/[pcre]/code/trunk/doc/pcrepattern.3
ViewVC logotype

Diff of /code/trunk/doc/pcrepattern.3

Parent Directory Parent Directory | Revision Log Revision Log | View Patch Patch

revision 607 by ph10, Sun Jun 12 15:09:49 2011 UTC revision 1395 by ph10, Sat Nov 9 16:54:52 2013 UTC
# Line 1  Line 1 
1  .TH PCREPATTERN 3  .TH PCREPATTERN 3 "09 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  .sp  option is set at compile time, (*UTF) etc. are not allowed, and their
77    (*UCP)  appearance causes an error.
78    .
79    .
80    .SS "Unicode property support"
81    .rs
82  .sp  .sp
83    Another special sequence that may appear at the start of a pattern is (*UCP).
84  This has the same effect as setting the PCRE_UCP option: it causes sequences  This has the same effect as setting the PCRE_UCP option: it causes sequences
85  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,
86  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
87  table.  table.
88  .P  .
89    .
90    .SS "Disabling auto-possessification"
91    .rs
92    .sp
93    If a pattern starts with (*NO_AUTO_POSSESS), it has the same effect as setting
94    the PCRE_NO_AUTO_POSSESSIFY option at compile time. This stops PCRE from making
95    quantifiers possessive when what follows cannot match the repeated item. For
96    example, by default a+b is treated as a++b. For more details, see the
97    .\" HREF
98    \fBpcreapi\fP
99    .\"
100    documentation.
101    .
102    .
103    .SS "Disabling start-up optimizations"
104    .rs
105    .sp
106  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
107  PCRE_NO_START_OPTIMIZE option either at compile or matching time. There are  PCRE_NO_START_OPTIMIZE option either at compile or matching time. This disables
108  also some more of these special sequences that are concerned with the handling  several optimizations for quickly reaching "no match" results. For more
109  of newlines; they are described below.  details, see the
 .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  
110  .\" HREF  .\" HREF
111  \fBpcrematching\fP  \fBpcreapi\fP
112  .\"  .\"
113  page.  documentation.
114  .  .
115  .  .
116  .\" HTML <a name="newlines"></a>  .\" HTML <a name="newlines"></a>
117  .SH "NEWLINE CONVENTIONS"  .SS "Newline conventions"
118  .rs  .rs
119  .sp  .sp
120  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 141  string with one of the following five se
141    (*ANYCRLF)   any of the three above    (*ANYCRLF)   any of the three above
142    (*ANY)       all Unicode newline sequences    (*ANY)       all Unicode newline sequences
143  .sp  .sp
144  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
145  \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  
146  .sp  .sp
147    (*CR)a.b    (*CR)a.b
148  .sp  .sp
149  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
150  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  
151  is used.  is used.
152  .P  .P
153  The newline convention affects the interpretation of the dot metacharacter when  The newline convention affects where the circumflex and dollar assertions are
154  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
155  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
156  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
157    sequence, for Perl compatibility. However, this can be changed; see the
158  description of \eR in the section entitled  description of \eR in the section entitled
159  .\" HTML <a href="#newlineseq">  .\" HTML <a href="#newlineseq">
160  .\" </a>  .\" </a>
# Line 124  below. A change of \eR setting can be co Line 164  below. A change of \eR setting can be co
164  convention.  convention.
165  .  .
166  .  .
167    .SS "Setting match and recursion limits"
168    .rs
169    .sp
170    The caller of \fBpcre_exec()\fP can set a limit on the number of times the
171    internal \fBmatch()\fP function is called and on the maximum depth of
172    recursive calls. These facilities are provided to catch runaway matches that
173    are provoked by patterns with huge matching trees (a typical example is a
174    pattern with nested unlimited repeats) and to avoid running out of system stack
175    by too much recursion. When one of these limits is reached, \fBpcre_exec()\fP
176    gives an error return. The limits can also be set by items at the start of the
177    pattern of the form
178    .sp
179      (*LIMIT_MATCH=d)
180      (*LIMIT_RECURSION=d)
181    .sp
182    where d is any number of decimal digits. However, the value of the setting must
183    be less than the value set (or defaulted) by the caller of \fBpcre_exec()\fP
184    for it to have any effect. In other words, the pattern writer can lower the
185    limits set by the programmer, but not raise them. If there is more than one
186    setting of one of these limits, the lower value is used.
187    .
188    .
189    .SH "EBCDIC CHARACTER CODES"
190    .rs
191    .sp
192    PCRE can be compiled to run in an environment that uses EBCDIC as its character
193    code rather than ASCII or Unicode (typically a mainframe system). In the
194    sections below, character code values are ASCII or Unicode; in an EBCDIC
195    environment these characters may have different code values, and there are no
196    code points greater than 255.
197    .
198    .
199  .SH "CHARACTERS AND METACHARACTERS"  .SH "CHARACTERS AND METACHARACTERS"
200  .rs  .rs
201  .sp  .sp
# Line 135  corresponding characters in the subject. Line 207  corresponding characters in the subject.
207  .sp  .sp
208  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
209  caseless matching is specified (the PCRE_CASELESS option), letters are matched  caseless matching is specified (the PCRE_CASELESS option), letters are matched
210  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
211  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
212  always possible. For characters with higher values, the concept of case is  always possible. For characters with higher values, the concept of case is
213  supported if PCRE is compiled with Unicode property support, but not otherwise.  supported if PCRE is compiled with Unicode property support, but not otherwise.
214  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
215  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
216  UTF-8 support.  UTF support.
217  .P  .P
218  The power of regular expressions comes from the ability to include alternatives  The power of regular expressions comes from the ability to include alternatives
219  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 197  otherwise be interpreted as a metacharac Line 269  otherwise be interpreted as a metacharac
269  non-alphanumeric with backslash to specify that it stands for itself. In  non-alphanumeric with backslash to specify that it stands for itself. In
270  particular, if you want to match a backslash, you write \e\e.  particular, if you want to match a backslash, you write \e\e.
271  .P  .P
272  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
273  backslash. All other characters (in particular, those whose codepoints are  backslash. All other characters (in particular, those whose codepoints are
274  greater than 127) are treated as literals.  greater than 127) are treated as literals.
275  .P  .P
276  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
277  pattern (other than in a character class) and characters between a # outside  pattern (other than in a character class) and characters between a # outside
278  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
279  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.
280  .P  .P
281  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
282  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 292  Perl, $ and @ cause variable interpolati
292    \eQabc\eE\e$\eQxyz\eE   abc$xyz        abc$xyz    \eQabc\eE\e$\eQxyz\eE   abc$xyz        abc$xyz
293  .sp  .sp
294  The \eQ...\eE sequence is recognized both inside and outside character classes.  The \eQ...\eE sequence is recognized both inside and outside character classes.
295  An isolated \eE that is not preceded by \eQ is ignored. If \eQ is not followed  An isolated \eE that is not preceded by \eQ is ignored. If \eQ is not followed
296  by \eE later in the pattern, the literal interpretation continues to the end of  by \eE later in the pattern, the literal interpretation continues to the end of
297  the pattern (that is, \eE is assumed at the end). If the isolated \eQ is inside  the pattern (that is, \eE is assumed at the end). If the isolated \eQ is inside
298  a character class, this causes an error, because the character class is not  a character class, this causes an error, because the character class is not
299  terminated.  terminated.
# Line 240  one of the following escape sequences th Line 312  one of the following escape sequences th
312    \ea        alarm, that is, the BEL character (hex 07)    \ea        alarm, that is, the BEL character (hex 07)
313    \ecx       "control-x", where x is any ASCII character    \ecx       "control-x", where x is any ASCII character
314    \ee        escape (hex 1B)    \ee        escape (hex 1B)
315    \ef        formfeed (hex 0C)    \ef        form feed (hex 0C)
316    \en        linefeed (hex 0A)    \en        linefeed (hex 0A)
317    \er        carriage return (hex 0D)    \er        carriage return (hex 0D)
318    \et        tab (hex 09)    \et        tab (hex 09)
319      \e0dd      character with octal code 0dd
320    \eddd      character with octal code ddd, or back reference    \eddd      character with octal code ddd, or back reference
321      \eo{ddd..} character with octal code ddd..
322    \exhh      character with hex code hh    \exhh      character with hex code hh
323    \ex{hhh..} character with hex code hhh..    \ex{hhh..} character with hex code hhh.. (non-JavaScript mode)
324      \euhhhh    character with hex code hhhh (JavaScript mode only)
325  .sp  .sp
326  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
327  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
328  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),
329  \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
330  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
331  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.
332  values are valid. A lower case letter is converted to upper case, and then the  .P
333  0xc0 bits are flipped.)  The \ec facility was designed for use with ASCII characters, but with the
334  .P  extension to Unicode it is even less useful than it once was. It is, however,
335  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
336  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
337  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
338  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
339  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
340  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}.  
341  .P  .P
342  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
343  digits, just those that are present are used. Thus the sequence \e0\ex\e07  digits, just those that are present are used. Thus the sequence \e0\ex\e07
# Line 279  specifies two binary zeros followed by a Line 345  specifies two binary zeros followed by a
345  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
346  follows is itself an octal digit.  follows is itself an octal digit.
347  .P  .P
348  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
349  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
350  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
351    numbers greater than 0777, and it also allows octal numbers and back references
352    to be unambiguously specified.
353    .P
354    For greater clarity and unambiguity, it is best to avoid following \e by a
355    digit greater than zero. Instead, use \eo{} or \ex{} to specify character
356    numbers, and \eg{} to specify back references. The following paragraphs
357    describe the old, ambiguous syntax.
