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1  .TH PCREPATTERN 3  .TH PCREPATTERN 3 "08 October 2013" "PCRE 8.34"
2  .SH NAME  .SH NAME
3  PCRE - Perl-compatible regular expressions  PCRE - Perl-compatible regular expressions
4  .SH "PCRE REGULAR EXPRESSION DETAILS"  .SH "PCRE REGULAR EXPRESSION DETAILS"
# Line 20  have copious examples. Jeffrey Friedl's Line 20  have copious examples. Jeffrey Friedl's
20  published by O'Reilly, covers regular expressions in great detail. This  published by O'Reilly, covers regular expressions in great detail. This
21  description of PCRE's regular expressions is intended as reference material.  description of PCRE's regular expressions is intended as reference material.
22  .P  .P
23    This document discusses the patterns that are supported by PCRE when one its
24    main matching functions, \fBpcre_exec()\fP (8-bit) or \fBpcre[16|32]_exec()\fP
25    (16- or 32-bit), is used. PCRE also has alternative matching functions,
26    \fBpcre_dfa_exec()\fP and \fBpcre[16|32_dfa_exec()\fP, which match using a
27    different algorithm that is not Perl-compatible. Some of the features discussed
28    below are not available when DFA matching is used. The advantages and
29    disadvantages of the alternative functions, and how they differ from the normal
30    functions, are discussed in the
31    .\" HREF
32    \fBpcrematching\fP
33    .\"
34    page.
35    .
36    .
37    .SH "SPECIAL START-OF-PATTERN ITEMS"
38    .rs
39    .sp
40    A number of options that can be passed to \fBpcre_compile()\fP can also be set
41    by special items at the start of a pattern. These are not Perl-compatible, but
42    are provided to make these options accessible to pattern writers who are not
43    able to change the program that processes the pattern. Any number of these
44    items may appear, but they must all be together right at the start of the
45    pattern string, and the letters must be in upper case.
46    .
47    .
48    .SS "UTF support"
49    .rs
50    .sp
51  The original operation of PCRE was on strings of one-byte characters. However,  The original operation of PCRE was on strings of one-byte characters. However,
52  there is now also support for UTF-8 character strings. To use this,  there is now also support for UTF-8 strings in the original library, an
53  PCRE must be built to include UTF-8 support, and you must call  extra library that supports 16-bit and UTF-16 character strings, and a
54  \fBpcre_compile()\fP or \fBpcre_compile2()\fP with the PCRE_UTF8 option. There  third library that supports 32-bit and UTF-32 character strings. To use these
55  is also a special sequence that can be given at the start of a pattern:  features, PCRE must be built to include appropriate support. When using UTF
56    strings you must either call the compiling function with the PCRE_UTF8,
57    PCRE_UTF16, or PCRE_UTF32 option, or the pattern must start with one of
58    these special sequences:
59  .sp  .sp
60    (*UTF8)    (*UTF8)
61  .sp    (*UTF16)
62  Starting a pattern with this sequence is equivalent to setting the PCRE_UTF8    (*UTF32)
63  option. This feature is not Perl-compatible. How setting UTF-8 mode affects    (*UTF)
64  pattern matching is mentioned in several places below. There is also a summary  .sp
65  of UTF-8 features in the  (*UTF) is a generic sequence that can be used with any of the libraries.
66  .\" HTML <a href="pcre.html#utf8support">  Starting a pattern with such a sequence is equivalent to setting the relevant
67  .\" </a>  option. How setting a UTF mode affects pattern matching is mentioned in several
68  section on UTF-8 support  places below. There is also a summary of features in the
 .\"  
 in the main  
69  .\" HREF  .\" HREF
70  \fBpcre\fP  \fBpcreunicode\fP
71  .\"  .\"
72  page.  page.
73  .P  .P
74  Another special sequence that may appear at the start of a pattern or in  Some applications that allow their users to supply patterns may wish to
75  combination with (*UTF8) is:  restrict them to non-UTF data for security reasons. If the PCRE_NEVER_UTF
76    option is set at compile time, (*UTF) etc. are not allowed, and their
77    appearance causes an error.
78    .
79    .
80    .SS "Unicode property support"
81    .rs
82    .sp
83    Another special sequence that may appear at the start of a pattern is
84  .sp  .sp
85    (*UCP)    (*UCP)
86  .sp  .sp
# Line 51  This has the same effect as setting the Line 88  This has the same effect as setting the
88  such as \ed and \ew to use Unicode properties to determine character types,  such as \ed and \ew to use Unicode properties to determine character types,
89  instead of recognizing only characters with codes less than 128 via a lookup  instead of recognizing only characters with codes less than 128 via a lookup
90  table.  table.
 .P  
 The remainder of this document discusses the patterns that are supported by  
 PCRE when its main matching function, \fBpcre_exec()\fP, is used.  
 From release 6.0, PCRE offers a second matching function,  
 \fBpcre_dfa_exec()\fP, which matches using a different algorithm that is not  
 Perl-compatible. Some of the features discussed below are not available when  
 \fBpcre_dfa_exec()\fP is used. The advantages and disadvantages of the  
 alternative function, and how it differs from the normal function, are  
 discussed in the  
 .\" HREF  
 \fBpcrematching\fP  
 .\"  
 page.  
91  .  .
92  .  .
93  .SH "NEWLINE CONVENTIONS"  .SS "Disabling start-up optimizations"
94    .rs
95    .sp
96    If a pattern starts with (*NO_START_OPT), it has the same effect as setting the
97    PCRE_NO_START_OPTIMIZE option either at compile or matching time.
98    .
99    .
100    .\" HTML <a name="newlines"></a>
101    .SS "Newline conventions"
102  .rs  .rs
103  .sp  .sp
104  PCRE supports five different conventions for indicating line breaks in  PCRE supports five different conventions for indicating line breaks in
# Line 93  string with one of the following five se Line 125  string with one of the following five se
125    (*ANYCRLF)   any of the three above    (*ANYCRLF)   any of the three above
126    (*ANY)       all Unicode newline sequences    (*ANY)       all Unicode newline sequences
127  .sp  .sp
128  These override the default and the options given to \fBpcre_compile()\fP or  These override the default and the options given to the compiling function. For
129  \fBpcre_compile2()\fP. For example, on a Unix system where LF is the default  example, on a Unix system where LF is the default newline sequence, the pattern
 newline sequence, the pattern  
130  .sp  .sp
131    (*CR)a.b    (*CR)a.b
132  .sp  .sp
133  changes the convention to CR. That pattern matches "a\enb" because LF is no  changes the convention to CR. That pattern matches "a\enb" because LF is no
134  longer a newline. Note that these special settings, which are not  longer a newline. If more than one of these settings is present, the last one
 Perl-compatible, are recognized only at the very start of a pattern, and that  
 they must be in upper case. If more than one of them is present, the last one  
135  is used.  is used.
136  .P  .P
137  The newline convention affects the interpretation of the dot metacharacter when  The newline convention affects where the circumflex and dollar assertions are
138  PCRE_DOTALL is not set, and also the behaviour of \eN. However, it does not  true. It also affects the interpretation of the dot metacharacter when
139  affect what the \eR escape sequence matches. By default, this is any Unicode  PCRE_DOTALL is not set, and the behaviour of \eN. However, it does not affect
140  newline sequence, for Perl compatibility. However, this can be changed; see the  what the \eR escape sequence matches. By default, this is any Unicode newline
141    sequence, for Perl compatibility. However, this can be changed; see the
142  description of \eR in the section entitled  description of \eR in the section entitled
143  .\" HTML <a href="#newlineseq">  .\" HTML <a href="#newlineseq">
144  .\" </a>  .\" </a>
# Line 118  below. A change of \eR setting can be co Line 148  below. A change of \eR setting can be co
148  convention.  convention.
149  .  .
150  .  .
151    .SS "Setting match and recursion limits"
152    .rs
153    .sp
154    The caller of \fBpcre_exec()\fP can set a limit on the number of times the
155    internal \fBmatch()\fP function is called and on the maximum depth of
156    recursive calls. These facilities are provided to catch runaway matches that
157    are provoked by patterns with huge matching trees (a typical example is a
158    pattern with nested unlimited repeats) and to avoid running out of system stack
159    by too much recursion. When one of these limits is reached, \fBpcre_exec()\fP
160    gives an error return. The limits can also be set by items at the start of the
161    pattern of the form
162    .sp
163      (*LIMIT_MATCH=d)
164      (*LIMIT_RECURSION=d)
165    .sp
166    where d is any number of decimal digits. However, the value of the setting must
167    be less than the value set by the caller of \fBpcre_exec()\fP for it to have
168    any effect. In other words, the pattern writer can lower the limit set by the
169    programmer, but not raise it. If there is more than one setting of one of these
170    limits, the lower value is used.
171    .
172    .
173    .SH "EBCDIC CHARACTER CODES"
174    .rs
175    .sp
176    PCRE can be compiled to run in an environment that uses EBCDIC as its character
177    code rather than ASCII or Unicode (typically a mainframe system). In the
178    sections below, character code values are ASCII or Unicode; in an EBCDIC
179    environment these characters may have different code values, and there are no
180    code points greater than 255.
181    .
182    .
183  .SH "CHARACTERS AND METACHARACTERS"  .SH "CHARACTERS AND METACHARACTERS"
184  .rs  .rs
185  .sp  .sp
# Line 129  corresponding characters in the subject. Line 191  corresponding characters in the subject.
191  .sp  .sp
192  matches a portion of a subject string that is identical to itself. When  matches a portion of a subject string that is identical to itself. When
193  caseless matching is specified (the PCRE_CASELESS option), letters are matched  caseless matching is specified (the PCRE_CASELESS option), letters are matched
194  independently of case. In UTF-8 mode, PCRE always understands the concept of  independently of case. In a UTF mode, PCRE always understands the concept of
195  case for characters whose values are less than 128, so caseless matching is  case for characters whose values are less than 128, so caseless matching is
196  always possible. For characters with higher values, the concept of case is  always possible. For characters with higher values, the concept of case is
197  supported if PCRE is compiled with Unicode property support, but not otherwise.  supported if PCRE is compiled with Unicode property support, but not otherwise.
198  If you want to use caseless matching for characters 128 and above, you must  If you want to use caseless matching for characters 128 and above, you must
199  ensure that PCRE is compiled with Unicode property support as well as with  ensure that PCRE is compiled with Unicode property support as well as with
200  UTF-8 support.  UTF support.
201  .P  .P
202  The power of regular expressions comes from the ability to include alternatives  The power of regular expressions comes from the ability to include alternatives
203  and repetitions in the pattern. These are encoded in the pattern by the use of  and repetitions in the pattern. These are encoded in the pattern by the use of
# Line 181  The following sections describe the use Line 243  The following sections describe the use
243  .rs  .rs
244  .sp  .sp
245  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
246  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
247  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
248  outside character classes.  both inside and outside character classes.
249  .P  .P
250  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.
251  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 253  otherwise be interpreted as a metacharac
253  non-alphanumeric with backslash to specify that it stands for itself. In  non-alphanumeric with backslash to specify that it stands for itself. In
254  particular, if you want to match a backslash, you write \e\e.  particular, if you want to match a backslash, you write \e\e.
255  .P  .P
256  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
257    backslash. All other characters (in particular, those whose codepoints are
258    greater than 127) are treated as literals.
259    .P
260    If a pattern is compiled with the PCRE_EXTENDED option, white space in the
261  pattern (other than in a character class) and characters between a # outside  pattern (other than in a character class) and characters between a # outside
262  a character class and the next newline are ignored. An escaping backslash can  a character class and the next newline are ignored. An escaping backslash can
263  be used to include a whitespace or # character as part of the pattern.  be used to include a white space or # character as part of the pattern.
264  .P  .P
265  If you want to remove the special meaning from a sequence of characters, you  If you want to remove the special meaning from a sequence of characters, you
266  can do so by putting them between \eQ and \eE. This is different from Perl in  can do so by putting them between \eQ and \eE. This is different from Perl in
# Line 210  Perl, $ and @ cause variable interpolati Line 276  Perl, $ and @ cause variable interpolati
276    \eQabc\eE\e$\eQxyz\eE   abc$xyz        abc$xyz    \eQabc\eE\e$\eQxyz\eE   abc$xyz        abc$xyz
277  .sp  .sp
278  The \eQ...\eE sequence is recognized both inside and outside character classes.  The \eQ...\eE sequence is recognized both inside and outside character classes.
