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1  .TH PCREPATTERN 3  .TH PCREPATTERN 3 "05 November 2013" "PCRE 8.34"
2  .SH NAME  .SH NAME
3  PCRE - Perl-compatible regular expressions  PCRE - Perl-compatible regular expressions
4  .SH "PCRE REGULAR EXPRESSION DETAILS"  .SH "PCRE REGULAR EXPRESSION DETAILS"
# Line 20  have copious examples. Jeffrey Friedl's Line 20  have copious examples. Jeffrey Friedl's
20  published by O'Reilly, covers regular expressions in great detail. This  published by O'Reilly, covers regular expressions in great detail. This
21  description of PCRE's regular expressions is intended as reference material.  description of PCRE's regular expressions is intended as reference material.
22  .P  .P
23    This document discusses the patterns that are supported by PCRE when one its
24    main matching functions, \fBpcre_exec()\fP (8-bit) or \fBpcre[16|32]_exec()\fP
25    (16- or 32-bit), is used. PCRE also has alternative matching functions,
26    \fBpcre_dfa_exec()\fP and \fBpcre[16|32_dfa_exec()\fP, which match using a
27    different algorithm that is not Perl-compatible. Some of the features discussed
28    below are not available when DFA matching is used. The advantages and
29    disadvantages of the alternative functions, and how they differ from the normal
30    functions, are discussed in the
31    .\" HREF
32    \fBpcrematching\fP
33    .\"
34    page.
35    .
36    .
37    .SH "SPECIAL START-OF-PATTERN ITEMS"
38    .rs
39    .sp
40    A number of options that can be passed to \fBpcre_compile()\fP can also be set
41    by special items at the start of a pattern. These are not Perl-compatible, but
42    are provided to make these options accessible to pattern writers who are not
43    able to change the program that processes the pattern. Any number of these
44    items may appear, but they must all be together right at the start of the
45    pattern string, and the letters must be in upper case.
46    .
47    .
48    .SS "UTF support"
49    .rs
50    .sp
51  The original operation of PCRE was on strings of one-byte characters. However,  The original operation of PCRE was on strings of one-byte characters. However,
52  there is now also support for UTF-8 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.
91  .P  .
92    .
93    .SS "Disabling start-up optimizations"
94    .rs
95    .sp
96  If a pattern starts with (*NO_START_OPT), it has the same effect as setting the  If a pattern starts with (*NO_START_OPT), it has the same effect as setting the
97  PCRE_NO_START_OPTIMIZE option either at compile or matching time. There are  PCRE_NO_START_OPTIMIZE option either at compile or matching time.
 also some more of these special sequences that are concerned with the handling  
 of newlines; they are described below.  
 .P  
 The remainder of this document discusses the patterns that are supported by  
 PCRE when its main matching function, \fBpcre_exec()\fP, is used.  
 From release 6.0, PCRE offers a second matching function,  
 \fBpcre_dfa_exec()\fP, which matches using a different algorithm that is not  
 Perl-compatible. Some of the features discussed below are not available when  
 \fBpcre_dfa_exec()\fP is used. The advantages and disadvantages of the  
 alternative function, and how it differs from the normal function, are  
 discussed in the  
 .\" HREF  
 \fBpcrematching\fP  
 .\"  
 page.  
98  .  .
99  .  .
100  .\" HTML <a name="newlines"></a>  .\" HTML <a name="newlines"></a>
101  .SH "NEWLINE CONVENTIONS"  .SS "Newline conventions"
102  .rs  .rs
103  .sp  .sp
104  PCRE supports five different conventions for indicating line breaks in  PCRE supports five different conventions for indicating line breaks in
# Line 99  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 124  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 (or defaulted) by the caller of \fBpcre_exec()\fP
168    for it to have any effect. In other words, the pattern writer can lower the
169    limits set by the programmer, but not raise them. If there is more than one
170    setting of one of these 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 135  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 189  The following sections describe the use Line 245  The following sections describe the use
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  character that is not a number or a letter, it takes away any special meaning  character that is not a number or a letter, it takes away any special meaning
247  that character may have. This use of backslash as an escape character applies  that character may have. This use of backslash as an escape character applies
248  both inside and 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 197  otherwise be interpreted as a metacharac Line 253  otherwise be interpreted as a metacharac
253  non-alphanumeric with backslash to specify that it stands for itself. In  non-alphanumeric with backslash to specify that it stands for itself. In
254  particular, if you want to match a backslash, you write \e\e.  particular, if you want to match a backslash, you write \e\e.
255  .P  .P
256  In UTF-8 mode, only ASCII numbers and letters have any special meaning after a  In a UTF mode, only ASCII numbers and letters have any special meaning after a
257  backslash. All other characters (in particular, those whose codepoints are  backslash. All other characters (in particular, those whose codepoints are
258  greater than 127) are treated as literals.  greater than 127) are treated as literals.
259  .P  .P
260  If a pattern is compiled with the PCRE_EXTENDED option, whitespace in the  If a pattern is compiled with the PCRE_EXTENDED option, white space in the
261  pattern (other than in a character class) and characters between a # outside  pattern (other than in a character class) and characters between a # outside
262  a character class and the next newline are ignored. An escaping backslash can  a character class and the next newline are ignored. An escaping backslash can
263  be used to include a whitespace or # character as part of the pattern.  be used to include a white space or # character as part of the pattern.
264  .P  .P
265  If you want to remove the special meaning from a sequence of characters, you  If you want to remove the special meaning from a sequence of characters, you
266  can do so by putting them between \eQ and \eE. This is different from Perl in  can do so by putting them between \eQ and \eE. This is different from Perl in
# Line 220  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 236  one of the following escape sequences th Line 296  one of the following escape sequences th
296    \ea        alarm, that is, the BEL character (hex 07)    \ea        alarm, that is, the BEL character (hex 07)
297    \ecx       "control-x", where x is any ASCII character    \ecx       "control-x", where x is any ASCII character
298    \ee        escape (hex 1B)    \ee        escape (hex 1B)
299    \ef        formfeed (hex 0C)    \ef        form feed (hex 0C)
300    \en        linefeed (hex 0A)    \en        linefeed (hex 0A)
301    \er        carriage return (hex 0D)    \er        carriage return (hex 0D)
302    \et        tab (hex 09)    \et        tab (hex 09)
303      \e0dd      character with octal code 0dd
304    \eddd      character with octal code ddd, or back reference    \eddd      character with octal code ddd, or back reference
305      \eo{ddd..} character with octal code ddd..
306    \exhh      character with hex code hh    \exhh      character with hex code hh
307    \ex{hhh..} character with hex code hhh..    \ex{hhh..} character with hex code hhh.. (non-JavaScript mode)
308      \euhhhh    character with hex code hhhh (JavaScript mode only)
309  .sp  .sp
310  The precise effect of \ecx is as follows: if x is a lower case letter, it  The precise effect of \ecx on ASCII characters is as follows: if x is a lower
311  is converted to upper case. Then bit 6 of the character (hex 40) is inverted.  case letter, it is converted to upper case. Then bit 6 of the character (hex
312  Thus \ecz becomes hex 1A (z is 7A), but \ec{ becomes hex 3B ({ is 7B), while  40) is inverted. Thus \ecA to \ecZ become hex 01 to hex 1A (A is 41, Z is 5A),
313  \ec; becomes hex 7B (; is 3B). If the byte following \ec has a value greater  but \ec{ becomes hex 3B ({ is 7B), and \ec; becomes hex 7B (; is 3B). If the
314  than 127, a compile-time error occurs. This locks out non-ASCII characters in  data item (byte or 16-bit value) following \ec has a value greater than 127, a
315  both byte mode and UTF-8 mode. (When PCRE is compiled in EBCDIC mode, all byte  compile-time error occurs. This locks out non-ASCII characters in all modes.
316  values are valid. A lower case letter is converted to upper case, and then the  .P
317  0xc0 bits are flipped.)  The \ec facility was designed for use with ASCII characters, but with the
318  .P  extension to Unicode it is even less useful than it once was. It is, however,
319  After \ex, from zero to two hexadecimal digits are read (letters can be in  recognized when PCRE is compiled in EBCDIC mode, where data items are always
320  upper or lower case). Any number of hexadecimal digits may appear between \ex{  bytes. In this mode, all values are valid after \ec. If the next character is a
321  and }, but the value of the character code must be less than 256 in non-UTF-8  lower case letter, it is converted to upper case. Then the 0xc0 bits of the
322  mode, and less than 2**31 in UTF-8 mode. That is, the maximum value in  byte are inverted. Thus \ecA becomes hex 01, as in ASCII (A is C1), but because
323  hexadecimal is 7FFFFFFF. Note that this is bigger than the largest Unicode code  the EBCDIC letters are disjoint, \ecZ becomes hex 29 (Z is E9), and other
324  point, which is 10FFFF.  characters also generate different values.
 .P  
 If characters other than hexadecimal digits appear between \ex{ and }, or if  
 there is no terminating }, this form of escape is not recognized. Instead, the  
 initial \ex will be interpreted as a basic hexadecimal escape, with no  
 following digits, giving a character whose value is zero.  
 .P  
 Characters whose value is less than 256 can be defined by either of the two  
 syntaxes for \ex. There is no difference in the way they are handled. For  
 example, \exdc is exactly the same as \ex{dc}.  
325  .P  .P
326  After \e0 up to two further octal digits are read. If there are fewer than two  After \e0 up to two further octal digits are read. If there are fewer than two
327  digits, just those that are present are used. Thus the sequence \e0\ex\e07  digits, just those that are present are used. Thus the sequence \e0\ex\e07
# Line 275  specifies two binary zeros followed by a Line 329  specifies two binary zeros followed by a
329  sure you supply two digits after the initial zero if the pattern character that  sure you supply two digits after the initial zero if the pattern character that
330  follows is itself an octal digit.  follows is itself an octal digit.
331  .P  .P
332  The handling of a backslash followed by a digit other than 0 is complicated.  The escape \eo must be followed by a sequence of octal digits, enclosed in
333  Outside a character class, PCRE reads it and any following digits as a decimal  braces. An error occurs if this is not the case. This escape is a recent
334  number. If the number is less than 10, or if there have been at least that many  addition to Perl; it provides way of specifying character code points as octal
335    numbers greater than 0777, and it also allows octal numbers and back references
336    to be unambiguously specified.
337    .P
338    For greater clarity and unambiguity, it is best to avoid following \e by a
339    digit greater than zero. Instead, use \eo{} or \ex{} to specify character
340    numbers, and \eg{} to specify back references. The following paragraphs
341    describe the old, ambiguous syntax.
342    .P
343    The handling of a backslash followed by a digit other than 0 is complicated,
344    and Perl has changed in recent releases, causing PCRE also to change. Outside a
345    character class, PCRE reads the digit and any following digits as a decimal
346    number. If the number is less than 8, or if there have been at least that many
347  previous capturing left parentheses in the expression, the entire sequence is  previous capturing left parentheses in the expression, the entire sequence is
348  taken as a \fIback reference\fP. A description of how this works is given  taken as a \fIback reference\fP. A description of how this works is given
349  .\" HTML <a href="#backreferences">  .\" HTML <a href="#backreferences">
# Line 290  following the discussion of Line 356  following the discussion of
356  parenthesized subpatterns.  parenthesized subpatterns.