358    .P
359    The handling of a backslash followed by a digit other than 0 is complicated,
360    and Perl has changed in recent releases, causing PCRE also to change. Outside a
361    character class, PCRE reads the digit and any following digits as a decimal
362    number. If the number is less than 8, or if there have been at least that many
363  previous capturing left parentheses in the expression, the entire sequence is  previous capturing left parentheses in the expression, the entire sequence is
364  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
365  .\" HTML <a href="#backreferences">  .\" HTML <a href="#backreferences">
# Line 294  following the discussion of Line 372  following the discussion of
372  parenthesized subpatterns.  parenthesized subpatterns.
373  .\"  .\"
374  .P  .P
375  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
376  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
377  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
378  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.
379  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:  
380  .sp  .sp
381    \e040   is another way of writing a space    \e040   is another way of writing an ASCII space
382  .\" JOIN  .\" JOIN
383    \e40    is the same, provided there are fewer than 40    \e40    is the same, provided there are fewer than 40
384              previous capturing subpatterns              previous capturing subpatterns
# Line 316  to \e777 are permitted. For example: Line 393  to \e777 are permitted. For example:
393              character with octal code 113              character with octal code 113
394  .\" JOIN  .\" JOIN
395    \e377   might be a back reference, otherwise    \e377   might be a back reference, otherwise
396              the byte consisting entirely of 1 bits              the value 255 (decimal)
397  .\" JOIN  .\" JOIN
398    \e81    is either a back reference, or a binary zero    \e81    is either a back reference, or the two
399              followed by the two characters "8" and "1"              characters "8" and "1"
400  .sp  .sp
401  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
402  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
403    digits are ever read.
404    .P
405    By default, after \ex that is not followed by {, from zero to two hexadecimal
406    digits are read (letters can be in upper or lower case). Any number of
407    hexadecimal digits may appear between \ex{ and }. If a character other than
408    a hexadecimal digit appears between \ex{ and }, or if there is no terminating
409    }, an error occurs.
410    .P
411    If the PCRE_JAVASCRIPT_COMPAT option is set, the interpretation of \ex is
412    as just described only when it is followed by two hexadecimal digits.
413    Otherwise, it matches a literal "x" character. In JavaScript mode, support for
414    code points greater than 256 is provided by \eu, which must be followed by
415    four hexadecimal digits; otherwise it matches a literal "u" character.
416  .P  .P
417    Characters whose value is less than 256 can be defined by either of the two
418    syntaxes for \ex (or by \eu in JavaScript mode). There is no difference in the
419    way they are handled. For example, \exdc is exactly the same as \ex{dc} (or
420    \eu00dc in JavaScript mode).
421    .
422    .
423    .SS "Constraints on character values"
424    .rs
425    .sp
426    Characters that are specified using octal or hexadecimal numbers are
427    limited to certain values, as follows:
428    .sp
429      8-bit non-UTF mode    less than 0x100
430      8-bit UTF-8 mode      less than 0x10ffff and a valid codepoint
431      16-bit non-UTF mode   less than 0x10000
432      16-bit UTF-16 mode    less than 0x10ffff and a valid codepoint
433      32-bit non-UTF mode   less than 0x100000000
434      32-bit UTF-32 mode    less than 0x10ffff and a valid codepoint
435    .sp
436    Invalid Unicode codepoints are the range 0xd800 to 0xdfff (the so-called
437    "surrogate" codepoints), and 0xffef.
438    .
439    .
440    .SS "Escape sequences in character classes"
441    .rs
442    .sp
443  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
444  and outside character classes. In addition, inside a character class, the  and outside character classes. In addition, inside a character class, \eb is
445  sequence \eb is interpreted as the backspace character (hex 08). The sequences  interpreted as the backspace character (hex 08).
446  \eB, \eN, \eR, and \eX are not special inside a character class. Like any other  .P
447  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
448  "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
449  set. Outside a character class, these sequences have different meanings.  treated as the literal characters "B", "R", and "X" by default, but cause an
450    error if the PCRE_EXTRA option is set. Outside a character class, these
451    sequences have different meanings.
452    .
453    .
454    .SS "Unsupported escape sequences"
455    .rs
456    .sp
457    In Perl, the sequences \el, \eL, \eu, and \eU are recognized by its string
458    handler and used to modify the case of following characters. By default, PCRE
459    does not support these escape sequences. However, if the PCRE_JAVASCRIPT_COMPAT
460    option is set, \eU matches a "U" character, and \eu can be used to define a
461    character by code point, as described in the previous section.
462  .  .
463  .  .
464  .SS "Absolute and relative back references"  .SS "Absolute and relative back references"
# Line 377  Another use of backslash is for specifyi Line 505  Another use of backslash is for specifyi
505  .sp  .sp
506    \ed     any decimal digit    \ed     any decimal digit
507    \eD     any character that is not a decimal digit    \eD     any character that is not a decimal digit
508    \eh     any horizontal whitespace character    \eh     any horizontal white space character
509    \eH     any character that is not a horizontal whitespace character    \eH     any character that is not a horizontal white space character
510    \es     any whitespace character    \es     any white space character
511    \eS     any character that is not a whitespace character    \eS     any character that is not a white space character
512    \ev     any vertical whitespace character    \ev     any vertical white space character
513    \eV     any character that is not a vertical whitespace character    \eV     any character that is not a vertical white space character
514    \ew     any "word" character    \ew     any "word" character
515    \eW     any "non-word" character    \eW     any "non-word" character
516  .sp  .sp
# Line 392  This is the same as Line 520  This is the same as
520  .\" </a>  .\" </a>
521  the "." metacharacter  the "." metacharacter
522  .\"  .\"
523  when PCRE_DOTALL is not set.  when PCRE_DOTALL is not set. Perl also uses \eN to match characters by name;
524    PCRE does not support this.
525  .P  .P
526  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
527  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 401  classes. They each match one character o Line 530  classes. They each match one character o
530  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
531  there is no character to match.  there is no character to match.
532  .P  .P
533  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
534  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
535  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
536  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.  
537  .P  .P
538  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.
539  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 424  or "french" in Windows, some character c Line 552  or "french" in Windows, some character c
552  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
553  Unicode is discouraged.  Unicode is discouraged.
554  .P  .P
555  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
556  \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
557  their original meanings from before UTF-8 support was available, mainly for  their original meanings from before UTF support was available, mainly for
558  efficiency reasons. However, if PCRE is compiled with Unicode property support,  efficiency reasons. However, if PCRE is compiled with Unicode property support,
559  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
560  properties are used to determine character types, as follows:  properties are used to determine character types, as follows:
561  .sp  .sp
562    \ed  any character that \ep{Nd} matches (decimal digit)    \ed  any character that matches \ep{Nd} (decimal digit)
563    \es  any character that \ep{Z} matches, plus HT, LF, FF, CR    \es  any character that matches \ep{Z} or \eh or \ev
564    \ew  any character that \ep{L} or \ep{N} matches, plus underscore    \ew  any character that matches \ep{L} or \ep{N}, plus underscore
565  .sp  .sp
566  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
567  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 443  is noticeably slower when PCRE_UCP is se Line 571  is noticeably slower when PCRE_UCP is se
571  .P  .P
572  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
573  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
574  characters by default, these always match certain high-valued codepoints in  characters by default, these always match certain high-valued codepoints,
575  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:  
576  .sp  .sp
577    U+0009     Horizontal tab    U+0009     Horizontal tab (HT)
578    U+0020     Space    U+0020     Space
579    U+00A0     Non-break space    U+00A0     Non-break space
580    U+1680     Ogham space mark    U+1680     Ogham space mark
# Line 469  are: Line 596  are:
596  .sp  .sp
597  The vertical space characters are:  The vertical space characters are:
598  .sp  .sp
599    U+000A     Linefeed    U+000A     Linefeed (LF)
600    U+000B     Vertical tab    U+000B     Vertical tab (VT)
601    U+000C     Formfeed    U+000C     Form feed (FF)
602    U+000D     Carriage return    U+000D     Carriage return (CR)
603    U+0085     Next line    U+0085     Next line (NEL)
604    U+2028     Line separator    U+2028     Line separator
605    U+2029     Paragraph separator    U+2029     Paragraph separator
606    .sp
607    In 8-bit, non-UTF-8 mode, only the characters with codepoints less than 256 are
608    relevant.
609  .  .
610  .  .
611  .\" HTML <a name="newlineseq"></a>  .\" HTML <a name="newlineseq"></a>
# Line 483  The vertical space characters are: Line 613  The vertical space characters are:
613  .rs  .rs
614  .sp  .sp
615  Outside a character class, by default, the escape sequence \eR matches any  Outside a character class, by default, the escape sequence \eR matches any
616  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
617    following:
618  .sp  .sp
619    (?>\er\en|\en|\ex0b|\ef|\er|\ex85)    (?>\er\en|\en|\ex0b|\ef|\er|\ex85)
620  .sp  .sp
# Line 494  below. Line 625  below.
625  .\"  .\"
626  This particular group matches either the two-character sequence CR followed by  This particular group matches either the two-character sequence CR followed by
627  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,
628  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
629  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
630  cannot be split.  cannot be split.
631  .P  .P
632  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
633  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).
634  Unicode character property support is not needed for these characters to be  Unicode character property support is not needed for these characters to be
635  recognized.  recognized.
# Line 514  one of the following sequences: Line 645  one of the following sequences:
645    (*BSR_ANYCRLF)   CR, LF, or CRLF only    (*BSR_ANYCRLF)   CR, LF, or CRLF only
646    (*BSR_UNICODE)   any Unicode newline sequence    (*BSR_UNICODE)   any Unicode newline sequence
647  .sp  .sp
648  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
649  \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
650  \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
651  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
652  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
653  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:  
654  .sp  .sp
655    (*ANY)(*BSR_ANYCRLF)    (*ANY)(*BSR_ANYCRLF)
656  .sp  .sp
657  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
658  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
659  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
660    causes an error if PCRE_EXTRA is set.
