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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    \eddd      character with octal code ddd, or back reference    \eddd      character with octal code ddd, or back reference
304    \exhh      character with hex code hh    \exhh      character with hex code hh
305    \ex{hhh..} character with hex code hhh..    \ex{hhh..} character with hex code hhh.. (non-JavaScript mode)
306      \euhhhh    character with hex code hhhh (JavaScript mode only)
307  .sp  .sp
308  The precise effect of \ecx is as follows: if x is a lower case letter, it  The precise effect of \ecx on ASCII characters is as follows: if x is a lower
309  is converted to upper case. Then bit 6 of the character (hex 40) is inverted.  case letter, it is converted to upper case. Then bit 6 of the character (hex
310  Thus \ecz becomes hex 1A, 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),
311  7B.  but \ec{ becomes hex 3B ({ is 7B), and \ec; becomes hex 7B (; is 3B). If the
312  .P  data item (byte or 16-bit value) following \ec has a value greater than 127, a
313  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.
314  upper or lower case). Any number of hexadecimal digits may appear between \ex{  .P
315  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
316  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,
317  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
318  point, which is 10FFFF.  bytes. In this mode, all values are valid after \ec. If the next character is a
319    lower case letter, it is converted to upper case. Then the 0xc0 bits of the
320    byte are inverted. Thus \ecA becomes hex 01, as in ASCII (A is C1), but because
321    the EBCDIC letters are disjoint, \ecZ becomes hex 29 (Z is E9), and other
322    characters also generate different values.
323    .P
324    By default, after \ex, from zero to two hexadecimal digits are read (letters
325    can be in upper or lower case). Any number of hexadecimal digits may appear
326    between \ex{ and }, but the character code is constrained as follows:
327    .sp
328      8-bit non-UTF mode    less than 0x100
329      8-bit UTF-8 mode      less than 0x10ffff and a valid codepoint
330      16-bit non-UTF mode   less than 0x10000
331      16-bit UTF-16 mode    less than 0x10ffff and a valid codepoint
332      32-bit non-UTF mode   less than 0x80000000
333      32-bit UTF-32 mode    less than 0x10ffff and a valid codepoint
334    .sp
335    Invalid Unicode codepoints are the range 0xd800 to 0xdfff (the so-called
336    "surrogate" codepoints), and 0xffef.
337  .P  .P
338  If characters other than hexadecimal digits appear between \ex{ and }, or if  If characters other than hexadecimal digits appear between \ex{ and }, or if
339  there is no terminating }, this form of escape is not recognized. Instead, the  there is no terminating }, this form of escape is not recognized. Instead, the
340  initial \ex will be interpreted as a basic hexadecimal escape, with no  initial \ex will be interpreted as a basic hexadecimal escape, with no
341  following digits, giving a character whose value is zero.  following digits, giving a character whose value is zero.
342  .P  .P
343    If the PCRE_JAVASCRIPT_COMPAT option is set, the interpretation of \ex is
344    as just described only when it is followed by two hexadecimal digits.
345    Otherwise, it matches a literal "x" character. In JavaScript mode, support for
346    code points greater than 256 is provided by \eu, which must be followed by
347    four hexadecimal digits; otherwise it matches a literal "u" character.
348    Character codes specified by \eu in JavaScript mode are constrained in the same
349    was as those specified by \ex in non-JavaScript mode.
350    .P
351  Characters whose value is less than 256 can be defined by either of the two  Characters whose value is less than 256 can be defined by either of the two
352  syntaxes for \ex. There is no difference in the way they are handled. For  syntaxes for \ex (or by \eu in JavaScript mode). There is no difference in the
353  example, \exdc is exactly the same as \ex{dc}.  way they are handled. For example, \exdc is exactly the same as \ex{dc} (or
354    \eu00dc in JavaScript mode).
355  .P  .P
356  After \e0 up to two further octal digits are read. If there are fewer than two  After \e0 up to two further octal digits are read. If there are fewer than two
357  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 359  specifies two binary zeros followed by a
359  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
360  follows is itself an octal digit.  follows is itself an octal digit.
361  .P  .P
362  The handling of a backslash followed by a digit other than 0 is complicated.  The handling of a backslash followed by a digit other than 0 is complicated,
363  Outside a character class, PCRE reads it and any following digits as a decimal  and Perl has changed in recent releases, causing PCRE also to change. Outside a
364  number. If the number is less than 10, or if there have been at least that many  character class, PCRE reads the digit and any following digits as a decimal
365    number. If the number is less than 8, or if there have been at least that many
366  previous capturing left parentheses in the expression, the entire sequence is  previous capturing left parentheses in the expression, the entire sequence is
367  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
368  .\" HTML <a href="#backreferences">  .\" HTML <a href="#backreferences">
# Line 276  following the discussion of Line 375  following the discussion of
375  parenthesized subpatterns.  parenthesized subpatterns.
376  .\"  .\"
377  .P  .P
378  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
379  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
380  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
381  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.
382  character specified in octal must be less than \e400. In UTF-8 mode, values up  Any subsequent digits stand for themselves. The value of the character is
383  to \e777 are permitted. For example:  constrained in the same way as characters specified in hexadecimal. For
384    example:
385  .sp  .sp
386    \e040   is another way of writing a space    \e040   is another way of writing an ASCII space
387  .\" JOIN  .\" JOIN
388    \e40    is the same, provided there are fewer than 40    \e40    is the same, provided there are fewer than 40
389              previous capturing subpatterns              previous capturing subpatterns
# Line 298  to \e777 are permitted. For example: Line 398  to \e777 are permitted. For example:
398              character with octal code 113              character with octal code 113
399  .\" JOIN  .\" JOIN
400    \e377   might be a back reference, otherwise    \e377   might be a back reference, otherwise
401              the byte consisting entirely of 1 bits              the value 255 (decimal)
402  .\" JOIN  .\" JOIN
403    \e81    is either a back reference, or a binary zero    \e81    is either a back reference, or the two
404              followed by the two characters "8" and "1"              characters "8" and "1"
405  .sp  .sp
406  Note that octal values of 100 or greater must not be introduced by a leading  Note that octal values of 100 or greater must not be introduced by a leading
407  zero, because no more than three octal digits are ever read.  zero, because no more than three octal digits are ever read.
408  .P  .P
409  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
410  and outside character classes. In addition, inside a character class, the  and outside character classes. In addition, inside a character class, \eb is
411  sequence \eb is interpreted as the backspace character (hex 08). The sequences  interpreted as the backspace character (hex 08).
412  \eB, \eN, \eR, and \eX are not special inside a character class. Like any other  .P
413  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
414  "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
415  set. Outside a character class, these sequences have different meanings.  treated as the literal characters "B", "R", and "X" by default, but cause an
416    error if the PCRE_EXTRA option is set. Outside a character class, these
417    sequences have different meanings.
418    .
419    .
420    .SS "Unsupported escape sequences"
421    .rs
422    .sp
423    In Perl, the sequences \el, \eL, \eu, and \eU are recognized by its string
424    handler and used to modify the case of following characters. By default, PCRE
425    does not support these escape sequences. However, if the PCRE_JAVASCRIPT_COMPAT
426    option is set, \eU matches a "U" character, and \eu can be used to define a
427    character by code point, as described in the previous section.
428  .  .
429  .  .
430  .SS "Absolute and relative back references"  .SS "Absolute and relative back references"
# Line 359  Another use of backslash is for specifyi Line 471  Another use of backslash is for specifyi
471  .sp  .sp
472    \ed     any decimal digit    \ed     any decimal digit
473    \eD     any character that is not a decimal digit    \eD     any character that is not a decimal digit
474    \eh     any horizontal whitespace character    \eh     any horizontal white space character
475    \eH     any character that is not a horizontal whitespace character    \eH     any character that is not a horizontal white space character
476    \es     any whitespace character    \es     any white space character
477    \eS     any character that is not a whitespace character    \eS     any character that is not a white space character
478    \ev     any vertical whitespace character    \ev     any vertical white space character
479    \eV     any character that is not a vertical whitespace character    \eV     any character that is not a vertical white space character
480    \ew     any "word" character    \ew     any "word" character
481    \eW     any "non-word" character    \eW     any "non-word" character
482  .sp  .sp
# Line 374  This is the same as Line 486  This is the same as
486  .\" </a>  .\" </a>
487  the "." metacharacter  the "." metacharacter
488  .\"  .\"
489  when PCRE_DOTALL is not set.  when PCRE_DOTALL is not set. Perl also uses \eN to match characters by name;
490    PCRE does not support this.
491  .P  .P
492  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
493  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 496  classes. They each match one character o
496  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
497  there is no character to match.  there is no character to match.
498  .P  .P
499  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
500  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
501  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
502  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.  
503  .P  .P
504  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.
505  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 518  or "french" in Windows, some character c
518  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
519  Unicode is discouraged.  Unicode is discouraged.
520  .P  .P
521  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
522  \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
523  their original meanings from before UTF-8 support was available, mainly for  their original meanings from before UTF support was available, mainly for
524  efficiency reasons. However, if PCRE is compiled with Unicode property support,  efficiency reasons. However, if PCRE is compiled with Unicode property support,
525  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
526  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 535  any Unicode letter, and underscore. Note
535  \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
536  is noticeably slower when PCRE_UCP is set.  is noticeably slower when PCRE_UCP is set.
