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revision 575 by ph10, Sun Nov 21 12:55:42 2010 UTC revision 643 by ph10, Fri Jul 29 15:56:39 2011 UTC
# Line 52  such as \ed and \ew to use Unicode prope Line 52  such as \ed and \ew to use Unicode prope
52  instead of recognizing only characters with codes less than 128 via a lookup  instead of recognizing only characters with codes less than 128 via a lookup
53  table.  table.
54  .P  .P
55    If a pattern starts with (*NO_START_OPT), it has the same effect as setting the
56    PCRE_NO_START_OPTIMIZE option either at compile or matching time. There are
57    also some more of these special sequences that are concerned with the handling
58    of newlines; they are described below.
59    .P
60  The remainder of this document discusses the patterns that are supported by  The remainder of this document discusses the patterns that are supported by
61  PCRE when its main matching function, \fBpcre_exec()\fP, is used.  PCRE when its main matching function, \fBpcre_exec()\fP, is used.
62  From release 6.0, PCRE offers a second matching function,  From release 6.0, PCRE offers a second matching function,
# Line 184  The following sections describe the use Line 189  The following sections describe the use
189  The backslash character has several uses. Firstly, if it is followed by a  The backslash character has several uses. Firstly, if it is followed by a
190  character that is not a number or a letter, it takes away any special meaning  character that is not a number or a letter, it takes away any special meaning
191  that character may have. This use of backslash as an escape character applies  that character may have. This use of backslash as an escape character applies
192  both inside and outside character classes.  both inside and outside character classes.
193  .P  .P
194  For example, if you want to match a * character, you write \e* in the pattern.  For example, if you want to match a * character, you write \e* in the pattern.
195  This escaping action applies whether or not the following character would  This escaping action applies whether or not the following character would
# Line 193  non-alphanumeric with backslash to speci Line 198  non-alphanumeric with backslash to speci
198  particular, if you want to match a backslash, you write \e\e.  particular, if you want to match a backslash, you write \e\e.
199  .P  .P
200  In UTF-8 mode, only ASCII numbers and letters have any special meaning after a  In UTF-8 mode, only ASCII numbers and letters have any special meaning after a
201  backslash. All other characters (in particular, those whose codepoints are  backslash. All other characters (in particular, those whose codepoints are
202  greater than 127) are treated as literals.  greater than 127) are treated as literals.
203  .P  .P
204  If a pattern is compiled with the PCRE_EXTENDED option, whitespace in the  If a pattern is compiled with the PCRE_EXTENDED option, whitespace in the
# Line 215  Perl, $ and @ cause variable interpolati Line 220  Perl, $ and @ cause variable interpolati
220    \eQabc\eE\e$\eQxyz\eE   abc$xyz        abc$xyz    \eQabc\eE\e$\eQxyz\eE   abc$xyz        abc$xyz
221  .sp  .sp
222  The \eQ...\eE sequence is recognized both inside and outside character classes.  The \eQ...\eE sequence is recognized both inside and outside character classes.
223  An isolated \eE that is not preceded by \eQ is ignored.  An isolated \eE that is not preceded by \eQ is ignored. If \eQ is not followed
224    by \eE later in the pattern, the literal interpretation continues to the end of
225    the pattern (that is, \eE is assumed at the end). If the isolated \eQ is inside
226    a character class, this causes an error, because the character class is not
227    terminated.
228  .  .
229  .  .
230  .\" HTML <a name="digitsafterbackslash"></a>  .\" HTML <a name="digitsafterbackslash"></a>
# Line 242  one of the following escape sequences th Line 251  one of the following escape sequences th
251  The precise effect of \ecx is as follows: if x is a lower case letter, it  The precise effect of \ecx is as follows: if x is a lower case letter, it
252  is converted to upper case. Then bit 6 of the character (hex 40) is inverted.  is converted to upper case. Then bit 6 of the character (hex 40) is inverted.