661  .  .
662  .  .
663  .\" HTML <a name="uniextseq"></a>  .\" HTML <a name="uniextseq"></a>
# Line 535  matches the letter "R" by default, but c Line 666  matches the letter "R" by default, but c
666  .sp  .sp
667  When PCRE is built with Unicode character property support, three additional  When PCRE is built with Unicode character property support, three additional
668  escape sequences that match characters with specific properties are available.  escape sequences that match characters with specific properties are available.
669  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
670  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.
671  The extra escape sequences are:  The extra escape sequences are:
672  .sp  .sp
673    \ep{\fIxx\fP}   a character with the \fIxx\fP property    \ep{\fIxx\fP}   a character with the \fIxx\fP property
674    \eP{\fIxx\fP}   a character without the \fIxx\fP property    \eP{\fIxx\fP}   a character without the \fIxx\fP property
675    \eX       an extended Unicode sequence    \eX       a Unicode extended grapheme cluster
676  .sp  .sp
677  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
678  script names, the general category properties, "Any", which matches any  script names, the general category properties, "Any", which matches any
# Line 570  Armenian, Line 701  Armenian,
701  Avestan,  Avestan,
702  Balinese,  Balinese,
703  Bamum,  Bamum,
704    Batak,
705  Bengali,  Bengali,
706  Bopomofo,  Bopomofo,
707    Brahmi,
708  Braille,  Braille,
709  Buginese,  Buginese,
710  Buhid,  Buhid,
711  Canadian_Aboriginal,  Canadian_Aboriginal,
712  Carian,  Carian,
713    Chakma,
714  Cham,  Cham,
715  Cherokee,  Cherokee,
716  Common,  Common,
# Line 619  Lisu, Line 753  Lisu,
753  Lycian,  Lycian,
754  Lydian,  Lydian,
755  Malayalam,  Malayalam,
756    Mandaic,
757  Meetei_Mayek,  Meetei_Mayek,
758    Meroitic_Cursive,
759    Meroitic_Hieroglyphs,
760    Miao,
761  Mongolian,  Mongolian,
762  Myanmar,  Myanmar,
763  New_Tai_Lue,  New_Tai_Lue,
# Line 638  Rejang, Line 776  Rejang,
776  Runic,  Runic,
777  Samaritan,  Samaritan,
778  Saurashtra,  Saurashtra,
779    Sharada,
780  Shavian,  Shavian,
781  Sinhala,  Sinhala,
782    Sora_Sompeng,
783  Sundanese,  Sundanese,
784  Syloti_Nagri,  Syloti_Nagri,
785  Syriac,  Syriac,
# Line 648  Tagbanwa, Line 788  Tagbanwa,
788  Tai_Le,  Tai_Le,
789  Tai_Tham,  Tai_Tham,
790  Tai_Viet,  Tai_Viet,
791    Takri,
792  Tamil,  Tamil,
793  Telugu,  Telugu,
794  Thaana,  Thaana,
# Line 722  the Lu, Ll, or Lt property, in other wor Line 863  the Lu, Ll, or Lt property, in other wor
863  a modifier or "other".  a modifier or "other".
864  .P  .P
865  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
866  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
867  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
868  (see the discussion of PCRE_NO_UTF8_CHECK in the  (see the discussion of PCRE_NO_UTF8_CHECK, PCRE_NO_UTF16_CHECK and
869    PCRE_NO_UTF32_CHECK in the
870  .\" HREF  .\" HREF
871  \fBpcreapi\fP  \fBpcreapi\fP
872  .\"  .\"
# Line 739  Instead, this property is assumed for an Line 881  Instead, this property is assumed for an
881  Unicode table.  Unicode table.
882  .P  .P
883  Specifying caseless matching does not affect these escape sequences. For  Specifying caseless matching does not affect these escape sequences. For
884  example, \ep{Lu} always matches only upper case letters.  example, \ep{Lu} always matches only upper case letters. This is different from
885    the behaviour of current versions of Perl.
886  .P  .P
887  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
888  Unicode sequence. \eX is equivalent to  multistage table lookup in order to find a character's property. That is why
889  .sp  the traditional escape sequences such as \ed and \ew do not use Unicode
890    (?>\ePM\epM*)  properties in PCRE by default, though you can make them do so by setting the
891    PCRE_UCP option or by starting the pattern with (*UCP).
892    .
893    .
894    .SS Extended grapheme clusters
895    .rs
896  .sp  .sp
897  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
898  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  
899  .\" HTML <a href="#atomicgroup">  .\" HTML <a href="#atomicgroup">
900  .\" </a>  .\" </a>
901  (see below).  (see below).
902  .\"  .\"
903  Characters with the "mark" property are typically accents that affect the  Up to and including release 8.31, PCRE matched an earlier, simpler definition
904  preceding character. None of them have codepoints less than 256, so in  that was equivalent to
905  non-UTF-8 mode \eX matches any one character.  .sp
906  .P    (?>\ePM\epM*)
907  Matching characters by Unicode property is not fast, because PCRE has to search  .sp
908  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
909  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"
910  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.
911  PCRE_UCP option for \fBpcre_compile()\fP or by starting the pattern with  .P
912  (*UCP).  This simple definition was extended in Unicode to include more complicated
913    kinds of composite character by giving each character a grapheme breaking
914    property, and creating rules that use these properties to define the boundaries
915    of extended grapheme clusters. In releases of PCRE later than 8.31, \eX matches
916    one of these clusters.
917    .P
918    \eX always matches at least one character. Then it decides whether to add
919    additional characters according to the following rules for ending a cluster:
920    .P
921    1. End at the end of the subject string.
922    .P
923    2. Do not end between CR and LF; otherwise end after any control character.
924    .P
925    3. Do not break Hangul (a Korean script) syllable sequences. Hangul characters
926    are of five types: L, V, T, LV, and LVT. An L character may be followed by an
927    L, V, LV, or LVT character; an LV or V character may be followed by a V or T
928    character; an LVT or T character may be follwed only by a T character.
929    .P
930    4. Do not end before extending characters or spacing marks. Characters with
931    the "mark" property always have the "extend" grapheme breaking property.
932    .P
933    5. Do not end after prepend characters.
934    .P
935    6. Otherwise, end the cluster.
936  .  .
937  .  .
938  .\" HTML <a name="extraprops"></a>  .\" HTML <a name="extraprops"></a>
939  .SS PCRE's additional properties  .SS PCRE's additional properties
940  .rs  .rs
941  .sp  .sp
942  As well as the standard Unicode properties described in the previous  As well as the standard Unicode properties described above, PCRE supports four
943  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
944  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
945  properties. PCRE uses these non-standard, non-Perl properties internally when  properties internally when PCRE_UCP is set. However, they may also be used
946  PCRE_UCP is set. They are:  explicitly. These properties are:
947  .sp  .sp
948    Xan   Any alphanumeric character    Xan   Any alphanumeric character
949    Xps   Any POSIX space character    Xps   Any POSIX space character
# Line 781  PCRE_UCP is set. They are: Line 951  PCRE_UCP is set. They are:
951    Xwd   Any Perl "word" character    Xwd   Any Perl "word" character
952  .sp  .sp
953  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)
954  property. Xps matches the characters tab, linefeed, vertical tab, formfeed, or  property. Xps matches the characters tab, linefeed, vertical tab, form feed, or
955  carriage return, and any other character that has the Z (separator) property.  carriage return, and any other character that has the Z (separator) property.
956  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
957  same characters as Xan, plus underscore.  compatibility, but Perl changed, and so PCRE followed at release 8.34. Xwd
958    matches the same characters as Xan, plus underscore.
959    .P
960    There is another non-standard property, Xuc, which matches any character that
961    can be represented by a Universal Character Name in C++ and other programming
962    languages. These are the characters $, @, ` (grave accent), and all characters
963    with Unicode code points greater than or equal to U+00A0, except for the
964    surrogates U+D800 to U+DFFF. Note that most base (ASCII) characters are
965    excluded. (Universal Character Names are of the form \euHHHH or \eUHHHHHHHH
966    where H is a hexadecimal digit. Note that the Xuc property does not match these
967    sequences but the characters that they represent.)
968  .  .
969  .  .
970  .\" HTML <a name="resetmatchstart"></a>  .\" HTML <a name="resetmatchstart"></a>
# Line 851  escape sequence" error is generated inst Line 1031  escape sequence" error is generated inst
1031  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
1032  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
1033  \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
1034  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
1035  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
1036  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
1037  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 890  regular expression. Line 1070  regular expression.
1070  .SH "CIRCUMFLEX AND DOLLAR"  .SH "CIRCUMFLEX AND DOLLAR"
1071  .rs  .rs
1072  .sp  .sp
1073    The circumflex and dollar metacharacters are zero-width assertions. That is,
1074    they test for a particular condition being true without consuming any
1075    characters from the subject string.
1076    .P
1077  Outside a character class, in the default matching mode, the circumflex  Outside a character class, in the default matching mode, the circumflex
1078  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
1079  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
1080  \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
1081  option is unset. Inside a character class, circumflex has an entirely different  option is unset. Inside a character class, circumflex has an entirely different
1082  meaning  meaning
# Line 909  constrained to match only at the start o Line 1093  constrained to match only at the start o
1093  "anchored" pattern. (There are also other constructs that can cause a pattern  "anchored" pattern. (There are also other constructs that can cause a pattern
1094  to be anchored.)  to be anchored.)