537  .P  .P
538  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
539  other sequences, which match only ASCII characters by default, these always  release 5.10. In contrast to the other sequences, which match only ASCII
540  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,
541  set. The horizontal space characters are:  whether or not PCRE_UCP is set. The horizontal space characters are:
542  .sp  .sp
543    U+0009     Horizontal tab    U+0009     Horizontal tab (HT)
544    U+0020     Space    U+0020     Space
545    U+00A0     Non-break space    U+00A0     Non-break space
546    U+1680     Ogham space mark    U+1680     Ogham space mark
# Line 450  set. The horizontal space characters are Line 562  set. The horizontal space characters are
562  .sp  .sp
563  The vertical space characters are:  The vertical space characters are:
564  .sp  .sp
565    U+000A     Linefeed    U+000A     Linefeed (LF)
566    U+000B     Vertical tab    U+000B     Vertical tab (VT)
567    U+000C     Formfeed    U+000C     Form feed (FF)
568    U+000D     Carriage return    U+000D     Carriage return (CR)
569    U+0085     Next line    U+0085     Next line (NEL)
570    U+2028     Line separator    U+2028     Line separator
571    U+2029     Paragraph separator    U+2029     Paragraph separator
572    .sp
573    In 8-bit, non-UTF-8 mode, only the characters with codepoints less than 256 are
574    relevant.
575  .  .
576  .  .
577  .\" HTML <a name="newlineseq"></a>  .\" HTML <a name="newlineseq"></a>
# Line 464  The vertical space characters are: Line 579  The vertical space characters are:
579  .rs  .rs
580  .sp  .sp
581  Outside a character class, by default, the escape sequence \eR matches any  Outside a character class, by default, the escape sequence \eR matches any
582  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
583  equivalent to the following:  following:
584  .sp  .sp
585    (?>\er\en|\en|\ex0b|\ef|\er|\ex85)    (?>\er\en|\en|\ex0b|\ef|\er|\ex85)
586  .sp  .sp
# Line 476  below. Line 591  below.
591  .\"  .\"
592  This particular group matches either the two-character sequence CR followed by  This particular group matches either the two-character sequence CR followed by
593  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,
594  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
595  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
596  cannot be split.  cannot be split.
597  .P  .P
598  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
599  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).
600  Unicode character property support is not needed for these characters to be  Unicode character property support is not needed for these characters to be
601  recognized.  recognized.
# Line 496  one of the following sequences: Line 611  one of the following sequences:
611    (*BSR_ANYCRLF)   CR, LF, or CRLF only    (*BSR_ANYCRLF)   CR, LF, or CRLF only
612    (*BSR_UNICODE)   any Unicode newline sequence    (*BSR_UNICODE)   any Unicode newline sequence
613  .sp  .sp
614  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
615  \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
616  \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
617  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
618  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
619  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:  
620  .sp  .sp
621    (*ANY)(*BSR_ANYCRLF)    (*ANY)(*BSR_ANYCRLF)
622  .sp  .sp
623  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
624  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
625  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
626    causes an error if PCRE_EXTRA is set.
627  .  .
628  .  .
629  .\" HTML <a name="uniextseq"></a>  .\" HTML <a name="uniextseq"></a>
# Line 517  matches the letter "R" by default, but c Line 632  matches the letter "R" by default, but c
632  .sp  .sp
633  When PCRE is built with Unicode character property support, three additional  When PCRE is built with Unicode character property support, three additional
634  escape sequences that match characters with specific properties are available.  escape sequences that match characters with specific properties are available.
635  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
636  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.
637  The extra escape sequences are:  The extra escape sequences are:
638  .sp  .sp
639    \ep{\fIxx\fP}   a character with the \fIxx\fP property    \ep{\fIxx\fP}   a character with the \fIxx\fP property
640    \eP{\fIxx\fP}   a character without the \fIxx\fP property    \eP{\fIxx\fP}   a character without the \fIxx\fP property
641    \eX       an extended Unicode sequence    \eX       a Unicode extended grapheme cluster
642  .sp  .sp
643  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
644  script names, the general category properties, "Any", which matches any  script names, the general category properties, "Any", which matches any
# Line 552  Armenian, Line 667  Armenian,
667  Avestan,  Avestan,
668  Balinese,  Balinese,
669  Bamum,  Bamum,
670    Batak,
671  Bengali,  Bengali,
672  Bopomofo,  Bopomofo,
673    Brahmi,
674  Braille,  Braille,
675  Buginese,  Buginese,
676  Buhid,  Buhid,
677  Canadian_Aboriginal,  Canadian_Aboriginal,
678  Carian,  Carian,
679    Chakma,
680  Cham,  Cham,
681  Cherokee,  Cherokee,
682  Common,  Common,
# Line 601  Lisu, Line 719  Lisu,
719  Lycian,  Lycian,
720  Lydian,  Lydian,
721  Malayalam,  Malayalam,
722    Mandaic,
723  Meetei_Mayek,  Meetei_Mayek,
724    Meroitic_Cursive,
725    Meroitic_Hieroglyphs,
726    Miao,
727  Mongolian,  Mongolian,
728  Myanmar,  Myanmar,
729  New_Tai_Lue,  New_Tai_Lue,
# Line 620  Rejang, Line 742  Rejang,
742  Runic,  Runic,
743  Samaritan,  Samaritan,
744  Saurashtra,  Saurashtra,
745    Sharada,
746  Shavian,  Shavian,
747  Sinhala,  Sinhala,
748    Sora_Sompeng,
749  Sundanese,  Sundanese,
750  Syloti_Nagri,  Syloti_Nagri,
751  Syriac,  Syriac,
# Line 630  Tagbanwa, Line 754  Tagbanwa,
754  Tai_Le,  Tai_Le,
755  Tai_Tham,  Tai_Tham,
756  Tai_Viet,  Tai_Viet,
757    Takri,
758  Tamil,  Tamil,
759  Telugu,  Telugu,
760  Thaana,  Thaana,
# Line 704  the Lu, Ll, or Lt property, in other wor Line 829  the Lu, Ll, or Lt property, in other wor
829  a modifier or "other".  a modifier or "other".
830  .P  .P
831  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
832  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
833  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
834  (see the discussion of PCRE_NO_UTF8_CHECK in the  (see the discussion of PCRE_NO_UTF8_CHECK, PCRE_NO_UTF16_CHECK and
835    PCRE_NO_UTF32_CHECK in the
836  .\" HREF  .\" HREF
837  \fBpcreapi\fP  \fBpcreapi\fP
838  .\"  .\"
# Line 721  Instead, this property is assumed for an Line 847  Instead, this property is assumed for an
847  Unicode table.  Unicode table.
848  .P  .P
849  Specifying caseless matching does not affect these escape sequences. For  Specifying caseless matching does not affect these escape sequences. For
850  example, \ep{Lu} always matches only upper case letters.  example, \ep{Lu} always matches only upper case letters. This is different from
851    the behaviour of current versions of Perl.
852  .P  .P
853  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
854  Unicode sequence. \eX is equivalent to  multistage table lookup in order to find a character's property. That is why
855  .sp  the traditional escape sequences such as \ed and \ew do not use Unicode
856    (?>\ePM\epM*)  properties in PCRE by default, though you can make them do so by setting the
857    PCRE_UCP option or by starting the pattern with (*UCP).
858    .
859    .
860    .SS Extended grapheme clusters
861    .rs
862  .sp  .sp
863  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
864  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  
865  .\" HTML <a href="#atomicgroup">  .\" HTML <a href="#atomicgroup">
866  .\" </a>  .\" </a>
867  (see below).  (see below).
868  .\"  .\"
869  Characters with the "mark" property are typically accents that affect the  Up to and including release 8.31, PCRE matched an earlier, simpler definition
870  preceding character. None of them have codepoints less than 256, so in  that was equivalent to
871  non-UTF-8 mode \eX matches any one character.  .sp
872  .P    (?>\ePM\epM*)
873  Matching characters by Unicode property is not fast, because PCRE has to search  .sp
874  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
875  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"
876  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.
877  PCRE_UCP option for \fBpcre_compile()\fP or by starting the pattern with  .P
878  (*UCP).  This simple definition was extended in Unicode to include more complicated
879    kinds of composite character by giving each character a grapheme breaking
880    property, and creating rules that use these properties to define the boundaries
881    of extended grapheme clusters. In releases of PCRE later than 8.31, \eX matches
882    one of these clusters.
883    .P
884    \eX always matches at least one character. Then it decides whether to add
885    additional characters according to the following rules for ending a cluster:
886    .P
887    1. End at the end of the subject string.
888    .P
889    2. Do not end between CR and LF; otherwise end after any control character.
890    .P
891    3. Do not break Hangul (a Korean script) syllable sequences. Hangul characters
892    are of five types: L, V, T, LV, and LVT. An L character may be followed by an
893    L, V, LV, or LVT character; an LV or V character may be followed by a V or T
894    character; an LVT or T character may be follwed only by a T character.