357  .\"  .\"
358  .P  .P
359  Inside a character class, or if the decimal number is greater than 9 and there  Inside a character class, or if the decimal number following \e is greater than
360  have not been that many capturing subpatterns, PCRE re-reads up to three octal  7 and there have not been that many capturing subpatterns, PCRE handles \e8 and
361  digits following the backslash, and uses them to generate a data character. Any  \e9 as the literal characters "8" and "9", and otherwise re-reads up to three
362  subsequent digits stand for themselves. In non-UTF-8 mode, the value of a  octal digits following the backslash, using them to generate a data character.
363  character specified in octal must be less than \e400. In UTF-8 mode, values up  Any subsequent digits stand for themselves. For example:
 to \e777 are permitted. For example:  
364  .sp  .sp
365    \e040   is another way of writing a space    \e040   is another way of writing an ASCII space
366  .\" JOIN  .\" JOIN
367    \e40    is the same, provided there are fewer than 40    \e40    is the same, provided there are fewer than 40
368              previous capturing subpatterns              previous capturing subpatterns
# Line 312  to \e777 are permitted. For example: Line 377  to \e777 are permitted. For example:
377              character with octal code 113              character with octal code 113
378  .\" JOIN  .\" JOIN
379    \e377   might be a back reference, otherwise    \e377   might be a back reference, otherwise
380              the byte consisting entirely of 1 bits              the value 255 (decimal)
381  .\" JOIN  .\" JOIN
382    \e81    is either a back reference, or a binary zero    \e81    is either a back reference, or the two
383              followed by the two characters "8" and "1"              characters "8" and "1"
384  .sp  .sp
385  Note that octal values of 100 or greater must not be introduced by a leading  Note that octal values of 100 or greater that are specified using this syntax
386  zero, because no more than three octal digits are ever read.  must not be introduced by a leading zero, because no more than three octal
387    digits are ever read.
388    .P
389    By default, after \ex that is not followed by {, from zero to two hexadecimal
390    digits are read (letters can be in upper or lower case). Any number of
391    hexadecimal digits may appear between \ex{ and }. If a character other than
392    a hexadecimal digit appears between \ex{ and }, or if there is no terminating
393    }, an error occurs.
394    .P
395    If the PCRE_JAVASCRIPT_COMPAT option is set, the interpretation of \ex is
396    as just described only when it is followed by two hexadecimal digits.
397    Otherwise, it matches a literal "x" character. In JavaScript mode, support for
398    code points greater than 256 is provided by \eu, which must be followed by
399    four hexadecimal digits; otherwise it matches a literal "u" character.
400  .P  .P
401    Characters whose value is less than 256 can be defined by either of the two
402    syntaxes for \ex (or by \eu in JavaScript mode). There is no difference in the
403    way they are handled. For example, \exdc is exactly the same as \ex{dc} (or
404    \eu00dc in JavaScript mode).
405    .
406    .
407    .SS "Constraints on character values"
408    .rs
409    .sp
410    Characters that are specified using octal or hexadecimal numbers are
411    limited to certain values, as follows:
412    .sp
413      8-bit non-UTF mode    less than 0x100
414      8-bit UTF-8 mode      less than 0x10ffff and a valid codepoint
415      16-bit non-UTF mode   less than 0x10000
416      16-bit UTF-16 mode    less than 0x10ffff and a valid codepoint
417      32-bit non-UTF mode   less than 0x100000000
418      32-bit UTF-32 mode    less than 0x10ffff and a valid codepoint
419    .sp
420    Invalid Unicode codepoints are the range 0xd800 to 0xdfff (the so-called
421    "surrogate" codepoints), and 0xffef.
422    .
423    .
424    .SS "Escape sequences in character classes"
425    .rs
426    .sp
427  All the sequences that define a single character value can be used both inside  All the sequences that define a single character value can be used both inside
428  and outside character classes. In addition, inside a character class, the  and outside character classes. In addition, inside a character class, \eb is
429  sequence \eb is interpreted as the backspace character (hex 08). The sequences  interpreted as the backspace character (hex 08).
430  \eB, \eN, \eR, and \eX are not special inside a character class. Like any other  .P
431  unrecognized escape sequences, they are treated as the literal characters "B",  \eN is not allowed in a character class. \eB, \eR, and \eX are not special
432  "N", "R", and "X" by default, but cause an error if the PCRE_EXTRA option is  inside a character class. Like other unrecognized escape sequences, they are
433  set. Outside a character class, these sequences have different meanings.  treated as the literal characters "B", "R", and "X" by default, but cause an
434    error if the PCRE_EXTRA option is set. Outside a character class, these
435    sequences have different meanings.
436    .
437    .
438    .SS "Unsupported escape sequences"
439    .rs
440    .sp
441    In Perl, the sequences \el, \eL, \eu, and \eU are recognized by its string
442    handler and used to modify the case of following characters. By default, PCRE
443    does not support these escape sequences. However, if the PCRE_JAVASCRIPT_COMPAT
444    option is set, \eU matches a "U" character, and \eu can be used to define a
445    character by code point, as described in the previous section.
446  .  .
447  .  .
448  .SS "Absolute and relative back references"  .SS "Absolute and relative back references"
# Line 373  Another use of backslash is for specifyi Line 489  Another use of backslash is for specifyi
489  .sp  .sp
490    \ed     any decimal digit    \ed     any decimal digit
491    \eD     any character that is not a decimal digit    \eD     any character that is not a decimal digit
492    \eh     any horizontal whitespace character    \eh     any horizontal white space character
493    \eH     any character that is not a horizontal whitespace character    \eH     any character that is not a horizontal white space character
494    \es     any whitespace character    \es     any white space character
495    \eS     any character that is not a whitespace character    \eS     any character that is not a white space character
496    \ev     any vertical whitespace character    \ev     any vertical white space character
497    \eV     any character that is not a vertical whitespace character    \eV     any character that is not a vertical white space character
498    \ew     any "word" character    \ew     any "word" character
499    \eW     any "non-word" character    \eW     any "non-word" character
500  .sp  .sp
# Line 388  This is the same as Line 504  This is the same as
504  .\" </a>  .\" </a>
505  the "." metacharacter  the "." metacharacter
506  .\"  .\"
507  when PCRE_DOTALL is not set.  when PCRE_DOTALL is not set. Perl also uses \eN to match characters by name;
508    PCRE does not support this.
509  .P  .P
510  Each pair of lower and upper case escape sequences partitions the complete set  Each pair of lower and upper case escape sequences partitions the complete set
511  of characters into two disjoint sets. Any given character matches one, and only  of characters into two disjoint sets. Any given character matches one, and only
# Line 397  classes. They each match one character o Line 514  classes. They each match one character o
514  matching point is at the end of the subject string, all of them fail, because  matching point is at the end of the subject string, all of them fail, because
515  there is no character to match.  there is no character to match.
516  .P  .P
517  For compatibility with Perl, \es does not match the VT character (code 11).  For compatibility with Perl, \es did not used to match the VT character (code
518  This makes it different from the the POSIX "space" class. The \es characters  11), which made it different from the the POSIX "space" class. However, Perl
519  are HT (9), LF (10), FF (12), CR (13), and space (32). If "use locale;" is  added VT at release 5.18, and PCRE followed suit at release 8.34. The \es
520  included in a Perl script, \es may match the VT character. In PCRE, it never  characters are now HT (9), LF (10), VT (11), FF (12), CR (13), and space (32).
 does.  
521  .P  .P
522  A "word" character is an underscore or any character that is a letter or digit.  A "word" character is an underscore or any character that is a letter or digit.
523  By default, the definition of letters and digits is controlled by PCRE's  By default, the definition of letters and digits is controlled by PCRE's
# Line 420  or "french" in Windows, some character c Line 536  or "french" in Windows, some character c
536  accented letters, and these are then matched by \ew. The use of locales with  accented letters, and these are then matched by \ew. The use of locales with
537  Unicode is discouraged.  Unicode is discouraged.
538  .P  .P
539  By default, in UTF-8 mode, characters with values greater than 128 never match  By default, in a UTF mode, characters with values greater than 128 never match
540  \ed, \es, or \ew, and always match \eD, \eS, and \eW. These sequences retain  \ed, \es, or \ew, and always match \eD, \eS, and \eW. These sequences retain
541  their original meanings from before UTF-8 support was available, mainly for  their original meanings from before UTF support was available, mainly for
542  efficiency reasons. However, if PCRE is compiled with Unicode property support,  efficiency reasons. However, if PCRE is compiled with Unicode property support,
543  and the PCRE_UCP option is set, the behaviour is changed so that Unicode  and the PCRE_UCP option is set, the behaviour is changed so that Unicode
544  properties are used to determine character types, as follows:  properties are used to determine character types, as follows:
545  .sp  .sp
546    \ed  any character that \ep{Nd} matches (decimal digit)    \ed  any character that matches \ep{Nd} (decimal digit)
547    \es  any character that \ep{Z} matches, plus HT, LF, FF, CR    \es  any character that matches \ep{Z} or \eh or \ev
548    \ew  any character that \ep{L} or \ep{N} matches, plus underscore    \ew  any character that matches \ep{L} or \ep{N}, plus underscore
549  .sp  .sp
550  The upper case escapes match the inverse sets of characters. Note that \ed  The upper case escapes match the inverse sets of characters. Note that \ed
551  matches only decimal digits, whereas \ew matches any Unicode digit, as well as  matches only decimal digits, whereas \ew matches any Unicode digit, as well as
# Line 437  any Unicode letter, and underscore. Note Line 553  any Unicode letter, and underscore. Note
553  \eB because they are defined in terms of \ew and \eW. Matching these sequences  \eB because they are defined in terms of \ew and \eW. Matching these sequences
554  is noticeably slower when PCRE_UCP is set.  is noticeably slower when PCRE_UCP is set.
555  .P  .P
556  The sequences \eh, \eH, \ev, and \eV are features that were added to Perl at  The sequences \eh, \eH, \ev, and \eV are features that were added to Perl at
557  release 5.10. In contrast to the other sequences, which match only ASCII  release 5.10. In contrast to the other sequences, which match only ASCII
558  characters by default, these always match certain high-valued codepoints in  characters by default, these always match certain high-valued codepoints,
559  UTF-8 mode, whether or not PCRE_UCP is set. The horizontal space characters  whether or not PCRE_UCP is set. The horizontal space characters are:
 are:  
560  .sp  .sp
561    U+0009     Horizontal tab    U+0009     Horizontal tab (HT)
562    U+0020     Space    U+0020     Space
563    U+00A0     Non-break space    U+00A0     Non-break space
564    U+1680     Ogham space mark    U+1680     Ogham space mark
# Line 465  are: Line 580  are:
580  .sp  .sp
581  The vertical space characters are:  The vertical space characters are:
582  .sp  .sp
583    U+000A     Linefeed    U+000A     Linefeed (LF)
584    U+000B     Vertical tab    U+000B     Vertical tab (VT)
585    U+000C     Formfeed    U+000C     Form feed (FF)
586    U+000D     Carriage return    U+000D     Carriage return (CR)
587    U+0085     Next line    U+0085     Next line (NEL)
588    U+2028     Line separator    U+2028     Line separator
589    U+2029     Paragraph separator    U+2029     Paragraph separator
590    .sp
591    In 8-bit, non-UTF-8 mode, only the characters with codepoints less than 256 are
592    relevant.