1095  .P  .P
1096  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
1097  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
1098  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
1099  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
1100  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
1101  character class.  branch in which it appears. Dollar has no special meaning in a character class.
1102  .P  .P
1103  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
1104  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 946  end of the subject in both modes, and if Line 1130  end of the subject in both modes, and if
1130  .sp  .sp
1131  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
1132  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
1133  line. In UTF-8 mode, the matched character may be more than one byte long.  line.
1134  .P  .P
1135  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
1136  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 966  special meaning in a character class. Line 1150  special meaning in a character class.
1150  .P  .P
1151  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
1152  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
1153  that signifies the end of a line.  that signifies the end of a line. Perl also uses \eN to match characters by
1154    name; PCRE does not support this.
1155  .  .
1156  .  .
1157  .SH "MATCHING A SINGLE BYTE"  .SH "MATCHING A SINGLE DATA UNIT"
1158  .rs  .rs
1159  .sp  .sp
1160  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,
1161  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
1162  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
1163  in UTF-8 mode. Because it breaks up UTF-8 characters into individual bytes, the  a 32-bit unit. Unlike a dot, \eC always
1164  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
1165  the \eC escape sequence is best avoided.  match individual bytes in UTF-8 mode, but it is unclear how it can usefully be
1166    used. Because \eC breaks up characters into individual data units, matching one
1167    unit with \eC in a UTF mode means that the rest of the string may start with a
1168    malformed UTF character. This has undefined results, because PCRE assumes that
1169    it is dealing with valid UTF strings (and by default it checks this at the
1170    start of processing unless the PCRE_NO_UTF8_CHECK, PCRE_NO_UTF16_CHECK or
1171    PCRE_NO_UTF32_CHECK option is used).
1172  .P  .P
1173  PCRE does not allow \eC to appear in lookbehind assertions  PCRE does not allow \eC to appear in lookbehind assertions
1174  .\" HTML <a href="#lookbehind">  .\" HTML <a href="#lookbehind">
1175  .\" </a>  .\" </a>
1176  (described below),  (described below)
1177  .\"  .\"
1178  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
1179  the lookbehind.  the lookbehind.
1180    .P
1181    In general, the \eC escape sequence is best avoided. However, one
1182    way of using it that avoids the problem of malformed UTF characters is to use a
1183    lookahead to check the length of the next character, as in this pattern, which
1184    could be used with a UTF-8 string (ignore white space and line breaks):
1185    .sp
1186      (?| (?=[\ex00-\ex7f])(\eC) |
1187          (?=[\ex80-\ex{7ff}])(\eC)(\eC) |
1188          (?=[\ex{800}-\ex{ffff}])(\eC)(\eC)(\eC) |
1189          (?=[\ex{10000}-\ex{1fffff}])(\eC)(\eC)(\eC)(\eC))
1190    .sp
1191    A group that starts with (?| resets the capturing parentheses numbers in each
1192    alternative (see
1193    .\" HTML <a href="#dupsubpatternnumber">
1194    .\" </a>
1195    "Duplicate Subpattern Numbers"
1196    .\"
1197    below). The assertions at the start of each branch check the next UTF-8
1198    character for values whose encoding uses 1, 2, 3, or 4 bytes, respectively. The
1199    character's individual bytes are then captured by the appropriate number of
1200    groups.
1201  .  .
1202  .  .
1203  .\" HTML <a name="characterclass"></a>  .\" HTML <a name="characterclass"></a>
# Line 999  bracket causes a compile-time error. If Line 1211  bracket causes a compile-time error. If
1211  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
1212  (after an initial circumflex, if present) or escaped with a backslash.  (after an initial circumflex, if present) or escaped with a backslash.
1213  .P  .P
1214  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
1215  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
1216  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
1217  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
1218  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
1219  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
1220  backslash.  backslash.
1221  .P  .P
1222  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 1015  circumflex is not an assertion; it still Line 1227  circumflex is not an assertion; it still
1227  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
1228  string.  string.
1229  .P  .P
1230  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)
1231  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
1232    \ex{ escaping mechanism.
1233  .P  .P
1234  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
1235  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
1236  "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
1237  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
1238  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
1239  always possible. For characters with higher values, the concept of case is  always possible. For characters with higher values, the concept of case is
1240  supported if PCRE is compiled with Unicode property support, but not otherwise.  supported if PCRE is compiled with Unicode property support, but not otherwise.
1241  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
1242  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
1243  with UTF-8 support.  well as with UTF support.
1244  .P  .P
1245  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
1246  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 1038  The minus (hyphen) character can be used Line 1251  The minus (hyphen) character can be used
1251  character class. For example, [d-m] matches any letter between d and m,  character class. For example, [d-m] matches any letter between d and m,
1252  inclusive. If a minus character is required in a class, it must be escaped with  inclusive. If a minus character is required in a class, it must be escaped with
1253  a backslash or appear in a position where it cannot be interpreted as  a backslash or appear in a position where it cannot be interpreted as
1254  indicating a range, typically as the first or last character in the class.  indicating a range, typically as the first or last character in the class, or
1255    immediately after a range. For example, [b-d-z] matches letters in the range b
1256    to d, a hyphen character, or z.
1257  .P  .P
1258  It is not possible to have the literal character "]" as the end character of a  It is not possible to have the literal character "]" as the end character of a
1259  range. A pattern such as [W-]46] is interpreted as a class of two characters  range. A pattern such as [W-]46] is interpreted as a class of two characters
# Line 1048  the end of range, so [W-\e]46] is interp Line 1263  the end of range, so [W-\e]46] is interp
1263  followed by two other characters. The octal or hexadecimal representation of  followed by two other characters. The octal or hexadecimal representation of
1264  "]" can also be used to end a range.  "]" can also be used to end a range.
1265  .P  .P
1266    An error is generated if a POSIX character class (see below) or an escape
1267    sequence other than one that defines a single character appears at a point
1268    where a range ending character is expected. For example, [z-\exff] is valid,
1269    but [A-\ed] and [A-[:digit:]] are not.
1270    .P
1271  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
1272  used for characters specified numerically, for example [\e000-\e037]. In UTF-8  used for characters specified numerically, for example [\e000-\e037]. Ranges
1273  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}].  
1274  .P  .P
1275  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
1276  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
1277  [][\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
1278  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
1279  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
1280  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
1281  property support.  property support.
1282  .P  .P
1283  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,
1284  \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
1285  they match to the class. For example, [\edABCDEF] matches any hexadecimal  they match to the class. For example, [\edABCDEF] matches any hexadecimal
1286  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
1287  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
1288  character class, as described in the section entitled  character class, as described in the section entitled
1289  .\" HTML <a href="#genericchartypes">  .\" HTML <a href="#genericchartypes">
# Line 1114  are: Line 1333  are:
1333    lower    lower case letters    lower    lower case letters
1334    print    printing characters, including space    print    printing characters, including space
1335    punct    printing characters, excluding letters and digits and space    punct    printing characters, excluding letters and digits and space
1336    space    white space (not quite the same as \es)    space    white space (the same as \es from PCRE 8.34)
1337    upper    upper case letters    upper    upper case letters
1338    word     "word" characters (same as \ew)    word     "word" characters (same as \ew)
1339    xdigit   hexadecimal digits    xdigit   hexadecimal digits
1340  .sp  .sp
1341  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
1342  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
1343  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
1344  compatibility).  release 8.34. "Space" and \es now match the same set of characters.
1345  .P  .P
1346  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
1347  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 1134  matches "1", "2", or any non-digit. PCRE Line 1353  matches "1", "2", or any non-digit. PCRE
1353  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
1354  supported, and an error is given if they are encountered.  supported, and an error is given if they are encountered.
1355  .P  .P
1356  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
1357  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
1358  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
1359  character properties are used. This is achieved by replacing the POSIX classes  character properties are used. This is achieved by replacing certain POSIX
1360  by other sequences, as follows:  classes by other sequences, as follows:
1361  .sp  .sp
1362    [:alnum:]  becomes  \ep{Xan}    [:alnum:]  becomes  \ep{Xan}
1363    [:alpha:]  becomes  \ep{L}    [:alpha:]  becomes  \ep{L}
# Line 1149  by other sequences, as follows: Line 1368  by other sequences, as follows:
1368    [:upper:]  becomes  \ep{Lu}    [:upper:]  becomes  \ep{Lu}
1369    [:word:]   becomes  \ep{Xwd}    [:word:]   becomes  \ep{Xwd}
1370  .sp  .sp
1371  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
1372  classes are unchanged, and match only characters with code points less than  classes are handled specially in UCP mode:
1373  128.  .TP 10
1374    [:graph:]
1375    This matches characters that have glyphs that mark the page when printed. In
1376    Unicode property terms, it matches all characters with the L, M, N, P, S, or Cf
1377    properties, except for:
1378    .sp
1379      U+061C           Arabic Letter Mark
1380      U+180E           Mongolian Vowel Separator
1381      U+2066 - U+2069  Various "isolate"s
1382    .sp
1383    .TP 10
1384    [:print:]
1385    This matches the same characters as [:graph:] plus space characters that are
1386    not controls, that is, characters with the Zs property.
1387    .TP 10
1388    [:punct:]
1389    This matches all characters that have the Unicode P (punctuation) property,
1390    plus those characters whose code points are less than 128 that have the S
1391    (Symbol) property.
1392    .P
1393    The other POSIX classes are unchanged, and match only characters with code
1394    points less than 128.
1395  .  .
1396  .  .
1397  .SH "VERTICAL BAR"  .SH "VERTICAL BAR"
# Line 1222  option settings happen at compile time. Line 1462  option settings happen at compile time.
1462  behaviour otherwise.  behaviour otherwise.