895    .P
896    4. Do not end before extending characters or spacing marks. Characters with
897    the "mark" property always have the "extend" grapheme breaking property.
898    .P
899    5. Do not end after prepend characters.
900    .P
901    6. Otherwise, end the cluster.
902  .  .
903  .  .
904  .\" HTML <a name="extraprops"></a>  .\" HTML <a name="extraprops"></a>
905  .SS PCRE's additional properties  .SS PCRE's additional properties
906  .rs  .rs
907  .sp  .sp
908  As well as the standard Unicode properties described in the previous  As well as the standard Unicode properties described above, PCRE supports four
909  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
910  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
911  properties. PCRE uses these non-standard, non-Perl properties internally when  non-standard, non-Perl properties internally when PCRE_UCP is set. However,
912  PCRE_UCP is set. They are:  they may also be used explicitly. These properties are:
913  .sp  .sp
914    Xan   Any alphanumeric character    Xan   Any alphanumeric character
915    Xps   Any POSIX space character    Xps   Any POSIX space character
# Line 763  PCRE_UCP is set. They are: Line 917  PCRE_UCP is set. They are:
917    Xwd   Any Perl "word" character    Xwd   Any Perl "word" character
918  .sp  .sp
919  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)
920  property. Xps matches the characters tab, linefeed, vertical tab, formfeed, or  property. Xps matches the characters tab, linefeed, vertical tab, form feed, or
921  carriage return, and any other character that has the Z (separator) property.  carriage return, and any other character that has the Z (separator) property.
922  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
923  same characters as Xan, plus underscore.  same characters as Xan, plus underscore.
924    .P
925    There is another non-standard property, Xuc, which matches any character that
926    can be represented by a Universal Character Name in C++ and other programming
927    languages. These are the characters $, @, ` (grave accent), and all characters
928    with Unicode code points greater than or equal to U+00A0, except for the
929    surrogates U+D800 to U+DFFF. Note that most base (ASCII) characters are
930    excluded. (Universal Character Names are of the form \euHHHH or \eUHHHHHHHH
931    where H is a hexadecimal digit. Note that the Xuc property does not match these
932    sequences but the characters that they represent.)
933  .  .
934  .  .
935  .\" HTML <a name="resetmatchstart"></a>  .\" HTML <a name="resetmatchstart"></a>
936  .SS "Resetting the match start"  .SS "Resetting the match start"
937  .rs  .rs
938  .sp  .sp
939  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
940  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:  
941  .sp  .sp
942    foo\eKbar    foo\eKbar
943  .sp  .sp
# Line 834  escape sequence" error is generated inst Line 996  escape sequence" error is generated inst
996  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
997  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
998  \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
999  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
1000  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
1001  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
1002  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 1035  regular expression.
1035  .SH "CIRCUMFLEX AND DOLLAR"  .SH "CIRCUMFLEX AND DOLLAR"
1036  .rs  .rs
1037  .sp  .sp
1038    The circumflex and dollar metacharacters are zero-width assertions. That is,
1039    they test for a particular condition being true without consuming any
1040    characters from the subject string.
1041    .P
1042  Outside a character class, in the default matching mode, the circumflex  Outside a character class, in the default matching mode, the circumflex
1043  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
1044  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
1045  \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
1046  option is unset. Inside a character class, circumflex has an entirely different  option is unset. Inside a character class, circumflex has an entirely different
1047  meaning  meaning
# Line 892  constrained to match only at the start o Line 1058  constrained to match only at the start o
1058  "anchored" pattern. (There are also other constructs that can cause a pattern  "anchored" pattern. (There are also other constructs that can cause a pattern
1059  to be anchored.)  to be anchored.)
1060  .P  .P
1061  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
1062  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
1063  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
1064  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
1065  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
1066  character class.  branch in which it appears. Dollar has no special meaning in a character class.
1067  .P  .P
1068  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
1069  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 1095  end of the subject in both modes, and if
1095  .sp  .sp
1096  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
1097  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
1098  line. In UTF-8 mode, the matched character may be more than one byte long.  line.
1099  .P  .P
1100  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
1101  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 1113  The handling of dot is entirely independ
1113  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
1114  special meaning in a character class.  special meaning in a character class.
1115  .P  .P
1116  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
1117  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
1118  end of a line.  that signifies the end of a line. Perl also uses \eN to match characters by
1119  .  name; PCRE does not support this.
1120  .  .
1121  .SH "MATCHING A SINGLE BYTE"  .
1122  .rs  .SH "MATCHING A SINGLE DATA UNIT"
1123  .sp  .rs
1124  Outside a character class, the escape sequence \eC matches any one byte, both  .sp
1125  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,
1126  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
1127  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
1128  what remains in the string may be a malformed UTF-8 string. For this reason,  a 32-bit unit. Unlike a dot, \eC always
1129  the \eC escape sequence is best avoided.  matches line-ending characters. The feature is provided in Perl in order to
1130    match individual bytes in UTF-8 mode, but it is unclear how it can usefully be
1131    used. Because \eC breaks up characters into individual data units, matching one
1132    unit with \eC in a UTF mode means that the rest of the string may start with a
1133    malformed UTF character. This has undefined results, because PCRE assumes that
1134    it is dealing with valid UTF strings (and by default it checks this at the
1135    start of processing unless the PCRE_NO_UTF8_CHECK, PCRE_NO_UTF16_CHECK or
1136    PCRE_NO_UTF32_CHECK option is used).
1137  .P  .P
1138  PCRE does not allow \eC to appear in lookbehind assertions  PCRE does not allow \eC to appear in lookbehind assertions
1139  .\" HTML <a href="#lookbehind">  .\" HTML <a href="#lookbehind">
1140  .\" </a>  .\" </a>
1141  (described below),  (described below)
1142  .\"  .\"
1143  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
1144  the lookbehind.  the lookbehind.
1145    .P
1146    In general, the \eC escape sequence is best avoided. However, one
1147    way of using it that avoids the problem of malformed UTF characters is to use a
1148    lookahead to check the length of the next character, as in this pattern, which
1149    could be used with a UTF-8 string (ignore white space and line breaks):
1150    .sp
1151      (?| (?=[\ex00-\ex7f])(\eC) |
1152          (?=[\ex80-\ex{7ff}])(\eC)(\eC) |
1153          (?=[\ex{800}-\ex{ffff}])(\eC)(\eC)(\eC) |
1154          (?=[\ex{10000}-\ex{1fffff}])(\eC)(\eC)(\eC)(\eC))
1155    .sp
1156    A group that starts with (?| resets the capturing parentheses numbers in each
1157    alternative (see
1158    .\" HTML <a href="#dupsubpatternnumber">
1159    .\" </a>
1160    "Duplicate Subpattern Numbers"
1161    .\"
1162    below). The assertions at the start of each branch check the next UTF-8
1163    character for values whose encoding uses 1, 2, 3, or 4 bytes, respectively. The
1164    character's individual bytes are then captured by the appropriate number of
1165    groups.
1166  .  .
1167  .  .
1168  .\" HTML <a name="characterclass"></a>  .\" HTML <a name="characterclass"></a>
# Line 982  bracket causes a compile-time error. If Line 1176  bracket causes a compile-time error. If
1176  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
1177  (after an initial circumflex, if present) or escaped with a backslash.  (after an initial circumflex, if present) or escaped with a backslash.
1178  .P  .P
1179  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
1180  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
1181  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
1182  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
1183  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
1184  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
1185  backslash.  backslash.
1186  .P  .P
1187  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 1192  circumflex is not an assertion; it still
1192  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
1193  string.  string.
1194  .P  .P
1195  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)
1196  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
1197    \ex{ escaping mechanism.
1198  .P  .P
1199  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
1200  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
1201  "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
1202  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
1203  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
1204  always possible. For characters with higher values, the concept of case is  always possible. For characters with higher values, the concept of case is
1205  supported if PCRE is compiled with Unicode property support, but not otherwise.  supported if PCRE is compiled with Unicode property support, but not otherwise.
1206  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
1207  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
1208  with UTF-8 support.  well as with UTF support.
1209  .P  .P
1210  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
1211  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 1227  followed by two other characters. The oc
1227  "]" can also be used to end a range.  "]" can also be used to end a range.
1228  .P  .P
1229  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
1230  used for characters specified numerically, for example [\e000-\e037]. In UTF-8  used for characters specified numerically, for example [\e000-\e037]. Ranges
1231  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}].  
1232  .P  .P
1233  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
1234  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
1235  [][\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
1236  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
1237  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
1238  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
1239  property support.  property support.
1240  .P  .P
1241  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,
1242  \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
1243  match to the class. For example, [\edABCDEF] matches any hexadecimal digit. A  they match to the class. For example, [\edABCDEF] matches any hexadecimal
1244  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
1245    and their upper case partners, just as it does when they appear outside a
1246    character class, as described in the section entitled
1247    .\" HTML <a href="#genericchartypes">
1248    .\" </a>
1249    "Generic character types"
1250    .\"
1251    above. The escape sequence \eb has a different meaning inside a character
1252    class; it matches the backspace character. The sequences \eB, \eN, \eR, and \eX
1253    are not special inside a character class. Like any other unrecognized escape
1254    sequences, they are treated as the literal characters "B", "N", "R", and "X" by
1255    default, but cause an error if the PCRE_EXTRA option is set.