279  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
280    by \eE later in the pattern, the literal interpretation continues to the end of
281    the pattern (that is, \eE is assumed at the end). If the isolated \eQ is inside
282    a character class, this causes an error, because the character class is not
283    terminated.
284  .  .
285  .  .
286  .\" HTML <a name="digitsafterbackslash"></a>  .\" HTML <a name="digitsafterbackslash"></a>
# Line 224  but when a pattern is being prepared by Line 294  but when a pattern is being prepared by
294  one of the following escape sequences than the binary character it represents:  one of the following escape sequences than the binary character it represents:
295  .sp  .sp
296    \ea        alarm, that is, the BEL character (hex 07)    \ea        alarm, that is, the BEL character (hex 07)
297    \ecx       "control-x", where x is any character    \ecx       "control-x", where x is any ASCII character
298    \ee        escape (hex 1B)    \ee        escape (hex 1B)
299    \ef        formfeed (hex 0C)    \ef        form feed (hex 0C)
300    \en        linefeed (hex 0A)    \en        linefeed (hex 0A)
301    \er        carriage return (hex 0D)    \er        carriage return (hex 0D)
302    \et        tab (hex 09)    \et        tab (hex 09)
303      \e0dd      character with octal code 0dd
304    \eddd      character with octal code ddd, or back reference    \eddd      character with octal code ddd, or back reference
305      \eo{ddd..} character with octal code ddd..
306    \exhh      character with hex code hh    \exhh      character with hex code hh
307    \ex{hhh..} character with hex code hhh..    \ex{hhh..} character with hex code hhh.. (non-JavaScript mode)
308      \euhhhh    character with hex code hhhh (JavaScript mode only)
309  .sp  .sp
310  The precise effect of \ecx is as follows: if x is a lower case letter, it  The precise effect of \ecx on ASCII characters is as follows: if x is a lower
311  is converted to upper case. Then bit 6 of the character (hex 40) is inverted.  case letter, it is converted to upper case. Then bit 6 of the character (hex
312  Thus \ecz becomes hex 1A, but \ec{ becomes hex 3B, while \ec; becomes hex  40) is inverted. Thus \ecA to \ecZ become hex 01 to hex 1A (A is 41, Z is 5A),
313  7B.  but \ec{ becomes hex 3B ({ is 7B), and \ec; becomes hex 7B (; is 3B). If the
314  .P  data item (byte or 16-bit value) following \ec has a value greater than 127, a
315  After \ex, from zero to two hexadecimal digits are read (letters can be in  compile-time error occurs. This locks out non-ASCII characters in all modes.
316  upper or lower case). Any number of hexadecimal digits may appear between \ex{  .P
317  and }, but the value of the character code must be less than 256 in non-UTF-8  The \ec facility was designed for use with ASCII characters, but with the
318  mode, and less than 2**31 in UTF-8 mode. That is, the maximum value in  extension to Unicode it is even less useful than it once was. It is, however,
319  hexadecimal is 7FFFFFFF. Note that this is bigger than the largest Unicode code  recognized when PCRE is compiled in EBCDIC mode, where data items are always
320  point, which is 10FFFF.  bytes. In this mode, all values are valid after \ec. If the next character is a
321  .P  lower case letter, it is converted to upper case. Then the 0xc0 bits of the
322  If characters other than hexadecimal digits appear between \ex{ and }, or if  byte are inverted. Thus \ecA becomes hex 01, as in ASCII (A is C1), but because
323  there is no terminating }, this form of escape is not recognized. Instead, the  the EBCDIC letters are disjoint, \ecZ becomes hex 29 (Z is E9), and other
324  initial \ex will be interpreted as a basic hexadecimal escape, with no  characters also generate different values.
 following digits, giving a character whose value is zero.  
 .P  
 Characters whose value is less than 256 can be defined by either of the two  
 syntaxes for \ex. There is no difference in the way they are handled. For  
 example, \exdc is exactly the same as \ex{dc}.  
325  .P  .P
326  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
327  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 261  specifies two binary zeros followed by a Line 329  specifies two binary zeros followed by a
329  sure you supply two digits after the initial zero if the pattern character that  sure you supply two digits after the initial zero if the pattern character that
330  follows is itself an octal digit.  follows is itself an octal digit.
331  .P  .P
332  The handling of a backslash followed by a digit other than 0 is complicated.  The escape \eo must be followed by a sequence of octal digits, enclosed in
333  Outside a character class, PCRE reads it and any following digits as a decimal  braces. An error occurs if this is not the case. This escape is a recent
334  number. If the number is less than 10, or if there have been at least that many  addition to Perl; it provides way of specifying character code points as octal
335    numbers greater than 0777, and it also allows octal numbers and back references
336    to be unambiguously specified.
337    .P
338    For greater clarity and unambiguity, it is best to avoid following \e by a
339    digit greater than zero. Instead, use \eo{} or \ex{} to specify character
340    numbers, and \eg{} to specify back references. The following paragraphs
341    describe the old, ambiguous syntax.
342    .P
343    The handling of a backslash followed by a digit other than 0 is complicated,
344    and Perl has changed in recent releases, causing PCRE also to change. Outside a
345    character class, PCRE reads the digit and any following digits as a decimal
346    number. If the number is less than 8, or if there have been at least that many
347  previous capturing left parentheses in the expression, the entire sequence is  previous capturing left parentheses in the expression, the entire sequence is
348  taken as a \fIback reference\fP. A description of how this works is given  taken as a \fIback reference\fP. A description of how this works is given
349  .\" HTML <a href="#backreferences">  .\" HTML <a href="#backreferences">
# Line 276  following the discussion of Line 356  following the discussion of
356  parenthesized subpatterns.  parenthesized subpatterns.
357  .\"  .\"
358  .P  .P
359  Inside a character class, or if the decimal number is greater than 9 and there  Inside a character class, or if the decimal number following \e is greater than
360  have not been that many capturing subpatterns, PCRE re-reads up to three octal  7 and there have not been that many capturing subpatterns, PCRE handles \e8 and
361  digits following the backslash, and uses them to generate a data character. Any  \e9 as the literal characters "8" and "9", and otherwise re-reads up to three
362  subsequent digits stand for themselves. In non-UTF-8 mode, the value of a  octal digits following the backslash, using them to generate a data character.
363  character specified in octal must be less than \e400. In UTF-8 mode, values up  Any subsequent digits stand for themselves. For example:
 to \e777 are permitted. For example:  
364  .sp  .sp
365    \e040   is another way of writing a space    \e040   is another way of writing an ASCII space
366  .\" JOIN  .\" JOIN
367    \e40    is the same, provided there are fewer than 40    \e40    is the same, provided there are fewer than 40
368              previous capturing subpatterns              previous capturing subpatterns
# Line 298  to \e777 are permitted. For example: Line 377  to \e777 are permitted. For example:
377              character with octal code 113              character with octal code 113
378  .\" JOIN  .\" JOIN
379    \e377   might be a back reference, otherwise    \e377   might be a back reference, otherwise
380              the byte consisting entirely of 1 bits              the value 255 (decimal)
381  .\" JOIN  .\" JOIN
382    \e81    is either a back reference, or a binary zero    \e81    is either a back reference, or the two
383              followed by the two characters "8" and "1"              characters "8" and "1"
384  .sp  .sp
385  Note that octal values of 100 or greater must not be introduced by a leading  Note that octal values of 100 or greater that are specified using this syntax
386  zero, because no more than three octal digits are ever read.  must not be introduced by a leading zero, because no more than three octal
387    digits are ever read.
388    .P
389    By default, after \ex that is not followed by {, from zero to two hexadecimal
390    digits are read (letters can be in upper or lower case). Any number of
391    hexadecimal digits may appear between \ex{ and }. If a character other than
392    a hexadecimal digit appears between \ex{ and }, or if there is no terminating
393    }, an error occurs.
394    .P
395    If the PCRE_JAVASCRIPT_COMPAT option is set, the interpretation of \ex is
396    as just described only when it is followed by two hexadecimal digits.
397    Otherwise, it matches a literal "x" character. In JavaScript mode, support for
398    code points greater than 256 is provided by \eu, which must be followed by
399    four hexadecimal digits; otherwise it matches a literal "u" character.
400  .P  .P
401    Characters whose value is less than 256 can be defined by either of the two
402    syntaxes for \ex (or by \eu in JavaScript mode). There is no difference in the
403    way they are handled. For example, \exdc is exactly the same as \ex{dc} (or
404    \eu00dc in JavaScript mode).
405    .
406    .
407    .SS "Constraints on character values"
408    .rs
409    .sp
410    Characters that are specified using octal or hexadecimal numbers are
411    limited to certain values, as follows:
412    .sp
413      8-bit non-UTF mode    less than 0x100
414      8-bit UTF-8 mode      less than 0x10ffff and a valid codepoint
415      16-bit non-UTF mode   less than 0x10000
416      16-bit UTF-16 mode    less than 0x10ffff and a valid codepoint
417      32-bit non-UTF mode   less than 0x100000000
418      32-bit UTF-32 mode    less than 0x10ffff and a valid codepoint
419    .sp
420    Invalid Unicode codepoints are the range 0xd800 to 0xdfff (the so-called
421    "surrogate" codepoints), and 0xffef.
422    .
423    .
424    .SS "Escape sequences in character classes"
425    .rs
426    .sp
427  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
428  and outside character classes. In addition, inside a character class, the  and outside character classes. In addition, inside a character class, \eb is
429  sequence \eb is interpreted as the backspace character (hex 08). The sequences  interpreted as the backspace character (hex 08).
430  \eB, \eN, \eR, and \eX are not special inside a character class. Like any other  .P
431  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
432  "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
433  set. Outside a character class, these sequences have different meanings.  treated as the literal characters "B", "R", and "X" by default, but cause an
434    error if the PCRE_EXTRA option is set. Outside a character class, these
435    sequences have different meanings.
436    .
437    .
438    .SS "Unsupported escape sequences"
439    .rs
440    .sp
441    In Perl, the sequences \el, \eL, \eu, and \eU are recognized by its string
442    handler and used to modify the case of following characters. By default, PCRE
443    does not support these escape sequences. However, if the PCRE_JAVASCRIPT_COMPAT
444    option is set, \eU matches a "U" character, and \eu can be used to define a
445    character by code point, as described in the previous section.
446  .  .
447  .  .
448  .SS "Absolute and relative back references"  .SS "Absolute and relative back references"
# Line 359  Another use of backslash is for specifyi Line 489  Another use of backslash is for specifyi
489  .sp  .sp
490    \ed     any decimal digit    \ed     any decimal digit
491    \eD     any character that is not a decimal digit    \eD     any character that is not a decimal digit
492    \eh     any horizontal whitespace character    \eh     any horizontal white space character
493    \eH     any character that is not a horizontal whitespace character    \eH     any character that is not a horizontal white space character
494    \es     any whitespace character    \es     any white space character
495    \eS     any character that is not a whitespace character    \eS     any character that is not a white space character
496    \ev     any vertical whitespace character    \ev     any vertical white space character
497    \eV     any character that is not a vertical whitespace character    \eV     any character that is not a vertical white space character
498    \ew     any "word" character    \ew     any "word" character
499    \eW     any "non-word" character    \eW     any "non-word" character
500  .sp  .sp
# Line 374  This is the same as Line 504  This is the same as
504  .\" </a>  .\" </a>
505  the "." metacharacter  the "." metacharacter
506  .\"  .\"
507  when PCRE_DOTALL is not set.  when PCRE_DOTALL is not set. Perl also uses \eN to match characters by name;
508    PCRE does not support this.
509  .P  .P
510  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
511  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 383  classes. They each match one character o Line 514  classes. They each match one character o
514  matching point is at the end of the subject string, all of them fail, because  matching point is at the end of the subject string, all of them fail, because
515  there is no character to match.  there is no character to match.
