ex, from zero to two hexadecimal digits are read (letters can be in  
 upper or lower case). Any number of hexadecimal digits may appear between \ex{  
 and }, but the value of the character code must be less than 256 in non-UTF-8  
 mode, and less than 2**31 in UTF-8 mode. That is, the maximum value in  
 hexadecimal is 7FFFFFFF. Note that this is bigger than the largest Unicode code  
 point, which is 10FFFF.  
291  .P  .P
292  If characters other than hexadecimal digits appear between \ex{ and }, or if  If characters other than hexadecimal digits appear between \ex{ and }, or if
293  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
294  initial \ex will be interpreted as a basic hexadecimal escape, with no  initial \ex will be interpreted as a basic hexadecimal escape, with no
295  following digits, giving a character whose value is zero.  following digits, giving a character whose value is zero.
296  .P  .P
297    If the PCRE_JAVASCRIPT_COMPAT option is set, the interpretation of \ex is
298    as just described only when it is followed by two hexadecimal digits.
299    Otherwise, it matches a literal "x" character. In JavaScript mode, support for
300    code points greater than 256 is provided by \eu, which must be followed by
301    four hexadecimal digits; otherwise it matches a literal "u" character.
302    Character codes specified by \eu in JavaScript mode are constrained in the same
303    was as those specified by \ex in non-JavaScript mode.
304    .P
305  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
306  syntaxes for \ex. There is no difference in the way they are handled. For  syntaxes for \ex (or by \eu in JavaScript mode). There is no difference in the
307  example, \exdc is exactly the same as \ex{dc}.  way they are handled. For example, \exdc is exactly the same as \ex{dc} (or
308    \eu00dc in JavaScript mode).
309  .P  .P
310  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
311  digits, just those that are present are used. Thus the sequence \e0\ex\e07  digits, just those that are present are used. Thus the sequence \e0\ex\e07
# Line 279  parenthesized subpatterns. Line 331  parenthesized subpatterns.
331  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
332  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
333  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
334  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
335  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.
336  to \e777 are permitted. For example:  For example:
337  .sp  .sp
338    \e040   is another way of writing a space    \e040   is another way of writing an ASCII space
339  .\" JOIN  .\" JOIN
340    \e40    is the same, provided there are fewer than 40    \e40    is the same, provided there are fewer than 40
341              previous capturing subpatterns              previous capturing subpatterns
# Line 298  to \e777 are permitted. For example: Line 350  to \e777 are permitted. For example:
350              character with octal code 113              character with octal code 113
351  .\" JOIN  .\" JOIN
352    \e377   might be a back reference, otherwise    \e377   might be a back reference, otherwise
353              the byte consisting entirely of 1 bits              the value 255 (decimal)
354  .\" JOIN  .\" JOIN
355    \e81    is either a back reference, or a binary zero    \e81    is either a back reference, or a binary zero
356              followed by the two characters "8" and "1"              followed by the two characters "8" and "1"
# Line 307  Note that octal values of 100 or greater Line 359  Note that octal values of 100 or greater
359  zero, because no more than three octal digits are ever read.  zero, because no more than three octal digits are ever read.
360  .P  .P
361  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
362  and outside character classes. In addition, inside a character class, the  and outside character classes. In addition, inside a character class, \eb is
363  sequence \eb is interpreted as the backspace character (hex 08). The sequences  interpreted as the backspace character (hex 08).
364  \eB, \eN, \eR, and \eX are not special inside a character class. Like any other  .P
365  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
366  "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
367  set. Outside a character class, these sequences have different meanings.  treated as the literal characters "B", "R", and "X" by default, but cause an
368    error if the PCRE_EXTRA option is set. Outside a character class, these
369    sequences have different meanings.
370    .
371    .
372    .SS "Unsupported escape sequences"
373    .rs
374    .sp
375    In Perl, the sequences \el, \eL, \eu, and \eU are recognized by its string
376    handler and used to modify the case of following characters. By default, PCRE
377    does not support these escape sequences. However, if the PCRE_JAVASCRIPT_COMPAT
378    option is set, \eU matches a "U" character, and \eu can be used to define a
379    character by code point, as described in the previous section.
380  .  .
381  .  .
382  .SS "Absolute and relative back references"  .SS "Absolute and relative back references"
# Line 359  Another use of backslash is for specifyi Line 423  Another use of backslash is for specifyi
423  .sp  .sp
424    \ed     any decimal digit    \ed     any decimal digit
425    \eD     any character that is not a decimal digit    \eD     any character that is not a decimal digit
426    \eh     any horizontal whitespace character    \eh     any horizontal white space character
427    \eH     any character that is not a horizontal whitespace character    \eH     any character that is not a horizontal white space character
428    \es     any whitespace character    \es     any white space character
429    \eS     any character that is not a whitespace character    \eS     any character that is not a white space character
430    \ev     any vertical whitespace character    \ev     any vertical white space character
431    \eV     any character that is not a vertical whitespace character    \eV     any character that is not a vertical white space character
432    \ew     any "word" character    \ew     any "word" character
433    \eW     any "non-word" character    \eW     any "non-word" character
434  .sp  .sp
# Line 374  This is the same as Line 438  This is the same as
438  .\" </a>  .\" </a>
439  the "." metacharacter  the "." metacharacter
440  .\"  .\"
441  when PCRE_DOTALL is not set.  when PCRE_DOTALL is not set. Perl also uses \eN to match characters by name;
442    PCRE does not support this.
443  .P  .P
444  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
445  of characters into two disjoint sets. Any given character matches one, and only  of characters into two disjoint sets. Any given character matches one, and only
# Line 406  or "french" in Windows, some character c Line 471  or "french" in Windows, some character c
471  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
472  Unicode is discouraged.  Unicode is discouraged.
473  .P  .P
474  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
475  \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
476  their original meanings from before UTF-8 support was available, mainly for  their original meanings from before UTF support was available, mainly for
477  efficiency reasons. However, if PCRE is compiled with Unicode property support,  efficiency reasons. However, if PCRE is compiled with Unicode property support,
478  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
479  properties are used to determine character types, as follows:  properties are used to determine character types, as follows:
# Line 423  any Unicode letter, and underscore. Note Line 488  any Unicode letter, and underscore. Note
488  \eB because they are defined in terms of \ew and \eW. Matching these sequences  \eB because they are defined in terms of \ew and \eW. Matching these sequences
489  is noticeably slower when PCRE_UCP is set.  is noticeably slower when PCRE_UCP is set.
490  .P  .P
491  The sequences \eh, \eH, \ev, and \eV are Perl 5.10 features. In contrast to the  The sequences \eh, \eH, \ev, and \eV are features that were added to Perl at
492  other sequences, which match only ASCII characters by default, these always  release 5.10. In contrast to the other sequences, which match only ASCII
493  match certain high-valued codepoints in UTF-8 mode, whether or not PCRE_UCP is  characters by default, these always match certain high-valued codepoints,
494  set. The horizontal space characters are:  whether or not PCRE_UCP is set. The horizontal space characters are:
495  .sp  .sp
496    U+0009     Horizontal tab    U+0009     Horizontal tab (HT)
497    U+0020     Space    U+0020     Space
498    U+00A0     Non-break space    U+00A0     Non-break space
499    U+1680     Ogham space mark    U+1680     Ogham space mark
# Line 450  set. The horizontal space characters are Line 515  set. The horizontal space characters are
515  .sp  .sp
516  The vertical space characters are:  The vertical space characters are:
517  .sp  .sp
518    U+000A     Linefeed    U+000A     Linefeed (LF)
519    U+000B     Vertical tab    U+000B     Vertical tab (VT)
520    U+000C     Formfeed    U+000C     Form feed (FF)
521    U+000D     Carriage return    U+000D     Carriage return (CR)
522    U+0085     Next line    U+0085     Next line (NEL)
523    U+2028     Line separator    U+2028     Line separator
524    U+2029     Paragraph separator    U+2029     Paragraph separator
525    .sp
526    In 8-bit, non-UTF-8 mode, only the characters with codepoints less than 256 are
527    relevant.
528  .  .
529  .  .
530  .\" HTML <a name="newlineseq"></a>  .\" HTML <a name="newlineseq"></a>
# Line 464  The vertical space characters are: Line 532  The vertical space characters are:
532  .rs  .rs
533  .sp  .sp
534  Outside a character class, by default, the escape sequence \eR matches any  Outside a character class, by default, the escape sequence \eR matches any
535  Unicode newline sequence. This is a Perl 5.10 feature. In non-UTF-8 mode \eR is  Unicode newline sequence. In 8-bit non-UTF-8 mode \eR is equivalent to the
536  equivalent to the following:  following:
537  .sp  .sp
538    (?>\er\en|\en|\ex0b|\ef|\er|\ex85)    (?>\er\en|\en|\ex0b|\ef|\er|\ex85)
539  .sp  .sp
# Line 476  below. Line 544  below.
544  .\"  .\"
545  This particular group matches either the two-character sequence CR followed by  This particular group matches either the two-character sequence CR followed by
546  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,
547  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
548  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
549  cannot be split.  cannot be split.
550  .P  .P
551  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
552  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).
553  Unicode character property support is not needed for these characters to be  Unicode character property support is not needed for these characters to be
554  recognized.  recognized.