1256    .P
1257    A circumflex can conveniently be used with the upper case character types to
1258  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.
1259  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,
1260    whereas [\ew] includes underscore. A positive character class should be read as
1261    "something OR something OR ..." and a negative class as "NOT something AND NOT
1262    something AND NOT ...".
1263  .P  .P
1264  The only metacharacters that are recognized in character classes are backslash,  The only metacharacters that are recognized in character classes are backslash,
1265  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 1297  are:
1297    xdigit   hexadecimal digits    xdigit   hexadecimal digits
1298  .sp  .sp
1299  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
1300  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
1301  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
1302  compatibility).  release 8.34. "Space" and \es now match the same set of characters.
1303  .P  .P
1304  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
1305  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 1311  matches "1", "2", or any non-digit. PCRE
1311  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
1312  supported, and an error is given if they are encountered.  supported, and an error is given if they are encountered.
1313  .P  .P
1314  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
1315  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
1316  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
1317  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 1382  extracts it into the global options (and
1382  extracted by the \fBpcre_fullinfo()\fP function).  extracted by the \fBpcre_fullinfo()\fP function).
1383  .P  .P
1384  An option change within a subpattern (see below for a description of  An option change within a subpattern (see below for a description of
1385  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
1386  .sp  .sp
1387    (a(?i)b)c    (a(?i)b)c
1388  .sp  .sp
# Line 1189  option settings happen at compile time. Line 1399  option settings happen at compile time.
1399  behaviour otherwise.  behaviour otherwise.
1400  .P  .P
1401  \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
1402  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
1403  pattern can contain special leading sequences such as (*CRLF) to override what  the pattern can contain special leading sequences such as (*CRLF) to override
1404  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
1405  section entitled  the section entitled
1406  .\" HTML <a href="#newlineseq">  .\" HTML <a href="#newlineseq">
1407  .\" </a>  .\" </a>
1408  "Newline sequences"  "Newline sequences"
1409  .\"  .\"
1410  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
1411  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
1412  PCRE_UTF8 and the PCRE_UCP options, respectively.  equivalent to setting the PCRE_UTF8, PCRE_UTF16, PCRE_UTF32 and the PCRE_UCP
1413    options, respectively. The (*UTF) sequence is a generic version that can be
1414    used with any of the libraries. However, the application can set the
1415    PCRE_NEVER_UTF option, which locks out the use of the (*UTF) sequences.
1416  .  .
1417  .  .
1418  .\" HTML <a name="subpattern"></a>  .\" HTML <a name="subpattern"></a>
# Line 1213  Turning part of a pattern into a subpatt Line 1426  Turning part of a pattern into a subpatt
1426  .sp  .sp
1427    cat(aract|erpillar|)    cat(aract|erpillar|)
1428  .sp  .sp
1429  matches one of the words "cat", "cataract", or "caterpillar". Without the  matches "cataract", "caterpillar", or "cat". Without the parentheses, it would
1430  parentheses, it would match "cataract", "erpillar" or an empty string.  match "cataract", "erpillar" or an empty string.
1431  .sp  .sp
1432  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
1433  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
1434  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
1435  \fBpcre_exec()\fP. Opening parentheses are counted from left to right (starting  matching function. (This applies only to the traditional matching functions;
1436  from 1) to obtain numbers for the capturing subpatterns.  the DFA matching functions do not support capturing.)
1437  .P  .P
1438  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
1439    numbers for the capturing subpatterns. For example, if the string "the red
1440    king" is matched against the pattern
1441  .sp  .sp
1442    the ((red|white) (king|queen))    the ((red|white) (king|queen))
1443  .sp  .sp
# Line 1271  at captured substring number one, whiche Line 1486  at captured substring number one, whiche
1486  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
1487  alternatives. Inside a (?| group, parentheses are numbered as usual, but the  alternatives. Inside a (?| group, parentheses are numbered as usual, but the
1488  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
1489  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
1490  branch. The following example is taken from the Perl documentation.  any branch. The following example is taken from the Perl documentation. The
1491  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.  
1492  .sp  .sp
1493    # before  ---------------branch-reset----------- after    # before  ---------------branch-reset----------- after
1494    / ( 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 1500  or "defdef":
1500  .sp  .sp
1501    /(?|(abc)|(def))\e1/    /(?|(abc)|(def))\e1/
1502  .sp  .sp
1503  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
1504  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
1505  pattern matches "abcabc" or "defabc":  "abcabc" or "defabc":
1506  .sp  .sp
1507    /(?|(abc)|(def))(?1)/    /(?|(abc)|(def))(?1)/
1508  .sp  .sp
# Line 1364  for the first (and in this example, the Line 1578  for the first (and in this example, the
1578  matched. This saves searching to find which numbered subpattern it was.  matched. This saves searching to find which numbered subpattern it was.
1579  .P  .P
1580  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
1581  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
1582  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
1583  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
1584    "barbar" but not "foobar" or "barfoo":
1585    .sp
1586      (?:(?<n>foo)|(?<n>bar))\k<n>
1587    .sp
1588    .P
1589    If you make a subroutine call to a non-unique named subpattern, the one that
1590    corresponds to the first occurrence of the name is used. In the absence of
1591    duplicate numbers (see the previous section) this is the one with the lowest
1592    number.
1593    .P
1594    If you use a named reference in a condition
1595  test (see the  test (see the
1596  .\"  .\"
1597  .\" HTML <a href="#conditions">  .\" HTML <a href="#conditions">
# Line 1386  documentation. Line 1611  documentation.
1611  \fBWarning:\fP You cannot use different names to distinguish between two  \fBWarning:\fP You cannot use different names to distinguish between two
1612  subpatterns with the same number because PCRE uses only the numbers when  subpatterns with the same number because PCRE uses only the numbers when
1613  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
1614  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
1615  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
1616    set.
1617  .  .
1618  .  .
1619  .SH REPETITION  .SH REPETITION
# Line 1399  items: Line 1625  items:
1625    a literal data character    a literal data character
1626    the dot metacharacter    the dot metacharacter
1627    the \eC escape sequence    the \eC escape sequence
1628    the \eX escape sequence (in UTF-8 mode with Unicode properties)    the \eX escape sequence
1629    the \eR escape sequence    the \eR escape sequence
1630    an escape such as \ed that matches a single character    an escape such as \ed or \epL that matches a single character
1631    a character class    a character class
1632    a back reference (see next section)    a back reference (see next section)
1633    a parenthesized subpattern (unless it is an assertion)    a parenthesized subpattern (including assertions)
1634    a recursive or "subroutine" call to a subpattern    a subroutine call to a subpattern (recursive or otherwise)
1635  .sp  .sp
1636  The general repetition quantifier specifies a minimum and maximum number of  The general repetition quantifier specifies a minimum and maximum number of
1637  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 1656  where a quantifier is not allowed, or on
1656  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
1657  quantifier, but a literal string of four characters.  quantifier, but a literal string of four characters.
1658  .P  .P
1659  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
1660  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
1661  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,
1662  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
1663  which may be several bytes long (and they may be of different lengths).  several data units long (and they may be of different lengths).
1664  .P  .P
1665  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
1666  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 1669  subpatterns that are referenced as
1669  .\" </a>  .\" </a>
1670  subroutines  subroutines
1671  .\"  .\"
1672  from elsewhere in the pattern. Items other than subpatterns that have a {0}  from elsewhere in the pattern (but see also the section entitled
1673  quantifier are omitted from the compiled pattern.  .\" HTML <a href="#subdefine">
1674    .\" </a>
1675    "Defining subpatterns for use by reference only"
1676    .\"
1677    below). Items other than subpatterns that have a {0} quantifier are omitted
1678    from the compiled pattern.
1679  .P  .P
1680  For convenience, the three most common quantifiers have single-character  For convenience, the three most common quantifiers have single-character
1681  abbreviations:  abbreviations:
# Line 1515  In cases where it is known that the subj Line 1746  In cases where it is known that the subj
1746  worth setting PCRE_DOTALL in order to obtain this optimization, or  worth setting PCRE_DOTALL in order to obtain this optimization, or
1747  alternatively using ^ to indicate anchoring explicitly.  alternatively using ^ to indicate anchoring explicitly.
1748  .P  .P
1749  However, there is one situation where the optimization cannot be used. When .*  However, there are some cases where the optimization cannot be used. When .*
1750  is inside capturing parentheses that are the subject of a back reference  is inside capturing parentheses that are the subject of a back reference
1751  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
1752  succeeds. Consider, for example:  succeeds. Consider, for example:
# Line 1525  succeeds. Consider, for example: Line 1756  succeeds. Consider, for example:
1756  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
1757  this reason, such a pattern is not implicitly anchored.  this reason, such a pattern is not implicitly anchored.