593  .  .
594  .  .
595  .\" HTML <a name="newlineseq"></a>  .\" HTML <a name="newlineseq"></a>
# Line 479  The vertical space characters are: Line 597  The vertical space characters are:
597  .rs  .rs
598  .sp  .sp
599  Outside a character class, by default, the escape sequence \eR matches any  Outside a character class, by default, the escape sequence \eR matches any
600  Unicode newline sequence. In non-UTF-8 mode \eR is equivalent to the following:  Unicode newline sequence. In 8-bit non-UTF-8 mode \eR is equivalent to the
601    following:
602  .sp  .sp
603    (?>\er\en|\en|\ex0b|\ef|\er|\ex85)    (?>\er\en|\en|\ex0b|\ef|\er|\ex85)
604  .sp  .sp
# Line 490  below. Line 609  below.
609  .\"  .\"
610  This particular group matches either the two-character sequence CR followed by  This particular group matches either the two-character sequence CR followed by
611  LF, or one of the single characters LF (linefeed, U+000A), VT (vertical tab,  LF, or one of the single characters LF (linefeed, U+000A), VT (vertical tab,
612  U+000B), FF (formfeed, U+000C), CR (carriage return, U+000D), or NEL (next  U+000B), FF (form feed, U+000C), CR (carriage return, U+000D), or NEL (next
613  line, U+0085). The two-character sequence is treated as a single unit that  line, U+0085). The two-character sequence is treated as a single unit that
614  cannot be split.  cannot be split.
615  .P  .P
616  In UTF-8 mode, two additional characters whose codepoints are greater than 255  In other modes, two additional characters whose codepoints are greater than 255
617  are added: LS (line separator, U+2028) and PS (paragraph separator, U+2029).  are added: LS (line separator, U+2028) and PS (paragraph separator, U+2029).
618  Unicode character property support is not needed for these characters to be  Unicode character property support is not needed for these characters to be
619  recognized.  recognized.
# Line 510  one of the following sequences: Line 629  one of the following sequences:
629    (*BSR_ANYCRLF)   CR, LF, or CRLF only    (*BSR_ANYCRLF)   CR, LF, or CRLF only
630    (*BSR_UNICODE)   any Unicode newline sequence    (*BSR_UNICODE)   any Unicode newline sequence
631  .sp  .sp
632  These override the default and the options given to \fBpcre_compile()\fP or  These override the default and the options given to the compiling function, but
633  \fBpcre_compile2()\fP, but they can be overridden by options given to  they can themselves be overridden by options given to a matching function. Note
634  \fBpcre_exec()\fP or \fBpcre_dfa_exec()\fP. Note that these special settings,  that these special settings, which are not Perl-compatible, are recognized only
635  which are not Perl-compatible, are recognized only at the very start of a  at the very start of a pattern, and that they must be in upper case. If more
636  pattern, and that they must be in upper case. If more than one of them is  than one of them is present, the last one is used. They can be combined with a
637  present, the last one is used. They can be combined with a change of newline  change of newline convention; for example, a pattern can start with:
 convention; for example, a pattern can start with:  
638  .sp  .sp
639    (*ANY)(*BSR_ANYCRLF)    (*ANY)(*BSR_ANYCRLF)
640  .sp  .sp
641  They can also be combined with the (*UTF8) or (*UCP) special sequences. Inside  They can also be combined with the (*UTF8), (*UTF16), (*UTF32), (*UTF) or
642  a character class, \eR is treated as an unrecognized escape sequence, and so  (*UCP) special sequences. Inside a character class, \eR is treated as an
643  matches the letter "R" by default, but causes an error if PCRE_EXTRA is set.  unrecognized escape sequence, and so matches the letter "R" by default, but
644    causes an error if PCRE_EXTRA is set.
645  .  .
646  .  .
647  .\" HTML <a name="uniextseq"></a>  .\" HTML <a name="uniextseq"></a>
# Line 531  matches the letter "R" by default, but c Line 650  matches the letter "R" by default, but c
650  .sp  .sp
651  When PCRE is built with Unicode character property support, three additional  When PCRE is built with Unicode character property support, three additional
652  escape sequences that match characters with specific properties are available.  escape sequences that match characters with specific properties are available.
653  When not in UTF-8 mode, these sequences are of course limited to testing  When in 8-bit non-UTF-8 mode, these sequences are of course limited to testing
654  characters whose codepoints are less than 256, but they do work in this mode.  characters whose codepoints are less than 256, but they do work in this mode.
655  The extra escape sequences are:  The extra escape sequences are:
656  .sp  .sp
657    \ep{\fIxx\fP}   a character with the \fIxx\fP property    \ep{\fIxx\fP}   a character with the \fIxx\fP property
658    \eP{\fIxx\fP}   a character without the \fIxx\fP property    \eP{\fIxx\fP}   a character without the \fIxx\fP property
659    \eX       an extended Unicode sequence    \eX       a Unicode extended grapheme cluster
660  .sp  .sp
661  The property names represented by \fIxx\fP above are limited to the Unicode  The property names represented by \fIxx\fP above are limited to the Unicode
662  script names, the general category properties, "Any", which matches any  script names, the general category properties, "Any", which matches any
# Line 566  Armenian, Line 685  Armenian,
685  Avestan,  Avestan,
686  Balinese,  Balinese,
687  Bamum,  Bamum,
688    Batak,
689  Bengali,  Bengali,
690  Bopomofo,  Bopomofo,
691    Brahmi,
692  Braille,  Braille,
693  Buginese,  Buginese,
694  Buhid,  Buhid,
695  Canadian_Aboriginal,  Canadian_Aboriginal,
696  Carian,  Carian,
697    Chakma,
698  Cham,  Cham,
699  Cherokee,  Cherokee,
700  Common,  Common,
# Line 615  Lisu, Line 737  Lisu,
737  Lycian,  Lycian,
738  Lydian,  Lydian,
739  Malayalam,  Malayalam,
740    Mandaic,
741  Meetei_Mayek,  Meetei_Mayek,
742    Meroitic_Cursive,
743    Meroitic_Hieroglyphs,
744    Miao,
745  Mongolian,  Mongolian,
746  Myanmar,  Myanmar,
747  New_Tai_Lue,  New_Tai_Lue,
# Line 634  Rejang, Line 760  Rejang,
760  Runic,  Runic,
761  Samaritan,  Samaritan,
762  Saurashtra,  Saurashtra,
763    Sharada,
764  Shavian,  Shavian,
765  Sinhala,  Sinhala,
766    Sora_Sompeng,
767  Sundanese,  Sundanese,
768  Syloti_Nagri,  Syloti_Nagri,
769  Syriac,  Syriac,
# Line 644  Tagbanwa, Line 772  Tagbanwa,
772  Tai_Le,  Tai_Le,
773  Tai_Tham,  Tai_Tham,
774  Tai_Viet,  Tai_Viet,
775    Takri,
776  Tamil,  Tamil,
777  Telugu,  Telugu,
778  Thaana,  Thaana,
# Line 718  the Lu, Ll, or Lt property, in other wor Line 847  the Lu, Ll, or Lt property, in other wor
847  a modifier or "other".  a modifier or "other".
848  .P  .P
849  The Cs (Surrogate) property applies only to characters in the range U+D800 to  The Cs (Surrogate) property applies only to characters in the range U+D800 to
850  U+DFFF. Such characters are not valid in UTF-8 strings (see RFC 3629) and so  U+DFFF. Such characters are not valid in Unicode strings and so
851  cannot be tested by PCRE, unless UTF-8 validity checking has been turned off  cannot be tested by PCRE, unless UTF validity checking has been turned off
852  (see the discussion of PCRE_NO_UTF8_CHECK in the  (see the discussion of PCRE_NO_UTF8_CHECK, PCRE_NO_UTF16_CHECK and
853    PCRE_NO_UTF32_CHECK in the
854  .\" HREF  .\" HREF
855  \fBpcreapi\fP  \fBpcreapi\fP
856  .\"  .\"
# Line 735  Instead, this property is assumed for an Line 865  Instead, this property is assumed for an
865  Unicode table.  Unicode table.
866  .P  .P
867  Specifying caseless matching does not affect these escape sequences. For  Specifying caseless matching does not affect these escape sequences. For
868  example, \ep{Lu} always matches only upper case letters.  example, \ep{Lu} always matches only upper case letters. This is different from
869    the behaviour of current versions of Perl.
870  .P  .P
871  The \eX escape matches any number of Unicode characters that form an extended  Matching characters by Unicode property is not fast, because PCRE has to do a
872  Unicode sequence. \eX is equivalent to  multistage table lookup in order to find a character's property. That is why
873  .sp  the traditional escape sequences such as \ed and \ew do not use Unicode
874    (?>\ePM\epM*)  properties in PCRE by default, though you can make them do so by setting the
875    PCRE_UCP option or by starting the pattern with (*UCP).
876    .
877    .
878    .SS Extended grapheme clusters
879    .rs
880  .sp  .sp
881  That is, it matches a character without the "mark" property, followed by zero  The \eX escape matches any number of Unicode characters that form an "extended
882  or more characters with the "mark" property, and treats the sequence as an  grapheme cluster", and treats the sequence as an atomic group
 atomic group  
883  .\" HTML <a href="#atomicgroup">  .\" HTML <a href="#atomicgroup">
884  .\" </a>  .\" </a>
885  (see below).  (see below).
886  .\"  .\"
887  Characters with the "mark" property are typically accents that affect the  Up to and including release 8.31, PCRE matched an earlier, simpler definition
888  preceding character. None of them have codepoints less than 256, so in  that was equivalent to
889  non-UTF-8 mode \eX matches any one character.  .sp
890  .P    (?>\ePM\epM*)
891  Matching characters by Unicode property is not fast, because PCRE has to search  .sp
892  a structure that contains data for over fifteen thousand characters. That is  That is, it matched a character without the "mark" property, followed by zero
893  why the traditional escape sequences such as \ed and \ew do not use Unicode  or more characters with the "mark" property. Characters with the "mark"
894  properties in PCRE by default, though you can make them do so by setting the  property are typically non-spacing accents that affect the preceding character.
895  PCRE_UCP option for \fBpcre_compile()\fP or by starting the pattern with  .P
896  (*UCP).  This simple definition was extended in Unicode to include more complicated
897    kinds of composite character by giving each character a grapheme breaking
898    property, and creating rules that use these properties to define the boundaries
899    of extended grapheme clusters. In releases of PCRE later than 8.31, \eX matches
900    one of these clusters.