# Line 496  one of the following sequences: Line 564  one of the following sequences:
564    (*BSR_ANYCRLF)   CR, LF, or CRLF only    (*BSR_ANYCRLF)   CR, LF, or CRLF only
565    (*BSR_UNICODE)   any Unicode newline sequence    (*BSR_UNICODE)   any Unicode newline sequence
566  .sp  .sp
567  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
568  \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
569  \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
570  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
571  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
572  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:  
573  .sp  .sp
574    (*ANY)(*BSR_ANYCRLF)    (*ANY)(*BSR_ANYCRLF)
575  .sp  .sp
576  They can also be combined with the (*UTF8) or (*UCP) special sequences. Inside  They can also be combined with the (*UTF8), (*UTF16), (*UTF32) or (*UCP) special
577  a character class, \eR is treated as an unrecognized escape sequence, and so  sequences. Inside a character class, \eR is treated as an unrecognized escape
578  matches the letter "R" by default, but causes an error if PCRE_EXTRA is set.  sequence, and so matches the letter "R" by default, but causes an error if
579    PCRE_EXTRA is set.
580  .  .
581  .  .
582  .\" HTML <a name="uniextseq"></a>  .\" HTML <a name="uniextseq"></a>
# Line 517  matches the letter "R" by default, but c Line 585  matches the letter "R" by default, but c
585  .sp  .sp
586  When PCRE is built with Unicode character property support, three additional  When PCRE is built with Unicode character property support, three additional
587  escape sequences that match characters with specific properties are available.  escape sequences that match characters with specific properties are available.
588  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
589  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.
590  The extra escape sequences are:  The extra escape sequences are:
591  .sp  .sp
592    \ep{\fIxx\fP}   a character with the \fIxx\fP property    \ep{\fIxx\fP}   a character with the \fIxx\fP property
593    \eP{\fIxx\fP}   a character without the \fIxx\fP property    \eP{\fIxx\fP}   a character without the \fIxx\fP property
594    \eX       an extended Unicode sequence    \eX       a Unicode extended grapheme cluster
595  .sp  .sp
596  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
597  script names, the general category properties, "Any", which matches any  script names, the general category properties, "Any", which matches any
# Line 552  Armenian, Line 620  Armenian,
620  Avestan,  Avestan,
621  Balinese,  Balinese,
622  Bamum,  Bamum,
623    Batak,
624  Bengali,  Bengali,
625  Bopomofo,  Bopomofo,
626    Brahmi,
627  Braille,  Braille,
628  Buginese,  Buginese,
629  Buhid,  Buhid,
630  Canadian_Aboriginal,  Canadian_Aboriginal,
631  Carian,  Carian,
632    Chakma,
633  Cham,  Cham,
634  Cherokee,  Cherokee,
635  Common,  Common,
# Line 601  Lisu, Line 672  Lisu,
672  Lycian,  Lycian,
673  Lydian,  Lydian,
674  Malayalam,  Malayalam,
675    Mandaic,
676  Meetei_Mayek,  Meetei_Mayek,
677    Meroitic_Cursive,
678    Meroitic_Hieroglyphs,
679    Miao,
680  Mongolian,  Mongolian,
681  Myanmar,  Myanmar,
682  New_Tai_Lue,  New_Tai_Lue,
# Line 620  Rejang, Line 695  Rejang,
695  Runic,  Runic,
696  Samaritan,  Samaritan,
697  Saurashtra,  Saurashtra,
698    Sharada,
699  Shavian,  Shavian,
700  Sinhala,  Sinhala,
701    Sora_Sompeng,
702  Sundanese,  Sundanese,
703  Syloti_Nagri,  Syloti_Nagri,
704  Syriac,  Syriac,
# Line 630  Tagbanwa, Line 707  Tagbanwa,
707  Tai_Le,  Tai_Le,
708  Tai_Tham,  Tai_Tham,
709  Tai_Viet,  Tai_Viet,
710    Takri,
711  Tamil,  Tamil,
712  Telugu,  Telugu,
713  Thaana,  Thaana,
# Line 704  the Lu, Ll, or Lt property, in other wor Line 782  the Lu, Ll, or Lt property, in other wor
782  a modifier or "other".  a modifier or "other".
783  .P  .P
784  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
785  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
786  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
787  (see the discussion of PCRE_NO_UTF8_CHECK in the  (see the discussion of PCRE_NO_UTF8_CHECK, PCRE_NO_UTF16_CHECK and
788    PCRE_NO_UTF32_CHECK in the
789  .\" HREF  .\" HREF
790  \fBpcreapi\fP  \fBpcreapi\fP
791  .\"  .\"
# Line 723  Unicode table. Line 802  Unicode table.
802  Specifying caseless matching does not affect these escape sequences. For  Specifying caseless matching does not affect these escape sequences. For
803  example, \ep{Lu} always matches only upper case letters.  example, \ep{Lu} always matches only upper case letters.
804  .P  .P
805  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
806  Unicode sequence. \eX is equivalent to  multistage table lookup in order to find a character's property. That is why
807  .sp  the traditional escape sequences such as \ed and \ew do not use Unicode
808    (?>\ePM\epM*)  properties in PCRE by default, though you can make them do so by setting the
809    PCRE_UCP option or by starting the pattern with (*UCP).
810    .
811    .
812    .SS Extended grapheme clusters
813    .rs
814  .sp  .sp
815  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
816  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  
817  .\" HTML <a href="#atomicgroup">  .\" HTML <a href="#atomicgroup">
818  .\" </a>  .\" </a>
819  (see below).  (see below).
820  .\"  .\"
821  Characters with the "mark" property are typically accents that affect the  Up to and including release 8.31, PCRE matched an earlier, simpler definition
822  preceding character. None of them have codepoints less than 256, so in  that was equivalent to
823  non-UTF-8 mode \eX matches any one character.  .sp
824  .P    (?>\ePM\epM*)
825  Matching characters by Unicode property is not fast, because PCRE has to search  .sp
826  a structure that contains data for over fifteen thousand characters. That is  That is, it matched a character without the "mark" property, followed by zero
827  why the traditional escape sequences such as \ed and \ew do not use Unicode  or more characters with the "mark" property. Characters with the "mark"
828  properties in PCRE by default, though you can make them do so by setting the  property are typically non-spacing accents that affect the preceding character.
829  PCRE_UCP option for \fBpcre_compile()\fP or by starting the pattern with  .P
830  (*UCP).  This simple definition was extended in Unicode to include more complicated
831    kinds of composite character by giving each character a grapheme breaking
832    property, and creating rules that use these properties to define the boundaries
833    of extended grapheme clusters. In releases of PCRE later than 8.31, \eX matches
834    one of these clusters.
835    .P
836    \eX always matches at least one character. Then it decides whether to add
837    additional characters according to the following rules for ending a cluster:
838    .P
839    1. End at the end of the subject string.
840    .P
841    2. Do not end between CR and LF; otherwise end after any control character.
842    .P
843    3. Do not break Hangul (a Korean script) syllable sequences. Hangul characters
844    are of five types: L, V, T, LV, and LVT. An L character may be followed by an
845    L, V, LV, or LVT character; an LV or V character may be followed by a V or T
846    character; an LVT or T character may be follwed only by a T character.
847    .P
848    4. Do not end before extending characters or spacing marks. Characters with
849    the "mark" property always have the "extend" grapheme breaking property.
850    .P
851    5. Do not end after prepend characters.
852    .P
853    6. Otherwise, end the cluster.
854  .  .
855  .  .
856  .\" HTML <a name="extraprops"></a>  .\" HTML <a name="extraprops"></a>
857  .SS PCRE's additional properties  .SS PCRE's additional properties
858  .rs  .rs
859  .sp  .sp
860  As well as the standard Unicode properties described in the previous  As well as the standard Unicode properties described above, PCRE supports four
861  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
862  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
863  properties. PCRE uses these non-standard, non-Perl properties internally when  non-standard, non-Perl properties internally when PCRE_UCP is set. They are:
 PCRE_UCP is set. They are:  
864  .sp  .sp
865    Xan   Any alphanumeric character    Xan   Any alphanumeric character
866    Xps   Any POSIX space character    Xps   Any POSIX space character
# Line 763  PCRE_UCP is set. They are: Line 868  PCRE_UCP is set. They are:
868    Xwd   Any Perl "word" character    Xwd   Any Perl "word" character
869  .sp  .sp
870  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)
871  property. Xps matches the characters tab, linefeed, vertical tab, formfeed, or  property. Xps matches the characters tab, linefeed, vertical tab, form feed, or
872  carriage return, and any other character that has the Z (separator) property.  carriage return, and any other character that has the Z (separator) property.
873  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
874  same characters as Xan, plus underscore.  same characters as Xan, plus underscore.
# Line 773  same characters as Xan, plus underscore. Line 878  same characters as Xan, plus underscore.
878  .SS "Resetting the match start"  .SS "Resetting the match start"
879  .rs  .rs
880  .sp  .sp
881  The escape sequence \eK, which is a Perl 5.10 feature, causes any previously  The escape sequence \eK causes any previously matched characters not to be
882  matched characters not to be included in the final matched sequence. For  included in the final matched sequence. For example, the pattern:
 example, the pattern:  
883  .sp  .sp
884    foo\eKbar    foo\eKbar
885  .sp  .sp
# Line 834  escape sequence" error is generated inst Line 938  escape sequence" error is generated inst
938  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
939  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
940  \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
941  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
942  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
943  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
944  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 873  regular expression. Line 977  regular expression.
977  .SH "CIRCUMFLEX AND DOLLAR"  .SH "CIRCUMFLEX AND DOLLAR"
978  .rs  .rs
979  .sp  .sp
980    The circumflex and dollar metacharacters are zero-width assertions. That is,
981    they test for a particular condition being true without consuming any
982    characters from the subject string.
983    .P
984  Outside a character class, in the default matching mode, the circumflex  Outside a character class, in the default matching mode, the circumflex
985  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
986  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
987  \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
988  option is unset. Inside a character class, circumflex has an entirely different  option is unset. Inside a character class, circumflex has an entirely different
989  meaning  meaning
# Line 892  constrained to match only at the start o Line 1000  constrained to match only at the start o
1000  "anchored" pattern. (There are also other constructs that can cause a pattern  "anchored" pattern. (There are also other constructs that can cause a pattern
1001  to be anchored.)  to be anchored.)