1758  .P  .P
1759    Another case where implicit anchoring is not applied is when the leading .* is
1760    inside an atomic group. Once again, a match at the start may fail where a later
1761    one succeeds. Consider this pattern:
1762    .sp
1763      (?>.*?a)b
1764    .sp
1765    It matches "ab" in the subject "aab". The use of the backtracking control verbs
1766    (*PRUNE) and (*SKIP) also disable this optimization.
1767    .P
1768  When a capturing subpattern is repeated, the value captured is the substring  When a capturing subpattern is repeated, the value captured is the substring
1769  that matched the final iteration. For example, after  that matched the final iteration. For example, after
1770  .sp  .sp
# Line 1669  no such problem when named parentheses a Line 1909  no such problem when named parentheses a
1909  subpattern is possible using named parentheses (see below).  subpattern is possible using named parentheses (see below).
1910  .P  .P
1911  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
1912  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
1913  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
1914  number, optionally enclosed in braces. These examples are all identical:  examples are all identical:
1915  .sp  .sp
1916    (ring), \e1    (ring), \e1
1917    (ring), \eg1    (ring), \eg1
# Line 1685  example: Line 1925  example:
1925    (abc(def)ghi)\eg{-1}    (abc(def)ghi)\eg{-1}
1926  .sp  .sp
1927  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
1928  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.
1929  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
1930  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
1931  fragments that contain references within themselves.  joining together fragments that contain references within themselves.
1932  .P  .P
1933  A back reference matches whatever actually matched the capturing subpattern in  A back reference matches whatever actually matched the capturing subpattern in
1934  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 1979  Because there may be many capturing pare
1979  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.
1980  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
1981  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
1982  whitespace. Otherwise, the \eg{ syntax or an empty comment (see  white space. Otherwise, the \eg{ syntax or an empty comment (see
1983  .\" HTML <a href="#comments">  .\" HTML <a href="#comments">
1984  .\" </a>  .\" </a>
1985  "Comments"  "Comments"
# Line 1790  those that look ahead of the current pos Line 2030  those that look ahead of the current pos
2030  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,
2031  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.
2032  .P  .P
2033  Assertion subpatterns are not capturing subpatterns, and may not be repeated,  Assertion subpatterns are not capturing subpatterns. If such an assertion
2034  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
2035  of assertion contains capturing subpatterns within it, these are counted for  numbering the capturing subpatterns in the whole pattern. However, substring
2036  the purposes of numbering the capturing subpatterns in the whole pattern.  capturing is carried out only for positive assertions. (Perl sometimes, but not
2037  However, substring capturing is carried out only for positive assertions,  always, does do capturing in negative assertions.)
2038  because it does not make sense for negative assertions.  .P
2039    For compatibility with Perl, assertion subpatterns may be repeated; though
2040    it makes no sense to assert the same thing several times, the side effect of
2041    capturing parentheses may occasionally be useful. In practice, there only three
2042    cases:
2043    .sp
2044    (1) If the quantifier is {0}, the assertion is never obeyed during matching.
2045    However, it may contain internal capturing parenthesized groups that are called
2046    from elsewhere via the
2047    .\" HTML <a href="#subpatternsassubroutines">
2048    .\" </a>
2049    subroutine mechanism.
2050    .\"
2051    .sp
2052    (2) If quantifier is {0,n} where n is greater than zero, it is treated as if it
2053    were {0,1}. At run time, the rest of the pattern match is tried with and
2054    without the assertion, the order depending on the greediness of the quantifier.
2055    .sp
2056    (3) If the minimum repetition is greater than zero, the quantifier is ignored.
2057    The assertion is obeyed just once when encountered during matching.
2058  .  .
2059  .  .
2060  .SS "Lookahead assertions"  .SS "Lookahead assertions"
# Line 1824  lookbehind assertion is needed to achiev Line 2083  lookbehind assertion is needed to achiev
2083  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
2084  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
2085  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.
2086  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 (?!).  
2087  .  .
2088  .  .
2089  .\" HTML <a name="lookbehind"></a>  .\" HTML <a name="lookbehind"></a>
# Line 1850  is permitted, but Line 2108  is permitted, but
2108  .sp  .sp
2109  causes an error at compile time. Branches that match different length strings  causes an error at compile time. Branches that match different length strings
2110  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
2111  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
2112  match the same length of string. An assertion such as  length of string. An assertion such as
2113  .sp  .sp
2114    (?<=ab(c|de))    (?<=ab(c|de))
2115  .sp  .sp
# Line 1861  branches: Line 2119  branches:
2119  .sp  .sp
2120    (?<=abc|abde)    (?<=abc|abde)
2121  .sp  .sp
2122  In some cases, the Perl 5.10 escape sequence \eK  In some cases, the escape sequence \eK
2123  .\" HTML <a href="#resetmatchstart">  .\" HTML <a href="#resetmatchstart">
2124  .\" </a>  .\" </a>
2125  (see above)  (see above)
# Line 1874  temporarily move the current position ba Line 2132  temporarily move the current position ba
2132  match. If there are insufficient characters before the current position, the  match. If there are insufficient characters before the current position, the
2133  assertion fails.  assertion fails.
2134  .P  .P
2135  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
2136  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
2137  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
2138  different numbers of bytes, are also not permitted.  escapes, which can match different numbers of data units, are also not
2139    permitted.
2140  .P  .P
2141  .\" HTML <a href="#subpatternsassubroutines">  .\" HTML <a href="#subpatternsassubroutines">
2142  .\" </a>  .\" </a>
# Line 1965  already been matched. The two possible f Line 2224  already been matched. The two possible f
2224  .sp  .sp
2225  If the condition is satisfied, the yes-pattern is used; otherwise the  If the condition is satisfied, the yes-pattern is used; otherwise the
2226  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
2227  subpattern, a compile-time error occurs.  subpattern, a compile-time error occurs. Each of the two alternatives may
2228    itself contain nested subpatterns of any form, including conditional
2229    subpatterns; the restriction to two alternatives applies only at the level of
2230    the condition. This pattern fragment is an example where the alternatives are
2231    complex:
2232    .sp
2233      (?(1) (A|B|C) | (D | (?(2)E|F) | E) )
2234    .sp
2235  .P  .P
2236  There are four kinds of condition: references to subpatterns, references to  There are four kinds of condition: references to subpatterns, references to
2237  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 2248  matched. If there is more than one captu
2248  .\" </a>  .\" </a>
2249  section about duplicate subpattern numbers),  section about duplicate subpattern numbers),
2250  .\"  .\"
2251  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
2252  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
2253  number is relative rather than absolute. The most recently opened parentheses  number is relative rather than absolute. The most recently opened parentheses
2254  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
2255  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
2256  constructs such as (?(+2).  parentheses to be opened can be referenced as (?(+1), and so on. (The value
2257    zero in any of these forms is not used; it provokes a compile-time error.)
2258  .P  .P
2259  Consider the following pattern, which contains non-significant white space to  Consider the following pattern, which contains non-significant white space to
2260  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 2265  three parts for ease of discussion:
2265  The first part matches an optional opening parenthesis, and if that  The first part matches an optional opening parenthesis, and if that
2266  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
2267  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
2268  conditional subpattern that tests whether the first set of parentheses matched  conditional subpattern that tests whether or not the first set of parentheses
2269  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,
2270  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
2271  parenthesis is required. Otherwise, since no-pattern is not present, the  parenthesis is required. Otherwise, since no-pattern is not present, the
2272  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 2322  The syntax for recursive patterns
2322  .\"  .\"
2323  is described below.  is described below.
2324  .  .
2325    .\" HTML <a name="subdefine"></a>
2326  .SS "Defining subpatterns for use by reference only"  .SS "Defining subpatterns for use by reference only"
2327  .rs  .rs
2328  .sp  .sp
# Line 2062  If the condition is the string (DEFINE), Line 2330  If the condition is the string (DEFINE),
2330  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
2331  alternative in the subpattern. It is always skipped if control reaches this  alternative in the subpattern. It is always skipped if control reaches this
2332  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
2333  "subroutines" that can be referenced from elsewhere. (The use of  subroutines that can be referenced from elsewhere. (The use of
2334  .\" HTML <a href="#subpatternsassubroutines">  .\" HTML <a href="#subpatternsassubroutines">
2335  .\" </a>  .\" </a>
2336  "subroutines"  subroutines
2337  .\"  .\"
2338  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
2339  written like this (ignore whitespace and line breaks):  "192.168.23.245" could be written like this (ignore white space and line
2340    breaks):
2341  .sp  .sp
2342    (?(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) )
2343    \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 2372  dd-aaa-dd or dd-dd-dd, where aaa are let
2372  .SH COMMENTS  .SH COMMENTS
2373  .rs  .rs
2374  .sp  .sp
2375  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
2376  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,
2377  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
2378    subpattern name or number. The characters that make up a comment play no part
2379    in the pattern matching.