1463  .P  .P
1464  \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
1465  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
1466  pattern can contain special leading sequences such as (*CRLF) to override what  the pattern can contain special leading sequences such as (*CRLF) to override
1467  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
1468  section entitled  the section entitled
1469  .\" HTML <a href="#newlineseq">  .\" HTML <a href="#newlineseq">
1470  .\" </a>  .\" </a>
1471  "Newline sequences"  "Newline sequences"
1472  .\"  .\"
1473  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
1474  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
1475  PCRE_UTF8 and the PCRE_UCP options, respectively.  equivalent to setting the PCRE_UTF8, PCRE_UTF16, PCRE_UTF32 and the PCRE_UCP
1476    options, respectively. The (*UTF) sequence is a generic version that can be
1477    used with any of the libraries. However, the application can set the
1478    PCRE_NEVER_UTF option, which locks out the use of the (*UTF) sequences.
1479  .  .
1480  .  .
1481  .\" HTML <a name="subpattern"></a>  .\" HTML <a name="subpattern"></a>
# Line 1251  match "cataract", "erpillar" or an empty Line 1494  match "cataract", "erpillar" or an empty
1494  .sp  .sp
1495  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
1496  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
1497  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
1498  \fBpcre_exec()\fP. Opening parentheses are counted from left to right (starting  matching function. (This applies only to the traditional matching functions;
1499  from 1) to obtain numbers for the capturing subpatterns. For example, if the  the DFA matching functions do not support capturing.)
1500  string "the red king" is matched against the pattern  .P
1501    Opening parentheses are counted from left to right (starting from 1) to obtain
1502    numbers for the capturing subpatterns. For example, if the string "the red
1503    king" is matched against the pattern
1504  .sp  .sp
1505    the ((red|white) (king|queen))    the ((red|white) (king|queen))
1506  .sp  .sp
# Line 1317  or "defdef": Line 1563  or "defdef":
1563  .sp  .sp
1564    /(?|(abc)|(def))\e1/    /(?|(abc)|(def))\e1/
1565  .sp  .sp
1566  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
1567  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
1568  pattern matches "abcabc" or "defabc":  "abcabc" or "defabc":
1569  .sp  .sp
1570    /(?|(abc)|(def))(?1)/    /(?|(abc)|(def))(?1)/
1571  .sp  .sp
# Line 1365  conditions, Line 1611  conditions,
1611  .\"  .\"
1612  can be made by name as well as by number.  can be made by name as well as by number.
1613  .P  .P
1614  Names consist of up to 32 alphanumeric characters and underscores. Named  Names consist of up to 32 alphanumeric characters and underscores, but must
1615  capturing parentheses are still allocated numbers as well as names, exactly as  start with a non-digit. Named capturing parentheses are still allocated numbers
1616  if the names were not present. The PCRE API provides function calls for  as well as names, exactly as if the names were not present. The PCRE API
1617  extracting the name-to-number translation table from a compiled pattern. There  provides function calls for extracting the name-to-number translation table
1618  is also a convenience function for extracting a captured substring by name.  from a compiled pattern. There is also a convenience function for extracting a
1619    captured substring by name.
1620  .P  .P
1621  By default, a name must be unique within a pattern, but it is possible to relax  By default, a name must be unique within a pattern, but it is possible to relax
1622  this constraint by setting the PCRE_DUPNAMES option at compile time. (Duplicate  this constraint by setting the PCRE_DUPNAMES option at compile time. (Duplicate
# Line 1395  for the first (and in this example, the Line 1642  for the first (and in this example, the
1642  matched. This saves searching to find which numbered subpattern it was.  matched. This saves searching to find which numbered subpattern it was.
1643  .P  .P
1644  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
1645  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
1646  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
1647  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
1648    "barbar" but not "foobar" or "barfoo":
1649    .sp
1650      (?:(?<n>foo)|(?<n>bar))\k<n>
1651    .sp
1652    .P
1653    If you make a subroutine call to a non-unique named subpattern, the one that
1654    corresponds to the first occurrence of the name is used. In the absence of
1655    duplicate numbers (see the previous section) this is the one with the lowest
1656    number.
1657    .P
1658    If you use a named reference in a condition
1659  test (see the  test (see the
1660  .\"  .\"
1661  .\" HTML <a href="#conditions">  .\" HTML <a href="#conditions">
# Line 1417  documentation. Line 1675  documentation.
1675  \fBWarning:\fP You cannot use different names to distinguish between two  \fBWarning:\fP You cannot use different names to distinguish between two
1676  subpatterns with the same number because PCRE uses only the numbers when  subpatterns with the same number because PCRE uses only the numbers when
1677  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
1678  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
1679  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
1680    set.
1681  .  .
1682  .  .
1683  .SH REPETITION  .SH REPETITION
# Line 1430  items: Line 1689  items:
1689    a literal data character    a literal data character
1690    the dot metacharacter    the dot metacharacter
1691    the \eC escape sequence    the \eC escape sequence
1692    the \eX escape sequence (in UTF-8 mode with Unicode properties)    the \eX escape sequence
1693    the \eR escape sequence    the \eR escape sequence
1694    an escape such as \ed or \epL that matches a single character    an escape such as \ed or \epL that matches a single character
1695    a character class    a character class
1696    a back reference (see next section)    a back reference (see next section)
1697    a parenthesized subpattern (unless it is an assertion)    a parenthesized subpattern (including assertions)
1698    a recursive or "subroutine" call to a subpattern    a subroutine call to a subpattern (recursive or otherwise)
1699  .sp  .sp
1700  The general repetition quantifier specifies a minimum and maximum number of  The general repetition quantifier specifies a minimum and maximum number of
1701  permitted matches, by giving the two numbers in curly brackets (braces),  permitted matches, by giving the two numbers in curly brackets (braces),
# Line 1461  where a quantifier is not allowed, or on Line 1720  where a quantifier is not allowed, or on
1720  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
1721  quantifier, but a literal string of four characters.  quantifier, but a literal string of four characters.
1722  .P  .P
1723  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
1724  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
1725  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,
1726  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
1727  which may be several bytes long (and they may be of different lengths).  several data units long (and they may be of different lengths).
1728  .P  .P
1729  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
1730  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 1551  In cases where it is known that the subj Line 1810  In cases where it is known that the subj
1810  worth setting PCRE_DOTALL in order to obtain this optimization, or  worth setting PCRE_DOTALL in order to obtain this optimization, or
1811  alternatively using ^ to indicate anchoring explicitly.  alternatively using ^ to indicate anchoring explicitly.
1812  .P  .P
1813  However, there is one situation where the optimization cannot be used. When .*  However, there are some cases where the optimization cannot be used. When .*
1814  is inside capturing parentheses that are the subject of a back reference  is inside capturing parentheses that are the subject of a back reference
1815  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
1816  succeeds. Consider, for example:  succeeds. Consider, for example:
# Line 1561  succeeds. Consider, for example: Line 1820  succeeds. Consider, for example:
1820  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
1821  this reason, such a pattern is not implicitly anchored.  this reason, such a pattern is not implicitly anchored.
1822  .P  .P
1823    Another case where implicit anchoring is not applied is when the leading .* is
1824    inside an atomic group. Once again, a match at the start may fail where a later
1825    one succeeds. Consider this pattern:
1826    .sp
1827      (?>.*?a)b
1828    .sp
1829    It matches "ab" in the subject "aab". The use of the backtracking control verbs
1830    (*PRUNE) and (*SKIP) also disable this optimization.
1831    .P
1832  When a capturing subpattern is repeated, the value captured is the substring  When a capturing subpattern is repeated, the value captured is the substring
1833  that matched the final iteration. For example, after  that matched the final iteration. For example, after
1834  .sp  .sp
# Line 1775  Because there may be many capturing pare Line 2043  Because there may be many capturing pare
2043  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.
2044  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
2045  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
2046  whitespace. Otherwise, the \eg{ syntax or an empty comment (see  white space. Otherwise, the \eg{ syntax or an empty comment (see
2047  .\" HTML <a href="#comments">  .\" HTML <a href="#comments">
2048  .\" </a>  .\" </a>
2049  "Comments"  "Comments"
# Line 1826  those that look ahead of the current pos Line 2094  those that look ahead of the current pos
2094  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,
2095  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.
2096  .P  .P
2097  Assertion subpatterns are not capturing subpatterns, and may not be repeated,  Assertion subpatterns are not capturing subpatterns. If such an assertion
2098  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
2099  of assertion contains capturing subpatterns within it, these are counted for  numbering the capturing subpatterns in the whole pattern. However, substring
2100  the purposes of numbering the capturing subpatterns in the whole pattern.  capturing is carried out only for positive assertions. (Perl sometimes, but not
2101  However, substring capturing is carried out only for positive assertions,  always, does do capturing in negative assertions.)
2102  because it does not make sense for negative assertions.  .P
2103    For compatibility with Perl, assertion subpatterns may be repeated; though
2104    it makes no sense to assert the same thing several times, the side effect of
2105    capturing parentheses may occasionally be useful. In practice, there only three
2106    cases:
2107    .sp
2108    (1) If the quantifier is {0}, the assertion is never obeyed during matching.
2109    However, it may contain internal capturing parenthesized groups that are called
2110    from elsewhere via the
2111    .\" HTML <a href="#subpatternsassubroutines">
2112    .\" </a>
2113    subroutine mechanism.
2114    .\"
2115    .sp
2116    (2) If quantifier is {0,n} where n is greater than zero, it is treated as if it
2117    were {0,1}. At run time, the rest of the pattern match is tried with and
2118    without the assertion, the order depending on the greediness of the quantifier.
2119    .sp
2120    (3) If the minimum repetition is greater than zero, the quantifier is ignored.