1002  .P  .P
1003  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
1004  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
1005  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
1006  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
1007  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
1008  character class.  branch in which it appears. Dollar has no special meaning in a character class.
1009  .P  .P
1010  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
1011  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 929  end of the subject in both modes, and if Line 1037  end of the subject in both modes, and if
1037  .sp  .sp
1038  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
1039  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
1040  line. In UTF-8 mode, the matched character may be more than one byte long.  line.
1041  .P  .P
1042  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
1043  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 947  The handling of dot is entirely independ Line 1055  The handling of dot is entirely independ
1055  dollar, the only relationship being that they both involve newlines. Dot has no  dollar, the only relationship being that they both involve newlines. Dot has no
1056  special meaning in a character class.  special meaning in a character class.
1057  .P  .P
1058  The escape sequence \eN always behaves as a dot does when PCRE_DOTALL is not  The escape sequence \eN behaves like a dot, except that it is not affected by
1059  set. In other words, it matches any one character except one that signifies the  the PCRE_DOTALL option. In other words, it matches any character except one
1060  end of a line.  that signifies the end of a line. Perl also uses \eN to match characters by
1061  .  name; PCRE does not support this.
1062  .  .
1063  .SH "MATCHING A SINGLE BYTE"  .
1064  .rs  .SH "MATCHING A SINGLE DATA UNIT"
1065  .sp  .rs
1066  Outside a character class, the escape sequence \eC matches any one byte, both  .sp
1067  in and out of UTF-8 mode. Unlike a dot, it always matches any line-ending  Outside a character class, the escape sequence \eC matches any one data unit,
1068  characters. The feature is provided in Perl in order to match individual bytes  whether or not a UTF mode is set. In the 8-bit library, one data unit is one
1069  in UTF-8 mode. Because it breaks up UTF-8 characters into individual bytes,  byte; in the 16-bit library it is a 16-bit unit; in the 32-bit library it is
1070  what remains in the string may be a malformed UTF-8 string. For this reason,  a 32-bit unit. Unlike a dot, \eC always
1071  the \eC escape sequence is best avoided.  matches line-ending characters. The feature is provided in Perl in order to
1072    match individual bytes in UTF-8 mode, but it is unclear how it can usefully be
1073    used. Because \eC breaks up characters into individual data units, matching one
1074    unit with \eC in a UTF mode means that the rest of the string may start with a
1075    malformed UTF character. This has undefined results, because PCRE assumes that
1076    it is dealing with valid UTF strings (and by default it checks this at the
1077    start of processing unless the PCRE_NO_UTF8_CHECK, PCRE_NO_UTF16_CHECK or
1078    PCRE_NO_UTF32_CHECK option is used).
1079  .P  .P
1080  PCRE does not allow \eC to appear in lookbehind assertions  PCRE does not allow \eC to appear in lookbehind assertions
1081  .\" HTML <a href="#lookbehind">  .\" HTML <a href="#lookbehind">
1082  .\" </a>  .\" </a>
1083  (described below),  (described below)
1084  .\"  .\"
1085  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
1086  the lookbehind.  the lookbehind.
1087    .P
1088    In general, the \eC escape sequence is best avoided. However, one
1089    way of using it that avoids the problem of malformed UTF characters is to use a
1090    lookahead to check the length of the next character, as in this pattern, which
1091    could be used with a UTF-8 string (ignore white space and line breaks):
1092    .sp
1093      (?| (?=[\ex00-\ex7f])(\eC) |
1094          (?=[\ex80-\ex{7ff}])(\eC)(\eC) |
1095          (?=[\ex{800}-\ex{ffff}])(\eC)(\eC)(\eC) |
1096          (?=[\ex{10000}-\ex{1fffff}])(\eC)(\eC)(\eC)(\eC))
1097    .sp
1098    A group that starts with (?| resets the capturing parentheses numbers in each
1099    alternative (see
1100    .\" HTML <a href="#dupsubpatternnumber">
1101    .\" </a>
1102    "Duplicate Subpattern Numbers"
1103    .\"
1104    below). The assertions at the start of each branch check the next UTF-8
1105    character for values whose encoding uses 1, 2, 3, or 4 bytes, respectively. The
1106    character's individual bytes are then captured by the appropriate number of
1107    groups.
1108  .  .
1109  .  .
1110  .\" HTML <a name="characterclass"></a>  .\" HTML <a name="characterclass"></a>
# Line 982  bracket causes a compile-time error. If Line 1118  bracket causes a compile-time error. If
1118  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
1119  (after an initial circumflex, if present) or escaped with a backslash.  (after an initial circumflex, if present) or escaped with a backslash.
1120  .P  .P
1121  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
1122  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
1123  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
1124  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
1125  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
1126  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
1127  backslash.  backslash.
1128  .P  .P
1129  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 998  circumflex is not an assertion; it still Line 1134  circumflex is not an assertion; it still
1134  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
1135  string.  string.
1136  .P  .P
1137  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)
1138  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
1139    \ex{ escaping mechanism.
1140  .P  .P
1141  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
1142  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
1143  "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
1144  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
1145  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
1146  always possible. For characters with higher values, the concept of case is  always possible. For characters with higher values, the concept of case is
1147  supported if PCRE is compiled with Unicode property support, but not otherwise.  supported if PCRE is compiled with Unicode property support, but not otherwise.
1148  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
1149  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
1150  with UTF-8 support.  well as with UTF support.
1151  .P  .P
1152  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
1153  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 1032  followed by two other characters. The oc Line 1169  followed by two other characters. The oc
1169  "]" can also be used to end a range.  "]" can also be used to end a range.
1170  .P  .P
1171  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
1172  used for characters specified numerically, for example [\e000-\e037]. In UTF-8  used for characters specified numerically, for example [\e000-\e037]. Ranges
1173  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}].  
1174  .P  .P
1175  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
1176  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
1177  [][\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
1178  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
1179  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
1180  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
1181  property support.  property support.
1182  .P  .P
1183  The character types \ed, \eD, \eh, \eH, \ep, \eP, \es, \eS, \ev, \eV, \ew, and  The character escape sequences \ed, \eD, \eh, \eH, \ep, \eP, \es, \eS, \ev,
1184  \eW may also appear in a character class, and add the characters that they  \eV, \ew, and \eW may appear in a character class, and add the characters that
1185  match to the class. For example, [\edABCDEF] matches any hexadecimal digit. A  they match to the class. For example, [\edABCDEF] matches any hexadecimal
1186  circumflex can conveniently be used with the upper case character types to  digit. In UTF modes, the PCRE_UCP option affects the meanings of \ed, \es, \ew
1187    and their upper case partners, just as it does when they appear outside a
1188    character class, as described in the section entitled
1189    .\" HTML <a href="#genericchartypes">
1190    .\" </a>
1191    "Generic character types"
1192    .\"
1193    above. The escape sequence \eb has a different meaning inside a character
1194    class; it matches the backspace character. The sequences \eB, \eN, \eR, and \eX
1195    are not special inside a character class. Like any other unrecognized escape
1196    sequences, they are treated as the literal characters "B", "N", "R", and "X" by
1197    default, but cause an error if the PCRE_EXTRA option is set.
1198    .P
1199    A circumflex can conveniently be used with the upper case character types to
1200  specify a more restricted set of characters than the matching lower case type.  specify a more restricted set of characters than the matching lower case type.
1201  For example, the class [^\eW_] matches any letter or digit, but not underscore.  For example, the class [^\eW_] matches any letter or digit, but not underscore,
1202    whereas [\ew] includes underscore. A positive character class should be read as
1203    "something OR something OR ..." and a negative class as "NOT something AND NOT
1204    something AND NOT ...".
1205  .P  .P
1206  The only metacharacters that are recognized in character classes are backslash,  The only metacharacters that are recognized in character classes are backslash,
1207  hyphen (only where it can be interpreted as specifying a range), circumflex  hyphen (only where it can be interpreted as specifying a range), circumflex
# Line 1101  matches "1", "2", or any non-digit. PCRE Line 1253  matches "1", "2", or any non-digit. PCRE
1253  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
1254  supported, and an error is given if they are encountered.  supported, and an error is given if they are encountered.
1255  .P  .P
1256  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
1257  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
1258  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
1259  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 1172  extracts it into the global options (and Line 1324  extracts it into the global options (and
1324  extracted by the \fBpcre_fullinfo()\fP function).  extracted by the \fBpcre_fullinfo()\fP function).
1325  .P  .P
1326  An option change within a subpattern (see below for a description of  An option change within a subpattern (see below for a description of
1327  subpatterns) affects only that part of the current pattern that follows it, so  subpatterns) affects only that part of the subpattern that follows it, so
1328  .sp  .sp
1329    (a(?i)b)c    (a(?i)b)c
1330  .sp  .sp
# Line 1189  option settings happen at compile time. Line 1341  option settings happen at compile time.
1341  behaviour otherwise.  behaviour otherwise.
1342  .P  .P
1343  \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
1344  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
1345  pattern can contain special leading sequences such as (*CRLF) to override what  the pattern can contain special leading sequences such as (*CRLF) to override
1346  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
1347  section entitled  the section entitled
1348  .\" HTML <a href="#newlineseq">  .\" HTML <a href="#newlineseq">
1349  .\" </a>  .\" </a>
1350  "Newline sequences"  "Newline sequences"
1351  .\"  .\"
1352  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
1353  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
1354  PCRE_UTF8 and the PCRE_UCP options, respectively.  equivalent to setting the PCRE_UTF8, PCRE_UTF16, PCRE_UTF32 and the PCRE_UCP
1355    options, respectively.