2380  .P  .P
2381  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
2382  character class introduces a comment that continues to immediately after the  closing parenthesis. Nested parentheses are not permitted. If the PCRE_EXTENDED
2383  next newline in the pattern.  option is set, an unescaped # character also introduces a comment, which in
2384    this case continues to immediately after the next newline character or
2385    character sequence in the pattern. Which characters are interpreted as newlines
2386    is controlled by the options passed to a compiling function or by a special
2387    sequence at the start of the pattern, as described in the section entitled
2388    .\" HTML <a href="#newlines">
2389    .\" </a>
2390    "Newline conventions"
2391    .\"
2392    above. Note that the end of this type of comment is a literal newline sequence
2393    in the pattern; escape sequences that happen to represent a newline do not
2394    count. For example, consider this pattern when PCRE_EXTENDED is set, and the
2395    default newline convention is in force:
2396    .sp
2397      abc #comment \en still comment
2398    .sp
2399    On encountering the # character, \fBpcre_compile()\fP skips along, looking for
2400    a newline in the pattern. The sequence \en is still literal at this stage, so
2401    it does not terminate the comment. Only an actual character with the code value
2402    0x0a (the default newline) does so.
2403  .  .
2404  .  .
2405  .\" HTML <a name="recursion"></a>  .\" HTML <a name="recursion"></a>
# Line 2138  individual subpattern recursion. After i Line 2428  individual subpattern recursion. After i
2428  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.
2429  .P  .P
2430  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
2431  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
2432  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
2433  .\" HTML <a href="#subpatternsassubroutines">  .\" HTML <a href="#subpatternsassubroutines">
2434  .\" </a>  .\" </a>
2435  "subroutine"  non-recursive subroutine
2436  .\"  .\"
2437  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
2438  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 2457  We have put the pattern into parentheses
2457  them instead of the whole pattern.  them instead of the whole pattern.
2458  .P  .P
2459  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
2460  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
2461  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
2462  most recently opened parentheses preceding the recursion. In other words, a  parentheses preceding the recursion. In other words, a negative number counts
2463  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.  
2464  .P  .P
2465  It is also possible to refer to subsequently opened parentheses, by writing  It is also possible to refer to subsequently opened parentheses, by writing
2466  references such as (?+2). However, these cannot be recursive because the  references such as (?+2). However, these cannot be recursive because the
2467  reference is not inside the parentheses that are referenced. They are always  reference is not inside the parentheses that are referenced. They are always
2468  .\" HTML <a href="#subpatternsassubroutines">  .\" HTML <a href="#subpatternsassubroutines">
2469  .\" </a>  .\" </a>
2470  "subroutine"  non-recursive subroutine
2471  .\"  .\"
2472  calls, as described in the next section.  calls, as described in the next section.
2473  .P  .P
# Line 2215  documentation). If the pattern above is Line 2504  documentation). If the pattern above is
2504  .sp  .sp
2505  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
2506  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
2507  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
2508  set at a deeper level.  (temporarily) set at a deeper level during the matching process.
2509  .P  .P
2510  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
2511  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 2525  is the actual recursive call.
2525  .  .
2526  .  .
2527  .\" HTML <a name="recursiondifference"></a>  .\" HTML <a name="recursiondifference"></a>
2528  .SS "Recursion difference from Perl"  .SS "Differences in recursion processing between PCRE and Perl"
2529  .rs  .rs
2530  .sp  .sp
2531  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
2532  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
2533  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
2534  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
2535  following pattern, which purports to match a palindromic string that contains  subsequent matching failure. This can be illustrated by the following pattern,
2536  an odd number of characters (for example, "a", "aba", "abcba", "abcdcba"):  which purports to match a palindromic string that contains an odd number of
2537    characters (for example, "a", "aba", "abcba", "abcdcba"):
2538  .sp  .sp
2539    ^(.|(.)(?1)\e2)$    ^(.|(.)(?1)\e2)$
2540  .sp  .sp
# Line 2274  time we do have another alternative to t Line 2564  time we do have another alternative to t
2564  difference: in the previous case the remaining alternative is at a deeper  difference: in the previous case the remaining alternative is at a deeper
2565  recursion level, which PCRE cannot use.  recursion level, which PCRE cannot use.
2566  .P  .P
2567  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
2568  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
2569    this:
2570  .sp  .sp
2571    ^((.)(?1)\e2|.?)$    ^((.)(?1)\e2|.?)$
2572  .sp  .sp
# Line 2304  For example, although "abcba" is correct Line 2595  For example, although "abcba" is correct
2595  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
2596  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
2597  recursion to try other alternatives, so the entire match fails.  recursion to try other alternatives, so the entire match fails.
2598    .P
2599    The second way in which PCRE and Perl differ in their recursion processing is
2600    in the handling of captured values. In Perl, when a subpattern is called
2601    recursively or as a subpattern (see the next section), it has no access to any
2602    values that were captured outside the recursion, whereas in PCRE these values
2603    can be referenced. Consider this pattern:
2604    .sp
2605      ^(.)(\e1|a(?2))
2606    .sp
2607    In PCRE, this pattern matches "bab". The first capturing parentheses match "b",
2608    then in the second group, when the back reference \e1 fails to match "b", the
2609    second alternative matches "a" and then recurses. In the recursion, \e1 does
2610    now match "b" and so the whole match succeeds. In Perl, the pattern fails to
2611    match because inside the recursive call \e1 cannot access the externally set
2612    value.
2613  .  .
2614  .  .
2615  .\" HTML <a name="subpatternsassubroutines"></a>  .\" HTML <a name="subpatternsassubroutines"></a>
2616  .SH "SUBPATTERNS AS SUBROUTINES"  .SH "SUBPATTERNS AS SUBROUTINES"
2617  .rs  .rs
2618  .sp  .sp
2619  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
2620  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
2621  subroutine in a programming language. The "called" subpattern may be defined  subroutine in a programming language. The called subpattern may be defined
2622  before or after the reference. A numbered reference can be absolute or  before or after the reference. A numbered reference can be absolute or
2623  relative, as in these examples:  relative, as in these examples:
2624  .sp  .sp
# Line 2332  matches "sense and sensibility" and "res Line 2638  matches "sense and sensibility" and "res
2638  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
2639  strings. Another example is given in the discussion of DEFINE above.  strings. Another example is given in the discussion of DEFINE above.
2640  .P  .P
2641  Like recursive subpatterns, a subroutine call is always treated as an atomic  All subroutine calls, whether recursive or not, are always treated as atomic
2642  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
2643  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
2644  matching failure. Any capturing parentheses that are set during the subroutine  subsequent matching failure. Any capturing parentheses that are set during the
2645  call revert to their previous values afterwards.  subroutine call revert to their previous values afterwards.
2646  .P  .P
2647  When a subpattern is used as a subroutine, processing options such as  Processing options such as case-independence are fixed when a subpattern is
2648  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
2649  changed for different calls. For example, consider this pattern:  different calls. For example, consider this pattern:
2650  .sp  .sp
2651    (abc)(?i:(?-1))    (abc)(?i:(?-1))
2652  .sp  .sp
# Line 2379  same pair of parentheses when there is a Line 2685  same pair of parentheses when there is a
2685  .P  .P
2686  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
2687  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
2688  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
2689    (8-bit library) or \fIpcre[16|32]_callout\fP (16-bit or 32-bit library).
2690  By default, this variable contains NULL, which disables all calling out.  By default, this variable contains NULL, which disables all calling out.
2691  .P  .P
2692  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 2696  For example, this pattern has two callou
2696  .sp  .sp
2697    (?C1)abc(?C2)def    (?C1)abc(?C2)def
2698  .sp  .sp
2699  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
2700  automatically installed before each item in the pattern. They are all numbered  automatically installed before each item in the pattern. They are all numbered
2701  255.  255. If there is a conditional group in the pattern whose condition is an
2702  .P  assertion, an additional callout is inserted just before the condition. An
2703  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:
2704  set), the external function is called. It is provided with the number of the  .sp
2705  callout, the position in the pattern, and, optionally, one item of data    (?(?C9)(?=a)abc|def)
2706  originally supplied by the caller of \fBpcre_exec()\fP. The callout function  .sp
2707  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
2708  description of the interface to the callout function is given in the  condition.
2709    .P
2710    During matching, when PCRE reaches a callout point, the external function is
2711    called. It is provided with the number of the callout, the position in the
2712    pattern, and, optionally, one item of data originally supplied by the caller of
2713    the matching function. The callout function may cause matching to proceed, to
2714    backtrack, or to fail altogether. A complete description of the interface to
2715    the callout function is given in the
2716  .\" HREF  .\" HREF
2717  \fBpcrecallout\fP  \fBpcrecallout\fP
2718  .\"  .\"
# Line 2410  documentation. Line 2724  documentation.
2724  .rs  .rs
2725  .sp  .sp
2726  Perl 5.10 introduced a number of "Special Backtracking Control Verbs", which  Perl 5.10 introduced a number of "Special Backtracking Control Verbs", which
2727  are described in the Perl documentation as "experimental and subject to change  are still described in the Perl documentation as "experimental and subject to
2728  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
2729  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
2730  remarks apply to the PCRE features described in this section.  remarks apply to the PCRE features described in this section.
2731  .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  
2732  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
2733  parenthesis followed by an asterisk. They are generally of the form  parenthesis followed by an asterisk. They are generally of the form
2734  (*VERB) or (*VERB:NAME). Some may take either form, with differing behaviour,  (*VERB) or (*VERB:NAME). Some may take either form, possibly behaving
2735  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
2736  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
2737  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
2738  not there. Any number of these verbs may occur in a pattern.  libraries. If the name is empty, that is, if the closing parenthesis
2739    immediately follows the colon, the effect is as if the colon were not there.