516  .P  .P
517  For compatibility with Perl, \es does not match the VT character (code 11).  For compatibility with Perl, \es did not used to match the VT character (code
518  This makes it different from the the POSIX "space" class. The \es characters  11), which made it different from the the POSIX "space" class. However, Perl
519  are HT (9), LF (10), FF (12), CR (13), and space (32). If "use locale;" is  added VT at release 5.18, and PCRE followed suit at release 8.34. The \es
520  included in a Perl script, \es may match the VT character. In PCRE, it never  characters are now HT (9), LF (10), VT (11), FF (12), CR (13), and space (32).
 does.  
521  .P  .P
522  A "word" character is an underscore or any character that is a letter or digit.  A "word" character is an underscore or any character that is a letter or digit.
523  By default, the definition of letters and digits is controlled by PCRE's  By default, the definition of letters and digits is controlled by PCRE's
# Line 406  or "french" in Windows, some character c Line 536  or "french" in Windows, some character c
536  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
537  Unicode is discouraged.  Unicode is discouraged.
538  .P  .P
539  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
540  \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
541  their original meanings from before UTF-8 support was available, mainly for  their original meanings from before UTF support was available, mainly for
542  efficiency reasons. However, if PCRE is compiled with Unicode property support,  efficiency reasons. However, if PCRE is compiled with Unicode property support,
543  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
544  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 553  any Unicode letter, and underscore. Note
553  \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
554  is noticeably slower when PCRE_UCP is set.  is noticeably slower when PCRE_UCP is set.
555  .P  .P
556  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
557  other sequences, which match only ASCII characters by default, these always  release 5.10. In contrast to the other sequences, which match only ASCII
558  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,
559  set. The horizontal space characters are:  whether or not PCRE_UCP is set. The horizontal space characters are:
560  .sp  .sp
561    U+0009     Horizontal tab    U+0009     Horizontal tab (HT)
562    U+0020     Space    U+0020     Space
563    U+00A0     Non-break space    U+00A0     Non-break space
564    U+1680     Ogham space mark    U+1680     Ogham space mark
# Line 450  set. The horizontal space characters are Line 580  set. The horizontal space characters are
580  .sp  .sp
581  The vertical space characters are:  The vertical space characters are:
582  .sp  .sp
583    U+000A     Linefeed    U+000A     Linefeed (LF)
584    U+000B     Vertical tab    U+000B     Vertical tab (VT)
585    U+000C     Formfeed    U+000C     Form feed (FF)
586    U+000D     Carriage return    U+000D     Carriage return (CR)
587    U+0085     Next line    U+0085     Next line (NEL)
588    U+2028     Line separator    U+2028     Line separator
589    U+2029     Paragraph separator    U+2029     Paragraph separator
590    .sp
591    In 8-bit, non-UTF-8 mode, only the characters with codepoints less than 256 are
592    relevant.
593  .  .
594  .  .
595  .\" HTML <a name="newlineseq"></a>  .\" HTML <a name="newlineseq"></a>
# Line 464  The vertical space characters are: Line 597  The vertical space characters are:
597  .rs  .rs
598  .sp  .sp
599  Outside a character class, by default, the escape sequence \eR matches any  Outside a character class, by default, the escape sequence \eR matches any
600  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
601  equivalent to the following:  following:
602  .sp  .sp
603    (?>\er\en|\en|\ex0b|\ef|\er|\ex85)    (?>\er\en|\en|\ex0b|\ef|\er|\ex85)
604  .sp  .sp
# Line 476  below. Line 609  below.
609  .\"  .\"
610  This particular group matches either the two-character sequence CR followed by  This particular group matches either the two-character sequence CR followed by
611  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,
612  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
613  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
614  cannot be split.  cannot be split.
615  .P  .P
616  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
617  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).
618  Unicode character property support is not needed for these characters to be  Unicode character property support is not needed for these characters to be
619  recognized.  recognized.
# Line 496  one of the following sequences: Line 629  one of the following sequences:
629    (*BSR_ANYCRLF)   CR, LF, or CRLF only    (*BSR_ANYCRLF)   CR, LF, or CRLF only
630    (*BSR_UNICODE)   any Unicode newline sequence    (*BSR_UNICODE)   any Unicode newline sequence
631  .sp  .sp
632  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
633  \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
634  \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
635  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
636  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
637  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:  
638  .sp  .sp
639    (*ANY)(*BSR_ANYCRLF)    (*ANY)(*BSR_ANYCRLF)
640  .sp  .sp
641  They can also be combined with the (*UTF8) or (*UCP) special sequences. Inside  They can also be combined with the (*UTF8), (*UTF16), (*UTF32), (*UTF) or
642  a character class, \eR is treated as an unrecognized escape sequence, and so  (*UCP) special sequences. Inside a character class, \eR is treated as an
643  matches the letter "R" by default, but causes an error if PCRE_EXTRA is set.  unrecognized escape sequence, and so matches the letter "R" by default, but
644    causes an error if PCRE_EXTRA is set.
645  .  .
646  .  .
647  .\" HTML <a name="uniextseq"></a>  .\" HTML <a name="uniextseq"></a>
# Line 517  matches the letter "R" by default, but c Line 650  matches the letter "R" by default, but c
650  .sp  .sp
651  When PCRE is built with Unicode character property support, three additional  When PCRE is built with Unicode character property support, three additional
652  escape sequences that match characters with specific properties are available.  escape sequences that match characters with specific properties are available.
653  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
654  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.
655  The extra escape sequences are:  The extra escape sequences are:
656  .sp  .sp
657    \ep{\fIxx\fP}   a character with the \fIxx\fP property    \ep{\fIxx\fP}   a character with the \fIxx\fP property
658    \eP{\fIxx\fP}   a character without the \fIxx\fP property    \eP{\fIxx\fP}   a character without the \fIxx\fP property
659    \eX       an extended Unicode sequence    \eX       a Unicode extended grapheme cluster
660  .sp  .sp
661  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
662  script names, the general category properties, "Any", which matches any  script names, the general category properties, "Any", which matches any
# Line 552  Armenian, Line 685  Armenian,
685  Avestan,  Avestan,
686  Balinese,  Balinese,
687  Bamum,  Bamum,
688    Batak,
689  Bengali,  Bengali,
690  Bopomofo,  Bopomofo,
691    Brahmi,
692  Braille,  Braille,
693  Buginese,  Buginese,
694  Buhid,  Buhid,
695  Canadian_Aboriginal,  Canadian_Aboriginal,
696  Carian,  Carian,
697    Chakma,
698  Cham,  Cham,
699  Cherokee,  Cherokee,
700  Common,  Common,
# Line 601  Lisu, Line 737  Lisu,
737  Lycian,  Lycian,
738  Lydian,  Lydian,
739  Malayalam,  Malayalam,
740    Mandaic,
741  Meetei_Mayek,  Meetei_Mayek,
742    Meroitic_Cursive,
743    Meroitic_Hieroglyphs,
744    Miao,
745  Mongolian,  Mongolian,
746  Myanmar,  Myanmar,
747  New_Tai_Lue,  New_Tai_Lue,
# Line 620  Rejang, Line 760  Rejang,
760  Runic,  Runic,
761  Samaritan,  Samaritan,
762  Saurashtra,  Saurashtra,
763    Sharada,
764  Shavian,  Shavian,
765  Sinhala,  Sinhala,
766    Sora_Sompeng,
767  Sundanese,  Sundanese,
768  Syloti_Nagri,  Syloti_Nagri,
769  Syriac,  Syriac,
# Line 630  Tagbanwa, Line 772  Tagbanwa,
772  Tai_Le,  Tai_Le,
773  Tai_Tham,  Tai_Tham,
774  Tai_Viet,  Tai_Viet,
775    Takri,
776  Tamil,  Tamil,
777  Telugu,  Telugu,
778  Thaana,  Thaana,
# Line 704  the Lu, Ll, or Lt property, in other wor Line 847  the Lu, Ll, or Lt property, in other wor
847  a modifier or "other".  a modifier or "other".
848  .P  .P
849  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
850  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
851  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
852  (see the discussion of PCRE_NO_UTF8_CHECK in the  (see the discussion of PCRE_NO_UTF8_CHECK, PCRE_NO_UTF16_CHECK and
853    PCRE_NO_UTF32_CHECK in the
854  .\" HREF  .\" HREF
855  \fBpcreapi\fP  \fBpcreapi\fP
856  .\"  .\"
# Line 721  Instead, this property is assumed for an Line 865  Instead, this property is assumed for an
865  Unicode table.  Unicode table.
866  .P  .P
867  Specifying caseless matching does not affect these escape sequences. For  Specifying caseless matching does not affect these escape sequences. For
868  example, \ep{Lu} always matches only upper case letters.  example, \ep{Lu} always matches only upper case letters. This is different from
869    the behaviour of current versions of Perl.
870  .P  .P
871  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
872  Unicode sequence. \eX is equivalent to  multistage table lookup in order to find a character's property. That is why
873  .sp  the traditional escape sequences such as \ed and \ew do not use Unicode
874    (?>\ePM\epM*)  properties in PCRE by default, though you can make them do so by setting the
875    PCRE_UCP option or by starting the pattern with (*UCP).
876    .
877    .
878    .SS Extended grapheme clusters
879    .rs
880  .sp  .sp
881  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
882  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  
883  .\" HTML <a href="#atomicgroup">  .\" HTML <a href="#atomicgroup">
884  .\" </a>  .\" </a>
885  (see below).  (see below).
886  .\"  .\"
887  Characters with the "mark" property are typically accents that affect the  Up to and including release 8.31, PCRE matched an earlier, simpler definition
888  preceding character. None of them have codepoints less than 256, so in  that was equivalent to
889  non-UTF-8 mode \eX matches any one character.  .sp
890  .P    (?>\ePM\epM*)
891  Matching characters by Unicode property is not fast, because PCRE has to search  .sp
892  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
893  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"
894  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.
895  PCRE_UCP option for \fBpcre_compile()\fP or by starting the pattern with  .P
896  (*UCP).  This simple definition was extended in Unicode to include more complicated
897    kinds of composite character by giving each character a grapheme breaking
898    property, and creating rules that use these properties to define the boundaries
899    of extended grapheme clusters. In releases of PCRE later than 8.31, \eX matches
900    one of these clusters.
901    .P
902    \eX always matches at least one character. Then it decides whether to add
903    additional characters according to the following rules for ending a cluster:
904    .P
905    1. End at the end of the subject string.
906    .P
907    2. Do not end between CR and LF; otherwise end after any control character.
908    .P
909    3. Do not break Hangul (a Korean script) syllable sequences. Hangul characters
910    are of five types: L, V, T, LV, and LVT. An L character may be followed by an
911    L, V, LV, or LVT character; an LV or V character may be followed by a V or T
912    character; an LVT or T character may be follwed only by a T character.
913    .P
914    4. Do not end before extending characters or spacing marks. Characters with
915    the "mark" property always have the "extend" grapheme breaking property.
916    .P
917    5. Do not end after prepend characters.
918    .P
919    6. Otherwise, end the cluster.
920  .  .
921  .  .
922  .\" HTML <a name="extraprops"></a>  .\" HTML <a name="extraprops"></a>
923  .SS PCRE's additional properties  .SS PCRE's additional properties
924  .rs  .rs
925  .sp  .sp
926  As well as the standard Unicode properties described in the previous  As well as the standard Unicode properties described above, PCRE supports four
927  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
928  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
929  properties. PCRE uses these non-standard, non-Perl properties internally when  non-standard, non-Perl properties internally when PCRE_UCP is set. However,
930  PCRE_UCP is set. They are:  they may also be used explicitly. These properties are:
931  .sp  .sp
932    Xan   Any alphanumeric character    Xan   Any alphanumeric character
933    Xps   Any POSIX space character    Xps   Any POSIX space character
# Line 763  PCRE_UCP is set. They are: Line 935  PCRE_UCP is set. They are:
935    Xwd   Any Perl "word" character    Xwd   Any Perl "word" character
936  .sp  .sp
937  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)
938  property. Xps matches the characters tab, linefeed, vertical tab, formfeed, or  property. Xps matches the characters tab, linefeed, vertical tab, form feed, or
939  carriage return, and any other character that has the Z (separator) property.  carriage return, and any other character that has the Z (separator) property.