901    .P
902    \eX always matches at least one character. Then it decides whether to add
903    additional characters according to the following rules for ending a cluster:
904    .P
905    1. End at the end of the subject string.
906    .P
907    2. Do not end between CR and LF; otherwise end after any control character.
908    .P
909    3. Do not break Hangul (a Korean script) syllable sequences. Hangul characters
910    are of five types: L, V, T, LV, and LVT. An L character may be followed by an
911    L, V, LV, or LVT character; an LV or V character may be followed by a V or T
912    character; an LVT or T character may be follwed only by a T character.
913    .P
914    4. Do not end before extending characters or spacing marks. Characters with
915    the "mark" property always have the "extend" grapheme breaking property.
916    .P
917    5. Do not end after prepend characters.
918    .P
919    6. Otherwise, end the cluster.
920  .  .
921  .  .
922  .\" HTML <a name="extraprops"></a>  .\" HTML <a name="extraprops"></a>
923  .SS PCRE's additional properties  .SS PCRE's additional properties
924  .rs  .rs
925  .sp  .sp
926  As well as the standard Unicode properties described in the previous  As well as the standard Unicode properties described above, PCRE supports four
927  section, PCRE supports four more that make it possible to convert traditional  more that make it possible to convert traditional escape sequences such as \ew
928  escape sequences such as \ew and \es and POSIX character classes to use Unicode  and \es to use Unicode properties. PCRE uses these non-standard, non-Perl
929  properties. PCRE uses these non-standard, non-Perl properties internally when  properties internally when PCRE_UCP is set. However, they may also be used
930  PCRE_UCP is set. They are:  explicitly. These properties are:
931  .sp  .sp
932    Xan   Any alphanumeric character    Xan   Any alphanumeric character
933    Xps   Any POSIX space character    Xps   Any POSIX space character
# Line 777  PCRE_UCP is set. They are: Line 935  PCRE_UCP is set. They are:
935    Xwd   Any Perl "word" character    Xwd   Any Perl "word" character
936  .sp  .sp
937  Xan matches characters that have either the L (letter) or the N (number)  Xan matches characters that have either the L (letter) or the N (number)
938  property. Xps matches the characters tab, linefeed, vertical tab, formfeed, or  property. Xps matches the characters tab, linefeed, vertical tab, form feed, or
939  carriage return, and any other character that has the Z (separator) property.  carriage return, and any other character that has the Z (separator) property.
940  Xsp is the same as Xps, except that vertical tab is excluded. Xwd matches the  Xsp is the same as Xps; it used to exclude vertical tab, for Perl
941  same characters as Xan, plus underscore.  compatibility, but Perl changed, and so PCRE followed at release 8.34. Xwd
942    matches the same characters as Xan, plus underscore.
943    .P
944    There is another non-standard property, Xuc, which matches any character that
945    can be represented by a Universal Character Name in C++ and other programming
946    languages. These are the characters $, @, ` (grave accent), and all characters
947    with Unicode code points greater than or equal to U+00A0, except for the
948    surrogates U+D800 to U+DFFF. Note that most base (ASCII) characters are
949    excluded. (Universal Character Names are of the form \euHHHH or \eUHHHHHHHH
950    where H is a hexadecimal digit. Note that the Xuc property does not match these
951    sequences but the characters that they represent.)
952  .  .
953  .  .
954  .\" HTML <a name="resetmatchstart"></a>  .\" HTML <a name="resetmatchstart"></a>
# Line 847  escape sequence" error is generated inst Line 1015  escape sequence" error is generated inst
1015  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
1016  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
1017  \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
1018  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
1019  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
1020  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
1021  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 886  regular expression. Line 1054  regular expression.
1054  .SH "CIRCUMFLEX AND DOLLAR"  .SH "CIRCUMFLEX AND DOLLAR"
1055  .rs  .rs
1056  .sp  .sp
1057    The circumflex and dollar metacharacters are zero-width assertions. That is,
1058    they test for a particular condition being true without consuming any
1059    characters from the subject string.
1060    .P
1061  Outside a character class, in the default matching mode, the circumflex  Outside a character class, in the default matching mode, the circumflex
1062  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
1063  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
1064  \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
1065  option is unset. Inside a character class, circumflex has an entirely different  option is unset. Inside a character class, circumflex has an entirely different
1066  meaning  meaning
# Line 905  constrained to match only at the start o Line 1077  constrained to match only at the start o
1077  "anchored" pattern. (There are also other constructs that can cause a pattern  "anchored" pattern. (There are also other constructs that can cause a pattern
1078  to be anchored.)  to be anchored.)
1079  .P  .P
1080  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
1081  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
1082  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
1083  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
1084  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
1085  character class.  branch in which it appears. Dollar has no special meaning in a character class.
1086  .P  .P
1087  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
1088  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 942  end of the subject in both modes, and if Line 1114  end of the subject in both modes, and if
1114  .sp  .sp
1115  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
1116  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
1117  line. In UTF-8 mode, the matched character may be more than one byte long.  line.
1118  .P  .P
1119  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
1120  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 960  The handling of dot is entirely independ Line 1132  The handling of dot is entirely independ
1132  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
1133  special meaning in a character class.  special meaning in a character class.
1134  .P  .P
1135  The escape sequence \eN behaves like a dot, except that it is not affected by  The escape sequence \eN behaves like a dot, except that it is not affected by
1136  the PCRE_DOTALL option. In other words, it matches any character except one  the PCRE_DOTALL option. In other words, it matches any character except one
1137  that signifies the end of a line.  that signifies the end of a line. Perl also uses \eN to match characters by
1138    name; PCRE does not support this.
1139  .  .
1140  .  .
1141  .SH "MATCHING A SINGLE BYTE"  .SH "MATCHING A SINGLE DATA UNIT"
1142  .rs  .rs
1143  .sp  .sp
1144  Outside a character class, the escape sequence \eC matches any one byte, both  Outside a character class, the escape sequence \eC matches any one data unit,
1145  in and out of UTF-8 mode. Unlike a dot, it always matches any line-ending  whether or not a UTF mode is set. In the 8-bit library, one data unit is one
1146  characters. The feature is provided in Perl in order to match individual bytes  byte; in the 16-bit library it is a 16-bit unit; in the 32-bit library it is
1147  in UTF-8 mode. Because it breaks up UTF-8 characters into individual bytes, the  a 32-bit unit. Unlike a dot, \eC always
1148  rest of the string may start with a malformed UTF-8 character. For this reason,  matches line-ending characters. The feature is provided in Perl in order to
1149  the \eC escape sequence is best avoided.  match individual bytes in UTF-8 mode, but it is unclear how it can usefully be
1150    used. Because \eC breaks up characters into individual data units, matching one
1151    unit with \eC in a UTF mode means that the rest of the string may start with a
1152    malformed UTF character. This has undefined results, because PCRE assumes that
1153    it is dealing with valid UTF strings (and by default it checks this at the
1154    start of processing unless the PCRE_NO_UTF8_CHECK, PCRE_NO_UTF16_CHECK or
1155    PCRE_NO_UTF32_CHECK option is used).
1156  .P  .P
1157  PCRE does not allow \eC to appear in lookbehind assertions  PCRE does not allow \eC to appear in lookbehind assertions
1158  .\" HTML <a href="#lookbehind">  .\" HTML <a href="#lookbehind">
1159  .\" </a>  .\" </a>
1160  (described below),  (described below)
1161  .\"  .\"
1162  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
1163  the lookbehind.  the lookbehind.
1164    .P
1165    In general, the \eC escape sequence is best avoided. However, one
1166    way of using it that avoids the problem of malformed UTF characters is to use a
1167    lookahead to check the length of the next character, as in this pattern, which
1168    could be used with a UTF-8 string (ignore white space and line breaks):
1169    .sp
1170      (?| (?=[\ex00-\ex7f])(\eC) |
1171          (?=[\ex80-\ex{7ff}])(\eC)(\eC) |
1172          (?=[\ex{800}-\ex{ffff}])(\eC)(\eC)(\eC) |
1173          (?=[\ex{10000}-\ex{1fffff}])(\eC)(\eC)(\eC)(\eC))
1174    .sp
1175    A group that starts with (?| resets the capturing parentheses numbers in each
1176    alternative (see
1177    .\" HTML <a href="#dupsubpatternnumber">
1178    .\" </a>
1179    "Duplicate Subpattern Numbers"
1180    .\"
1181    below). The assertions at the start of each branch check the next UTF-8
1182    character for values whose encoding uses 1, 2, 3, or 4 bytes, respectively. The
1183    character's individual bytes are then captured by the appropriate number of
1184    groups.
1185  .  .
1186  .  .
1187  .\" HTML <a name="characterclass"></a>  .\" HTML <a name="characterclass"></a>
# Line 995  bracket causes a compile-time error. If Line 1195  bracket causes a compile-time error. If
1195  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
1196  (after an initial circumflex, if present) or escaped with a backslash.  (after an initial circumflex, if present) or escaped with a backslash.
1197  .P  .P
1198  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
1199  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
1200  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
1201  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
1202  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
1203  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
1204  backslash.  backslash.
1205  .P  .P
1206  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 1011  circumflex is not an assertion; it still Line 1211  circumflex is not an assertion; it still
1211  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
1212  string.  string.
1213  .P  .P
1214  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)
1215  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
1216    \ex{ escaping mechanism.
1217  .P  .P
1218  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
1219  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
1220  "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
1221  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
1222  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
1223  always possible. For characters with higher values, the concept of case is  always possible. For characters with higher values, the concept of case is
1224  supported if PCRE is compiled with Unicode property support, but not otherwise.  supported if PCRE is compiled with Unicode property support, but not otherwise.
1225  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
1226  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
1227  with UTF-8 support.  well as with UTF support.
1228  .P  .P
1229  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
1230  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 1045  followed by two other characters. The oc Line 1246  followed by two other characters. The oc
1246  "]" can also be used to end a range.  "]" can also be used to end a range.
1247  .P  .P
1248  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
1249  used for characters specified numerically, for example [\e000-\e037]. In UTF-8  used for characters specified numerically, for example [\e000-\e037]. Ranges
1250  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}].  
1251  .P  .P
1252  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
1253  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
1254  [][\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
1255  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
1256  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
1257  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
1258  property support.  property support.
1259  .P  .P
1260  The character escape sequences \ed, \eD, \eh, \eH, \ep, \eP, \es, \eS, \ev,  The character escape sequences \ed, \eD, \eh, \eH, \ep, \eP, \es, \eS, \ev,
1261  \eV, \ew, and \eW may appear in a character class, and add the characters that  \eV, \ew, and \eW may appear in a character class, and add the characters that
1262  they match to the class. For example, [\edABCDEF] matches any hexadecimal  they match to the class. For example, [\edABCDEF] matches any hexadecimal
1263  digit. In UTF-8 mode, the PCRE_UCP option affects the meanings of \ed, \es, \ew  digit. In UTF modes, the PCRE_UCP option affects the meanings of \ed, \es, \ew
1264  and their upper case partners, just as it does when they appear outside a  and their upper case partners, just as it does when they appear outside a
1265  character class, as described in the section entitled  character class, as described in the section entitled
1266  .\" HTML <a href="#genericchartypes">  .\" HTML <a href="#genericchartypes">
# Line 1076  default, but cause an error if the PCRE_ Line 1276  default, but cause an error if the PCRE_
1276  A circumflex can conveniently be used with the upper case character types to  A circumflex can conveniently be used with the upper case character types to
1277  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.