253  Thus \ecz becomes hex 1A (z is 7A), but \ec{ becomes hex 3B ({ is 7B), while  Thus \ecz becomes hex 1A (z is 7A), but \ec{ becomes hex 3B ({ is 7B), while
254  \ec; becomes hex 7B (; is 3B). If the byte following \ec has a value greater  \ec; becomes hex 7B (; is 3B). If the byte following \ec has a value greater
255  than 127, a compile-time error occurs. This locks out non-ASCII characters in  than 127, a compile-time error occurs. This locks out non-ASCII characters in
256  both byte mode and UTF-8 mode. (When PCRE is compiled in EBCDIC mode, all byte  both byte mode and UTF-8 mode. (When PCRE is compiled in EBCDIC mode, all byte
257  values are valid. A lower case letter is converted to upper case, and then the  values are valid. A lower case letter is converted to upper case, and then the
258  0xc0 bits are flipped.)  0xc0 bits are flipped.)
259  .P  .P
260  After \ex, from zero to two hexadecimal digits are read (letters can be in  After \ex, from zero to two hexadecimal digits are read (letters can be in
# Line 432  any Unicode letter, and underscore. Note Line 441  any Unicode letter, and underscore. Note
441  \eB because they are defined in terms of \ew and \eW. Matching these sequences  \eB because they are defined in terms of \ew and \eW. Matching these sequences
442  is noticeably slower when PCRE_UCP is set.  is noticeably slower when PCRE_UCP is set.
443  .P  .P
444  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
445  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
446  characters by default, these always match certain high-valued codepoints in  characters by default, these always match certain high-valued codepoints in
447  UTF-8 mode, whether or not PCRE_UCP is set. The horizontal space characters  UTF-8 mode, whether or not PCRE_UCP is set. The horizontal space characters
# Line 748  Characters with the "mark" property are Line 757  Characters with the "mark" property are
757  preceding character. None of them have codepoints less than 256, so in  preceding character. None of them have codepoints less than 256, so in
758  non-UTF-8 mode \eX matches any one character.  non-UTF-8 mode \eX matches any one character.
759  .P  .P
760    Note that recent versions of Perl have changed \eX to match what Unicode calls
761    an "extended grapheme cluster", which has a more complicated definition.
762    .P
763  Matching characters by Unicode property is not fast, because PCRE has to search  Matching characters by Unicode property is not fast, because PCRE has to search
764  a structure that contains data for over fifteen thousand characters. That is  a structure that contains data for over fifteen thousand characters. That is
765  why the traditional escape sequences such as \ed and \ew do not use Unicode  why the traditional escape sequences such as \ed and \ew do not use Unicode
# Line 955  The handling of dot is entirely independ Line 967  The handling of dot is entirely independ
967  dollar, the only relationship being that they both involve newlines. Dot has no  dollar, the only relationship being that they both involve newlines. Dot has no
968  special meaning in a character class.  special meaning in a character class.
969  .P  .P
970  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
971  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
972  that signifies the end of a line.  that signifies the end of a line.
973  .  .
# Line 1071  default, but cause an error if the PCRE_ Line 1083  default, but cause an error if the PCRE_
1083  A circumflex can conveniently be used with the upper case character types to  A circumflex can conveniently be used with the upper case character types to
1084  specify a more restricted set of characters than the matching lower case type.  specify a more restricted set of characters than the matching lower case type.
1085  For example, the class [^\eW_] matches any letter or digit, but not underscore,  For example, the class [^\eW_] matches any letter or digit, but not underscore,
1086  whereas [\ew] includes underscore. A positive character class should be read as  whereas [\ew] includes underscore. A positive character class should be read as
1087  "something OR something OR ..." and a negative class as "NOT something AND NOT  "something OR something OR ..." and a negative class as "NOT something AND NOT
1088  something AND NOT ...".  something AND NOT ...".
1089  .P  .P
1090  The only metacharacters that are recognized in character classes are backslash,  The only metacharacters that are recognized in character classes are backslash,
# Line 1426  items: Line 1438  items:
1438    an escape such as \ed or \epL that matches a single character    an escape such as \ed or \epL that matches a single character
1439    a character class    a character class
1440    a back reference (see next section)    a back reference (see next section)
1441    a parenthesized subpattern (unless it is an assertion)    a parenthesized subpattern (including assertions)
1442    a recursive or "subroutine" call to a subpattern    a recursive or "subroutine" call to a subpattern
1443  .sp  .sp
1444  The general repetition quantifier specifies a minimum and maximum number of  The general repetition quantifier specifies a minimum and maximum number of
# Line 1817  those that look ahead of the current pos Line 1829  those that look ahead of the current pos
1829  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,
1830  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.