1356  .  .
1357  .  .
1358  .\" HTML <a name="subpattern"></a>  .\" HTML <a name="subpattern"></a>
# Line 1213  Turning part of a pattern into a subpatt Line 1366  Turning part of a pattern into a subpatt
1366  .sp  .sp
1367    cat(aract|erpillar|)    cat(aract|erpillar|)
1368  .sp  .sp
1369  matches one of the words "cat", "cataract", or "caterpillar". Without the  matches "cataract", "caterpillar", or "cat". Without the parentheses, it would
1370  parentheses, it would match "cataract", "erpillar" or an empty string.  match "cataract", "erpillar" or an empty string.
1371  .sp  .sp
1372  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
1373  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
1374  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
1375  \fBpcre_exec()\fP. Opening parentheses are counted from left to right (starting  matching function. (This applies only to the traditional matching functions;
1376  from 1) to obtain numbers for the capturing subpatterns.  the DFA matching functions do not support capturing.)
1377  .P  .P
1378  For example, if the string "the red king" is matched against the pattern  Opening parentheses are counted from left to right (starting from 1) to obtain
1379    numbers for the capturing subpatterns. For example, if the string "the red
1380    king" is matched against the pattern
1381  .sp  .sp
1382    the ((red|white) (king|queen))    the ((red|white) (king|queen))
1383  .sp  .sp
# Line 1271  at captured substring number one, whiche Line 1426  at captured substring number one, whiche
1426  is useful when you want to capture part, but not all, of one of a number of  is useful when you want to capture part, but not all, of one of a number of
1427  alternatives. Inside a (?| group, parentheses are numbered as usual, but the  alternatives. Inside a (?| group, parentheses are numbered as usual, but the
1428  number is reset at the start of each branch. The numbers of any capturing  number is reset at the start of each branch. The numbers of any capturing
1429  buffers that follow the subpattern start after the highest number used in any  parentheses that follow the subpattern start after the highest number used in
1430  branch. The following example is taken from the Perl documentation.  any branch. The following example is taken from the Perl documentation. The
1431  The numbers underneath show in which buffer the captured content will be  numbers underneath show in which buffer the captured content will be stored.
 stored.  
1432  .sp  .sp
1433    # before  ---------------branch-reset----------- after    # before  ---------------branch-reset----------- after
1434    / ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x    / ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x
# Line 1286  or "defdef": Line 1440  or "defdef":
1440  .sp  .sp
1441    /(?|(abc)|(def))\e1/    /(?|(abc)|(def))\e1/
1442  .sp  .sp
1443  In contrast, a recursive or "subroutine" call to a numbered subpattern always  In contrast, a subroutine call to a numbered subpattern always refers to the
1444  refers to the first one in the pattern with the given number. The following  first one in the pattern with the given number. The following pattern matches
1445  pattern matches "abcabc" or "defabc":  "abcabc" or "defabc":
1446  .sp  .sp
1447    /(?|(abc)|(def))(?1)/    /(?|(abc)|(def))(?1)/
1448  .sp  .sp
# Line 1399  items: Line 1553  items:
1553    a literal data character    a literal data character
1554    the dot metacharacter    the dot metacharacter
1555    the \eC escape sequence    the \eC escape sequence
1556    the \eX escape sequence (in UTF-8 mode with Unicode properties)    the \eX escape sequence
1557    the \eR escape sequence    the \eR escape sequence
1558    an escape such as \ed that matches a single character    an escape such as \ed or \epL that matches a single character
1559    a character class    a character class
1560    a back reference (see next section)    a back reference (see next section)
1561    a parenthesized subpattern (unless it is an assertion)    a parenthesized subpattern (including assertions)
1562    a recursive or "subroutine" call to a subpattern    a subroutine call to a subpattern (recursive or otherwise)
1563  .sp  .sp
1564  The general repetition quantifier specifies a minimum and maximum number of  The general repetition quantifier specifies a minimum and maximum number of
1565  permitted matches, by giving the two numbers in curly brackets (braces),  permitted matches, by giving the two numbers in curly brackets (braces),
# Line 1430  where a quantifier is not allowed, or on Line 1584  where a quantifier is not allowed, or on
1584  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
1585  quantifier, but a literal string of four characters.  quantifier, but a literal string of four characters.
1586  .P  .P
1587  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
1588  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
1589  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,
1590  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
1591  which may be several bytes long (and they may be of different lengths).  several data units long (and they may be of different lengths).
1592  .P  .P
1593  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
1594  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 1443  subpatterns that are referenced as Line 1597  subpatterns that are referenced as
1597  .\" </a>  .\" </a>
1598  subroutines  subroutines
1599  .\"  .\"
1600  from elsewhere in the pattern. Items other than subpatterns that have a {0}  from elsewhere in the pattern (but see also the section entitled
1601  quantifier are omitted from the compiled pattern.  .\" HTML <a href="#subdefine">
1602    .\" </a>
1603    "Defining subpatterns for use by reference only"
1604    .\"
1605    below). Items other than subpatterns that have a {0} quantifier are omitted
1606    from the compiled pattern.
1607  .P  .P
1608  For convenience, the three most common quantifiers have single-character  For convenience, the three most common quantifiers have single-character
1609  abbreviations:  abbreviations:
# Line 1515  In cases where it is known that the subj Line 1674  In cases where it is known that the subj
1674  worth setting PCRE_DOTALL in order to obtain this optimization, or  worth setting PCRE_DOTALL in order to obtain this optimization, or
1675  alternatively using ^ to indicate anchoring explicitly.  alternatively using ^ to indicate anchoring explicitly.
1676  .P  .P
1677  However, there is one situation where the optimization cannot be used. When .*  However, there are some cases where the optimization cannot be used. When .*
1678  is inside capturing parentheses that are the subject of a back reference  is inside capturing parentheses that are the subject of a back reference
1679  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
1680  succeeds. Consider, for example:  succeeds. Consider, for example:
# Line 1525  succeeds. Consider, for example: Line 1684  succeeds. Consider, for example:
1684  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
1685  this reason, such a pattern is not implicitly anchored.  this reason, such a pattern is not implicitly anchored.
1686  .P  .P
1687    Another case where implicit anchoring is not applied is when the leading .* is
1688    inside an atomic group. Once again, a match at the start may fail where a later
1689    one succeeds. Consider this pattern:
1690    .sp
1691      (?>.*?a)b
1692    .sp
1693    It matches "ab" in the subject "aab". The use of the backtracking control verbs
1694    (*PRUNE) and (*SKIP) also disable this optimization.
1695    .P
1696  When a capturing subpattern is repeated, the value captured is the substring  When a capturing subpattern is repeated, the value captured is the substring
1697  that matched the final iteration. For example, after  that matched the final iteration. For example, after
1698  .sp  .sp
# Line 1669  no such problem when named parentheses a Line 1837  no such problem when named parentheses a
1837  subpattern is possible using named parentheses (see below).  subpattern is possible using named parentheses (see below).
1838  .P  .P
1839  Another way of avoiding the ambiguity inherent in the use of digits following a  Another way of avoiding the ambiguity inherent in the use of digits following a
1840  backslash is to use the \eg escape sequence, which is a feature introduced in  backslash is to use the \eg escape sequence. This escape must be followed by an
1841  Perl 5.10. This escape must be followed by an unsigned number or a negative  unsigned number or a negative number, optionally enclosed in braces. These
1842  number, optionally enclosed in braces. These examples are all identical:  examples are all identical:
1843  .sp  .sp
1844    (ring), \e1    (ring), \e1
1845    (ring), \eg1    (ring), \eg1
# Line 1685  example: Line 1853  example:
1853    (abc(def)ghi)\eg{-1}    (abc(def)ghi)\eg{-1}
1854  .sp  .sp
1855  The sequence \eg{-1} is a reference to the most recently started capturing  The sequence \eg{-1} is a reference to the most recently started capturing
1856  subpattern before \eg, that is, is it equivalent to \e2. Similarly, \eg{-2}  subpattern before \eg, that is, is it equivalent to \e2 in this example.
1857  would be equivalent to \e1. The use of relative references can be helpful in  Similarly, \eg{-2} would be equivalent to \e1. The use of relative references
1858  long patterns, and also in patterns that are created by joining together  can be helpful in long patterns, and also in patterns that are created by
1859  fragments that contain references within themselves.  joining together fragments that contain references within themselves.
1860  .P  .P
1861  A back reference matches whatever actually matched the capturing subpattern in  A back reference matches whatever actually matched the capturing subpattern in
1862  the current subject string, rather than anything matching the subpattern  the current subject string, rather than anything matching the subpattern
# Line 1739  Because there may be many capturing pare Line 1907  Because there may be many capturing pare
1907  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.
1908  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
1909  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
1910  whitespace. Otherwise, the \eg{ syntax or an empty comment (see  white space. Otherwise, the \eg{ syntax or an empty comment (see
1911  .\" HTML <a href="#comments">  .\" HTML <a href="#comments">
1912  .\" </a>  .\" </a>
1913  "Comments"  "Comments"
# Line 1790  those that look ahead of the current pos Line 1958  those that look ahead of the current pos
1958  that look behind it. An assertion subpattern is matched in the normal way,  that look behind it. An assertion subpattern is matched in the normal way,
1959  except that it does not cause the current matching position to be changed.  except that it does not cause the current matching position to be changed.