2740    Any number of these verbs may occur in a pattern.
2741    .P
2742    Since these verbs are specifically related to backtracking, most of them can be
2743    used only when the pattern is to be matched using one of the traditional
2744    matching functions, because these use a backtracking algorithm. With the
2745    exception of (*FAIL), which behaves like a failing negative assertion, the
2746    backtracking control verbs cause an error if encountered by a DFA matching
2747    function.
2748  .P  .P
2749    The behaviour of these verbs in
2750    .\" HTML <a href="#btrepeat">
2751    .\" </a>
2752    repeated groups,
2753    .\"
2754    .\" HTML <a href="#btassert">
2755    .\" </a>
2756    assertions,
2757    .\"
2758    and in
2759    .\" HTML <a href="#btsub">
2760    .\" </a>
2761    subpatterns called as subroutines
2762    .\"
2763    (whether or not recursively) is documented below.
2764    .
2765    .
2766    .\" HTML <a name="nooptimize"></a>
2767    .SS "Optimizations that affect backtracking verbs"
2768    .rs
2769    .sp
2770  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
2771  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
2772  minimum length of matching subject, or that a particular character must be  minimum length of matching subject, or that a particular character must be
2773  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
2774  included backtracking verbs will not, of course, be processed. You can suppress  included backtracking verbs will not, of course, be processed. You can suppress
2775  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
2776  when calling \fBpcre_exec()\fP.  when calling \fBpcre_compile()\fP or \fBpcre_exec()\fP, or by starting the
2777    pattern with (*NO_START_OPT). There is more discussion of this option in the
2778    section entitled
2779    .\" HTML <a href="pcreapi.html#execoptions">
2780    .\" </a>
2781    "Option bits for \fBpcre_exec()\fP"
2782    .\"
2783    in the
2784    .\" HREF
2785    \fBpcreapi\fP
2786    .\"
2787    documentation.
2788    .P
2789    Experiments with Perl suggest that it too has similar optimizations, sometimes
2790    leading to anomalous results.
2791  .  .
2792  .  .
2793  .SS "Verbs that act immediately"  .SS "Verbs that act immediately"
# Line 2452  followed by a name. Line 2799  followed by a name.
2799     (*ACCEPT)     (*ACCEPT)
2800  .sp  .sp
2801  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
2802  pattern. When inside a recursion, only the innermost pattern is ended  pattern. However, when it is inside a subpattern that is called as a
2803  immediately. If (*ACCEPT) is inside capturing parentheses, the data so far is  subroutine, only that subpattern is ended successfully. Matching then continues
2804  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
2805    assertion succeeds; in a negative assertion, the assertion fails.
2806    .P
2807    If (*ACCEPT) is inside capturing parentheses, the data so far is captured. For
2808    example:
2809  .sp  .sp
2810    A((?:A|B(*ACCEPT)|C)D)    A((?:A|B(*ACCEPT)|C)D)
2811  .sp  .sp
# Line 2463  the outer parentheses. Line 2814  the outer parentheses.
2814  .sp  .sp
2815    (*FAIL) or (*F)    (*FAIL) or (*F)
2816  .sp  .sp
2817  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
2818  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
2819  probably useful only when combined with (?{}) or (??{}). Those are, of course,  probably useful only when combined with (?{}) or (??{}). Those are, of course,
2820  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 2838  starting point (see (*SKIP) below).
2838  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
2839  (*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.
2840  .P  .P
2841  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),
2842  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
2843    caller as described in the section entitled
2844  .\" HTML <a href="pcreapi.html#extradata">  .\" HTML <a href="pcreapi.html#extradata">
2845  .\" </a>  .\" </a>
2846  section on \fIpcre_extra\fP  "Extra data for \fBpcre_exec()\fP"
2847  .\"  .\"
2848  in the  in the
2849  .\" HREF  .\" HREF
2850  \fBpcreapi\fP  \fBpcreapi\fP
2851  .\"  .\"
2852  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
2853  \fBpcretest\fP output, where the /K modifier requests the retrieval and  modifier requests the retrieval and outputting of (*MARK) data:
 outputting of (*MARK) data:  
2854  .sp  .sp
2855    /X(*MARK:A)Y|X(*MARK:B)Z/K      re> /X(*MARK:A)Y|X(*MARK:B)Z/K
2856    XY    data> XY
2857     0: XY     0: XY
2858    MK: A    MK: A
2859    XZ    XZ
# Line 2514  indicates which of the two alternatives Line 2865  indicates which of the two alternatives
2865  of obtaining this information than putting each alternative in its own  of obtaining this information than putting each alternative in its own
2866  capturing parentheses.  capturing parentheses.
2867  .P  .P
2868  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
2869  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
2870  (*COMMIT), this is unlikely to happen for an unanchored pattern because, as the  happen for negative assertions or failing positive assertions.
2871  starting point for matching is advanced, the final check is often with an empty  .P
2872  string, causing a failure before (*MARK) is reached. For example:  After a partial match or a failed match, the last encountered name in the
2873  .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:  
2874  .sp  .sp
2875    /^X(*MARK:A)Y|^X(*MARK:B)Z/K      re> /X(*MARK:A)Y|X(*MARK:B)Z/K
2876    XP    data> XP
2877    No match, mark = B    No match, mark = B
2878  .sp  .sp
2879  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
2880  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
2881  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
2882  .P  (*MARK) item, but nevertheless do not reset it.
2883  Note that similar anomalies (though different in detail) exist in Perl, no  .P
2884  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
2885  unanchored pattern is not recommended, unless (*COMMIT) is involved.  probably set the PCRE_NO_START_OPTIMIZE option
2886    .\" HTML <a href="#nooptimize">
2887    .\" </a>
2888    (see above)
2889    .\"
2890    to ensure that the match is always attempted.
2891  .  .
2892  .  .
2893  .SS "Verbs that act after backtracking"  .SS "Verbs that act after backtracking"
# Line 2547  unanchored pattern is not recommended, u Line 2896  unanchored pattern is not recommended, u
2896  The following verbs do nothing when they are encountered. Matching continues  The following verbs do nothing when they are encountered. Matching continues
2897  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
2898  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
2899  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
2900  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
2901  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
2902  "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
2903  above, that this localization also applies in subroutine calls and assertions.)  or assertion. (Remember also, as stated above, that this localization also
2904    applies in subroutine calls.)
2905  .P  .P
2906  These verbs differ in exactly what kind of failure occurs when backtracking  These verbs differ in exactly what kind of failure occurs when backtracking
2907  reaches them.  reaches them. The behaviour described below is what happens when the verb is
2908    not in a subroutine or an assertion. Subsequent sections cover these special
2909    cases.
2910  .sp  .sp
2911    (*COMMIT)    (*COMMIT)
2912  .sp  .sp
2913  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
2914  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
2915  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
2916  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
2917  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
2918    committed to finding a match at the current starting point, or not at all. For
2919    example:
2920  .sp  .sp
2921    a+(*COMMIT)b    a+(*COMMIT)b
2922  .sp  .sp
# Line 2571  dynamic anchor, or "I've started, so I m Line 2925  dynamic anchor, or "I've started, so I m
2925  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
2926  match failure.  match failure.
2927  .P  .P
2928    If there is more than one backtracking verb in a pattern, a different one that
2929    follows (*COMMIT) may be triggered first, so merely passing (*COMMIT) during a
2930    match does not always guarantee that a match must be at this starting point.
2931    .P
2932  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,
2933  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
2934  \fBpcretest\fP example:  \fBpcretest\fP example:
2935  .sp  .sp
2936    /(*COMMIT)abc/      re> /(*COMMIT)abc/
2937    xyzabc    data> xyzabc
2938     0: abc     0: abc
2939    xyzabc\eY    xyzabc\eY
2940    No match    No match
# Line 2590  starting points. Line 2948  starting points.
2948    (*PRUNE) or (*PRUNE:NAME)    (*PRUNE) or (*PRUNE:NAME)
2949  .sp  .sp
2950  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
2951  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
2952  unanchored, the normal "bumpalong" advance to the next starting character then  it. If the pattern is unanchored, the normal "bumpalong" advance to the next
2953  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
2954  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
2955  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
2956  (*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
2957  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
2958  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
2959  match fails completely; the name is passed back if this is the final attempt.  as (*COMMIT).
2960  (*PRUNE:NAME) does not pass back a name if the match succeeds. In an anchored  .P
2961  pattern (*PRUNE) has the same effect as (*COMMIT).  The behaviour of (*PRUNE:NAME) is the not the same as (*MARK:NAME)(*PRUNE).
2962    It is like (*MARK:NAME) in that the name is remembered for passing back to the
2963    caller. However, (*SKIP:NAME) searches only for names set with (*MARK).