2121    The assertion is obeyed just once when encountered during matching.
2122  .  .
2123  .  .
2124  .SS "Lookahead assertions"  .SS "Lookahead assertions"
# Line 1909  temporarily move the current position ba Line 2196  temporarily move the current position ba
2196  match. If there are insufficient characters before the current position, the  match. If there are insufficient characters before the current position, the
2197  assertion fails.  assertion fails.
2198  .P  .P
2199  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
2200  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
2201  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
2202  different numbers of bytes, are also not permitted.  escapes, which can match different numbers of data units, are also not
2203    permitted.
2204  .P  .P
2205  .\" HTML <a href="#subpatternsassubroutines">  .\" HTML <a href="#subpatternsassubroutines">
2206  .\" </a>  .\" </a>
# Line 2060  This makes the fragment independent of t Line 2348  This makes the fragment independent of t
2348  .sp  .sp
2349  Perl uses the syntax (?(<name>)...) or (?('name')...) to test for a used  Perl uses the syntax (?(<name>)...) or (?('name')...) to test for a used
2350  subpattern by name. For compatibility with earlier versions of PCRE, which had  subpattern by name. For compatibility with earlier versions of PCRE, which had
2351  this facility before Perl, the syntax (?(name)...) is also recognized. However,  this facility before Perl, the syntax (?(name)...) is also recognized.
 there is a possible ambiguity with this syntax, because subpattern names may  
 consist entirely of digits. PCRE looks first for a named subpattern; if it  
 cannot find one and the name consists entirely of digits, PCRE looks for a  
 subpattern of that number, which must be greater than zero. Using subpattern  
 names that consist entirely of digits is not recommended.  
2352  .P  .P
2353  Rewriting the above example to use a named subpattern gives this:  Rewriting the above example to use a named subpattern gives this:
2354  .sp  .sp
# Line 2106  If the condition is the string (DEFINE), Line 2389  If the condition is the string (DEFINE),
2389  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
2390  alternative in the subpattern. It is always skipped if control reaches this  alternative in the subpattern. It is always skipped if control reaches this
2391  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
2392  "subroutines" that can be referenced from elsewhere. (The use of  subroutines that can be referenced from elsewhere. (The use of
2393  .\" HTML <a href="#subpatternsassubroutines">  .\" HTML <a href="#subpatternsassubroutines">
2394  .\" </a>  .\" </a>
2395  "subroutines"  subroutines
2396  .\"  .\"
2397  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
2398  "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
2399  breaks):  breaks):
2400  .sp  .sp
2401    (?(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 2159  closing parenthesis. Nested parentheses Line 2442  closing parenthesis. Nested parentheses
2442  option is set, an unescaped # character also introduces a comment, which in  option is set, an unescaped # character also introduces a comment, which in
2443  this case continues to immediately after the next newline character or  this case continues to immediately after the next newline character or
2444  character sequence in the pattern. Which characters are interpreted as newlines  character sequence in the pattern. Which characters are interpreted as newlines
2445  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
2446  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
2447  .\" HTML <a href="#newlines">  .\" HTML <a href="#newlines">
2448  .\" </a>  .\" </a>
# Line 2204  individual subpattern recursion. After i Line 2487  individual subpattern recursion. After i
2487  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.
2488  .P  .P
2489  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
2490  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
2491  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
2492  .\" HTML <a href="#subpatternsassubroutines">  .\" HTML <a href="#subpatternsassubroutines">
2493  .\" </a>  .\" </a>
2494  "subroutine"  non-recursive subroutine
2495  .\"  .\"
2496  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
2497  a recursive call of the entire regular expression.  a recursive call of the entire regular expression.
# Line 2243  references such as (?+2). However, these Line 2526  references such as (?+2). However, these
2526  reference is not inside the parentheses that are referenced. They are always  reference is not inside the parentheses that are referenced. They are always
2527  .\" HTML <a href="#subpatternsassubroutines">  .\" HTML <a href="#subpatternsassubroutines">
2528  .\" </a>  .\" </a>
2529  "subroutine"  non-recursive subroutine
2530  .\"  .\"
2531  calls, as described in the next section.  calls, as described in the next section.
2532  .P  .P
# Line 2280  documentation). If the pattern above is Line 2563  documentation). If the pattern above is
2563  .sp  .sp
2564  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
2565  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
2566  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
2567  set at a deeper level.  (temporarily) set at a deeper level during the matching process.
2568  .P  .P
2569  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
2570  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 2301  is the actual recursive call. Line 2584  is the actual recursive call.
2584  .  .
2585  .  .
2586  .\" HTML <a name="recursiondifference"></a>  .\" HTML <a name="recursiondifference"></a>
2587  .SS "Recursion difference from Perl"  .SS "Differences in recursion processing between PCRE and Perl"
2588  .rs  .rs
2589  .sp  .sp
2590  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
2591  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
2592  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
2593  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
2594  following pattern, which purports to match a palindromic string that contains  subsequent matching failure. This can be illustrated by the following pattern,
2595  an odd number of characters (for example, "a", "aba", "abcba", "abcdcba"):  which purports to match a palindromic string that contains an odd number of
2596    characters (for example, "a", "aba", "abcba", "abcdcba"):
2597  .sp  .sp
2598    ^(.|(.)(?1)\e2)$    ^(.|(.)(?1)\e2)$
2599  .sp  .sp
# Line 2370  For example, although "abcba" is correct Line 2654  For example, although "abcba" is correct
2654  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
2655  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
2656  recursion to try other alternatives, so the entire match fails.  recursion to try other alternatives, so the entire match fails.
2657    .P
2658    The second way in which PCRE and Perl differ in their recursion processing is
2659    in the handling of captured values. In Perl, when a subpattern is called
2660    recursively or as a subpattern (see the next section), it has no access to any
2661    values that were captured outside the recursion, whereas in PCRE these values
2662    can be referenced. Consider this pattern:
2663    .sp
2664      ^(.)(\e1|a(?2))
2665    .sp
2666    In PCRE, this pattern matches "bab". The first capturing parentheses match "b",
2667    then in the second group, when the back reference \e1 fails to match "b", the
2668    second alternative matches "a" and then recurses. In the recursion, \e1 does
2669    now match "b" and so the whole match succeeds. In Perl, the pattern fails to
2670    match because inside the recursive call \e1 cannot access the externally set
2671    value.
2672  .  .
2673  .  .
2674  .\" HTML <a name="subpatternsassubroutines"></a>  .\" HTML <a name="subpatternsassubroutines"></a>
2675  .SH "SUBPATTERNS AS SUBROUTINES"  .SH "SUBPATTERNS AS SUBROUTINES"
2676  .rs  .rs
2677  .sp  .sp
2678  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
2679  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
2680  subroutine in a programming language. The "called" subpattern may be defined  subroutine in a programming language. The called subpattern may be defined
2681  before or after the reference. A numbered reference can be absolute or  before or after the reference. A numbered reference can be absolute or
2682  relative, as in these examples:  relative, as in these examples:
2683  .sp  .sp
# Line 2398  matches "sense and sensibility" and "res Line 2697  matches "sense and sensibility" and "res
2697  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
2698  strings. Another example is given in the discussion of DEFINE above.  strings. Another example is given in the discussion of DEFINE above.
2699  .P  .P
2700  Like recursive subpatterns, a subroutine call is always treated as an atomic  All subroutine calls, whether recursive or not, are always treated as atomic
2701  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
2702  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
2703  matching failure. Any capturing parentheses that are set during the subroutine  subsequent matching failure. Any capturing parentheses that are set during the
2704  call revert to their previous values afterwards.  subroutine call revert to their previous values afterwards.
2705  .P  .P
2706  When a subpattern is used as a subroutine, processing options such as  Processing options such as case-independence are fixed when a subpattern is
2707  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
2708  changed for different calls. For example, consider this pattern:  different calls. For example, consider this pattern:
2709  .sp  .sp
2710    (abc)(?i:(?-1))    (abc)(?i:(?-1))
2711  .sp  .sp
# Line 2445  same pair of parentheses when there is a Line 2744  same pair of parentheses when there is a
2744  .P  .P
2745  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
2746  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
2747  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
2748    (8-bit library) or \fIpcre[16|32]_callout\fP (16-bit or 32-bit library).
2749  By default, this variable contains NULL, which disables all calling out.  By default, this variable contains NULL, which disables all calling out.
2750  .P  .P
2751  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 2455  For example, this pattern has two callou Line 2755  For example, this pattern has two callou
2755  .sp  .sp
2756    (?C1)abc(?C2)def    (?C1)abc(?C2)def
2757  .sp  .sp
2758  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
2759  automatically installed before each item in the pattern. They are all numbered  automatically installed before each item in the pattern. They are all numbered
2760  255.  255. If there is a conditional group in the pattern whose condition is an
2761  .P  assertion, an additional callout is inserted just before the condition. An
2762  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:
2763  set), the external function is called. It is provided with the number of the  .sp
2764  callout, the position in the pattern, and, optionally, one item of data    (?(?C9)(?=a)abc|def)
2765  originally supplied by the caller of \fBpcre_exec()\fP. The callout function  .sp
2766  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
2767  description of the interface to the callout function is given in the  condition.
2768    .P
2769    During matching, when PCRE reaches a callout point, the external function is
2770    called. It is provided with the number of the callout, the position in the
2771    pattern, and, optionally, one item of data originally supplied by the caller of
2772    the matching function. The callout function may cause matching to proceed, to
2773    backtrack, or to fail altogether.