940  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
941  same characters as Xan, plus underscore.  same characters as Xan, plus underscore.
942    .P
943    There is another non-standard property, Xuc, which matches any character that
944    can be represented by a Universal Character Name in C++ and other programming
945    languages. These are the characters $, @, ` (grave accent), and all characters
946    with Unicode code points greater than or equal to U+00A0, except for the
947    surrogates U+D800 to U+DFFF. Note that most base (ASCII) characters are
948    excluded. (Universal Character Names are of the form \euHHHH or \eUHHHHHHHH
949    where H is a hexadecimal digit. Note that the Xuc property does not match these
950    sequences but the characters that they represent.)
951  .  .
952  .  .
953  .\" HTML <a name="resetmatchstart"></a>  .\" HTML <a name="resetmatchstart"></a>
954  .SS "Resetting the match start"  .SS "Resetting the match start"
955  .rs  .rs
956  .sp  .sp
957  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
958  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:  
959  .sp  .sp
960    foo\eKbar    foo\eKbar
961  .sp  .sp
# Line 834  escape sequence" error is generated inst Line 1014  escape sequence" error is generated inst
1014  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
1015  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
1016  \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
1017  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
1018  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
1019  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
1020  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 1053  regular expression.
1053  .SH "CIRCUMFLEX AND DOLLAR"  .SH "CIRCUMFLEX AND DOLLAR"
1054  .rs  .rs
1055  .sp  .sp
1056    The circumflex and dollar metacharacters are zero-width assertions. That is,
1057    they test for a particular condition being true without consuming any
1058    characters from the subject string.
1059    .P
1060  Outside a character class, in the default matching mode, the circumflex  Outside a character class, in the default matching mode, the circumflex
1061  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
1062  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
1063  \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
1064  option is unset. Inside a character class, circumflex has an entirely different  option is unset. Inside a character class, circumflex has an entirely different
1065  meaning  meaning
# Line 892  constrained to match only at the start o Line 1076  constrained to match only at the start o
1076  "anchored" pattern. (There are also other constructs that can cause a pattern  "anchored" pattern. (There are also other constructs that can cause a pattern
1077  to be anchored.)  to be anchored.)
1078  .P  .P
1079  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
1080  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
1081  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
1082  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
1083  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
1084  character class.  branch in which it appears. Dollar has no special meaning in a character class.
1085  .P  .P
1086  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
1087  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 1113  end of the subject in both modes, and if
1113  .sp  .sp
1114  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
1115  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
1116  line. In UTF-8 mode, the matched character may be more than one byte long.  line.
1117  .P  .P
1118  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
1119  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 1131  The handling of dot is entirely independ
1131  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
1132  special meaning in a character class.  special meaning in a character class.
1133  .P  .P
1134  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
1135  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
1136  end of a line.  that signifies the end of a line. Perl also uses \eN to match characters by
1137  .  name; PCRE does not support this.
1138  .  .
1139  .SH "MATCHING A SINGLE BYTE"  .
1140  .rs  .SH "MATCHING A SINGLE DATA UNIT"
1141  .sp  .rs
1142  Outside a character class, the escape sequence \eC matches any one byte, both  .sp
1143  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,
1144  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
1145  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
1146  what remains in the string may be a malformed UTF-8 string. For this reason,  a 32-bit unit. Unlike a dot, \eC always
1147  the \eC escape sequence is best avoided.  matches line-ending characters. The feature is provided in Perl in order to
1148    match individual bytes in UTF-8 mode, but it is unclear how it can usefully be
1149    used. Because \eC breaks up characters into individual data units, matching one
1150    unit with \eC in a UTF mode means that the rest of the string may start with a
1151    malformed UTF character. This has undefined results, because PCRE assumes that
1152    it is dealing with valid UTF strings (and by default it checks this at the
1153    start of processing unless the PCRE_NO_UTF8_CHECK, PCRE_NO_UTF16_CHECK or
1154    PCRE_NO_UTF32_CHECK option is used).
1155  .P  .P
1156  PCRE does not allow \eC to appear in lookbehind assertions  PCRE does not allow \eC to appear in lookbehind assertions
1157  .\" HTML <a href="#lookbehind">  .\" HTML <a href="#lookbehind">
1158  .\" </a>  .\" </a>
1159  (described below),  (described below)
1160  .\"  .\"
1161  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
1162  the lookbehind.  the lookbehind.
1163    .P
1164    In general, the \eC escape sequence is best avoided. However, one
1165    way of using it that avoids the problem of malformed UTF characters is to use a
1166    lookahead to check the length of the next character, as in this pattern, which
1167    could be used with a UTF-8 string (ignore white space and line breaks):
1168    .sp
1169      (?| (?=[\ex00-\ex7f])(\eC) |
1170          (?=[\ex80-\ex{7ff}])(\eC)(\eC) |
1171          (?=[\ex{800}-\ex{ffff}])(\eC)(\eC)(\eC) |
1172          (?=[\ex{10000}-\ex{1fffff}])(\eC)(\eC)(\eC)(\eC))
1173    .sp
1174    A group that starts with (?| resets the capturing parentheses numbers in each
1175    alternative (see
1176    .\" HTML <a href="#dupsubpatternnumber">
1177    .\" </a>
1178    "Duplicate Subpattern Numbers"
1179    .\"
1180    below). The assertions at the start of each branch check the next UTF-8
1181    character for values whose encoding uses 1, 2, 3, or 4 bytes, respectively. The
1182    character's individual bytes are then captured by the appropriate number of
1183    groups.
1184  .  .
1185  .  .
1186  .\" HTML <a name="characterclass"></a>  .\" HTML <a name="characterclass"></a>
# Line 982  bracket causes a compile-time error. If Line 1194  bracket causes a compile-time error. If
1194  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
1195  (after an initial circumflex, if present) or escaped with a backslash.  (after an initial circumflex, if present) or escaped with a backslash.
1196  .P  .P
1197  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
1198  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
1199  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
1200  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
1201  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
1202  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
1203  backslash.  backslash.
1204  .P  .P
1205  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 1210  circumflex is not an assertion; it still
1210  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
1211  string.  string.
1212  .P  .P
1213  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)
1214  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
1215    \ex{ escaping mechanism.
1216  .P  .P
1217  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
1218  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
1219  "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
1220  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
1221  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
1222  always possible. For characters with higher values, the concept of case is  always possible. For characters with higher values, the concept of case is
1223  supported if PCRE is compiled with Unicode property support, but not otherwise.  supported if PCRE is compiled with Unicode property support, but not otherwise.
1224  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
1225  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
1226  with UTF-8 support.  well as with UTF support.
1227  .P  .P
1228  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
1229  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 1245  followed by two other characters. The oc
1245  "]" can also be used to end a range.  "]" can also be used to end a range.
1246  .P  .P
1247  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
1248  used for characters specified numerically, for example [\e000-\e037]. In UTF-8  used for characters specified numerically, for example [\e000-\e037]. Ranges
1249  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}].  
1250  .P  .P
1251  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
1252  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
1253  [][\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
1254  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
1255  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
1256  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
1257  property support.  property support.
1258  .P  .P
1259  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,
1260  \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
1261  match to the class. For example, [\edABCDEF] matches any hexadecimal digit. A  they match to the class. For example, [\edABCDEF] matches any hexadecimal
1262  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
1263    and their upper case partners, just as it does when they appear outside a
1264    character class, as described in the section entitled
1265    .\" HTML <a href="#genericchartypes">
1266    .\" </a>
1267    "Generic character types"
1268    .\"
1269    above. The escape sequence \eb has a different meaning inside a character
1270    class; it matches the backspace character. The sequences \eB, \eN, \eR, and \eX
1271    are not special inside a character class. Like any other unrecognized escape
1272    sequences, they are treated as the literal characters "B", "N", "R", and "X" by
1273    default, but cause an error if the PCRE_EXTRA option is set.
1274    .P
1275    A circumflex can conveniently be used with the upper case character types to
1276  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.
1277  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,
1278    whereas [\ew] includes underscore. A positive character class should be read as
1279    "something OR something OR ..." and a negative class as "NOT something AND NOT
1280    something AND NOT ...".
1281  .P  .P
1282  The only metacharacters that are recognized in character classes are backslash,  The only metacharacters that are recognized in character classes are backslash,
1283  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 1087  are: Line 1315  are:
1315    xdigit   hexadecimal digits    xdigit   hexadecimal digits
1316  .sp  .sp
1317  The "space" characters are HT (9), LF (10), VT (11), FF (12), CR (13), and  The "space" characters are HT (9), LF (10), VT (11), FF (12), CR (13), and
1318  space (32). Notice that this list includes the VT character (code 11). This  space (32). "Space" used to be different to \es, which did not include VT, for
1319  makes "space" different to \es, which does not include VT (for Perl  Perl compatibility. However, Perl changed at release 5.18, and PCRE followed at
1320  compatibility).  release 8.34. "Space" and \es now match the same set of characters.
1321  .P  .P
1322  The name "word" is a Perl extension, and "blank" is a GNU extension from Perl  The name "word" is a Perl extension, and "blank" is a GNU extension from Perl
1323  5.8. Another Perl extension is negation, which is indicated by a ^ character  5.8. Another Perl extension is negation, which is indicated by a ^ character
# Line 1101  matches "1", "2", or any non-digit. PCRE Line 1329  matches "1", "2", or any non-digit. PCRE
1329  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
1330  supported, and an error is given if they are encountered.  supported, and an error is given if they are encountered.
1331  .P  .P
1332  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
1333  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
1334  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
1335  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 1400  extracts it into the global options (and
1400  extracted by the \fBpcre_fullinfo()\fP function).  extracted by the \fBpcre_fullinfo()\fP function).
1401  .P  .P
1402  An option change within a subpattern (see below for a description of  An option change within a subpattern (see below for a description of
1403  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
1404  .sp  .sp
1405    (a(?i)b)c    (a(?i)b)c
1406  .sp  .sp
# Line 1189  option settings happen at compile time. Line 1417  option settings happen at compile time.
1417  behaviour otherwise.  behaviour otherwise.
1418  .P  .P
1419  \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
1420  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
1421  pattern can contain special leading sequences such as (*CRLF) to override what  the pattern can contain special leading sequences such as (*CRLF) to override
1422  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
1423  section entitled  the section entitled
1424  .\" HTML <a href="#newlineseq">  .\" HTML <a href="#newlineseq">
1425  .\" </a>  .\" </a>
1426  "Newline sequences"  "Newline sequences"
1427  .\"  .\"
1428  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
1429  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
1430  PCRE_UTF8 and the PCRE_UCP options, respectively.  equivalent to setting the PCRE_UTF8, PCRE_UTF16, PCRE_UTF32 and the PCRE_UCP
1431    options, respectively. The (*UTF) sequence is a generic version that can be
1432    used with any of the libraries. However, the application can set the
1433    PCRE_NEVER_UTF option, which locks out the use of the (*UTF) sequences.
1434  .  .
1435  .  .
1436  .\" HTML <a name="subpattern"></a>  .\" HTML <a name="subpattern"></a>
# Line 1213  Turning part of a pattern into a subpatt Line 1444  Turning part of a pattern into a subpatt
1444  .sp  .sp
1445    cat(aract|erpillar|)    cat(aract|erpillar|)
1446  .sp  .sp
1447  matches one of the words "cat", "cataract", or "caterpillar". Without the  matches "cataract", "caterpillar", or "cat". Without the parentheses, it would
1448  parentheses, it would match "cataract", "erpillar" or an empty string.  match "cataract", "erpillar" or an empty string.
1449  .sp  .sp
1450  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
1451  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
1452  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
1453  \fBpcre_exec()\fP. Opening parentheses are counted from left to right (starting  matching function. (This applies only to the traditional matching functions;
1454  from 1) to obtain numbers for the capturing subpatterns.  the DFA matching functions do not support capturing.)