1278  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,
1279  whereas [\ew] includes underscore. A positive character class should be read as  whereas [\ew] includes underscore. A positive character class should be read as
1280  "something OR something OR ..." and a negative class as "NOT something AND NOT  "something OR something OR ..." and a negative class as "NOT something AND NOT
1281  something AND NOT ...".  something AND NOT ...".
1282  .P  .P
1283  The only metacharacters that are recognized in character classes are backslash,  The only metacharacters that are recognized in character classes are backslash,
# Line 1110  are: Line 1310  are:
1310    lower    lower case letters    lower    lower case letters
1311    print    printing characters, including space    print    printing characters, including space
1312    punct    printing characters, excluding letters and digits and space    punct    printing characters, excluding letters and digits and space
1313    space    white space (not quite the same as \es)    space    white space (the same as \es from PCRE 8.34)
1314    upper    upper case letters    upper    upper case letters
1315    word     "word" characters (same as \ew)    word     "word" characters (same as \ew)
1316    xdigit   hexadecimal digits    xdigit   hexadecimal digits
1317  .sp  .sp
1318  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
1319  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
1320  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
1321  compatibility).  release 8.34. "Space" and \es now match the same set of characters.
1322  .P  .P
1323  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
1324  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 1130  matches "1", "2", or any non-digit. PCRE Line 1330  matches "1", "2", or any non-digit. PCRE
1330  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
1331  supported, and an error is given if they are encountered.  supported, and an error is given if they are encountered.
1332  .P  .P
1333  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
1334  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
1335  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
1336  character properties are used. This is achieved by replacing the POSIX classes  character properties are used. This is achieved by replacing certain POSIX
1337  by other sequences, as follows:  classes by other sequences, as follows:
1338  .sp  .sp
1339    [:alnum:]  becomes  \ep{Xan}    [:alnum:]  becomes  \ep{Xan}
1340    [:alpha:]  becomes  \ep{L}    [:alpha:]  becomes  \ep{L}
# Line 1145  by other sequences, as follows: Line 1345  by other sequences, as follows:
1345    [:upper:]  becomes  \ep{Lu}    [:upper:]  becomes  \ep{Lu}
1346    [:word:]   becomes  \ep{Xwd}    [:word:]   becomes  \ep{Xwd}
1347  .sp  .sp
1348  Negated versions, such as [:^alpha:] use \eP instead of \ep. The other POSIX  Negated versions, such as [:^alpha:] use \eP instead of \ep. Three other POSIX
1349  classes are unchanged, and match only characters with code points less than  classes are handled specially in UCP mode:
1350  128.  .TP 10
1351    [:graph:]
1352    This matches characters that have glyphs that mark the page when printed. In
1353    Unicode property terms, it matches all characters with the L, M, N, P, S, or Cf
1354    properties, except for:
1355    .sp
1356      U+061C           Arabic Letter Mark
1357      U+180E           Mongolian Vowel Separator
1358      U+2066 - U+2069  Various "isolate"s
1359    .sp
1360    .TP 10
1361    [:print:]
1362    This matches the same characters as [:graph:] plus space characters that are
1363    not controls, that is, characters with the Zs property.
1364    .TP 10
1365    [:punct:]
1366    This matches all characters that have the Unicode P (punctuation) property,
1367    plus those characters whose code points are less than 128 that have the S
1368    (Symbol) property.
1369    .P
1370    The other POSIX classes are unchanged, and match only characters with code
1371    points less than 128.
1372  .  .
1373  .  .
1374  .SH "VERTICAL BAR"  .SH "VERTICAL BAR"
# Line 1218  option settings happen at compile time. Line 1439  option settings happen at compile time.
1439  behaviour otherwise.  behaviour otherwise.
1440  .P  .P
1441  \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
1442  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
1443  pattern can contain special leading sequences such as (*CRLF) to override what  the pattern can contain special leading sequences such as (*CRLF) to override
1444  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
1445  section entitled  the section entitled
1446  .\" HTML <a href="#newlineseq">  .\" HTML <a href="#newlineseq">
1447  .\" </a>  .\" </a>
1448  "Newline sequences"  "Newline sequences"
1449  .\"  .\"
1450  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
1451  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
1452  PCRE_UTF8 and the PCRE_UCP options, respectively.  equivalent to setting the PCRE_UTF8, PCRE_UTF16, PCRE_UTF32 and the PCRE_UCP
1453    options, respectively. The (*UTF) sequence is a generic version that can be
1454    used with any of the libraries. However, the application can set the
1455    PCRE_NEVER_UTF option, which locks out the use of the (*UTF) sequences.
1456  .  .
1457  .  .
1458  .\" HTML <a name="subpattern"></a>  .\" HTML <a name="subpattern"></a>
# Line 1247  match "cataract", "erpillar" or an empty Line 1471  match "cataract", "erpillar" or an empty
1471  .sp  .sp
1472  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
1473  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
1474  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
1475  \fBpcre_exec()\fP. Opening parentheses are counted from left to right (starting  matching function. (This applies only to the traditional matching functions;
1476  from 1) to obtain numbers for the capturing subpatterns. For example, if the  the DFA matching functions do not support capturing.)
1477  string "the red king" is matched against the pattern  .P
1478    Opening parentheses are counted from left to right (starting from 1) to obtain
1479    numbers for the capturing subpatterns. For example, if the string "the red
1480    king" is matched against the pattern
1481  .sp  .sp
1482    the ((red|white) (king|queen))    the ((red|white) (king|queen))
1483  .sp  .sp
# Line 1313  or "defdef": Line 1540  or "defdef":
1540  .sp  .sp
1541    /(?|(abc)|(def))\e1/    /(?|(abc)|(def))\e1/
1542  .sp  .sp
1543  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
1544  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
1545  pattern matches "abcabc" or "defabc":  "abcabc" or "defabc":
1546  .sp  .sp
1547    /(?|(abc)|(def))(?1)/    /(?|(abc)|(def))(?1)/
1548  .sp  .sp
# Line 1391  for the first (and in this example, the Line 1618  for the first (and in this example, the
1618  matched. This saves searching to find which numbered subpattern it was.  matched. This saves searching to find which numbered subpattern it was.
1619  .P  .P
1620  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
1621  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
1622  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
1623  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
1624    "barbar" but not "foobar" or "barfoo":
1625    .sp
1626      (?:(?<n>foo)|(?<n>bar))\k<n>
1627    .sp
1628    .P
1629    If you make a subroutine call to a non-unique named subpattern, the one that
1630    corresponds to the first occurrence of the name is used. In the absence of
1631    duplicate numbers (see the previous section) this is the one with the lowest
1632    number.
1633    .P
1634    If you use a named reference in a condition
1635  test (see the  test (see the
1636  .\"  .\"
1637  .\" HTML <a href="#conditions">  .\" HTML <a href="#conditions">
# Line 1413  documentation. Line 1651  documentation.
1651  \fBWarning:\fP You cannot use different names to distinguish between two  \fBWarning:\fP You cannot use different names to distinguish between two
1652  subpatterns with the same number because PCRE uses only the numbers when  subpatterns with the same number because PCRE uses only the numbers when
1653  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
1654  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
1655  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
1656    set.
1657  .  .
1658  .  .
1659  .SH REPETITION  .SH REPETITION
# Line 1426  items: Line 1665  items:
1665    a literal data character    a literal data character
1666    the dot metacharacter    the dot metacharacter
1667    the \eC escape sequence    the \eC escape sequence
1668    the \eX escape sequence (in UTF-8 mode with Unicode properties)    the \eX escape sequence
1669    the \eR escape sequence    the \eR escape sequence
1670    an escape such as \ed or \epL that matches a single character    an escape such as \ed or \epL that matches a single character
1671    a character class    a character class
1672    a back reference (see next section)    a back reference (see next section)
1673    a parenthesized subpattern (unless it is an assertion)    a parenthesized subpattern (including assertions)
1674    a recursive or "subroutine" call to a subpattern    a subroutine call to a subpattern (recursive or otherwise)
1675  .sp  .sp
1676  The general repetition quantifier specifies a minimum and maximum number of  The general repetition quantifier specifies a minimum and maximum number of
1677  permitted matches, by giving the two numbers in curly brackets (braces),  permitted matches, by giving the two numbers in curly brackets (braces),
# Line 1457  where a quantifier is not allowed, or on Line 1696  where a quantifier is not allowed, or on
1696  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
1697  quantifier, but a literal string of four characters.  quantifier, but a literal string of four characters.
1698  .P  .P
1699  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
1700  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
1701  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,
1702  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
1703  which may be several bytes long (and they may be of different lengths).  several data units long (and they may be of different lengths).
1704  .P  .P
1705  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
1706  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 1547  In cases where it is known that the subj Line 1786  In cases where it is known that the subj
1786  worth setting PCRE_DOTALL in order to obtain this optimization, or  worth setting PCRE_DOTALL in order to obtain this optimization, or
1787  alternatively using ^ to indicate anchoring explicitly.  alternatively using ^ to indicate anchoring explicitly.
1788  .P  .P
1789  However, there is one situation where the optimization cannot be used. When .*  However, there are some cases where the optimization cannot be used. When .*
1790  is inside capturing parentheses that are the subject of a back reference  is inside capturing parentheses that are the subject of a back reference
1791  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
1792  succeeds. Consider, for example:  succeeds. Consider, for example:
# Line 1557  succeeds. Consider, for example: Line 1796  succeeds. Consider, for example:
1796  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
1797  this reason, such a pattern is not implicitly anchored.  this reason, such a pattern is not implicitly anchored.
1798  .P  .P
1799    Another case where implicit anchoring is not applied is when the leading .* is
1800    inside an atomic group. Once again, a match at the start may fail where a later
1801    one succeeds. Consider this pattern:
1802    .sp
1803      (?>.*?a)b
1804    .sp
1805    It matches "ab" in the subject "aab". The use of the backtracking control verbs
1806    (*PRUNE) and (*SKIP) also disable this optimization.
1807    .P
1808  When a capturing subpattern is repeated, the value captured is the substring  When a capturing subpattern is repeated, the value captured is the substring
1809  that matched the final iteration. For example, after  that matched the final iteration. For example, after
1810  .sp  .sp
# Line 1771  Because there may be many capturing pare Line 2019  Because there may be many capturing pare
2019  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.
2020  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
2021  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
2022  whitespace. Otherwise, the \eg{ syntax or an empty comment (see  white space. Otherwise, the \eg{ syntax or an empty comment (see
2023  .\" HTML <a href="#comments">  .\" HTML <a href="#comments">
2024  .\" </a>  .\" </a>
2025  "Comments"  "Comments"
# Line 1822  those that look ahead of the current pos Line 2070  those that look ahead of the current pos
2070  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,
2071  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.