1831  .P  .P
1832  Assertion subpatterns are not capturing subpatterns, and may not be repeated,  Assertion subpatterns are not capturing subpatterns. If such an assertion
1833  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
1834  of assertion contains capturing subpatterns within it, these are counted for  numbering the capturing subpatterns in the whole pattern. However, substring
1835  the purposes of numbering the capturing subpatterns in the whole pattern.  capturing is carried out only for positive assertions, because it does not make
1836  However, substring capturing is carried out only for positive assertions,  sense for negative assertions.
1837  because it does not make sense for negative assertions.  .P
1838    For compatibility with Perl, assertion subpatterns may be repeated; though
1839    it makes no sense to assert the same thing several times, the side effect of
1840    capturing parentheses may occasionally be useful. In practice, there only three
1841    cases:
1842    .sp
1843    (1) If the quantifier is {0}, the assertion is never obeyed during matching.
1844    However, it may contain internal capturing parenthesized groups that are called
1845    from elsewhere via the
1846    .\" HTML <a href="#subpatternsassubroutines">
1847    .\" </a>
1848    subroutine mechanism.
1849    .\"
1850    .sp
1851    (2) If quantifier is {0,n} where n is greater than zero, it is treated as if it
1852    were {0,1}. At run time, the rest of the pattern match is tried with and
1853    without the assertion, the order depending on the greediness of the quantifier.
1854    .sp
1855    (3) If the minimum repetition is greater than zero, the quantifier is ignored.
1856    The assertion is obeyed just once when encountered during matching.
1857  .  .
1858  .  .
1859  .SS "Lookahead assertions"  .SS "Lookahead assertions"
# Line 1992  already been matched. The two possible f Line 2023  already been matched. The two possible f
2023  If the condition is satisfied, the yes-pattern is used; otherwise the  If the condition is satisfied, the yes-pattern is used; otherwise the
2024  no-pattern (if present) is used. If there are more than two alternatives in the  no-pattern (if present) is used. If there are more than two alternatives in the
2025  subpattern, a compile-time error occurs. Each of the two alternatives may  subpattern, a compile-time error occurs. Each of the two alternatives may
2026  itself contain nested subpatterns of any form, including conditional  itself contain nested subpatterns of any form, including conditional
2027  subpatterns; the restriction to two alternatives applies only at the level of  subpatterns; the restriction to two alternatives applies only at the level of
2028  the condition. This pattern fragment is an example where the alternatives are  the condition. This pattern fragment is an example where the alternatives are
2029  complex:  complex:
2030  .sp  .sp
2031    (?(1) (A|B|C) | (D | (?(2)E|F) | E) )    (?(1) (A|B|C) | (D | (?(2)E|F) | E) )
# Line 2019  the condition is true if any of them hav Line 2050  the condition is true if any of them hav
2050  to precede the digits with a plus or minus sign. In this case, the subpattern  to precede the digits with a plus or minus sign. In this case, the subpattern
2051  number is relative rather than absolute. The most recently opened parentheses  number is relative rather than absolute. The most recently opened parentheses
2052  can be referenced by (?(-1), the next most recent by (?(-2), and so on. Inside  can be referenced by (?(-1), the next most recent by (?(-2), and so on. Inside
2053  loops it can also make sense to refer to subsequent groups. The next  loops it can also make sense to refer to subsequent groups. The next
2054  parentheses to be opened can be referenced as (?(+1), and so on. (The value  parentheses to be opened can be referenced as (?(+1), and so on. (The value
2055  zero in any of these forms is not used; it provokes a compile-time error.)  zero in any of these forms is not used; it provokes a compile-time error.)