1455  .P  .P
1456  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
1457    numbers for the capturing subpatterns. For example, if the string "the red
1458    king" is matched against the pattern
1459  .sp  .sp
1460    the ((red|white) (king|queen))    the ((red|white) (king|queen))
1461  .sp  .sp
# Line 1271  at captured substring number one, whiche Line 1504  at captured substring number one, whiche
1504  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
1505  alternatives. Inside a (?| group, parentheses are numbered as usual, but the  alternatives. Inside a (?| group, parentheses are numbered as usual, but the
1506  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
1507  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
1508  branch. The following example is taken from the Perl documentation.  any branch. The following example is taken from the Perl documentation. The
1509  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.  
1510  .sp  .sp
1511    # before  ---------------branch-reset----------- after    # before  ---------------branch-reset----------- after
1512    / ( 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 1518  or "defdef":
1518  .sp  .sp
1519    /(?|(abc)|(def))\e1/    /(?|(abc)|(def))\e1/
1520  .sp  .sp
1521  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
1522  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
1523  pattern matches "abcabc" or "defabc":  "abcabc" or "defabc":
1524  .sp  .sp
1525    /(?|(abc)|(def))(?1)/    /(?|(abc)|(def))(?1)/
1526  .sp  .sp
# Line 1364  for the first (and in this example, the Line 1596  for the first (and in this example, the
1596  matched. This saves searching to find which numbered subpattern it was.  matched. This saves searching to find which numbered subpattern it was.
1597  .P  .P
1598  If you make a back reference to a non-unique named subpattern from elsewhere in  If you make a back reference to a non-unique named subpattern from elsewhere in
1599  the pattern, the one that corresponds to the first occurrence of the name is  the pattern, the subpatterns to which the name refers are checked in the order
1600  used. In the absence of duplicate numbers (see the previous section) this is  in which they appear in the overall pattern. The first one that is set is used
1601  the one with the lowest number. If you use a named reference in a condition  for the reference. For example, this pattern matches both "foofoo" and
1602    "barbar" but not "foobar" or "barfoo":
1603    .sp
1604      (?:(?<n>foo)|(?<n>bar))\k<n>
1605    .sp
1606    .P
1607    If you make a subroutine call to a non-unique named subpattern, the one that
1608    corresponds to the first occurrence of the name is used. In the absence of
1609    duplicate numbers (see the previous section) this is the one with the lowest
1610    number.
1611    .P
1612    If you use a named reference in a condition
1613  test (see the  test (see the
1614  .\"  .\"
1615  .\" HTML <a href="#conditions">  .\" HTML <a href="#conditions">
# Line 1386  documentation. Line 1629  documentation.
1629  \fBWarning:\fP You cannot use different names to distinguish between two  \fBWarning:\fP You cannot use different names to distinguish between two
1630  subpatterns with the same number because PCRE uses only the numbers when  subpatterns with the same number because PCRE uses only the numbers when
1631  matching. For this reason, an error is given at compile time if different names  matching. For this reason, an error is given at compile time if different names
1632  are given to subpatterns with the same number. However, you can give the same  are given to subpatterns with the same number. However, you can always give the
1633  name to subpatterns with the same number, even when PCRE_DUPNAMES is not set.  same name to subpatterns with the same number, even when PCRE_DUPNAMES is not
1634    set.
1635  .  .
1636  .  .
1637  .SH REPETITION  .SH REPETITION
# Line 1399  items: Line 1643  items:
1643    a literal data character    a literal data character
1644    the dot metacharacter    the dot metacharacter
1645    the \eC escape sequence    the \eC escape sequence
1646    the \eX escape sequence (in UTF-8 mode with Unicode properties)    the \eX escape sequence
1647    the \eR escape sequence    the \eR escape sequence
1648    an escape such as \ed that matches a single character    an escape such as \ed or \epL that matches a single character
1649    a character class    a character class
1650    a back reference (see next section)    a back reference (see next section)
1651    a parenthesized subpattern (unless it is an assertion)    a parenthesized subpattern (including assertions)
1652    a recursive or "subroutine" call to a subpattern    a subroutine call to a subpattern (recursive or otherwise)
1653  .sp  .sp
1654  The general repetition quantifier specifies a minimum and maximum number of  The general repetition quantifier specifies a minimum and maximum number of
1655  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 1674  where a quantifier is not allowed, or on
1674  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
1675  quantifier, but a literal string of four characters.  quantifier, but a literal string of four characters.
1676  .P  .P
1677  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
1678  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
1679  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,
1680  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
1681  which may be several bytes long (and they may be of different lengths).  several data units long (and they may be of different lengths).
1682  .P  .P
1683  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
1684  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 1687  subpatterns that are referenced as
1687  .\" </a>  .\" </a>
1688  subroutines  subroutines
1689  .\"  .\"
1690  from elsewhere in the pattern. Items other than subpatterns that have a {0}  from elsewhere in the pattern (but see also the section entitled
1691  quantifier are omitted from the compiled pattern.  .\" HTML <a href="#subdefine">
1692    .\" </a>
1693    "Defining subpatterns for use by reference only"
1694    .\"
1695    below). Items other than subpatterns that have a {0} quantifier are omitted
1696    from the compiled pattern.
1697  .P  .P
1698  For convenience, the three most common quantifiers have single-character  For convenience, the three most common quantifiers have single-character
1699  abbreviations:  abbreviations:
# Line 1515  In cases where it is known that the subj Line 1764  In cases where it is known that the subj
1764  worth setting PCRE_DOTALL in order to obtain this optimization, or  worth setting PCRE_DOTALL in order to obtain this optimization, or
1765  alternatively using ^ to indicate anchoring explicitly.  alternatively using ^ to indicate anchoring explicitly.
1766  .P  .P
1767  However, there is one situation where the optimization cannot be used. When .*  However, there are some cases where the optimization cannot be used. When .*
1768  is inside capturing parentheses that are the subject of a back reference  is inside capturing parentheses that are the subject of a back reference
1769  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
1770  succeeds. Consider, for example:  succeeds. Consider, for example:
# Line 1525  succeeds. Consider, for example: Line 1774  succeeds. Consider, for example:
1774  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
1775  this reason, such a pattern is not implicitly anchored.  this reason, such a pattern is not implicitly anchored.
1776  .P  .P
1777    Another case where implicit anchoring is not applied is when the leading .* is
1778    inside an atomic group. Once again, a match at the start may fail where a later
1779    one succeeds. Consider this pattern:
1780    .sp
1781      (?>.*?a)b
1782    .sp
1783    It matches "ab" in the subject "aab". The use of the backtracking control verbs
1784    (*PRUNE) and (*SKIP) also disable this optimization.
1785    .P
1786  When a capturing subpattern is repeated, the value captured is the substring  When a capturing subpattern is repeated, the value captured is the substring
1787  that matched the final iteration. For example, after  that matched the final iteration. For example, after
1788  .sp  .sp
# Line 1669  no such problem when named parentheses a Line 1927  no such problem when named parentheses a
1927  subpattern is possible using named parentheses (see below).  subpattern is possible using named parentheses (see below).
1928  .P  .P
1929  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
1930  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
1931  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
1932  number, optionally enclosed in braces. These examples are all identical:  examples are all identical:
1933  .sp  .sp
1934    (ring), \e1    (ring), \e1
1935    (ring), \eg1    (ring), \eg1
# Line 1685  example: Line 1943  example:
1943    (abc(def)ghi)\eg{-1}    (abc(def)ghi)\eg{-1}
1944  .sp  .sp
1945  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
1946  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.
1947  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
1948  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
1949  fragments that contain references within themselves.  joining together fragments that contain references within themselves.
1950  .P  .P
1951  A back reference matches whatever actually matched the capturing subpattern in  A back reference matches whatever actually matched the capturing subpattern in
1952  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 1997  Because there may be many capturing pare
1997  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.
1998  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
1999  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
2000  whitespace. Otherwise, the \eg{ syntax or an empty comment (see  white space. Otherwise, the \eg{ syntax or an empty comment (see
2001  .\" HTML <a href="#comments">  .\" HTML <a href="#comments">
2002  .\" </a>  .\" </a>
2003  "Comments"  "Comments"
# Line 1790  those that look ahead of the current pos Line 2048  those that look ahead of the current pos
2048  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,
2049  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.
2050  .P  .P
2051  Assertion subpatterns are not capturing subpatterns, and may not be repeated,  Assertion subpatterns are not capturing subpatterns. If such an assertion
2052  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
2053  of assertion contains capturing subpatterns within it, these are counted for  numbering the capturing subpatterns in the whole pattern. However, substring
2054  the purposes of numbering the capturing subpatterns in the whole pattern.  capturing is carried out only for positive assertions. (Perl sometimes, but not
2055  However, substring capturing is carried out only for positive assertions,  always, does do capturing in negative assertions.)
2056  because it does not make sense for negative assertions.  .P
2057    For compatibility with Perl, assertion subpatterns may be repeated; though
2058    it makes no sense to assert the same thing several times, the side effect of
2059    capturing parentheses may occasionally be useful. In practice, there only three
2060    cases:
2061    .sp
2062    (1) If the quantifier is {0}, the assertion is never obeyed during matching.
2063    However, it may contain internal capturing parenthesized groups that are called
2064    from elsewhere via the
2065    .\" HTML <a href="#subpatternsassubroutines">
2066    .\" </a>
2067    subroutine mechanism.
2068    .\"
2069    .sp
2070    (2) If quantifier is {0,n} where n is greater than zero, it is treated as if it
2071    were {0,1}. At run time, the rest of the pattern match is tried with and
2072    without the assertion, the order depending on the greediness of the quantifier.
2073    .sp
2074    (3) If the minimum repetition is greater than zero, the quantifier is ignored.
2075    The assertion is obeyed just once when encountered during matching.
2076  .  .
2077  .  .
2078  .SS "Lookahead assertions"  .SS "Lookahead assertions"
# Line 1824  lookbehind assertion is needed to achiev Line 2101  lookbehind assertion is needed to achiev
2101  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
2102  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
2103  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.
2104  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 (?!).  
2105  .  .
2106  .  .
2107  .\" HTML <a name="lookbehind"></a>  .\" HTML <a name="lookbehind"></a>
# Line 1850  is permitted, but Line 2126  is permitted, but
2126  .sp  .sp
2127  causes an error at compile time. Branches that match different length strings  causes an error at compile time. Branches that match different length strings
2128  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
2129  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
2130  match the same length of string. An assertion such as  length of string. An assertion such as
2131  .sp  .sp
2132    (?<=ab(c|de))    (?<=ab(c|de))
2133  .sp  .sp
# Line 1861  branches: Line 2137  branches:
2137  .sp  .sp
2138    (?<=abc|abde)    (?<=abc|abde)
2139  .sp  .sp
2140  In some cases, the Perl 5.10 escape sequence \eK  In some cases, the escape sequence \eK
2141  .\" HTML <a href="#resetmatchstart">  .\" HTML <a href="#resetmatchstart">
2142  .\" </a>  .\" </a>
2143  (see above)  (see above)
# Line 1874  temporarily move the current position ba Line 2150  temporarily move the current position ba
2150  match. If there are insufficient characters before the current position, the  match. If there are insufficient characters before the current position, the
2151  assertion fails.  assertion fails.
2152  .P  .P
2153  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
2154  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
2155  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
2156  different numbers of bytes, are also not permitted.  escapes, which can match different numbers of data units, are also not
2157    permitted.
2158  .P  .P
2159  .\" HTML <a href="#subpatternsassubroutines">  .\" HTML <a href="#subpatternsassubroutines">
2160  .\" </a>  .\" </a>
# Line 1965  already been matched. The two possible f Line 2242  already been matched. The two possible f
2242  .sp  .sp
2243  If the condition is satisfied, the yes-pattern is used; otherwise the  If the condition is satisfied, the yes-pattern is used; otherwise the
2244  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
2245  subpattern, a compile-time error occurs.  subpattern, a compile-time error occurs. Each of the two alternatives may
2246    itself contain nested subpatterns of any form, including conditional
2247    subpatterns; the restriction to two alternatives applies only at the level of
2248    the condition. This pattern fragment is an example where the alternatives are
2249    complex:
2250    .sp
2251      (?(1) (A|B|C) | (D | (?(2)E|F) | E) )
2252    .sp
2253  .P  .P
2254  There are four kinds of condition: references to subpatterns, references to  There are four kinds of condition: references to subpatterns, references to
2255  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 2266  matched. If there is more than one captu
2266  .\" </a>  .\" </a>
2267  section about duplicate subpattern numbers),  section about duplicate subpattern numbers),
2268  .\"  .\"
2269  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
2270  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
2271  number is relative rather than absolute. The most recently opened parentheses  number is relative rather than absolute. The most recently opened parentheses
2272  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
2273  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
2274  constructs such as (?(+2).  parentheses to be opened can be referenced as (?(+1), and so on. (The value
2275    zero in any of these forms is not used; it provokes a compile-time error.)