1960  .P  .P
1961  Assertion subpatterns are not capturing subpatterns, and may not be repeated,  Assertion subpatterns are not capturing subpatterns. If such an assertion
1962  because it makes no sense to assert the same thing several times. If any kind  contains capturing subpatterns within it, these are counted for the purposes of
1963  of assertion contains capturing subpatterns within it, these are counted for  numbering the capturing subpatterns in the whole pattern. However, substring
1964  the purposes of numbering the capturing subpatterns in the whole pattern.  capturing is carried out only for positive assertions, because it does not make
1965  However, substring capturing is carried out only for positive assertions,  sense for negative assertions.
1966  because it does not make sense for negative assertions.  .P
1967    For compatibility with Perl, assertion subpatterns may be repeated; though
1968    it makes no sense to assert the same thing several times, the side effect of
1969    capturing parentheses may occasionally be useful. In practice, there only three
1970    cases:
1971    .sp
1972    (1) If the quantifier is {0}, the assertion is never obeyed during matching.
1973    However, it may contain internal capturing parenthesized groups that are called
1974    from elsewhere via the
1975    .\" HTML <a href="#subpatternsassubroutines">
1976    .\" </a>
1977    subroutine mechanism.
1978    .\"
1979    .sp
1980    (2) If quantifier is {0,n} where n is greater than zero, it is treated as if it
1981    were {0,1}. At run time, the rest of the pattern match is tried with and
1982    without the assertion, the order depending on the greediness of the quantifier.
1983    .sp
1984    (3) If the minimum repetition is greater than zero, the quantifier is ignored.
1985    The assertion is obeyed just once when encountered during matching.
1986  .  .
1987  .  .
1988  .SS "Lookahead assertions"  .SS "Lookahead assertions"
# Line 1824  lookbehind assertion is needed to achiev Line 2011  lookbehind assertion is needed to achiev
2011  If you want to force a matching failure at some point in a pattern, the most  If you want to force a matching failure at some point in a pattern, the most
2012  convenient way to do it is with (?!) because an empty string always matches, so  convenient way to do it is with (?!) because an empty string always matches, so
2013  an assertion that requires there not to be an empty string must always fail.  an assertion that requires there not to be an empty string must always fail.
2014  The Perl 5.10 backtracking control verb (*FAIL) or (*F) is essentially a  The backtracking control verb (*FAIL) or (*F) is a synonym for (?!).
 synonym for (?!).  
2015  .  .
2016  .  .
2017  .\" HTML <a name="lookbehind"></a>  .\" HTML <a name="lookbehind"></a>
# Line 1850  is permitted, but Line 2036  is permitted, but
2036  .sp  .sp
2037  causes an error at compile time. Branches that match different length strings  causes an error at compile time. Branches that match different length strings
2038  are permitted only at the top level of a lookbehind assertion. This is an  are permitted only at the top level of a lookbehind assertion. This is an
2039  extension compared with Perl (5.8 and 5.10), which requires all branches to  extension compared with Perl, which requires all branches to match the same
2040  match the same length of string. An assertion such as  length of string. An assertion such as
2041  .sp  .sp
2042    (?<=ab(c|de))    (?<=ab(c|de))
2043  .sp  .sp
# Line 1861  branches: Line 2047  branches:
2047  .sp  .sp
2048    (?<=abc|abde)    (?<=abc|abde)
2049  .sp  .sp
2050  In some cases, the Perl 5.10 escape sequence \eK  In some cases, the escape sequence \eK
2051  .\" HTML <a href="#resetmatchstart">  .\" HTML <a href="#resetmatchstart">
2052  .\" </a>  .\" </a>
2053  (see above)  (see above)
# Line 1874  temporarily move the current position ba Line 2060  temporarily move the current position ba
2060  match. If there are insufficient characters before the current position, the  match. If there are insufficient characters before the current position, the
2061  assertion fails.  assertion fails.
2062  .P  .P
2063  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
2064  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
2065  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
2066  different numbers of bytes, are also not permitted.  escapes, which can match different numbers of data units, are also not
2067    permitted.
2068  .P  .P
2069  .\" HTML <a href="#subpatternsassubroutines">  .\" HTML <a href="#subpatternsassubroutines">
2070  .\" </a>  .\" </a>
# Line 1965  already been matched. The two possible f Line 2152  already been matched. The two possible f
2152  .sp  .sp
2153  If the condition is satisfied, the yes-pattern is used; otherwise the  If the condition is satisfied, the yes-pattern is used; otherwise the
2154  no-pattern (if present) is used. If there are more than two alternatives in the  no-pattern (if present) is used. If there are more than two alternatives in the
2155  subpattern, a compile-time error occurs.  subpattern, a compile-time error occurs. Each of the two alternatives may
2156    itself contain nested subpatterns of any form, including conditional
2157    subpatterns; the restriction to two alternatives applies only at the level of
2158    the condition. This pattern fragment is an example where the alternatives are
2159    complex:
2160    .sp
2161      (?(1) (A|B|C) | (D | (?(2)E|F) | E) )
2162    .sp
2163  .P  .P
2164  There are four kinds of condition: references to subpatterns, references to  There are four kinds of condition: references to subpatterns, references to
2165  recursion, a pseudo-condition called DEFINE, and assertions.  recursion, a pseudo-condition called DEFINE, and assertions.
# Line 1982  matched. If there is more than one captu Line 2176  matched. If there is more than one captu
2176  .\" </a>  .\" </a>
2177  section about duplicate subpattern numbers),  section about duplicate subpattern numbers),
2178  .\"  .\"
2179  the condition is true if any of them have been set. An alternative notation is  the condition is true if any of them have matched. An alternative notation is
2180  to precede the digits with a plus or minus sign. In this case, the subpattern  to precede the digits with a plus or minus sign. In this case, the subpattern
2181  number is relative rather than absolute. The most recently opened parentheses  number is relative rather than absolute. The most recently opened parentheses
2182  can be referenced by (?(-1), the next most recent by (?(-2), and so on. In  can be referenced by (?(-1), the next most recent by (?(-2), and so on. Inside
2183  looping constructs it can also make sense to refer to subsequent groups with  loops it can also make sense to refer to subsequent groups. The next
2184  constructs such as (?(+2).  parentheses to be opened can be referenced as (?(+1), and so on. (The value
2185    zero in any of these forms is not used; it provokes a compile-time error.)
2186  .P  .P
2187  Consider the following pattern, which contains non-significant white space to  Consider the following pattern, which contains non-significant white space to
2188  make it more readable (assume the PCRE_EXTENDED option) and to divide it into  make it more readable (assume the PCRE_EXTENDED option) and to divide it into
# Line 1998  three parts for ease of discussion: Line 2193  three parts for ease of discussion:
2193  The first part matches an optional opening parenthesis, and if that  The first part matches an optional opening parenthesis, and if that
2194  character is present, sets it as the first captured substring. The second part  character is present, sets it as the first captured substring. The second part
2195  matches one or more characters that are not parentheses. The third part is a  matches one or more characters that are not parentheses. The third part is a
2196  conditional subpattern that tests whether the first set of parentheses matched  conditional subpattern that tests whether or not the first set of parentheses
2197  or not. If they did, that is, if subject started with an opening parenthesis,  matched. If they did, that is, if subject started with an opening parenthesis,
2198  the condition is true, and so the yes-pattern is executed and a closing  the condition is true, and so the yes-pattern is executed and a closing
2199  parenthesis is required. Otherwise, since no-pattern is not present, the  parenthesis is required. Otherwise, since no-pattern is not present, the
2200  subpattern matches nothing. In other words, this pattern matches a sequence of  subpattern matches nothing. In other words, this pattern matches a sequence of
# Line 2055  The syntax for recursive patterns Line 2250  The syntax for recursive patterns
2250  .\"  .\"
2251  is described below.  is described below.
2252  .  .
2253    .\" HTML <a name="subdefine"></a>
2254  .SS "Defining subpatterns for use by reference only"  .SS "Defining subpatterns for use by reference only"
2255  .rs  .rs
2256  .sp  .sp
# Line 2062  If the condition is the string (DEFINE), Line 2258  If the condition is the string (DEFINE),
2258  name DEFINE, the condition is always false. In this case, there may be only one  name DEFINE, the condition is always false. In this case, there may be only one
2259  alternative in the subpattern. It is always skipped if control reaches this  alternative in the subpattern. It is always skipped if control reaches this
2260  point in the pattern; the idea of DEFINE is that it can be used to define  point in the pattern; the idea of DEFINE is that it can be used to define
2261  "subroutines" that can be referenced from elsewhere. (The use of  subroutines that can be referenced from elsewhere. (The use of
2262  .\" HTML <a href="#subpatternsassubroutines">  .\" HTML <a href="#subpatternsassubroutines">
2263  .\" </a>  .\" </a>
2264  "subroutines"  subroutines
2265  .\"  .\"
2266  is described below.) For example, a pattern to match an IPv4 address could be  is described below.) For example, a pattern to match an IPv4 address such as
2267  written like this (ignore whitespace and line breaks):  "192.168.23.245" could be written like this (ignore white space and line
2268    breaks):
2269  .sp  .sp
2270    (?(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) )
2271    \eb (?&byte) (\e.(?&byte)){3} \eb    \eb (?&byte) (\e.(?&byte)){3} \eb
# Line 2103  dd-aaa-dd or dd-dd-dd, where aaa are let Line 2300  dd-aaa-dd or dd-dd-dd, where aaa are let
2300  .SH COMMENTS  .SH COMMENTS
2301  .rs  .rs
2302  .sp  .sp
2303  The sequence (?# marks the start of a comment that continues up to the next  There are two ways of including comments in patterns that are processed by
2304  closing parenthesis. Nested parentheses are not permitted. The characters  PCRE. In both cases, the start of the comment must not be in a character class,
2305  that make up a comment play no part in the pattern matching at all.  nor in the middle of any other sequence of related characters such as (?: or a
2306    subpattern name or number. The characters that make up a comment play no part
2307    in the pattern matching.