2774    .P
2775    By default, PCRE implements a number of optimizations at compile time and
2776    matching time, and one side-effect is that sometimes callouts are skipped. If
2777    you need all possible callouts to happen, you need to set options that disable
2778    the relevant optimizations. More details, and a complete description of the
2779    interface to the callout function, are given in the
2780  .\" HREF  .\" HREF
2781  \fBpcrecallout\fP  \fBpcrecallout\fP
2782  .\"  .\"
# Line 2476  documentation. Line 2788  documentation.
2788  .rs  .rs
2789  .sp  .sp
2790  Perl 5.10 introduced a number of "Special Backtracking Control Verbs", which  Perl 5.10 introduced a number of "Special Backtracking Control Verbs", which
2791  are described in the Perl documentation as "experimental and subject to change  are still described in the Perl documentation as "experimental and subject to
2792  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
2793  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
2794  remarks apply to the PCRE features described in this section.  remarks apply to the PCRE features described in this section.
2795  .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  
2796  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
2797  parenthesis followed by an asterisk. They are generally of the form  parenthesis followed by an asterisk. They are generally of the form
2798  (*VERB) or (*VERB:NAME). Some may take either form, with differing behaviour,  (*VERB) or (*VERB:NAME). Some may take either form, possibly behaving
2799  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
2800  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
2801  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
2802  not there. Any number of these verbs may occur in a pattern.  libraries. If the name is empty, that is, if the closing parenthesis
2803    immediately follows the colon, the effect is as if the colon were not there.
2804    Any number of these verbs may occur in a pattern.
2805    .P
2806    Since these verbs are specifically related to backtracking, most of them can be
2807    used only when the pattern is to be matched using one of the traditional
2808    matching functions, because these use a backtracking algorithm. With the
2809    exception of (*FAIL), which behaves like a failing negative assertion, the
2810    backtracking control verbs cause an error if encountered by a DFA matching
2811    function.
2812  .P  .P
2813    The behaviour of these verbs in
2814    .\" HTML <a href="#btrepeat">
2815    .\" </a>
2816    repeated groups,
2817    .\"
2818    .\" HTML <a href="#btassert">
2819    .\" </a>
2820    assertions,
2821    .\"
2822    and in
2823    .\" HTML <a href="#btsub">
2824    .\" </a>
2825    subpatterns called as subroutines
2826    .\"
2827    (whether or not recursively) is documented below.
2828    .
2829    .
2830    .\" HTML <a name="nooptimize"></a>
2831    .SS "Optimizations that affect backtracking verbs"
2832    .rs
2833    .sp
2834  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
2835  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
2836  minimum length of matching subject, or that a particular character must be  minimum length of matching subject, or that a particular character must be
2837  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
2838  included backtracking verbs will not, of course, be processed. You can suppress  included backtracking verbs will not, of course, be processed. You can suppress
2839  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
2840  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
2841  pattern with (*NO_START_OPT).  pattern with (*NO_START_OPT). There is more discussion of this option in the
2842    section entitled
2843    .\" HTML <a href="pcreapi.html#execoptions">
2844    .\" </a>
2845    "Option bits for \fBpcre_exec()\fP"
2846    .\"
2847    in the
2848    .\" HREF
2849    \fBpcreapi\fP
2850    .\"
2851    documentation.
2852    .P
2853    Experiments with Perl suggest that it too has similar optimizations, sometimes
2854    leading to anomalous results.
2855  .  .
2856  .  .
2857  .SS "Verbs that act immediately"  .SS "Verbs that act immediately"
# Line 2519  followed by a name. Line 2863  followed by a name.
2863     (*ACCEPT)     (*ACCEPT)
2864  .sp  .sp
2865  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
2866  pattern. When inside a recursion, only the innermost pattern is ended  pattern. However, when it is inside a subpattern that is called as a
2867  immediately. If (*ACCEPT) is inside capturing parentheses, the data so far is  subroutine, only that subpattern is ended successfully. Matching then continues
2868  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
2869    assertion succeeds; in a negative assertion, the assertion fails.
2870    .P
2871    If (*ACCEPT) is inside capturing parentheses, the data so far is captured. For
2872    example:
2873  .sp  .sp
2874    A((?:A|B(*ACCEPT)|C)D)    A((?:A|B(*ACCEPT)|C)D)
2875  .sp  .sp
# Line 2530  the outer parentheses. Line 2878  the outer parentheses.
2878  .sp  .sp
2879    (*FAIL) or (*F)    (*FAIL) or (*F)
2880  .sp  .sp
2881  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
2882  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
2883  probably useful only when combined with (?{}) or (??{}). Those are, of course,  probably useful only when combined with (?{}) or (??{}). Those are, of course,
2884  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 2554  starting point (see (*SKIP) below). Line 2902  starting point (see (*SKIP) below).
2902  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
2903  (*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.
2904  .P  .P
2905  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),
2906  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
2907    caller as described in the section entitled
2908  .\" HTML <a href="pcreapi.html#extradata">  .\" HTML <a href="pcreapi.html#extradata">
2909  .\" </a>  .\" </a>
2910  section on \fIpcre_extra\fP  "Extra data for \fBpcre_exec()\fP"
2911  .\"  .\"
2912  in the  in the
2913  .\" HREF  .\" HREF
2914  \fBpcreapi\fP  \fBpcreapi\fP
2915  .\"  .\"
2916  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
2917  \fBpcretest\fP output, where the /K modifier requests the retrieval and  modifier requests the retrieval and outputting of (*MARK) data:
 outputting of (*MARK) data:  
2918  .sp  .sp
2919    /X(*MARK:A)Y|X(*MARK:B)Z/K      re> /X(*MARK:A)Y|X(*MARK:B)Z/K
2920    XY    data> XY
2921     0: XY     0: XY
2922    MK: A    MK: A
2923    XZ    XZ
# Line 2581  indicates which of the two alternatives Line 2929  indicates which of the two alternatives
2929  of obtaining this information than putting each alternative in its own  of obtaining this information than putting each alternative in its own
2930  capturing parentheses.  capturing parentheses.
2931  .P  .P
2932  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
2933  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
2934  (*COMMIT), this is unlikely to happen for an unanchored pattern because, as the  happen for negative assertions or failing positive assertions.
2935  starting point for matching is advanced, the final check is often with an empty  .P
2936  string, causing a failure before (*MARK) is reached. For example:  After a partial match or a failed match, the last encountered name in the
2937  .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:  
2938  .sp  .sp
2939    /^X(*MARK:A)Y|^X(*MARK:B)Z/K      re> /X(*MARK:A)Y|X(*MARK:B)Z/K
2940    XP    data> XP
2941    No match, mark = B    No match, mark = B
2942  .sp  .sp
2943  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
2944  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
2945  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
2946  .P  (*MARK) item, but nevertheless do not reset it.
2947  Note that similar anomalies (though different in detail) exist in Perl, no  .P
2948  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
2949  unanchored pattern is not recommended, unless (*COMMIT) is involved.  probably set the PCRE_NO_START_OPTIMIZE option
2950    .\" HTML <a href="#nooptimize">
2951    .\" </a>
2952    (see above)
2953    .\"
2954    to ensure that the match is always attempted.
2955  .  .
2956  .  .
2957  .SS "Verbs that act after backtracking"  .SS "Verbs that act after backtracking"
# Line 2614  unanchored pattern is not recommended, u Line 2960  unanchored pattern is not recommended, u
2960  The following verbs do nothing when they are encountered. Matching continues  The following verbs do nothing when they are encountered. Matching continues
2961  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
2962  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
2963  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
2964  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
2965  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
2966  "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
2967  above, that this localization also applies in subroutine calls and assertions.)  or assertion. (Remember also, as stated above, that this localization also
2968    applies in subroutine calls.)
2969  .P  .P
2970  These verbs differ in exactly what kind of failure occurs when backtracking  These verbs differ in exactly what kind of failure occurs when backtracking
2971  reaches them.  reaches them. The behaviour described below is what happens when the verb is
2972    not in a subroutine or an assertion. Subsequent sections cover these special
2973    cases.
2974  .sp  .sp
2975    (*COMMIT)    (*COMMIT)
2976  .sp  .sp
2977  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
2978  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
2979  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
2980  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
2981  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
2982    committed to finding a match at the current starting point, or not at all. For
2983    example:
2984  .sp  .sp
2985    a+(*COMMIT)b    a+(*COMMIT)b
2986  .sp  .sp
# Line 2638  dynamic anchor, or "I've started, so I m Line 2989  dynamic anchor, or "I've started, so I m
2989  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
2990  match failure.  match failure.
2991  .P  .P
2992    If there is more than one backtracking verb in a pattern, a different one that
2993    follows (*COMMIT) may be triggered first, so merely passing (*COMMIT) during a
2994    match does not always guarantee that a match must be at this starting point.
2995    .P
2996  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,
2997  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
2998  \fBpcretest\fP example:  \fBpcretest\fP example:
2999  .sp  .sp
3000    /(*COMMIT)abc/      re> /(*COMMIT)abc/
3001    xyzabc    data> xyzabc
3002     0: abc     0: abc
3003    xyzabc\eY    xyzabc\eY
3004    No match    No match
# Line 2657  starting points. Line 3012  starting points.
3012    (*PRUNE) or (*PRUNE:NAME)    (*PRUNE) or (*PRUNE:NAME)
3013  .sp  .sp
3014  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
3015  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
3016  unanchored, the normal "bumpalong" advance to the next starting character then  it. If the pattern is unanchored, the normal "bumpalong" advance to the next
3017  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
3018  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
3019  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
3020  (*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
3021  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
3022  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
3023  match fails completely; the name is passed back if this is the final attempt.  as (*COMMIT).
3024  (*PRUNE:NAME) does not pass back a name if the match succeeds. In an anchored  .P
3025  pattern (*PRUNE) has the same effect as (*COMMIT).  The behaviour of (*PRUNE:NAME) is the not the same as (*MARK:NAME)(*PRUNE).