2276  .P  .P
2277  Consider the following pattern, which contains non-significant white space to  Consider the following pattern, which contains non-significant white space to
2278  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 2283  three parts for ease of discussion:
2283  The first part matches an optional opening parenthesis, and if that  The first part matches an optional opening parenthesis, and if that
2284  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
2285  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
2286  conditional subpattern that tests whether the first set of parentheses matched  conditional subpattern that tests whether or not the first set of parentheses
2287  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,
2288  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
2289  parenthesis is required. Otherwise, since no-pattern is not present, the  parenthesis is required. Otherwise, since no-pattern is not present, the
2290  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 2340  The syntax for recursive patterns
2340  .\"  .\"
2341  is described below.  is described below.
2342  .  .
2343    .\" HTML <a name="subdefine"></a>
2344  .SS "Defining subpatterns for use by reference only"  .SS "Defining subpatterns for use by reference only"
2345  .rs  .rs
2346  .sp  .sp
# Line 2062  If the condition is the string (DEFINE), Line 2348  If the condition is the string (DEFINE),
2348  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
2349  alternative in the subpattern. It is always skipped if control reaches this  alternative in the subpattern. It is always skipped if control reaches this
2350  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
2351  "subroutines" that can be referenced from elsewhere. (The use of  subroutines that can be referenced from elsewhere. (The use of
2352  .\" HTML <a href="#subpatternsassubroutines">  .\" HTML <a href="#subpatternsassubroutines">
2353  .\" </a>  .\" </a>
2354  "subroutines"  subroutines
2355  .\"  .\"
2356  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
2357  written like this (ignore whitespace and line breaks):  "192.168.23.245" could be written like this (ignore white space and line
2358    breaks):
2359  .sp  .sp
2360    (?(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) )
2361    \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 2390  dd-aaa-dd or dd-dd-dd, where aaa are let
2390  .SH COMMENTS  .SH COMMENTS
2391  .rs  .rs
2392  .sp  .sp
2393  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
2394  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,
2395  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
2396    subpattern name or number. The characters that make up a comment play no part
2397    in the pattern matching.
2398  .P  .P
2399  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
2400  character class introduces a comment that continues to immediately after the  closing parenthesis. Nested parentheses are not permitted. If the PCRE_EXTENDED
2401  next newline in the pattern.  option is set, an unescaped # character also introduces a comment, which in
2402    this case continues to immediately after the next newline character or
2403    character sequence in the pattern. Which characters are interpreted as newlines
2404    is controlled by the options passed to a compiling function or by a special
2405    sequence at the start of the pattern, as described in the section entitled
2406    .\" HTML <a href="#newlines">
2407    .\" </a>
2408    "Newline conventions"
2409    .\"
2410    above. Note that the end of this type of comment is a literal newline sequence
2411    in the pattern; escape sequences that happen to represent a newline do not
2412    count. For example, consider this pattern when PCRE_EXTENDED is set, and the
2413    default newline convention is in force:
2414    .sp
2415      abc #comment \en still comment
2416    .sp
2417    On encountering the # character, \fBpcre_compile()\fP skips along, looking for
2418    a newline in the pattern. The sequence \en is still literal at this stage, so
2419    it does not terminate the comment. Only an actual character with the code value
2420    0x0a (the default newline) does so.
2421  .  .
2422  .  .
2423  .\" HTML <a name="recursion"></a>  .\" HTML <a name="recursion"></a>
# Line 2138  individual subpattern recursion. After i Line 2446  individual subpattern recursion. After i
2446  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.
2447  .P  .P
2448  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
2449  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
2450  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
2451  .\" HTML <a href="#subpatternsassubroutines">  .\" HTML <a href="#subpatternsassubroutines">
2452  .\" </a>  .\" </a>
2453  "subroutine"  non-recursive subroutine
2454  .\"  .\"
2455  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
2456  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 2475  We have put the pattern into parentheses
2475  them instead of the whole pattern.  them instead of the whole pattern.
2476  .P  .P
2477  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
2478  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
2479  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
2480  most recently opened parentheses preceding the recursion. In other words, a  parentheses preceding the recursion. In other words, a negative number counts
2481  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.  
2482  .P  .P
2483  It is also possible to refer to subsequently opened parentheses, by writing  It is also possible to refer to subsequently opened parentheses, by writing
2484  references such as (?+2). However, these cannot be recursive because the  references such as (?+2). However, these cannot be recursive because the
2485  reference is not inside the parentheses that are referenced. They are always  reference is not inside the parentheses that are referenced. They are always
2486  .\" HTML <a href="#subpatternsassubroutines">  .\" HTML <a href="#subpatternsassubroutines">
2487  .\" </a>  .\" </a>
2488  "subroutine"  non-recursive subroutine
2489  .\"  .\"
2490  calls, as described in the next section.  calls, as described in the next section.
2491  .P  .P
# Line 2215  documentation). If the pattern above is Line 2522  documentation). If the pattern above is
2522  .sp  .sp
2523  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
2524  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
2525  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
2526  set at a deeper level.  (temporarily) set at a deeper level during the matching process.
2527  .P  .P
2528  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
2529  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 2543  is the actual recursive call.
2543  .  .
2544  .  .
2545  .\" HTML <a name="recursiondifference"></a>  .\" HTML <a name="recursiondifference"></a>
2546  .SS "Recursion difference from Perl"  .SS "Differences in recursion processing between PCRE and Perl"
2547  .rs  .rs
2548  .sp  .sp
2549  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
2550  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
2551  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
2552  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
2553  following pattern, which purports to match a palindromic string that contains  subsequent matching failure. This can be illustrated by the following pattern,
2554  an odd number of characters (for example, "a", "aba", "abcba", "abcdcba"):  which purports to match a palindromic string that contains an odd number of
2555    characters (for example, "a", "aba", "abcba", "abcdcba"):
2556  .sp  .sp
2557    ^(.|(.)(?1)\e2)$    ^(.|(.)(?1)\e2)$
2558  .sp  .sp
# Line 2274  time we do have another alternative to t Line 2582  time we do have another alternative to t
2582  difference: in the previous case the remaining alternative is at a deeper  difference: in the previous case the remaining alternative is at a deeper
2583  recursion level, which PCRE cannot use.  recursion level, which PCRE cannot use.
2584  .P  .P
2585  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
2586  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
2587    this:
2588  .sp  .sp
2589    ^((.)(?1)\e2|.?)$    ^((.)(?1)\e2|.?)$
2590  .sp  .sp
# Line 2304  For example, although "abcba" is correct Line 2613  For example, although "abcba" is correct
2613  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
2614  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
2615  recursion to try other alternatives, so the entire match fails.  recursion to try other alternatives, so the entire match fails.
2616    .P
2617    The second way in which PCRE and Perl differ in their recursion processing is
2618    in the handling of captured values. In Perl, when a subpattern is called
2619    recursively or as a subpattern (see the next section), it has no access to any
2620    values that were captured outside the recursion, whereas in PCRE these values
2621    can be referenced. Consider this pattern:
2622    .sp
2623      ^(.)(\e1|a(?2))
2624    .sp
2625    In PCRE, this pattern matches "bab". The first capturing parentheses match "b",
2626    then in the second group, when the back reference \e1 fails to match "b", the
2627    second alternative matches "a" and then recurses. In the recursion, \e1 does
2628    now match "b" and so the whole match succeeds. In Perl, the pattern fails to
2629    match because inside the recursive call \e1 cannot access the externally set
2630    value.
2631  .  .
2632  .  .
2633  .\" HTML <a name="subpatternsassubroutines"></a>  .\" HTML <a name="subpatternsassubroutines"></a>
2634  .SH "SUBPATTERNS AS SUBROUTINES"  .SH "SUBPATTERNS AS SUBROUTINES"
2635  .rs  .rs
2636  .sp  .sp
2637  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
2638  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
2639  subroutine in a programming language. The "called" subpattern may be defined  subroutine in a programming language. The called subpattern may be defined
2640  before or after the reference. A numbered reference can be absolute or  before or after the reference. A numbered reference can be absolute or
2641  relative, as in these examples:  relative, as in these examples:
2642  .sp  .sp
# Line 2332  matches "sense and sensibility" and "res Line 2656  matches "sense and sensibility" and "res
2656  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
2657  strings. Another example is given in the discussion of DEFINE above.  strings. Another example is given in the discussion of DEFINE above.
2658  .P  .P
2659  Like recursive subpatterns, a subroutine call is always treated as an atomic  All subroutine calls, whether recursive or not, are always treated as atomic
2660  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
2661  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
2662  matching failure. Any capturing parentheses that are set during the subroutine  subsequent matching failure. Any capturing parentheses that are set during the
2663  call revert to their previous values afterwards.  subroutine call revert to their previous values afterwards.
2664  .P  .P
2665  When a subpattern is used as a subroutine, processing options such as  Processing options such as case-independence are fixed when a subpattern is
2666  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
2667  changed for different calls. For example, consider this pattern:  different calls. For example, consider this pattern:
2668  .sp  .sp
2669    (abc)(?i:(?-1))    (abc)(?i:(?-1))
2670  .sp  .sp
# Line 2379  same pair of parentheses when there is a Line 2703  same pair of parentheses when there is a
2703  .P  .P
2704  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
2705  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
2706  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
2707    (8-bit library) or \fIpcre[16|32]_callout\fP (16-bit or 32-bit library).
2708  By default, this variable contains NULL, which disables all calling out.  By default, this variable contains NULL, which disables all calling out.
2709  .P  .P
2710  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 2714  For example, this pattern has two callou
2714  .sp  .sp
2715    (?C1)abc(?C2)def    (?C1)abc(?C2)def
2716  .sp  .sp
2717  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
2718  automatically installed before each item in the pattern. They are all numbered  automatically installed before each item in the pattern. They are all numbered
2719  255.  255. If there is a conditional group in the pattern whose condition is an
2720  .P  assertion, an additional callout is inserted just before the condition. An
2721  During matching, when PCRE reaches a callout point (and \fIpcre_callout\fP is  explicit callout may also be set at this position, as in this example:
2722  set), the external function is called. It is provided with the number of the  .sp
2723  callout, the position in the pattern, and, optionally, one item of data    (?(?C9)(?=a)abc|def)
2724  originally supplied by the caller of \fBpcre_exec()\fP. The callout function  .sp
2725  may cause matching to proceed, to backtrack, or to fail altogether. A complete  Note that this applies only to assertion conditions, not to other types of
2726  description of the interface to the callout function is given in the  condition.
2727    .P
2728    During matching, when PCRE reaches a callout point, the external function is
2729    called. It is provided with the number of the callout, the position in the
2730    pattern, and, optionally, one item of data originally supplied by the caller of
2731    the matching function. The callout function may cause matching to proceed, to
2732    backtrack, or to fail altogether. A complete description of the interface to
2733    the callout function is given in the
2734  .\" HREF  .\" HREF
2735  \fBpcrecallout\fP  \fBpcrecallout\fP
2736  .\"  .\"
# Line 2410  documentation. Line 2742  documentation.
2742  .rs  .rs
2743  .sp  .sp
2744  Perl 5.10 introduced a number of "Special Backtracking Control Verbs", which  Perl 5.10 introduced a number of "Special Backtracking Control Verbs", which
2745  are described in the Perl documentation as "experimental and subject to change  are still described in the Perl documentation as "experimental and subject to
2746  or removal in a future version of Perl". It goes on to say: "Their usage in  change or removal in a future version of Perl". It goes on to say: "Their usage
2747  production code should be noted to avoid problems during upgrades." The same  in production code should be noted to avoid problems during upgrades." The same
2748  remarks apply to the PCRE features described in this section.  remarks apply to the PCRE features described in this section.