2308  .P  .P
2309  If the PCRE_EXTENDED option is set, an unescaped # character outside a  The sequence (?# marks the start of a comment that continues up to the next
2310  character class introduces a comment that continues to immediately after the  closing parenthesis. Nested parentheses are not permitted. If the PCRE_EXTENDED
2311  next newline in the pattern.  option is set, an unescaped # character also introduces a comment, which in
2312    this case continues to immediately after the next newline character or
2313    character sequence in the pattern. Which characters are interpreted as newlines
2314    is controlled by the options passed to a compiling function or by a special
2315    sequence at the start of the pattern, as described in the section entitled
2316    .\" HTML <a href="#newlines">
2317    .\" </a>
2318    "Newline conventions"
2319    .\"
2320    above. Note that the end of this type of comment is a literal newline sequence
2321    in the pattern; escape sequences that happen to represent a newline do not
2322    count. For example, consider this pattern when PCRE_EXTENDED is set, and the
2323    default newline convention is in force:
2324    .sp
2325      abc #comment \en still comment
2326    .sp
2327    On encountering the # character, \fBpcre_compile()\fP skips along, looking for
2328    a newline in the pattern. The sequence \en is still literal at this stage, so
2329    it does not terminate the comment. Only an actual character with the code value
2330    0x0a (the default newline) does so.
2331  .  .
2332  .  .
2333  .\" HTML <a name="recursion"></a>  .\" HTML <a name="recursion"></a>
# Line 2138  individual subpattern recursion. After i Line 2356  individual subpattern recursion. After i
2356  this kind of recursion was subsequently introduced into Perl at release 5.10.  this kind of recursion was subsequently introduced into Perl at release 5.10.
2357  .P  .P
2358  A special item that consists of (? followed by a number greater than zero and a  A special item that consists of (? followed by a number greater than zero and a
2359  closing parenthesis is a recursive call of the subpattern of the given number,  closing parenthesis is a recursive subroutine call of the subpattern of the
2360  provided that it occurs inside that subpattern. (If not, it is a  given number, provided that it occurs inside that subpattern. (If not, it is a
2361  .\" HTML <a href="#subpatternsassubroutines">  .\" HTML <a href="#subpatternsassubroutines">
2362  .\" </a>  .\" </a>
2363  "subroutine"  non-recursive subroutine
2364  .\"  .\"
2365  call, which is described in the next section.) The special item (?R) or (?0) is  call, which is described in the next section.) The special item (?R) or (?0) is
2366  a recursive call of the entire regular expression.  a recursive call of the entire regular expression.
# Line 2167  We have put the pattern into parentheses Line 2385  We have put the pattern into parentheses
2385  them instead of the whole pattern.  them instead of the whole pattern.
2386  .P  .P
2387  In a larger pattern, keeping track of parenthesis numbers can be tricky. This  In a larger pattern, keeping track of parenthesis numbers can be tricky. This
2388  is made easier by the use of relative references (a Perl 5.10 feature).  is made easier by the use of relative references. Instead of (?1) in the
2389  Instead of (?1) in the pattern above you can write (?-2) to refer to the second  pattern above you can write (?-2) to refer to the second most recently opened
2390  most recently opened parentheses preceding the recursion. In other words, a  parentheses preceding the recursion. In other words, a negative number counts
2391  negative number counts capturing parentheses leftwards from the point at which  capturing parentheses leftwards from the point at which it is encountered.
 it is encountered.  
2392  .P  .P
2393  It is also possible to refer to subsequently opened parentheses, by writing  It is also possible to refer to subsequently opened parentheses, by writing
2394  references such as (?+2). However, these cannot be recursive because the  references such as (?+2). However, these cannot be recursive because the
2395  reference is not inside the parentheses that are referenced. They are always  reference is not inside the parentheses that are referenced. They are always
2396  .\" HTML <a href="#subpatternsassubroutines">  .\" HTML <a href="#subpatternsassubroutines">
2397  .\" </a>  .\" </a>
2398  "subroutine"  non-recursive subroutine
2399  .\"  .\"
2400  calls, as described in the next section.  calls, as described in the next section.
2401  .P  .P
# Line 2215  documentation). If the pattern above is Line 2432  documentation). If the pattern above is
2432  .sp  .sp
2433  the value for the inner capturing parentheses (numbered 2) is "ef", which is  the value for the inner capturing parentheses (numbered 2) is "ef", which is
2434  the last value taken on at the top level. If a capturing subpattern is not  the last value taken on at the top level. If a capturing subpattern is not
2435  matched at the top level, its final value is unset, even if it is (temporarily)  matched at the top level, its final captured value is unset, even if it was
2436  set at a deeper level.  (temporarily) set at a deeper level during the matching process.
2437  .P  .P
2438  If there are more than 15 capturing parentheses in a pattern, PCRE has to  If there are more than 15 capturing parentheses in a pattern, PCRE has to
2439  obtain extra memory to store data during a recursion, which it does by using  obtain extra memory to store data during a recursion, which it does by using
# Line 2236  is the actual recursive call. Line 2453  is the actual recursive call.
2453  .  .
2454  .  .
2455  .\" HTML <a name="recursiondifference"></a>  .\" HTML <a name="recursiondifference"></a>
2456  .SS "Recursion difference from Perl"  .SS "Differences in recursion processing between PCRE and Perl"
2457  .rs  .rs
2458  .sp  .sp
2459  In PCRE (like Python, but unlike Perl), a recursive subpattern call is always  Recursion processing in PCRE differs from Perl in two important ways. In PCRE
2460  treated as an atomic group. That is, once it has matched some of the subject  (like Python, but unlike Perl), a recursive subpattern call is always treated
2461  string, it is never re-entered, even if it contains untried alternatives and  as an atomic group. That is, once it has matched some of the subject string, it
2462  there is a subsequent matching failure. This can be illustrated by the  is never re-entered, even if it contains untried alternatives and there is a
2463  following pattern, which purports to match a palindromic string that contains  subsequent matching failure. This can be illustrated by the following pattern,
2464  an odd number of characters (for example, "a", "aba", "abcba", "abcdcba"):  which purports to match a palindromic string that contains an odd number of
2465    characters (for example, "a", "aba", "abcba", "abcdcba"):
2466  .sp  .sp
2467    ^(.|(.)(?1)\e2)$    ^(.|(.)(?1)\e2)$
2468  .sp  .sp
# Line 2274  time we do have another alternative to t Line 2492  time we do have another alternative to t
2492  difference: in the previous case the remaining alternative is at a deeper  difference: in the previous case the remaining alternative is at a deeper
2493  recursion level, which PCRE cannot use.  recursion level, which PCRE cannot use.
2494  .P  .P
2495  To change the pattern so that matches all palindromic strings, not just those  To change the pattern so that it matches all palindromic strings, not just
2496  with an odd number of characters, it is tempting to change the pattern to this:  those with an odd number of characters, it is tempting to change the pattern to
2497    this:
2498  .sp  .sp
2499    ^((.)(?1)\e2|.?)$    ^((.)(?1)\e2|.?)$
2500  .sp  .sp
# Line 2304  For example, although "abcba" is correct Line 2523  For example, although "abcba" is correct
2523  PCRE finds the palindrome "aba" at the start, then fails at top level because  PCRE finds the palindrome "aba" at the start, then fails at top level because
2524  the end of the string does not follow. Once again, it cannot jump back into the  the end of the string does not follow. Once again, it cannot jump back into the
2525  recursion to try other alternatives, so the entire match fails.  recursion to try other alternatives, so the entire match fails.
2526    .P
2527    The second way in which PCRE and Perl differ in their recursion processing is
2528    in the handling of captured values. In Perl, when a subpattern is called
2529    recursively or as a subpattern (see the next section), it has no access to any
2530    values that were captured outside the recursion, whereas in PCRE these values
2531    can be referenced. Consider this pattern:
2532    .sp
2533      ^(.)(\e1|a(?2))
2534    .sp
2535    In PCRE, this pattern matches "bab". The first capturing parentheses match "b",
2536    then in the second group, when the back reference \e1 fails to match "b", the
2537    second alternative matches "a" and then recurses. In the recursion, \e1 does
2538    now match "b" and so the whole match succeeds. In Perl, the pattern fails to
2539    match because inside the recursive call \e1 cannot access the externally set
2540    value.
2541  .  .
2542  .  .
2543  .\" HTML <a name="subpatternsassubroutines"></a>  .\" HTML <a name="subpatternsassubroutines"></a>
2544  .SH "SUBPATTERNS AS SUBROUTINES"  .SH "SUBPATTERNS AS SUBROUTINES"
2545  .rs  .rs
2546  .sp  .sp
2547  If the syntax for a recursive subpattern reference (either by number or by  If the syntax for a recursive subpattern call (either by number or by
2548  name) is used outside the parentheses to which it refers, it operates like a  name) is used outside the parentheses to which it refers, it operates like a
2549  subroutine in a programming language. The "called" subpattern may be defined  subroutine in a programming language. The called subpattern may be defined
2550  before or after the reference. A numbered reference can be absolute or  before or after the reference. A numbered reference can be absolute or
2551  relative, as in these examples:  relative, as in these examples:
2552  .sp  .sp
# Line 2332  matches "sense and sensibility" and "res Line 2566  matches "sense and sensibility" and "res
2566  is used, it does match "sense and responsibility" as well as the other two  is used, it does match "sense and responsibility" as well as the other two
2567  strings. Another example is given in the discussion of DEFINE above.  strings. Another example is given in the discussion of DEFINE above.