2964  .sp  .sp
2965    (*SKIP)    (*SKIP)
2966  .sp  .sp
# Line 2621  instead of skipping on to "c". Line 2981  instead of skipping on to "c".
2981  .sp  .sp
2982    (*SKIP:NAME)    (*SKIP:NAME)
2983  .sp  .sp
2984  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
2985  following pattern fails to match, the previous path through the pattern is  triggered, the previous path through the pattern is searched for the most
2986  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
2987  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
2988  (*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
2989  matching name is found, normal "bumpalong" of one character happens (the  (*SKIP) is ignored.
2990  (*SKIP) is ignored).  .P
2991    Note that (*SKIP:NAME) searches only for names set by (*MARK:NAME). It ignores
2992    names that are set by (*PRUNE:NAME) or (*THEN:NAME).
2993  .sp  .sp
2994    (*THEN) or (*THEN:NAME)    (*THEN) or (*THEN:NAME)
2995  .sp  .sp
2996  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
2997  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
2998  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
2999  observation that it can be used for a pattern-based if-then-else block:  pattern-based if-then-else block:
3000  .sp  .sp
3001    ( COND1 (*THEN) FOO | COND2 (*THEN) BAR | COND3 (*THEN) BAZ ) ...    ( COND1 (*THEN) FOO | COND2 (*THEN) BAR | COND3 (*THEN) BAZ ) ...
3002  .sp  .sp
3003  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
3004  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
3005  second alternative and tries COND2, without backtracking into COND1. The  second alternative and tries COND2, without backtracking into COND1. If that
3006  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
3007  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
3008  like (*PRUNE).  group. If (*THEN) is not inside an alternation, it acts like (*PRUNE).
3009  .  .P
3010  .P  The behaviour of (*THEN:NAME) is the not the same as (*MARK:NAME)(*THEN).
3011  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
3012  matching fails. (*THEN) is the weakest, carrying on the match at the next  caller. However, (*SKIP:NAME) searches only for names set with (*MARK).
3013  alternation. (*PRUNE) comes next, failing the match at the current starting  .P
3014  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
3015  pattern). (*SKIP) is similar, except that the advance may be more than one  enclosing alternative; it is not a nested alternation with only one
3016  character. (*COMMIT) is the strongest, causing the entire match to fail.  alternative. The effect of (*THEN) extends beyond such a subpattern to the
3017  .P  enclosing alternative. Consider this pattern, where A, B, etc. are complex
3018  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:
3019  consider this pattern, where A, B, etc. are complex pattern fragments:  .sp
3020  .sp    A (B(*THEN)C) | D
3021    (A(*COMMIT)B(*THEN)C|D)  .sp
3022  .sp  If A and B are matched, but there is a failure in C, matching does not
3023  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.
3024  position. If subsequently B matches, but C does not, the normal (*THEN) action  However, if the subpattern containing (*THEN) is given an alternative, it
3025  of trying the next alternation (that is, D) does not happen because (*COMMIT)  behaves differently:
3026  overrides.  .sp
3027      A (B(*THEN)C | (*FAIL)) | D
3028    .sp
3029    The effect of (*THEN) is now confined to the inner subpattern. After a failure
3030    in C, matching moves to (*FAIL), which causes the whole subpattern to fail
3031    because there are no more alternatives to try. In this case, matching does now
3032    backtrack into A.
3033    .P
3034    Note that a conditional subpattern is not considered as having two
3035    alternatives, because only one is ever used. In other words, the | character in
3036    a conditional subpattern has a different meaning. Ignoring white space,
3037    consider:
3038    .sp
3039      ^.*? (?(?=a) a | b(*THEN)c )
3040    .sp
3041    If the subject is "ba", this pattern does not match. Because .*? is ungreedy,
3042    it initially matches zero characters. The condition (?=a) then fails, the
3043    character "b" is matched, but "c" is not. At this point, matching does not
3044    backtrack to .*? as might perhaps be expected from the presence of the |
3045    character. The conditional subpattern is part of the single alternative that
3046    comprises the whole pattern, and so the match fails. (If there was a backtrack
3047    into .*?, allowing it to match "b", the match would succeed.)
3048    .P
3049    The verbs just described provide four different "strengths" of control when
3050    subsequent matching fails. (*THEN) is the weakest, carrying on the match at the
3051    next alternative. (*PRUNE) comes next, failing the match at the current
3052    starting position, but allowing an advance to the next character (for an
3053    unanchored pattern). (*SKIP) is similar, except that the advance may be more
3054    than one character. (*COMMIT) is the strongest, causing the entire match to
3055    fail.
3056    .
3057    .
3058    .SS "More than one backtracking verb"
3059    .rs
3060    .sp
3061    If more than one backtracking verb is present in a pattern, the one that is
3062    backtracked onto first acts. For example, consider this pattern, where A, B,
3063    etc. are complex pattern fragments:
3064    .sp
3065      (A(*COMMIT)B(*THEN)C|ABD)
3066    .sp
3067    If A matches but B fails, the backtrack to (*COMMIT) causes the entire match to
3068    fail. However, if A and B match, but C fails, the backtrack to (*THEN) causes
3069    the next alternative (ABD) to be tried. This behaviour is consistent, but is
3070    not always the same as Perl's. It means that if two or more backtracking verbs
3071    appear in succession, all the the last of them has no effect. Consider this
3072    example:
3073    .sp
3074      ...(*COMMIT)(*PRUNE)...
3075    .sp
3076    If there is a matching failure to the right, backtracking onto (*PRUNE) causes
3077    it to be triggered, and its action is taken. There can never be a backtrack
3078    onto (*COMMIT).
3079    .
3080    .
3081    .\" HTML <a name="btrepeat"></a>
3082    .SS "Backtracking verbs in repeated groups"
3083    .rs
3084    .sp
3085    PCRE differs from Perl in its handling of backtracking verbs in repeated
3086    groups. For example, consider:
3087    .sp
3088      /(a(*COMMIT)b)+ac/
3089    .sp
3090    If the subject is "abac", Perl matches, but PCRE fails because the (*COMMIT) in
3091    the second repeat of the group acts.
3092    .
3093    .
3094    .\" HTML <a name="btassert"></a>
3095    .SS "Backtracking verbs in assertions"
3096    .rs
3097    .sp
3098    (*FAIL) in an assertion has its normal effect: it forces an immediate backtrack.
3099    .P
3100    (*ACCEPT) in a positive assertion causes the assertion to succeed without any
3101    further processing. In a negative assertion, (*ACCEPT) causes the assertion to
3102    fail without any further processing.
3103    .P
3104    The other backtracking verbs are not treated specially if they appear in a
3105    positive assertion. In particular, (*THEN) skips to the next alternative in the
3106    innermost enclosing group that has alternations, whether or not this is within
3107    the assertion.
3108    .P
3109    Negative assertions are, however, different, in order to ensure that changing a
3110    positive assertion into a negative assertion changes its result. Backtracking
3111    into (*COMMIT), (*SKIP), or (*PRUNE) causes a negative assertion to be true,
3112    without considering any further alternative branches in the assertion.
3113    Backtracking into (*THEN) causes it to skip to the next enclosing alternative
3114    within the assertion (the normal behaviour), but if the assertion does not have
3115    such an alternative, (*THEN) behaves like (*PRUNE).
3116    .
3117    .
3118    .\" HTML <a name="btsub"></a>
3119    .SS "Backtracking verbs in subroutines"
3120    .rs
3121    .sp
3122    These behaviours occur whether or not the subpattern is called recursively.
3123    Perl's treatment of subroutines is different in some cases.
3124    .P
3125    (*FAIL) in a subpattern called as a subroutine has its normal effect: it forces
3126    an immediate backtrack.
3127    .P
3128    (*ACCEPT) in a subpattern called as a subroutine causes the subroutine match to
3129    succeed without any further processing. Matching then continues after the
3130    subroutine call.
3131    .P
3132    (*COMMIT), (*SKIP), and (*PRUNE) in a subpattern called as a subroutine cause
3133    the subroutine match to fail.
3134    .P
3135    (*THEN) skips to the next alternative in the innermost enclosing group within
3136    the subpattern that has alternatives. If there is no such group within the
3137    subpattern, (*THEN) causes the subroutine match to fail.
3138  .  .
3139  .  .
3140  .SH "SEE ALSO"  .SH "SEE ALSO"
3141  .rs  .rs
3142  .sp  .sp
3143  \fBpcreapi\fP(3), \fBpcrecallout\fP(3), \fBpcrematching\fP(3),  \fBpcreapi\fP(3), \fBpcrecallout\fP(3), \fBpcrematching\fP(3),
3144  \fBpcresyntax\fP(3), \fBpcre\fP(3).  \fBpcresyntax\fP(3), \fBpcre\fP(3), \fBpcre16(3)\fP, \fBpcre32(3)\fP.
3145  .  .
3146  .  .
3147  .SH AUTHOR  .SH AUTHOR
# Line 2685  Cambridge CB2 3QH, England. Line 3158  Cambridge CB2 3QH, England.
3158  .rs  .rs
3159  .sp  .sp
3160  .nf  .nf
3161  Last updated: 26 October 2010  Last updated: 08 October 2013
3162  Copyright (c) 1997-2010 University of Cambridge.  Copyright (c) 1997-2013 University of Cambridge.
3163  .fi  .fi

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