2749  .P  .P
 Since these verbs are specifically related to backtracking, most of them can be  
 used only when the pattern is to be matched using \fBpcre_exec()\fP, which uses  
 a backtracking algorithm. With the exception of (*FAIL), which behaves like a  
 failing negative assertion, they cause an error if encountered by  
 \fBpcre_dfa_exec()\fP.  
 .P  
 If any of these verbs are used in an assertion or subroutine subpattern  
 (including recursive subpatterns), their effect is confined to that subpattern;  
 it does not extend to the surrounding pattern. Note that such subpatterns are  
 processed as anchored at the point where they are tested.  
 .P  
2750  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
2751  parenthesis followed by an asterisk. They are generally of the form  parenthesis followed by an asterisk. They are generally of the form
2752  (*VERB) or (*VERB:NAME). Some may take either form, with differing behaviour,  (*VERB) or (*VERB:NAME). Some may take either form, possibly behaving
2753  depending on whether or not an argument is present. An name is a sequence of  differently depending on whether or not a name is present. A name is any
2754  letters, digits, and underscores. If the name is empty, that is, if the closing  sequence of characters that does not include a closing parenthesis. The maximum
2755  parenthesis immediately follows the colon, the effect is as if the colon were  length of name is 255 in the 8-bit library and 65535 in the 16-bit and 32-bit
2756  not there. Any number of these verbs may occur in a pattern.  libraries. If the name is empty, that is, if the closing parenthesis
2757    immediately follows the colon, the effect is as if the colon were not there.
2758    Any number of these verbs may occur in a pattern.
2759  .P  .P
2760    Since these verbs are specifically related to backtracking, most of them can be
2761    used only when the pattern is to be matched using one of the traditional
2762    matching functions, because these use a backtracking algorithm. With the
2763    exception of (*FAIL), which behaves like a failing negative assertion, the
2764    backtracking control verbs cause an error if encountered by a DFA matching
2765    function.
2766    .P
2767    The behaviour of these verbs in
2768    .\" HTML <a href="#btrepeat">
2769    .\" </a>
2770    repeated groups,
2771    .\"
2772    .\" HTML <a href="#btassert">
2773    .\" </a>
2774    assertions,
2775    .\"
2776    and in
2777    .\" HTML <a href="#btsub">
2778    .\" </a>
2779    subpatterns called as subroutines
2780    .\"
2781    (whether or not recursively) is documented below.
2782    .
2783    .
2784    .\" HTML <a name="nooptimize"></a>
2785    .SS "Optimizations that affect backtracking verbs"
2786    .rs
2787    .sp
2788  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
2789  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
2790  minimum length of matching subject, or that a particular character must be  minimum length of matching subject, or that a particular character must be
2791  present. When one of these optimizations suppresses the running of a match, any  present. When one of these optimizations bypasses the running of a match, any
2792  included backtracking verbs will not, of course, be processed. You can suppress  included backtracking verbs will not, of course, be processed. You can suppress
2793  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
2794  when calling \fBpcre_exec()\fP.  when calling \fBpcre_compile()\fP or \fBpcre_exec()\fP, or by starting the
2795    pattern with (*NO_START_OPT). There is more discussion of this option in the
2796    section entitled
2797    .\" HTML <a href="pcreapi.html#execoptions">
2798    .\" </a>
2799    "Option bits for \fBpcre_exec()\fP"
2800    .\"
2801    in the
2802    .\" HREF
2803    \fBpcreapi\fP
2804    .\"
2805    documentation.
2806    .P
2807    Experiments with Perl suggest that it too has similar optimizations, sometimes
2808    leading to anomalous results.
2809  .  .
2810  .  .
2811  .SS "Verbs that act immediately"  .SS "Verbs that act immediately"
# Line 2452  followed by a name. Line 2817  followed by a name.
2817     (*ACCEPT)     (*ACCEPT)
2818  .sp  .sp
2819  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
2820  pattern. When inside a recursion, only the innermost pattern is ended  pattern. However, when it is inside a subpattern that is called as a
2821  immediately. If (*ACCEPT) is inside capturing parentheses, the data so far is  subroutine, only that subpattern is ended successfully. Matching then continues
2822  captured. (This feature was added to PCRE at release 8.00.) For example:  at the outer level. If (*ACCEPT) in triggered in a positive assertion, the
2823    assertion succeeds; in a negative assertion, the assertion fails.
2824    .P
2825    If (*ACCEPT) is inside capturing parentheses, the data so far is captured. For
2826    example:
2827  .sp  .sp
2828    A((?:A|B(*ACCEPT)|C)D)    A((?:A|B(*ACCEPT)|C)D)
2829  .sp  .sp
# Line 2463  the outer parentheses. Line 2832  the outer parentheses.
2832  .sp  .sp
2833    (*FAIL) or (*F)    (*FAIL) or (*F)
2834  .sp  .sp
2835  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
2836  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
2837  probably useful only when combined with (?{}) or (??{}). Those are, of course,  probably useful only when combined with (?{}) or (??{}). Those are, of course,
2838  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 2856  starting point (see (*SKIP) below).
2856  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
2857  (*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.
2858  .P  .P
2859  When a match succeeds, the name of the last-encountered (*MARK) is passed back  When a match succeeds, the name of the last-encountered (*MARK:NAME),
2860  to the caller via the \fIpcre_extra\fP data structure, as described in the  (*PRUNE:NAME), or (*THEN:NAME) on the matching path is passed back to the
2861    caller as described in the section entitled
2862  .\" HTML <a href="pcreapi.html#extradata">  .\" HTML <a href="pcreapi.html#extradata">
2863  .\" </a>  .\" </a>
2864  section on \fIpcre_extra\fP  "Extra data for \fBpcre_exec()\fP"
2865  .\"  .\"
2866  in the  in the
2867  .\" HREF  .\" HREF
2868  \fBpcreapi\fP  \fBpcreapi\fP
2869  .\"  .\"
2870  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
2871  \fBpcretest\fP output, where the /K modifier requests the retrieval and  modifier requests the retrieval and outputting of (*MARK) data:
 outputting of (*MARK) data:  
2872  .sp  .sp
2873    /X(*MARK:A)Y|X(*MARK:B)Z/K      re> /X(*MARK:A)Y|X(*MARK:B)Z/K
2874    XY    data> XY
2875     0: XY     0: XY
2876    MK: A    MK: A
2877    XZ    XZ
# Line 2514  indicates which of the two alternatives Line 2883  indicates which of the two alternatives
2883  of obtaining this information than putting each alternative in its own  of obtaining this information than putting each alternative in its own
2884  capturing parentheses.  capturing parentheses.
2885  .P  .P
2886  A name may also be returned after a failed match if the final path through the  If a verb with a name is encountered in a positive assertion that is true, the
2887  pattern involves (*MARK). However, unless (*MARK) used in conjunction with  name is recorded and passed back if it is the last-encountered. This does not
2888  (*COMMIT), this is unlikely to happen for an unanchored pattern because, as the  happen for negative assertions or failing positive assertions.
2889  starting point for matching is advanced, the final check is often with an empty  .P
2890  string, causing a failure before (*MARK) is reached. For example:  After a partial match or a failed match, the last encountered name in the
2891  .sp  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:  
2892  .sp  .sp
2893    /^X(*MARK:A)Y|^X(*MARK:B)Z/K      re> /X(*MARK:A)Y|X(*MARK:B)Z/K
2894    XP    data> XP
2895    No match, mark = B    No match, mark = B
2896  .sp  .sp
2897  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
2898  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
2899  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
2900  .P  (*MARK) item, but nevertheless do not reset it.
2901  Note that similar anomalies (though different in detail) exist in Perl, no  .P
2902  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
2903  unanchored pattern is not recommended, unless (*COMMIT) is involved.  probably set the PCRE_NO_START_OPTIMIZE option
2904    .\" HTML <a href="#nooptimize">
2905    .\" </a>
2906    (see above)
2907    .\"
2908    to ensure that the match is always attempted.
2909  .  .
2910  .  .
2911  .SS "Verbs that act after backtracking"  .SS "Verbs that act after backtracking"
# Line 2547  unanchored pattern is not recommended, u Line 2914  unanchored pattern is not recommended, u
2914  The following verbs do nothing when they are encountered. Matching continues  The following verbs do nothing when they are encountered. Matching continues
2915  with what follows, but if there is no subsequent match, causing a backtrack to  with what follows, but if there is no subsequent match, causing a backtrack to
2916  the verb, a failure is forced. That is, backtracking cannot pass to the left of  the verb, a failure is forced. That is, backtracking cannot pass to the left of
2917  the verb. However, when one of these verbs appears inside an atomic group, its  the verb. However, when one of these verbs appears inside an atomic group or an
2918  effect is confined to that group, because once the group has been matched,  assertion that is true, its effect is confined to that group, because once the
2919  there is never any backtracking into it. In this situation, backtracking can  group has been matched, there is never any backtracking into it. In this
2920  "jump back" to the left of the entire atomic group. (Remember also, as stated  situation, backtracking can "jump back" to the left of the entire atomic group
2921  above, that this localization also applies in subroutine calls and assertions.)  or assertion. (Remember also, as stated above, that this localization also
2922    applies in subroutine calls.)
2923  .P  .P
2924  These verbs differ in exactly what kind of failure occurs when backtracking  These verbs differ in exactly what kind of failure occurs when backtracking
2925  reaches them.  reaches them. The behaviour described below is what happens when the verb is
2926    not in a subroutine or an assertion. Subsequent sections cover these special
2927    cases.
2928  .sp  .sp
2929    (*COMMIT)    (*COMMIT)
2930  .sp  .sp
2931  This verb, which may not be followed by a name, causes the whole match to fail  This verb, which may not be followed by a name, causes the whole match to fail
2932  outright if the rest of the pattern does not match. Even if the pattern is  outright if there is a later matching failure that causes backtracking to reach
2933  unanchored, no further attempts to find a match by advancing the starting point  it. Even if the pattern is unanchored, no further attempts to find a match by
2934  take place. Once (*COMMIT) has been passed, \fBpcre_exec()\fP is committed to  advancing the starting point take place. If (*COMMIT) is the only backtracking
2935  finding a match at the current starting point, or not at all. For example:  verb that is encountered, once it has been passed \fBpcre_exec()\fP is
2936    committed to finding a match at the current starting point, or not at all. For
2937    example:
2938  .sp  .sp
2939    a+(*COMMIT)b    a+(*COMMIT)b
2940  .sp  .sp
# Line 2571  dynamic anchor, or "I've started, so I m Line 2943  dynamic anchor, or "I've started, so I m
2943  recently passed (*MARK) in the path is passed back when (*COMMIT) forces a  recently passed (*MARK) in the path is passed back when (*COMMIT) forces a
2944  match failure.  match failure.
2945  .P  .P
2946    If there is more than one backtracking verb in a pattern, a different one that
2947    follows (*COMMIT) may be triggered first, so merely passing (*COMMIT) during a
2948    match does not always guarantee that a match must be at this starting point.
2949    .P
2950  Note that (*COMMIT) at the start of a pattern is not the same as an anchor,  Note that (*COMMIT) at the start of a pattern is not the same as an anchor,
2951  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
2952  \fBpcretest\fP example:  \fBpcretest\fP example:
2953  .sp  .sp
2954    /(*COMMIT)abc/      re> /(*COMMIT)abc/
2955    xyzabc    data> xyzabc
2956     0: abc     0: abc
2957    xyzabc\eY    xyzabc\eY
2958    No match    No match
# Line 2590  starting points. Line 2966  starting points.
2966    (*PRUNE) or (*PRUNE:NAME)    (*PRUNE) or (*PRUNE:NAME)
2967  .sp  .sp
2968  This verb causes the match to fail at the current starting position in the  This verb causes the match to fail at the current starting position in the
2969  subject if the rest of the pattern does not match. If the pattern is  subject if there is a later matching failure that causes backtracking to reach
2970  unanchored, the normal "bumpalong" advance to the next starting character then  it. If the pattern is unanchored, the normal "bumpalong" advance to the next
2971  happens. Backtracking can occur as usual to the left of (*PRUNE), before it is  starting character then happens. Backtracking can occur as usual to the left of
2972  reached, or when matching to the right of (*PRUNE), but if there is no match to  (*PRUNE), before it is reached, or when matching to the right of (*PRUNE), but
2973  the right, backtracking cannot cross (*PRUNE). In simple cases, the use of  if there is no match to the right, backtracking cannot cross (*PRUNE). In
2974  (*PRUNE) is just an alternative to an atomic group or possessive quantifier,  simple cases, the use of (*PRUNE) is just an alternative to an atomic group or
2975  but there are some uses of (*PRUNE) that cannot be expressed in any other way.  possessive quantifier, but there are some uses of (*PRUNE) that cannot be
2976  The behaviour of (*PRUNE:NAME) is the same as (*MARK:NAME)(*PRUNE) when the  expressed in any other way. In an anchored pattern (*PRUNE) has the same effect
2977  match fails completely; the name is passed back if this is the final attempt.  as (*COMMIT).