2568  .P  .P
2569  Like recursive subpatterns, a subroutine call is always treated as an atomic  All subroutine calls, whether recursive or not, are always treated as atomic
2570  group. That is, once it has matched some of the subject string, it is never  groups. That is, once a subroutine has matched some of the subject string, it
2571  re-entered, even if it contains untried alternatives and there is a subsequent  is never re-entered, even if it contains untried alternatives and there is a
2572  matching failure. Any capturing parentheses that are set during the subroutine  subsequent matching failure. Any capturing parentheses that are set during the
2573  call revert to their previous values afterwards.  subroutine call revert to their previous values afterwards.
2574  .P  .P
2575  When a subpattern is used as a subroutine, processing options such as  Processing options such as case-independence are fixed when a subpattern is
2576  case-independence are fixed when the subpattern is defined. They cannot be  defined, so if it is used as a subroutine, such options cannot be changed for
2577  changed for different calls. For example, consider this pattern:  different calls. For example, consider this pattern:
2578  .sp  .sp
2579    (abc)(?i:(?-1))    (abc)(?i:(?-1))
2580  .sp  .sp
# Line 2379  same pair of parentheses when there is a Line 2613  same pair of parentheses when there is a
2613  .P  .P
2614  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
2615  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
2616  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
2617    (8-bit library) or \fIpcre[16|32]_callout\fP (16-bit or 32-bit library).
2618  By default, this variable contains NULL, which disables all calling out.  By default, this variable contains NULL, which disables all calling out.
2619  .P  .P
2620  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 2389  For example, this pattern has two callou Line 2624  For example, this pattern has two callou
2624  .sp  .sp
2625    (?C1)abc(?C2)def    (?C1)abc(?C2)def
2626  .sp  .sp
2627  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
2628  automatically installed before each item in the pattern. They are all numbered  automatically installed before each item in the pattern. They are all numbered
2629  255.  255.
2630  .P  .P
2631  During matching, when PCRE reaches a callout point (and \fIpcre_callout\fP is  During matching, when PCRE reaches a callout point, the external function is
2632  set), the external function is called. It is provided with the number of the  called. It is provided with the number of the callout, the position in the
2633  callout, the position in the pattern, and, optionally, one item of data  pattern, and, optionally, one item of data originally supplied by the caller of
2634  originally supplied by the caller of \fBpcre_exec()\fP. The callout function  the matching function. The callout function may cause matching to proceed, to
2635  may cause matching to proceed, to backtrack, or to fail altogether. A complete  backtrack, or to fail altogether. A complete description of the interface to
2636  description of the interface to the callout function is given in the  the callout function is given in the
2637  .\" HREF  .\" HREF
2638  \fBpcrecallout\fP  \fBpcrecallout\fP
2639  .\"  .\"
# Line 2416  production code should be noted to avoid Line 2651  production code should be noted to avoid
2651  remarks apply to the PCRE features described in this section.  remarks apply to the PCRE features described in this section.
2652  .P  .P
2653  Since these verbs are specifically related to backtracking, most of them can be  Since these verbs are specifically related to backtracking, most of them can be
2654  used only when the pattern is to be matched using \fBpcre_exec()\fP, which uses  used only when the pattern is to be matched using one of the traditional
2655  a backtracking algorithm. With the exception of (*FAIL), which behaves like a  matching functions, which use a backtracking algorithm. With the exception of
2656  failing negative assertion, they cause an error if encountered by  (*FAIL), which behaves like a failing negative assertion, they cause an error
2657  \fBpcre_dfa_exec()\fP.  if encountered by a DFA matching function.
2658  .P  .P
2659  If any of these verbs are used in an assertion or subroutine subpattern  If any of these verbs are used in an assertion or in a subpattern that is
2660  (including recursive subpatterns), their effect is confined to that subpattern;  called as a subroutine (whether or not recursively), their effect is confined
2661  it does not extend to the surrounding pattern. Note that such subpatterns are  to that subpattern; it does not extend to the surrounding pattern, with one
2662  processed as anchored at the point where they are tested.  exception: the name from a *(MARK), (*PRUNE), or (*THEN) that is encountered in
2663    a successful positive assertion \fIis\fP passed back when a match succeeds
2664    (compare capturing parentheses in assertions). Note that such subpatterns are
2665    processed as anchored at the point where they are tested. Note also that Perl's
2666    treatment of subroutines and assertions is different in some cases.
2667  .P  .P
2668  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
2669  parenthesis followed by an asterisk. They are generally of the form  parenthesis followed by an asterisk. They are generally of the form
2670  (*VERB) or (*VERB:NAME). Some may take either form, with differing behaviour,  (*VERB) or (*VERB:NAME). Some may take either form, with differing behaviour,
2671  depending on whether or not an argument is present. An name is a sequence of  depending on whether or not an argument is present. A name is any sequence of
2672  letters, digits, and underscores. If the name is empty, that is, if the closing  characters that does not include a closing parenthesis. The maximum length of
2673  parenthesis immediately follows the colon, the effect is as if the colon were  name is 255 in the 8-bit library and 65535 in the 16-bit and 32-bit library.
2674  not there. Any number of these verbs may occur in a pattern.  If the name is empty, that is, if the closing parenthesis immediately follows
2675  .P  the colon, the effect is as if the colon were not there. Any number of these
2676    verbs may occur in a pattern.
2677    .
2678    .
2679    .\" HTML <a name="nooptimize"></a>
2680    .SS "Optimizations that affect backtracking verbs"
2681    .rs
2682    .sp
2683  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
2684  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
2685  minimum length of matching subject, or that a particular character must be  minimum length of matching subject, or that a particular character must be
2686  present. When one of these optimizations suppresses the running of a match, any  present. When one of these optimizations suppresses the running of a match, any
2687  included backtracking verbs will not, of course, be processed. You can suppress  included backtracking verbs will not, of course, be processed. You can suppress
2688  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
2689  when calling \fBpcre_exec()\fP.  when calling \fBpcre_compile()\fP or \fBpcre_exec()\fP, or by starting the
2690    pattern with (*NO_START_OPT). There is more discussion of this option in the
2691    section entitled
2692    .\" HTML <a href="pcreapi.html#execoptions">
2693    .\" </a>
2694    "Option bits for \fBpcre_exec()\fP"
2695    .\"
2696    in the
2697    .\" HREF
2698    \fBpcreapi\fP
2699    .\"
2700    documentation.
2701    .P
2702    Experiments with Perl suggest that it too has similar optimizations, sometimes
2703    leading to anomalous results.
2704  .  .
2705  .  .
2706  .SS "Verbs that act immediately"  .SS "Verbs that act immediately"
# Line 2452  followed by a name. Line 2712  followed by a name.
2712     (*ACCEPT)     (*ACCEPT)
2713  .sp  .sp
2714  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
2715  pattern. When inside a recursion, only the innermost pattern is ended  pattern. However, when it is inside a subpattern that is called as a
2716  immediately. If (*ACCEPT) is inside capturing parentheses, the data so far is  subroutine, only that subpattern is ended successfully. Matching then continues
2717  captured. (This feature was added to PCRE at release 8.00.) For example:  at the outer level. If (*ACCEPT) is inside capturing parentheses, the data so
2718    far is captured. For example:
2719  .sp  .sp
2720    A((?:A|B(*ACCEPT)|C)D)    A((?:A|B(*ACCEPT)|C)D)
2721  .sp  .sp
# Line 2463  the outer parentheses. Line 2724  the outer parentheses.
2724  .sp  .sp
2725    (*FAIL) or (*F)    (*FAIL) or (*F)
2726  .sp  .sp
2727  This verb causes the match to fail, forcing backtracking to occur. It is  This verb causes a matching failure, forcing backtracking to occur. It is
2728  equivalent to (?!) but easier to read. The Perl documentation notes that it is  equivalent to (?!) but easier to read. The Perl documentation notes that it is
2729  probably useful only when combined with (?{}) or (??{}). Those are, of course,  probably useful only when combined with (?{}) or (??{}). Those are, of course,
2730  Perl features that are not present in PCRE. The nearest equivalent is the  Perl features that are not present in PCRE. The nearest equivalent is the
# Line 2487  starting point (see (*SKIP) below). Line 2748  starting point (see (*SKIP) below).
2748  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
2749  (*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.
2750  .P  .P
2751  When a match succeeds, the name of the last-encountered (*MARK) is passed back  When a match succeeds, the name of the last-encountered (*MARK) on the matching
2752  to the caller via the \fIpcre_extra\fP data structure, as described in the  path is passed back to the caller as described in the section entitled
2753  .\" HTML <a href="pcreapi.html#extradata">  .\" HTML <a href="pcreapi.html#extradata">
2754  .\" </a>  .\" </a>
2755  section on \fIpcre_extra\fP  "Extra data for \fBpcre_exec()\fP"
2756  .\"  .\"
2757  in the  in the
2758  .\" HREF  .\" HREF
2759  \fBpcreapi\fP  \fBpcreapi\fP
2760  .\"  .\"
2761  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
2762  \fBpcretest\fP output, where the /K modifier requests the retrieval and  modifier requests the retrieval and outputting of (*MARK) data:
 outputting of (*MARK) data:  
2763  .sp  .sp
2764    /X(*MARK:A)Y|X(*MARK:B)Z/K      re> /X(*MARK:A)Y|X(*MARK:B)Z/K
2765    XY    data> XY
2766     0: XY     0: XY
2767    MK: A    MK: A
2768    XZ    XZ
# Line 2514  indicates which of the two alternatives Line 2774  indicates which of the two alternatives
2774  of obtaining this information than putting each alternative in its own  of obtaining this information than putting each alternative in its own
2775  capturing parentheses.  capturing parentheses.
2776  .P  .P
2777  A name may also be returned after a failed match if the final path through the  If (*MARK) is encountered in a positive assertion, its name is recorded and
2778  pattern involves (*MARK). However, unless (*MARK) used in conjunction with  passed back if it is the last-encountered. This does not happen for negative
2779  (*COMMIT), this is unlikely to happen for an unanchored pattern because, as the  assertions.