2072  .P  .P
2073  Assertion subpatterns are not capturing subpatterns, and may not be repeated,  Assertion subpatterns are not capturing subpatterns. If such an assertion
2074  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
2075  of assertion contains capturing subpatterns within it, these are counted for  numbering the capturing subpatterns in the whole pattern. However, substring
2076  the purposes of numbering the capturing subpatterns in the whole pattern.  capturing is carried out only for positive assertions. (Perl sometimes, but not
2077  However, substring capturing is carried out only for positive assertions,  always, does do capturing in negative assertions.)
2078  because it does not make sense for negative assertions.  .P
2079    For compatibility with Perl, assertion subpatterns may be repeated; though
2080    it makes no sense to assert the same thing several times, the side effect of
2081    capturing parentheses may occasionally be useful. In practice, there only three
2082    cases:
2083    .sp
2084    (1) If the quantifier is {0}, the assertion is never obeyed during matching.
2085    However, it may contain internal capturing parenthesized groups that are called
2086    from elsewhere via the
2087    .\" HTML <a href="#subpatternsassubroutines">
2088    .\" </a>
2089    subroutine mechanism.
2090    .\"
2091    .sp
2092    (2) If quantifier is {0,n} where n is greater than zero, it is treated as if it
2093    were {0,1}. At run time, the rest of the pattern match is tried with and
2094    without the assertion, the order depending on the greediness of the quantifier.
2095    .sp
2096    (3) If the minimum repetition is greater than zero, the quantifier is ignored.
2097    The assertion is obeyed just once when encountered during matching.
2098  .  .
2099  .  .
2100  .SS "Lookahead assertions"  .SS "Lookahead assertions"
# Line 1905  temporarily move the current position ba Line 2172  temporarily move the current position ba
2172  match. If there are insufficient characters before the current position, the  match. If there are insufficient characters before the current position, the
2173  assertion fails.  assertion fails.
2174  .P  .P
2175  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
2176  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
2177  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
2178  different numbers of bytes, are also not permitted.  escapes, which can match different numbers of data units, are also not
2179    permitted.
2180  .P  .P
2181  .\" HTML <a href="#subpatternsassubroutines">  .\" HTML <a href="#subpatternsassubroutines">
2182  .\" </a>  .\" </a>
# Line 1997  already been matched. The two possible f Line 2265  already been matched. The two possible f
2265  If the condition is satisfied, the yes-pattern is used; otherwise the  If the condition is satisfied, the yes-pattern is used; otherwise the
2266  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
2267  subpattern, a compile-time error occurs. Each of the two alternatives may  subpattern, a compile-time error occurs. Each of the two alternatives may
2268  itself contain nested subpatterns of any form, including conditional  itself contain nested subpatterns of any form, including conditional
2269  subpatterns; the restriction to two alternatives applies only at the level of  subpatterns; the restriction to two alternatives applies only at the level of
2270  the condition. This pattern fragment is an example where the alternatives are  the condition. This pattern fragment is an example where the alternatives are
2271  complex:  complex:
2272  .sp  .sp
2273    (?(1) (A|B|C) | (D | (?(2)E|F) | E) )    (?(1) (A|B|C) | (D | (?(2)E|F) | E) )
# Line 2024  the condition is true if any of them hav Line 2292  the condition is true if any of them hav
2292  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
2293  number is relative rather than absolute. The most recently opened parentheses  number is relative rather than absolute. The most recently opened parentheses
2294  can be referenced by (?(-1), the next most recent by (?(-2), and so on. Inside  can be referenced by (?(-1), the next most recent by (?(-2), and so on. Inside
2295  loops it can also make sense to refer to subsequent groups. The next  loops it can also make sense to refer to subsequent groups. The next
2296  parentheses to be opened can be referenced as (?(+1), and so on. (The value  parentheses to be opened can be referenced as (?(+1), and so on. (The value
2297  zero in any of these forms is not used; it provokes a compile-time error.)  zero in any of these forms is not used; it provokes a compile-time error.)
2298  .P  .P
# Line 2102  If the condition is the string (DEFINE), Line 2370  If the condition is the string (DEFINE),
2370  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
2371  alternative in the subpattern. It is always skipped if control reaches this  alternative in the subpattern. It is always skipped if control reaches this
2372  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
2373  "subroutines" that can be referenced from elsewhere. (The use of  subroutines that can be referenced from elsewhere. (The use of
2374  .\" HTML <a href="#subpatternsassubroutines">  .\" HTML <a href="#subpatternsassubroutines">
2375  .\" </a>  .\" </a>
2376  "subroutines"  subroutines
2377  .\"  .\"
2378  is described below.) For example, a pattern to match an IPv4 address such as  is described below.) For example, a pattern to match an IPv4 address such as
2379  "192.168.23.245" could be written like this (ignore whitespace and line  "192.168.23.245" could be written like this (ignore white space and line
2380  breaks):  breaks):
2381  .sp  .sp
2382    (?(DEFINE) (?<byte> 2[0-4]\ed | 25[0-5] | 1\ed\ed | [1-9]?\ed) )    (?(DEFINE) (?<byte> 2[0-4]\ed | 25[0-5] | 1\ed\ed | [1-9]?\ed) )
# Line 2144  dd-aaa-dd or dd-dd-dd, where aaa are let Line 2412  dd-aaa-dd or dd-dd-dd, where aaa are let
2412  .SH COMMENTS  .SH COMMENTS
2413  .rs  .rs
2414  .sp  .sp
2415  There are two ways of including comments in patterns that are processed by  There are two ways of including comments in patterns that are processed by
2416  PCRE. In both cases, the start of the comment must not be in a character class,  PCRE. In both cases, the start of the comment must not be in a character class,
2417  nor in the middle of any other sequence of related characters such as (?: or a  nor in the middle of any other sequence of related characters such as (?: or a
2418  subpattern name or number. The characters that make up a comment play no part  subpattern name or number. The characters that make up a comment play no part
# Line 2155  closing parenthesis. Nested parentheses Line 2423  closing parenthesis. Nested parentheses
2423  option is set, an unescaped # character also introduces a comment, which in  option is set, an unescaped # character also introduces a comment, which in
2424  this case continues to immediately after the next newline character or  this case continues to immediately after the next newline character or
2425  character sequence in the pattern. Which characters are interpreted as newlines  character sequence in the pattern. Which characters are interpreted as newlines
2426  is controlled by the options passed to \fBpcre_compile()\fP or by a special  is controlled by the options passed to a compiling function or by a special
2427  sequence at the start of the pattern, as described in the section entitled  sequence at the start of the pattern, as described in the section entitled
2428  .\" HTML <a href="#newlines">  .\" HTML <a href="#newlines">
2429  .\" </a>  .\" </a>
# Line 2168  default newline convention is in force: Line 2436  default newline convention is in force:
2436  .sp  .sp
2437    abc #comment \en still comment    abc #comment \en still comment
2438  .sp  .sp
2439  On encountering the # character, \fBpcre_compile()\fP skips along, looking for  On encountering the # character, \fBpcre_compile()\fP skips along, looking for
2440  a newline in the pattern. The sequence \en is still literal at this stage, so  a newline in the pattern. The sequence \en is still literal at this stage, so
2441  it does not terminate the comment. Only an actual character with the code value  it does not terminate the comment. Only an actual character with the code value
2442  0x0a (the default newline) does so.  0x0a (the default newline) does so.
# Line 2200  individual subpattern recursion. After i Line 2468  individual subpattern recursion. After i
2468  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.
2469  .P  .P
2470  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
2471  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
2472  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
2473  .\" HTML <a href="#subpatternsassubroutines">  .\" HTML <a href="#subpatternsassubroutines">
2474  .\" </a>  .\" </a>
2475  "subroutine"  non-recursive subroutine
2476  .\"  .\"
2477  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
2478  a recursive call of the entire regular expression.  a recursive call of the entire regular expression.
# Line 2239  references such as (?+2). However, these Line 2507  references such as (?+2). However, these
2507  reference is not inside the parentheses that are referenced. They are always  reference is not inside the parentheses that are referenced. They are always
2508  .\" HTML <a href="#subpatternsassubroutines">  .\" HTML <a href="#subpatternsassubroutines">
2509  .\" </a>  .\" </a>
2510  "subroutine"  non-recursive subroutine
2511  .\"  .\"
2512  calls, as described in the next section.  calls, as described in the next section.
2513  .P  .P
# Line 2276  documentation). If the pattern above is Line 2544  documentation). If the pattern above is
2544  .sp  .sp
2545  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
2546  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
2547  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
2548  set at a deeper level.  (temporarily) set at a deeper level during the matching process.
2549  .P  .P
2550  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
2551  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 2297  is the actual recursive call. Line 2565  is the actual recursive call.
2565  .  .
2566  .  .
2567  .\" HTML <a name="recursiondifference"></a>  .\" HTML <a name="recursiondifference"></a>
2568  .SS "Recursion difference from Perl"  .SS "Differences in recursion processing between PCRE and Perl"
2569  .rs  .rs
2570  .sp  .sp
2571  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
2572  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
2573  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
2574  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
2575  following pattern, which purports to match a palindromic string that contains  subsequent matching failure. This can be illustrated by the following pattern,
2576  an odd number of characters (for example, "a", "aba", "abcba", "abcdcba"):  which purports to match a palindromic string that contains an odd number of
2577    characters (for example, "a", "aba", "abcba", "abcdcba"):
2578  .sp  .sp
2579    ^(.|(.)(?1)\e2)$    ^(.|(.)(?1)\e2)$
2580  .sp  .sp
# Line 2366  For example, although "abcba" is correct Line 2635  For example, although "abcba" is correct
2635  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
2636  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
2637  recursion to try other alternatives, so the entire match fails.  recursion to try other alternatives, so the entire match fails.
2638    .P
2639    The second way in which PCRE and Perl differ in their recursion processing is
2640    in the handling of captured values. In Perl, when a subpattern is called
2641    recursively or as a subpattern (see the next section), it has no access to any
2642    values that were captured outside the recursion, whereas in PCRE these values
2643    can be referenced. Consider this pattern:
2644    .sp
2645      ^(.)(\e1|a(?2))
2646    .sp
2647    In PCRE, this pattern matches "bab". The first capturing parentheses match "b",
2648    then in the second group, when the back reference \e1 fails to match "b", the
2649    second alternative matches "a" and then recurses. In the recursion, \e1 does
2650    now match "b" and so the whole match succeeds. In Perl, the pattern fails to
2651    match because inside the recursive call \e1 cannot access the externally set
2652    value.
2653  .  .
2654  .  .