2978  (*PRUNE:NAME) does not pass back a name if the match succeeds. In an anchored  .P
2979  pattern (*PRUNE) has the same effect as (*COMMIT).  The behaviour of (*PRUNE:NAME) is the not the same as (*MARK:NAME)(*PRUNE).
2980    It is like (*MARK:NAME) in that the name is remembered for passing back to the
2981    caller. However, (*SKIP:NAME) searches only for names set with (*MARK).
2982  .sp  .sp
2983    (*SKIP)    (*SKIP)
2984  .sp  .sp
# Line 2621  instead of skipping on to "c". Line 2999  instead of skipping on to "c".
2999  .sp  .sp
3000    (*SKIP:NAME)    (*SKIP:NAME)
3001  .sp  .sp
3002  When (*SKIP) has an associated name, its behaviour is modified. If the  When (*SKIP) has an associated name, its behaviour is modified. When it is
3003  following pattern fails to match, the previous path through the pattern is  triggered, the previous path through the pattern is searched for the most
3004  searched for the most recent (*MARK) that has the same name. If one is found,  recent (*MARK) that has the same name. If one is found, the "bumpalong" advance
3005  the "bumpalong" advance is to the subject position that corresponds to that  is to the subject position that corresponds to that (*MARK) instead of to where
3006  (*MARK) instead of to where (*SKIP) was encountered. If no (*MARK) with a  (*SKIP) was encountered. If no (*MARK) with a matching name is found, the
3007  matching name is found, normal "bumpalong" of one character happens (the  (*SKIP) is ignored.
3008  (*SKIP) is ignored).  .P
3009    Note that (*SKIP:NAME) searches only for names set by (*MARK:NAME). It ignores
3010    names that are set by (*PRUNE:NAME) or (*THEN:NAME).
3011  .sp  .sp
3012    (*THEN) or (*THEN:NAME)    (*THEN) or (*THEN:NAME)
3013  .sp  .sp
3014  This verb causes a skip to the next alternation in the innermost enclosing  This verb causes a skip to the next innermost alternative when backtracking
3015  group if the rest of the pattern does not match. That is, it cancels pending  reaches it. That is, it cancels any further backtracking within the current
3016  backtracking, but only within the current alternation. Its name comes from the  alternative. Its name comes from the observation that it can be used for a
3017  observation that it can be used for a pattern-based if-then-else block:  pattern-based if-then-else block:
3018  .sp  .sp
3019    ( COND1 (*THEN) FOO | COND2 (*THEN) BAR | COND3 (*THEN) BAZ ) ...    ( COND1 (*THEN) FOO | COND2 (*THEN) BAR | COND3 (*THEN) BAZ ) ...
3020  .sp  .sp
3021  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
3022  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
3023  second alternative and tries COND2, without backtracking into COND1. The  second alternative and tries COND2, without backtracking into COND1. If that
3024  behaviour of (*THEN:NAME) is exactly the same as (*MARK:NAME)(*THEN) if the  succeeds and BAR fails, COND3 is tried. If subsequently BAZ fails, there are no
3025  overall match fails. If (*THEN) is not directly inside an alternation, it acts  more alternatives, so there is a backtrack to whatever came before the entire
3026  like (*PRUNE).  group. If (*THEN) is not inside an alternation, it acts like (*PRUNE).
3027  .  .P
3028  .P  The behaviour of (*THEN:NAME) is the not the same as (*MARK:NAME)(*THEN).
3029  The above verbs provide four different "strengths" of control when subsequent  It is like (*MARK:NAME) in that the name is remembered for passing back to the
3030  matching fails. (*THEN) is the weakest, carrying on the match at the next  caller. However, (*SKIP:NAME) searches only for names set with (*MARK).
3031  alternation. (*PRUNE) comes next, failing the match at the current starting  .P
3032  position, but allowing an advance to the next character (for an unanchored  A subpattern that does not contain a | character is just a part of the
3033  pattern). (*SKIP) is similar, except that the advance may be more than one  enclosing alternative; it is not a nested alternation with only one
3034  character. (*COMMIT) is the strongest, causing the entire match to fail.  alternative. The effect of (*THEN) extends beyond such a subpattern to the
3035  .P  enclosing alternative. Consider this pattern, where A, B, etc. are complex
3036  If more than one is present in a pattern, the "stongest" one wins. For example,  pattern fragments that do not contain any | characters at this level:
3037  consider this pattern, where A, B, etc. are complex pattern fragments:  .sp
3038  .sp    A (B(*THEN)C) | D
3039    (A(*COMMIT)B(*THEN)C|D)  .sp
3040  .sp  If A and B are matched, but there is a failure in C, matching does not
3041  Once A has matched, PCRE is committed to this match, at the current starting  backtrack into A; instead it moves to the next alternative, that is, D.
3042  position. If subsequently B matches, but C does not, the normal (*THEN) action  However, if the subpattern containing (*THEN) is given an alternative, it
3043  of trying the next alternation (that is, D) does not happen because (*COMMIT)  behaves differently:
3044  overrides.  .sp
3045      A (B(*THEN)C | (*FAIL)) | D
3046    .sp
3047    The effect of (*THEN) is now confined to the inner subpattern. After a failure
3048    in C, matching moves to (*FAIL), which causes the whole subpattern to fail
3049    because there are no more alternatives to try. In this case, matching does now
3050    backtrack into A.
3051    .P
3052    Note that a conditional subpattern is not considered as having two
3053    alternatives, because only one is ever used. In other words, the | character in
3054    a conditional subpattern has a different meaning. Ignoring white space,
3055    consider:
3056    .sp
3057      ^.*? (?(?=a) a | b(*THEN)c )
3058    .sp
3059    If the subject is "ba", this pattern does not match. Because .*? is ungreedy,
3060    it initially matches zero characters. The condition (?=a) then fails, the
3061    character "b" is matched, but "c" is not. At this point, matching does not
3062    backtrack to .*? as might perhaps be expected from the presence of the |
3063    character. The conditional subpattern is part of the single alternative that
3064    comprises the whole pattern, and so the match fails. (If there was a backtrack
3065    into .*?, allowing it to match "b", the match would succeed.)
3066    .P
3067    The verbs just described provide four different "strengths" of control when
3068    subsequent matching fails. (*THEN) is the weakest, carrying on the match at the
3069    next alternative. (*PRUNE) comes next, failing the match at the current
3070    starting position, but allowing an advance to the next character (for an
3071    unanchored pattern). (*SKIP) is similar, except that the advance may be more
3072    than one character. (*COMMIT) is the strongest, causing the entire match to
3073    fail.
3074    .
3075    .
3076    .SS "More than one backtracking verb"
3077    .rs
3078    .sp
3079    If more than one backtracking verb is present in a pattern, the one that is
3080    backtracked onto first acts. For example, consider this pattern, where A, B,
3081    etc. are complex pattern fragments:
3082    .sp
3083      (A(*COMMIT)B(*THEN)C|ABD)
3084    .sp
3085    If A matches but B fails, the backtrack to (*COMMIT) causes the entire match to
3086    fail. However, if A and B match, but C fails, the backtrack to (*THEN) causes
3087    the next alternative (ABD) to be tried. This behaviour is consistent, but is
3088    not always the same as Perl's. It means that if two or more backtracking verbs
3089    appear in succession, all the the last of them has no effect. Consider this
3090    example:
3091    .sp
3092      ...(*COMMIT)(*PRUNE)...
3093    .sp
3094    If there is a matching failure to the right, backtracking onto (*PRUNE) causes
3095    it to be triggered, and its action is taken. There can never be a backtrack
3096    onto (*COMMIT).
3097    .
3098    .
3099    .\" HTML <a name="btrepeat"></a>
3100    .SS "Backtracking verbs in repeated groups"
3101    .rs
3102    .sp
3103    PCRE differs from Perl in its handling of backtracking verbs in repeated
3104    groups. For example, consider:
3105    .sp
3106      /(a(*COMMIT)b)+ac/
3107    .sp
3108    If the subject is "abac", Perl matches, but PCRE fails because the (*COMMIT) in
3109    the second repeat of the group acts.
3110    .
3111    .
3112    .\" HTML <a name="btassert"></a>
3113    .SS "Backtracking verbs in assertions"
3114    .rs
3115    .sp
3116    (*FAIL) in an assertion has its normal effect: it forces an immediate backtrack.
3117    .P
3118    (*ACCEPT) in a positive assertion causes the assertion to succeed without any
3119    further processing. In a negative assertion, (*ACCEPT) causes the assertion to
3120    fail without any further processing.
3121    .P
3122    The other backtracking verbs are not treated specially if they appear in a
3123    positive assertion. In particular, (*THEN) skips to the next alternative in the
3124    innermost enclosing group that has alternations, whether or not this is within
3125    the assertion.
3126    .P
3127    Negative assertions are, however, different, in order to ensure that changing a
3128    positive assertion into a negative assertion changes its result. Backtracking
3129    into (*COMMIT), (*SKIP), or (*PRUNE) causes a negative assertion to be true,
3130    without considering any further alternative branches in the assertion.
3131    Backtracking into (*THEN) causes it to skip to the next enclosing alternative
3132    within the assertion (the normal behaviour), but if the assertion does not have
3133    such an alternative, (*THEN) behaves like (*PRUNE).
3134    .
3135    .
3136    .\" HTML <a name="btsub"></a>
3137    .SS "Backtracking verbs in subroutines"
3138    .rs
3139    .sp
3140    These behaviours occur whether or not the subpattern is called recursively.
3141    Perl's treatment of subroutines is different in some cases.
3142    .P
3143    (*FAIL) in a subpattern called as a subroutine has its normal effect: it forces
3144    an immediate backtrack.
3145    .P
3146    (*ACCEPT) in a subpattern called as a subroutine causes the subroutine match to
3147    succeed without any further processing. Matching then continues after the
3148    subroutine call.
3149    .P
3150    (*COMMIT), (*SKIP), and (*PRUNE) in a subpattern called as a subroutine cause
3151    the subroutine match to fail.
3152    .P
3153    (*THEN) skips to the next alternative in the innermost enclosing group within
3154    the subpattern that has alternatives. If there is no such group within the
3155    subpattern, (*THEN) causes the subroutine match to fail.
3156  .  .
3157  .  .
3158  .SH "SEE ALSO"  .SH "SEE ALSO"
3159  .rs  .rs
3160  .sp  .sp
3161  \fBpcreapi\fP(3), \fBpcrecallout\fP(3), \fBpcrematching\fP(3),  \fBpcreapi\fP(3), \fBpcrecallout\fP(3), \fBpcrematching\fP(3),
3162  \fBpcresyntax\fP(3), \fBpcre\fP(3).  \fBpcresyntax\fP(3), \fBpcre\fP(3), \fBpcre16(3)\fP, \fBpcre32(3)\fP.
3163  .  .
3164  .  .
3165  .SH AUTHOR  .SH AUTHOR
# Line 2685  Cambridge CB2 3QH, England. Line 3176  Cambridge CB2 3QH, England.
3176  .rs  .rs
3177  .sp  .sp
3178  .nf  .nf
3179  Last updated: 26 October 2010  Last updated: 08 October 2013
3180  Copyright (c) 1997-2010 University of Cambridge.  Copyright (c) 1997-2013 University of Cambridge.
3181  .fi  .fi

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