3026    It is like (*MARK:NAME) in that the name is remembered for passing back to the
3027    caller. However, (*SKIP:NAME) searches only for names set with (*MARK).
3028  .sp  .sp
3029    (*SKIP)    (*SKIP)
3030  .sp  .sp
# Line 2688  instead of skipping on to "c". Line 3045  instead of skipping on to "c".
3045  .sp  .sp
3046    (*SKIP:NAME)    (*SKIP:NAME)
3047  .sp  .sp
3048  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
3049  following pattern fails to match, the previous path through the pattern is  triggered, the previous path through the pattern is searched for the most
3050  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
3051  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
3052  (*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
3053  matching name is found, normal "bumpalong" of one character happens (the  (*SKIP) is ignored.
3054  (*SKIP) is ignored).  .P
3055    Note that (*SKIP:NAME) searches only for names set by (*MARK:NAME). It ignores
3056    names that are set by (*PRUNE:NAME) or (*THEN:NAME).
3057  .sp  .sp
3058    (*THEN) or (*THEN:NAME)    (*THEN) or (*THEN:NAME)
3059  .sp  .sp
3060  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
3061  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
3062  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
3063  observation that it can be used for a pattern-based if-then-else block:  pattern-based if-then-else block:
3064  .sp  .sp
3065    ( COND1 (*THEN) FOO | COND2 (*THEN) BAR | COND3 (*THEN) BAZ ) ...    ( COND1 (*THEN) FOO | COND2 (*THEN) BAR | COND3 (*THEN) BAZ ) ...
3066  .sp  .sp
3067  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
3068  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
3069  second alternative and tries COND2, without backtracking into COND1. The  second alternative and tries COND2, without backtracking into COND1. If that
3070  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
3071  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
3072  like (*PRUNE).  group. If (*THEN) is not inside an alternation, it acts like (*PRUNE).
3073  .  .P
3074  .P  The behaviour of (*THEN:NAME) is the not the same as (*MARK:NAME)(*THEN).
3075  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
3076  matching fails. (*THEN) is the weakest, carrying on the match at the next  caller. However, (*SKIP:NAME) searches only for names set with (*MARK).
3077  alternation. (*PRUNE) comes next, failing the match at the current starting  .P
3078  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
3079  pattern). (*SKIP) is similar, except that the advance may be more than one  enclosing alternative; it is not a nested alternation with only one
3080  character. (*COMMIT) is the strongest, causing the entire match to fail.  alternative. The effect of (*THEN) extends beyond such a subpattern to the
3081  .P  enclosing alternative. Consider this pattern, where A, B, etc. are complex
3082  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:
3083  consider this pattern, where A, B, etc. are complex pattern fragments:  .sp
3084  .sp    A (B(*THEN)C) | D
3085    (A(*COMMIT)B(*THEN)C|D)  .sp
3086  .sp  If A and B are matched, but there is a failure in C, matching does not
3087  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.
3088  position. If subsequently B matches, but C does not, the normal (*THEN) action  However, if the subpattern containing (*THEN) is given an alternative, it
3089  of trying the next alternation (that is, D) does not happen because (*COMMIT)  behaves differently:
3090  overrides.  .sp
3091      A (B(*THEN)C | (*FAIL)) | D
3092    .sp
3093    The effect of (*THEN) is now confined to the inner subpattern. After a failure
3094    in C, matching moves to (*FAIL), which causes the whole subpattern to fail
3095    because there are no more alternatives to try. In this case, matching does now
3096    backtrack into A.
3097    .P
3098    Note that a conditional subpattern is not considered as having two
3099    alternatives, because only one is ever used. In other words, the | character in
3100    a conditional subpattern has a different meaning. Ignoring white space,
3101    consider:
3102    .sp
3103      ^.*? (?(?=a) a | b(*THEN)c )
3104    .sp
3105    If the subject is "ba", this pattern does not match. Because .*? is ungreedy,
3106    it initially matches zero characters. The condition (?=a) then fails, the
3107    character "b" is matched, but "c" is not. At this point, matching does not
3108    backtrack to .*? as might perhaps be expected from the presence of the |
3109    character. The conditional subpattern is part of the single alternative that
3110    comprises the whole pattern, and so the match fails. (If there was a backtrack
3111    into .*?, allowing it to match "b", the match would succeed.)
3112    .P
3113    The verbs just described provide four different "strengths" of control when
3114    subsequent matching fails. (*THEN) is the weakest, carrying on the match at the
3115    next alternative. (*PRUNE) comes next, failing the match at the current
3116    starting position, but allowing an advance to the next character (for an
3117    unanchored pattern). (*SKIP) is similar, except that the advance may be more
3118    than one character. (*COMMIT) is the strongest, causing the entire match to
3119    fail.
3120    .
3121    .
3122    .SS "More than one backtracking verb"
3123    .rs
3124    .sp
3125    If more than one backtracking verb is present in a pattern, the one that is
3126    backtracked onto first acts. For example, consider this pattern, where A, B,
3127    etc. are complex pattern fragments:
3128    .sp
3129      (A(*COMMIT)B(*THEN)C|ABD)
3130    .sp
3131    If A matches but B fails, the backtrack to (*COMMIT) causes the entire match to
3132    fail. However, if A and B match, but C fails, the backtrack to (*THEN) causes
3133    the next alternative (ABD) to be tried. This behaviour is consistent, but is
3134    not always the same as Perl's. It means that if two or more backtracking verbs
3135    appear in succession, all the the last of them has no effect. Consider this
3136    example:
3137    .sp
3138      ...(*COMMIT)(*PRUNE)...
3139    .sp
3140    If there is a matching failure to the right, backtracking onto (*PRUNE) causes
3141    it to be triggered, and its action is taken. There can never be a backtrack
3142    onto (*COMMIT).
3143    .
3144    .
3145    .\" HTML <a name="btrepeat"></a>
3146    .SS "Backtracking verbs in repeated groups"
3147    .rs
3148    .sp
3149    PCRE differs from Perl in its handling of backtracking verbs in repeated
3150    groups. For example, consider:
3151    .sp
3152      /(a(*COMMIT)b)+ac/
3153    .sp
3154    If the subject is "abac", Perl matches, but PCRE fails because the (*COMMIT) in
3155    the second repeat of the group acts.
3156    .
3157    .
3158    .\" HTML <a name="btassert"></a>
3159    .SS "Backtracking verbs in assertions"
3160    .rs
3161    .sp
3162    (*FAIL) in an assertion has its normal effect: it forces an immediate backtrack.
3163    .P
3164    (*ACCEPT) in a positive assertion causes the assertion to succeed without any
3165    further processing. In a negative assertion, (*ACCEPT) causes the assertion to
3166    fail without any further processing.
3167    .P
3168    The other backtracking verbs are not treated specially if they appear in a
3169    positive assertion. In particular, (*THEN) skips to the next alternative in the
3170    innermost enclosing group that has alternations, whether or not this is within
3171    the assertion.
3172    .P
3173    Negative assertions are, however, different, in order to ensure that changing a
3174    positive assertion into a negative assertion changes its result. Backtracking
3175    into (*COMMIT), (*SKIP), or (*PRUNE) causes a negative assertion to be true,
3176    without considering any further alternative branches in the assertion.
3177    Backtracking into (*THEN) causes it to skip to the next enclosing alternative
3178    within the assertion (the normal behaviour), but if the assertion does not have
3179    such an alternative, (*THEN) behaves like (*PRUNE).
3180    .
3181    .
3182    .\" HTML <a name="btsub"></a>
3183    .SS "Backtracking verbs in subroutines"
3184    .rs
3185    .sp
3186    These behaviours occur whether or not the subpattern is called recursively.
3187    Perl's treatment of subroutines is different in some cases.
3188    .P
3189    (*FAIL) in a subpattern called as a subroutine has its normal effect: it forces
3190    an immediate backtrack.
3191    .P
3192    (*ACCEPT) in a subpattern called as a subroutine causes the subroutine match to
3193    succeed without any further processing. Matching then continues after the
3194    subroutine call.
3195    .P
3196    (*COMMIT), (*SKIP), and (*PRUNE) in a subpattern called as a subroutine cause
3197    the subroutine match to fail.
3198    .P
3199    (*THEN) skips to the next alternative in the innermost enclosing group within
3200    the subpattern that has alternatives. If there is no such group within the
3201    subpattern, (*THEN) causes the subroutine match to fail.
3202  .  .
3203  .  .
3204  .SH "SEE ALSO"  .SH "SEE ALSO"
3205  .rs  .rs
3206  .sp  .sp
3207  \fBpcreapi\fP(3), \fBpcrecallout\fP(3), \fBpcrematching\fP(3),  \fBpcreapi\fP(3), \fBpcrecallout\fP(3), \fBpcrematching\fP(3),
3208  \fBpcresyntax\fP(3), \fBpcre\fP(3).  \fBpcresyntax\fP(3), \fBpcre\fP(3), \fBpcre16(3)\fP, \fBpcre32(3)\fP.
3209  .  .
3210  .  .
3211  .SH AUTHOR  .SH AUTHOR
# Line 2752  Cambridge CB2 3QH, England. Line 3222  Cambridge CB2 3QH, England.
3222  .rs  .rs
3223  .sp  .sp
3224  .nf  .nf
3225  Last updated: 12 June 2011  Last updated: 09 November 2013
3226  Copyright (c) 1997-2011 University of Cambridge.  Copyright (c) 1997-2013 University of Cambridge.
3227  .fi  .fi

Legend:
Removed from v.607  
changed lines
  Added in v.1395

  ViewVC Help
Powered by ViewVC 1.1.5