2655  .\" HTML <a name="subpatternsassubroutines"></a>  .\" HTML <a name="subpatternsassubroutines"></a>
2656  .SH "SUBPATTERNS AS SUBROUTINES"  .SH "SUBPATTERNS AS SUBROUTINES"
2657  .rs  .rs
2658  .sp  .sp
2659  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
2660  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
2661  subroutine in a programming language. The "called" subpattern may be defined  subroutine in a programming language. The called subpattern may be defined
2662  before or after the reference. A numbered reference can be absolute or  before or after the reference. A numbered reference can be absolute or
2663  relative, as in these examples:  relative, as in these examples:
2664  .sp  .sp
# Line 2394  matches "sense and sensibility" and "res Line 2678  matches "sense and sensibility" and "res
2678  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
2679  strings. Another example is given in the discussion of DEFINE above.  strings. Another example is given in the discussion of DEFINE above.
2680  .P  .P
2681  Like recursive subpatterns, a subroutine call is always treated as an atomic  All subroutine calls, whether recursive or not, are always treated as atomic
2682  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
2683  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
2684  matching failure. Any capturing parentheses that are set during the subroutine  subsequent matching failure. Any capturing parentheses that are set during the
2685  call revert to their previous values afterwards.  subroutine call revert to their previous values afterwards.
2686  .P  .P
2687  When a subpattern is used as a subroutine, processing options such as  Processing options such as case-independence are fixed when a subpattern is
2688  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
2689  changed for different calls. For example, consider this pattern:  different calls. For example, consider this pattern:
2690  .sp  .sp
2691    (abc)(?i:(?-1))    (abc)(?i:(?-1))
2692  .sp  .sp
# Line 2441  same pair of parentheses when there is a Line 2725  same pair of parentheses when there is a
2725  .P  .P
2726  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
2727  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
2728  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
2729    (8-bit library) or \fIpcre[16|32]_callout\fP (16-bit or 32-bit library).
2730  By default, this variable contains NULL, which disables all calling out.  By default, this variable contains NULL, which disables all calling out.
2731  .P  .P
2732  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 2451  For example, this pattern has two callou Line 2736  For example, this pattern has two callou
2736  .sp  .sp
2737    (?C1)abc(?C2)def    (?C1)abc(?C2)def
2738  .sp  .sp
2739  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
2740  automatically installed before each item in the pattern. They are all numbered  automatically installed before each item in the pattern. They are all numbered
2741  255.  255. If there is a conditional group in the pattern whose condition is an
2742  .P  assertion, an additional callout is inserted just before the condition. An
2743  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:
2744  set), the external function is called. It is provided with the number of the  .sp
2745  callout, the position in the pattern, and, optionally, one item of data    (?(?C9)(?=a)abc|def)
2746  originally supplied by the caller of \fBpcre_exec()\fP. The callout function  .sp
2747  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
2748  description of the interface to the callout function is given in the  condition.
2749    .P
2750    During matching, when PCRE reaches a callout point, the external function is
2751    called. It is provided with the number of the callout, the position in the
2752    pattern, and, optionally, one item of data originally supplied by the caller of
2753    the matching function. The callout function may cause matching to proceed, to
2754    backtrack, or to fail altogether. A complete description of the interface to
2755    the callout function is given in the
2756  .\" HREF  .\" HREF
2757  \fBpcrecallout\fP  \fBpcrecallout\fP
2758  .\"  .\"
# Line 2472  documentation. Line 2764  documentation.
2764  .rs  .rs
2765  .sp  .sp
2766  Perl 5.10 introduced a number of "Special Backtracking Control Verbs", which  Perl 5.10 introduced a number of "Special Backtracking Control Verbs", which
2767  are described in the Perl documentation as "experimental and subject to change  are still described in the Perl documentation as "experimental and subject to
2768  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
2769  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
2770  remarks apply to the PCRE features described in this section.  remarks apply to the PCRE features described in this section.
2771  .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  
2772  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
2773  parenthesis followed by an asterisk. They are generally of the form  parenthesis followed by an asterisk. They are generally of the form
2774  (*VERB) or (*VERB:NAME). Some may take either form, with differing behaviour,  (*VERB) or (*VERB:NAME). Some may take either form, possibly behaving
2775  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
2776  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
2777  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
2778  not there. Any number of these verbs may occur in a pattern.  libraries. If the name is empty, that is, if the closing parenthesis
2779    immediately follows the colon, the effect is as if the colon were not there.
2780    Any number of these verbs may occur in a pattern.
2781  .P  .P
2782    Since these verbs are specifically related to backtracking, most of them can be
2783    used only when the pattern is to be matched using one of the traditional
2784    matching functions, because these use a backtracking algorithm. With the
2785    exception of (*FAIL), which behaves like a failing negative assertion, the
2786    backtracking control verbs cause an error if encountered by a DFA matching
2787    function.
2788    .P
2789    The behaviour of these verbs in
2790    .\" HTML <a href="#btrepeat">
2791    .\" </a>
2792    repeated groups,
2793    .\"
2794    .\" HTML <a href="#btassert">
2795    .\" </a>
2796    assertions,
2797    .\"
2798    and in
2799    .\" HTML <a href="#btsub">
2800    .\" </a>
2801    subpatterns called as subroutines
2802    .\"
2803    (whether or not recursively) is documented below.
2804    .
2805    .
2806    .\" HTML <a name="nooptimize"></a>
2807    .SS "Optimizations that affect backtracking verbs"
2808    .rs
2809    .sp
2810  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
2811  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
2812  minimum length of matching subject, or that a particular character must be  minimum length of matching subject, or that a particular character must be
2813  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
2814  included backtracking verbs will not, of course, be processed. You can suppress  included backtracking verbs will not, of course, be processed. You can suppress
2815  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
2816  when calling \fBpcre_compile()\fP or \fBpcre_exec()\fP, or by starting the  when calling \fBpcre_compile()\fP or \fBpcre_exec()\fP, or by starting the
2817  pattern with (*NO_START_OPT).  pattern with (*NO_START_OPT). There is more discussion of this option in the
2818    section entitled
2819    .\" HTML <a href="pcreapi.html#execoptions">
2820    .\" </a>
2821    "Option bits for \fBpcre_exec()\fP"
2822    .\"
2823    in the
2824    .\" HREF
2825    \fBpcreapi\fP
2826    .\"
2827    documentation.
2828    .P
2829    Experiments with Perl suggest that it too has similar optimizations, sometimes
2830    leading to anomalous results.
2831  .  .
2832  .  .
2833  .SS "Verbs that act immediately"  .SS "Verbs that act immediately"
# Line 2515  followed by a name. Line 2839  followed by a name.
2839     (*ACCEPT)     (*ACCEPT)
2840  .sp  .sp
2841  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
2842  pattern. When inside a recursion, only the innermost pattern is ended  pattern. However, when it is inside a subpattern that is called as a
2843  immediately. If (*ACCEPT) is inside capturing parentheses, the data so far is  subroutine, only that subpattern is ended successfully. Matching then continues
2844  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
2845    assertion succeeds; in a negative assertion, the assertion fails.
2846    .P
2847    If (*ACCEPT) is inside capturing parentheses, the data so far is captured. For
2848    example:
2849  .sp  .sp
2850    A((?:A|B(*ACCEPT)|C)D)    A((?:A|B(*ACCEPT)|C)D)
2851  .sp  .sp
# Line 2526  the outer parentheses. Line 2854  the outer parentheses.
2854  .sp  .sp
2855    (*FAIL) or (*F)    (*FAIL) or (*F)
2856  .sp  .sp
2857  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
2858  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
2859  probably useful only when combined with (?{}) or (??{}). Those are, of course,  probably useful only when combined with (?{}) or (??{}). Those are, of course,
2860  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 2550  starting point (see (*SKIP) below). Line 2878  starting point (see (*SKIP) below).
2878  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
2879  (*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.
2880  .P  .P
2881  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),
2882  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
2883    caller as described in the section entitled
2884  .\" HTML <a href="pcreapi.html#extradata">  .\" HTML <a href="pcreapi.html#extradata">
2885  .\" </a>  .\" </a>
2886  section on \fIpcre_extra\fP  "Extra data for \fBpcre_exec()\fP"
2887  .\"  .\"
2888  in the  in the
2889  .\" HREF  .\" HREF
2890  \fBpcreapi\fP  \fBpcreapi\fP
2891  .\"  .\"
2892  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
2893  \fBpcretest\fP output, where the /K modifier requests the retrieval and  modifier requests the retrieval and outputting of (*MARK) data:
 outputting of (*MARK) data:  
2894  .sp  .sp
2895    /X(*MARK:A)Y|X(*MARK:B)Z/K      re> /X(*MARK:A)Y|X(*MARK:B)Z/K
2896    XY    data> XY
2897     0: XY     0: XY
2898    MK: A    MK: A
2899    XZ    XZ
# Line 2577  indicates which of the two alternatives Line 2905  indicates which of the two alternatives
2905  of obtaining this information than putting each alternative in its own  of obtaining this information than putting each alternative in its own
2906  capturing parentheses.  capturing parentheses.
2907  .P  .P
2908  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
2909  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
2910  (*COMMIT), this is unlikely to happen for an unanchored pattern because, as the  happen for negative assertions or failing positive assertions.
2911  starting point for matching is advanced, the final check is often with an empty  .P
2912  string, causing a failure before (*MARK) is reached. For example:  After a partial match or a failed match, the last encountered name in the
2913  .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:  
2914  .sp  .sp
2915    /^X(*MARK:A)Y|^X(*MARK:B)Z/K      re> /X(*MARK:A)Y|X(*MARK:B)Z/K
2916    XP    data> XP
2917    No match, mark = B    No match, mark = B
2918  .sp  .sp
2919  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
2920  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
2921  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
2922  .P  (*MARK) item, but nevertheless do not reset it.
2923  Note that similar anomalies (though different in detail) exist in Perl, no  .P
2924  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
2925  unanchored pattern is not recommended, unless (*COMMIT) is involved.  probably set the PCRE_NO_START_OPTIMIZE option
2926    .\" HTML <a href="#nooptimize">
2927    .\" </a>
2928    (see above)
2929    .\"
2930    to ensure that the match is always attempted.
2931  .  .
2932  .  .
2933  .SS "Verbs that act after backtracking"  .SS "Verbs that act after backtracking"
# Line 2610  unanchored pattern is not recommended, u Line 2936  unanchored pattern is not recommended, u
2936  The following verbs do nothing when they are encountered. Matching continues  The following verbs do nothing when they are encountered. Matching continues
2937  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
2938  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
2939  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
2940  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
2941  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
2942  "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
2943  above, that this localization also applies in subroutine calls and assertions.)  or assertion. (Remember also, as stated above, that this localization also
2944    applies in subroutine calls.)
2945  .P  .P
2946  These verbs differ in exactly what kind of failure occurs when backtracking  These verbs differ in exactly what kind of failure occurs when backtracking
2947  reaches them.  reaches them. The behaviour described below is what happens when the verb is
2948    not in a subroutine or an assertion. Subsequent sections cover these special
2949    cases.
2950  .sp  .sp
2951    (*COMMIT)    (*COMMIT)
2952  .sp  .sp
2953  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
2954  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
2955  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
2956  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
2957  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
2958    committed to finding a match at the current starting point, or not at all. For
2959    example:
2960  .sp  .sp
2961    a+(*COMMIT)b    a+(*COMMIT)b
2962  .sp  .sp
# Line 2634  dynamic anchor, or "I've started, so I m Line 2965  dynamic anchor, or "I've started, so I m
2965  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
2966  match failure.  match failure.