2780  starting point for matching is advanced, the final check is often with an empty  .P
2781  string, causing a failure before (*MARK) is reached. For example:  After a partial match or a failed match, the name of the last encountered
2782  .sp  (*MARK) in the entire match process is returned. For example:
   /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:  
2783  .sp  .sp
2784    /^X(*MARK:A)Y|^X(*MARK:B)Z/K      re> /X(*MARK:A)Y|X(*MARK:B)Z/K
2785    XP    data> XP
2786    No match, mark = B    No match, mark = B
2787  .sp  .sp
2788  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
2789  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
2790  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
2791  .P  (*MARK) item, but nevertheless do not reset it.
2792  Note that similar anomalies (though different in detail) exist in Perl, no  .P
2793  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
2794  unanchored pattern is not recommended, unless (*COMMIT) is involved.  probably set the PCRE_NO_START_OPTIMIZE option
2795    .\" HTML <a href="#nooptimize">
2796    .\" </a>
2797    (see above)
2798    .\"
2799    to ensure that the match is always attempted.
2800  .  .
2801  .  .
2802  .SS "Verbs that act after backtracking"  .SS "Verbs that act after backtracking"
# Line 2575  Note that (*COMMIT) at the start of a pa Line 2833  Note that (*COMMIT) at the start of a pa
2833  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
2834  \fBpcretest\fP example:  \fBpcretest\fP example:
2835  .sp  .sp
2836    /(*COMMIT)abc/      re> /(*COMMIT)abc/
2837    xyzabc    data> xyzabc
2838     0: abc     0: abc
2839    xyzabc\eY    xyzabc\eY
2840    No match    No match
# Line 2597  reached, or when matching to the right o Line 2855  reached, or when matching to the right o
2855  the right, backtracking cannot cross (*PRUNE). In simple cases, the use of  the right, backtracking cannot cross (*PRUNE). In simple cases, the use of
2856  (*PRUNE) is just an alternative to an atomic group or possessive quantifier,  (*PRUNE) is just an alternative to an atomic group or possessive quantifier,
2857  but there are some uses of (*PRUNE) that cannot be expressed in any other way.  but there are some uses of (*PRUNE) that cannot be expressed in any other way.
2858  The behaviour of (*PRUNE:NAME) is the same as (*MARK:NAME)(*PRUNE) when the  The behaviour of (*PRUNE:NAME) is the same as (*MARK:NAME)(*PRUNE). In an
2859  match fails completely; the name is passed back if this is the final attempt.  anchored pattern (*PRUNE) has the same effect as (*COMMIT).
 (*PRUNE:NAME) does not pass back a name if the match succeeds. In an anchored  
 pattern (*PRUNE) has the same effect as (*COMMIT).  
2860  .sp  .sp
2861    (*SKIP)    (*SKIP)
2862  .sp  .sp
# Line 2626  following pattern fails to match, the pr Line 2882  following pattern fails to match, the pr
2882  searched for the most recent (*MARK) that has the same name. If one is found,  searched for the most recent (*MARK) that has the same name. If one is found,
2883  the "bumpalong" advance is to the subject position that corresponds to that  the "bumpalong" advance is to the subject position that corresponds to that
2884  (*MARK) instead of to where (*SKIP) was encountered. If no (*MARK) with a  (*MARK) instead of to where (*SKIP) was encountered. If no (*MARK) with a
2885  matching name is found, normal "bumpalong" of one character happens (the  matching name is found, the (*SKIP) is ignored.
 (*SKIP) is ignored).  
2886  .sp  .sp
2887    (*THEN) or (*THEN:NAME)    (*THEN) or (*THEN:NAME)
2888  .sp  .sp
2889  This verb causes a skip to the next alternation in the innermost enclosing  This verb causes a skip to the next innermost alternative if the rest of the
2890  group if the rest of the pattern does not match. That is, it cancels pending  pattern does not match. That is, it cancels pending backtracking, but only
2891  backtracking, but only within the current alternation. Its name comes from the  within the current alternative. Its name comes from the observation that it can
2892  observation that it can be used for a pattern-based if-then-else block:  be used for a pattern-based if-then-else block:
2893  .sp  .sp
2894    ( COND1 (*THEN) FOO | COND2 (*THEN) BAR | COND3 (*THEN) BAZ ) ...    ( COND1 (*THEN) FOO | COND2 (*THEN) BAR | COND3 (*THEN) BAZ ) ...
2895  .sp  .sp
2896  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
2897  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
2898  second alternative and tries COND2, without backtracking into COND1. The  second alternative and tries COND2, without backtracking into COND1. The
2899  behaviour of (*THEN:NAME) is exactly the same as (*MARK:NAME)(*THEN) if the  behaviour of (*THEN:NAME) is exactly the same as (*MARK:NAME)(*THEN).
2900  overall match fails. If (*THEN) is not directly inside an alternation, it acts  If (*THEN) is not inside an alternation, it acts like (*PRUNE).
 like (*PRUNE).  
 .  
 .P  
 The above verbs provide four different "strengths" of control when subsequent  
 matching fails. (*THEN) is the weakest, carrying on the match at the next  
 alternation. (*PRUNE) comes next, failing the match at the current starting  
 position, but allowing an advance to the next character (for an unanchored  
 pattern). (*SKIP) is similar, except that the advance may be more than one  
 character. (*COMMIT) is the strongest, causing the entire match to fail.  
2901  .P  .P
2902  If more than one is present in a pattern, the "stongest" one wins. For example,  Note that a subpattern that does not contain a | character is just a part of
2903  consider this pattern, where A, B, etc. are complex pattern fragments:  the enclosing alternative; it is not a nested alternation with only one
2904    alternative. The effect of (*THEN) extends beyond such a subpattern to the
2905    enclosing alternative. Consider this pattern, where A, B, etc. are complex
2906    pattern fragments that do not contain any | characters at this level:
2907    .sp
2908      A (B(*THEN)C) | D
2909    .sp
2910    If A and B are matched, but there is a failure in C, matching does not
2911    backtrack into A; instead it moves to the next alternative, that is, D.
2912    However, if the subpattern containing (*THEN) is given an alternative, it
2913    behaves differently:
2914    .sp
2915      A (B(*THEN)C | (*FAIL)) | D
2916    .sp
2917    The effect of (*THEN) is now confined to the inner subpattern. After a failure
2918    in C, matching moves to (*FAIL), which causes the whole subpattern to fail
2919    because there are no more alternatives to try. In this case, matching does now
2920    backtrack into A.
2921    .P
2922    Note also that a conditional subpattern is not considered as having two
2923    alternatives, because only one is ever used. In other words, the | character in
2924    a conditional subpattern has a different meaning. Ignoring white space,
2925    consider:
2926    .sp
2927      ^.*? (?(?=a) a | b(*THEN)c )
2928    .sp
2929    If the subject is "ba", this pattern does not match. Because .*? is ungreedy,
2930    it initially matches zero characters. The condition (?=a) then fails, the
2931    character "b" is matched, but "c" is not. At this point, matching does not
2932    backtrack to .*? as might perhaps be expected from the presence of the |
2933    character. The conditional subpattern is part of the single alternative that
2934    comprises the whole pattern, and so the match fails. (If there was a backtrack
2935    into .*?, allowing it to match "b", the match would succeed.)
2936    .P
2937    The verbs just described provide four different "strengths" of control when
2938    subsequent matching fails. (*THEN) is the weakest, carrying on the match at the
2939    next alternative. (*PRUNE) comes next, failing the match at the current
2940    starting position, but allowing an advance to the next character (for an
2941    unanchored pattern). (*SKIP) is similar, except that the advance may be more
2942    than one character. (*COMMIT) is the strongest, causing the entire match to
2943    fail.
2944    .P
2945    If more than one such verb is present in a pattern, the "strongest" one wins.
2946    For example, consider this pattern, where A, B, etc. are complex pattern
2947    fragments:
2948  .sp  .sp
2949    (A(*COMMIT)B(*THEN)C|D)    (A(*COMMIT)B(*THEN)C|D)
2950  .sp  .sp
2951  Once A has matched, PCRE is committed to this match, at the current starting  Once A has matched, PCRE is committed to this match, at the current starting
2952  position. If subsequently B matches, but C does not, the normal (*THEN) action  position. If subsequently B matches, but C does not, the normal (*THEN) action
2953  of trying the next alternation (that is, D) does not happen because (*COMMIT)  of trying the next alternative (that is, D) does not happen because (*COMMIT)
2954  overrides.  overrides.
2955  .  .
2956  .  .
# Line 2668  overrides. Line 2958  overrides.
2958  .rs  .rs
2959  .sp  .sp
2960  \fBpcreapi\fP(3), \fBpcrecallout\fP(3), \fBpcrematching\fP(3),  \fBpcreapi\fP(3), \fBpcrecallout\fP(3), \fBpcrematching\fP(3),
2961  \fBpcresyntax\fP(3), \fBpcre\fP(3).  \fBpcresyntax\fP(3), \fBpcre\fP(3), \fBpcre16(3)\fP, \fBpcre32(3)\fP.
2962  .  .
2963  .  .
2964  .SH AUTHOR  .SH AUTHOR
# Line 2685  Cambridge CB2 3QH, England. Line 2975  Cambridge CB2 3QH, England.
2975  .rs  .rs
2976  .sp  .sp
2977  .nf  .nf
2978  Last updated: 26 October 2010  Last updated: 07 November 2012
2979  Copyright (c) 1997-2010 University of Cambridge.  Copyright (c) 1997-2012 University of Cambridge.
2980  .fi  .fi

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