2967  .P  .P
2968    If there is more than one backtracking verb in a pattern, a different one that
2969    follows (*COMMIT) may be triggered first, so merely passing (*COMMIT) during a
2970    match does not always guarantee that a match must be at this starting point.
2971    .P
2972  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,
2973  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
2974  \fBpcretest\fP example:  \fBpcretest\fP example:
2975  .sp  .sp
2976    /(*COMMIT)abc/      re> /(*COMMIT)abc/
2977    xyzabc    data> xyzabc
2978     0: abc     0: abc
2979    xyzabc\eY    xyzabc\eY
2980    No match    No match
# Line 2653  starting points. Line 2988  starting points.
2988    (*PRUNE) or (*PRUNE:NAME)    (*PRUNE) or (*PRUNE:NAME)
2989  .sp  .sp
2990  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
2991  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
2992  unanchored, the normal "bumpalong" advance to the next starting character then  it. If the pattern is unanchored, the normal "bumpalong" advance to the next
2993  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
2994  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
2995  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
2996  (*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
2997  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
2998  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
2999  match fails completely; the name is passed back if this is the final attempt.  as (*COMMIT).
3000  (*PRUNE:NAME) does not pass back a name if the match succeeds. In an anchored  .P
3001  pattern (*PRUNE) has the same effect as (*COMMIT).  The behaviour of (*PRUNE:NAME) is the not the same as (*MARK:NAME)(*PRUNE).
3002    It is like (*MARK:NAME) in that the name is remembered for passing back to the
3003    caller. However, (*SKIP:NAME) searches only for names set with (*MARK).
3004  .sp  .sp
3005    (*SKIP)    (*SKIP)
3006  .sp  .sp
# Line 2684  instead of skipping on to "c". Line 3021  instead of skipping on to "c".
3021  .sp  .sp
3022    (*SKIP:NAME)    (*SKIP:NAME)
3023  .sp  .sp
3024  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
3025  following pattern fails to match, the previous path through the pattern is  triggered, the previous path through the pattern is searched for the most
3026  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
3027  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
3028  (*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
3029  matching name is found, normal "bumpalong" of one character happens (the  (*SKIP) is ignored.
3030  (*SKIP) is ignored).  .P
3031    Note that (*SKIP:NAME) searches only for names set by (*MARK:NAME). It ignores
3032    names that are set by (*PRUNE:NAME) or (*THEN:NAME).
3033  .sp  .sp
3034    (*THEN) or (*THEN:NAME)    (*THEN) or (*THEN:NAME)
3035  .sp  .sp
3036  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
3037  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
3038  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
3039  observation that it can be used for a pattern-based if-then-else block:  pattern-based if-then-else block:
3040  .sp  .sp
3041    ( COND1 (*THEN) FOO | COND2 (*THEN) BAR | COND3 (*THEN) BAZ ) ...    ( COND1 (*THEN) FOO | COND2 (*THEN) BAR | COND3 (*THEN) BAZ ) ...
3042  .sp  .sp
3043  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
3044  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
3045  second alternative and tries COND2, without backtracking into COND1. The  second alternative and tries COND2, without backtracking into COND1. If that
3046  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
3047  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
3048  like (*PRUNE).  group. If (*THEN) is not inside an alternation, it acts like (*PRUNE).
3049  .  .P
3050  .P  The behaviour of (*THEN:NAME) is the not the same as (*MARK:NAME)(*THEN).
3051  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
3052  matching fails. (*THEN) is the weakest, carrying on the match at the next  caller. However, (*SKIP:NAME) searches only for names set with (*MARK).
3053  alternation. (*PRUNE) comes next, failing the match at the current starting  .P
3054  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
3055  pattern). (*SKIP) is similar, except that the advance may be more than one  enclosing alternative; it is not a nested alternation with only one
3056  character. (*COMMIT) is the strongest, causing the entire match to fail.  alternative. The effect of (*THEN) extends beyond such a subpattern to the
3057  .P  enclosing alternative. Consider this pattern, where A, B, etc. are complex
3058  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:
3059  consider this pattern, where A, B, etc. are complex pattern fragments:  .sp
3060  .sp    A (B(*THEN)C) | D
3061    (A(*COMMIT)B(*THEN)C|D)  .sp
3062  .sp  If A and B are matched, but there is a failure in C, matching does not
3063  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.
3064  position. If subsequently B matches, but C does not, the normal (*THEN) action  However, if the subpattern containing (*THEN) is given an alternative, it
3065  of trying the next alternation (that is, D) does not happen because (*COMMIT)  behaves differently:
3066  overrides.  .sp
3067      A (B(*THEN)C | (*FAIL)) | D
3068    .sp
3069    The effect of (*THEN) is now confined to the inner subpattern. After a failure
3070    in C, matching moves to (*FAIL), which causes the whole subpattern to fail
3071    because there are no more alternatives to try. In this case, matching does now
3072    backtrack into A.
3073    .P
3074    Note that a conditional subpattern is not considered as having two
3075    alternatives, because only one is ever used. In other words, the | character in
3076    a conditional subpattern has a different meaning. Ignoring white space,
3077    consider:
3078    .sp
3079      ^.*? (?(?=a) a | b(*THEN)c )
3080    .sp
3081    If the subject is "ba", this pattern does not match. Because .*? is ungreedy,
3082    it initially matches zero characters. The condition (?=a) then fails, the
3083    character "b" is matched, but "c" is not. At this point, matching does not
3084    backtrack to .*? as might perhaps be expected from the presence of the |
3085    character. The conditional subpattern is part of the single alternative that
3086    comprises the whole pattern, and so the match fails. (If there was a backtrack
3087    into .*?, allowing it to match "b", the match would succeed.)
3088    .P
3089    The verbs just described provide four different "strengths" of control when
3090    subsequent matching fails. (*THEN) is the weakest, carrying on the match at the
3091    next alternative. (*PRUNE) comes next, failing the match at the current
3092    starting position, but allowing an advance to the next character (for an
3093    unanchored pattern). (*SKIP) is similar, except that the advance may be more
3094    than one character. (*COMMIT) is the strongest, causing the entire match to
3095    fail.
3096    .
3097    .
3098    .SS "More than one backtracking verb"
3099    .rs
3100    .sp
3101    If more than one backtracking verb is present in a pattern, the one that is
3102    backtracked onto first acts. For example, consider this pattern, where A, B,
3103    etc. are complex pattern fragments:
3104    .sp
3105      (A(*COMMIT)B(*THEN)C|ABD)
3106    .sp
3107    If A matches but B fails, the backtrack to (*COMMIT) causes the entire match to
3108    fail. However, if A and B match, but C fails, the backtrack to (*THEN) causes
3109    the next alternative (ABD) to be tried. This behaviour is consistent, but is
3110    not always the same as Perl's. It means that if two or more backtracking verbs
3111    appear in succession, all the the last of them has no effect. Consider this
3112    example:
3113    .sp
3114      ...(*COMMIT)(*PRUNE)...
3115    .sp
3116    If there is a matching failure to the right, backtracking onto (*PRUNE) causes
3117    it to be triggered, and its action is taken. There can never be a backtrack
3118    onto (*COMMIT).
3119    .
3120    .
3121    .\" HTML <a name="btrepeat"></a>
3122    .SS "Backtracking verbs in repeated groups"
3123    .rs
3124    .sp
3125    PCRE differs from Perl in its handling of backtracking verbs in repeated
3126    groups. For example, consider:
3127    .sp
3128      /(a(*COMMIT)b)+ac/
3129    .sp
3130    If the subject is "abac", Perl matches, but PCRE fails because the (*COMMIT) in
3131    the second repeat of the group acts.
3132    .
3133    .
3134    .\" HTML <a name="btassert"></a>
3135    .SS "Backtracking verbs in assertions"
3136    .rs
3137    .sp
3138    (*FAIL) in an assertion has its normal effect: it forces an immediate backtrack.
3139    .P
3140    (*ACCEPT) in a positive assertion causes the assertion to succeed without any
3141    further processing. In a negative assertion, (*ACCEPT) causes the assertion to
3142    fail without any further processing.
3143    .P
3144    The other backtracking verbs are not treated specially if they appear in a
3145    positive assertion. In particular, (*THEN) skips to the next alternative in the
3146    innermost enclosing group that has alternations, whether or not this is within
3147    the assertion.
3148    .P
3149    Negative assertions are, however, different, in order to ensure that changing a
3150    positive assertion into a negative assertion changes its result. Backtracking
3151    into (*COMMIT), (*SKIP), or (*PRUNE) causes a negative assertion to be true,
3152    without considering any further alternative branches in the assertion.
3153    Backtracking into (*THEN) causes it to skip to the next enclosing alternative
3154    within the assertion (the normal behaviour), but if the assertion does not have
3155    such an alternative, (*THEN) behaves like (*PRUNE).
3156    .
3157    .
3158    .\" HTML <a name="btsub"></a>
3159    .SS "Backtracking verbs in subroutines"
3160    .rs
3161    .sp
3162    These behaviours occur whether or not the subpattern is called recursively.
3163    Perl's treatment of subroutines is different in some cases.
3164    .P
3165    (*FAIL) in a subpattern called as a subroutine has its normal effect: it forces
3166    an immediate backtrack.
3167    .P
3168    (*ACCEPT) in a subpattern called as a subroutine causes the subroutine match to
3169    succeed without any further processing. Matching then continues after the
3170    subroutine call.
3171    .P
3172    (*COMMIT), (*SKIP), and (*PRUNE) in a subpattern called as a subroutine cause
3173    the subroutine match to fail.
3174    .P
3175    (*THEN) skips to the next alternative in the innermost enclosing group within
3176    the subpattern that has alternatives. If there is no such group within the
3177    subpattern, (*THEN) causes the subroutine match to fail.
3178  .  .
3179  .  .
3180  .SH "SEE ALSO"  .SH "SEE ALSO"
3181  .rs  .rs
3182  .sp  .sp
3183  \fBpcreapi\fP(3), \fBpcrecallout\fP(3), \fBpcrematching\fP(3),  \fBpcreapi\fP(3), \fBpcrecallout\fP(3), \fBpcrematching\fP(3),
3184  \fBpcresyntax\fP(3), \fBpcre\fP(3).  \fBpcresyntax\fP(3), \fBpcre\fP(3), \fBpcre16(3)\fP, \fBpcre32(3)\fP.
3185  .  .
3186  .  .
3187  .SH AUTHOR  .SH AUTHOR
# Line 2748  Cambridge CB2 3QH, England. Line 3198  Cambridge CB2 3QH, England.
3198  .rs  .rs
3199  .sp  .sp
3200  .nf  .nf
3201  Last updated: 21 November 2010  Last updated: 05 November 2013
3202  Copyright (c) 1997-2010 University of Cambridge.  Copyright (c) 1997-2013 University of Cambridge.
3203  .fi  .fi

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