2056  .P  .P
# Line 2139  dd-aaa-dd or dd-dd-dd, where aaa are let Line 2170  dd-aaa-dd or dd-dd-dd, where aaa are let
2170  .SH COMMENTS  .SH COMMENTS
2171  .rs  .rs
2172  .sp  .sp
2173  There are two ways of including comments in patterns that are processed by  There are two ways of including comments in patterns that are processed by
2174  PCRE. In both cases, the start of the comment must not be in a character class,  PCRE. In both cases, the start of the comment must not be in a character class,
2175  nor in the middle of any other sequence of related characters such as (?: or a  nor in the middle of any other sequence of related characters such as (?: or a
2176  subpattern name or number. The characters that make up a comment play no part  subpattern name or number. The characters that make up a comment play no part
# Line 2163  default newline convention is in force: Line 2194  default newline convention is in force:
2194  .sp  .sp
2195    abc #comment \en still comment    abc #comment \en still comment
2196  .sp  .sp
2197  On encountering the # character, \fBpcre_compile()\fP skips along, looking for  On encountering the # character, \fBpcre_compile()\fP skips along, looking for
2198  a newline in the pattern. The sequence \en is still literal at this stage, so  a newline in the pattern. The sequence \en is still literal at this stage, so
2199  it does not terminate the comment. Only an actual character with the code value  it does not terminate the comment. Only an actual character with the code value
2200  0x0a (the default newline) does so.  0x0a (the default newline) does so.
# Line 2480  failing negative assertion, they cause a Line 2511  failing negative assertion, they cause a
2511  .P  .P
2512  If any of these verbs are used in an assertion or subroutine subpattern  If any of these verbs are used in an assertion or subroutine subpattern
2513  (including recursive subpatterns), their effect is confined to that subpattern;  (including recursive subpatterns), their effect is confined to that subpattern;
2514  it does not extend to the surrounding pattern. Note that such subpatterns are  it does not extend to the surrounding pattern, with one exception: a *MARK that
2515  processed as anchored at the point where they are tested.  is encountered in a positive assertion \fIis\fP passed back (compare capturing
2516    parentheses in assertions). Note that such subpatterns are processed as
2517    anchored at the point where they are tested.
2518  .P  .P
2519  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
2520  parenthesis followed by an asterisk. They are generally of the form  parenthesis followed by an asterisk. They are generally of the form
# Line 2497  minimum length of matching subject, or t Line 2530  minimum length of matching subject, or t
2530  present. When one of these optimizations suppresses the running of a match, any  present. When one of these optimizations suppresses the running of a match, any
2531  included backtracking verbs will not, of course, be processed. You can suppress  included backtracking verbs will not, of course, be processed. You can suppress
2532  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
2533  when calling \fBpcre_exec()\fP.  when calling \fBpcre_compile()\fP or \fBpcre_exec()\fP, or by starting the
2534    pattern with (*NO_START_OPT).
2535  .  .
2536  .  .
2537  .SS "Verbs that act immediately"  .SS "Verbs that act immediately"
# Line 2571  indicates which of the two alternatives Line 2605  indicates which of the two alternatives
2605  of obtaining this information than putting each alternative in its own  of obtaining this information than putting each alternative in its own
2606  capturing parentheses.  capturing parentheses.
2607  .P  .P
2608    If (*MARK) is encountered in a positive assertion, its name is recorded and
2609    passed back if it is the last-encountered. This does not happen for negative
2610    assetions.
2611    .P
2612  A name may also be returned after a failed match if the final path through the  A name may also be returned after a failed match if the final path through the
2613  pattern involves (*MARK). However, unless (*MARK) used in conjunction with  pattern involves (*MARK). However, unless (*MARK) used in conjunction with
2614  (*COMMIT), this is unlikely to happen for an unanchored pattern because, as the  (*COMMIT), this is unlikely to happen for an unanchored pattern because, as the
# Line 2688  matching name is found, normal "bumpalon Line 2726  matching name is found, normal "bumpalon
2726  .sp  .sp
2727    (*THEN) or (*THEN:NAME)    (*THEN) or (*THEN:NAME)
2728  .sp  .sp
2729  This verb causes a skip to the next alternation in the innermost enclosing  This verb causes a skip to the next alternation in the innermost enclosing
2730  group if the rest of the pattern does not match. That is, it cancels pending  group if the rest of the pattern does not match. That is, it cancels pending
2731  backtracking, but only within the current alternation. Its name comes from the  backtracking, but only within the current alternation. Its name comes from the
2732  observation that it can be used for a pattern-based if-then-else block:  observation that it can be used for a pattern-based if-then-else block:
# Line 2703  overall match fails. If (*THEN) is not d Line 2741  overall match fails. If (*THEN) is not d
2741  like (*PRUNE).  like (*PRUNE).
2742  .  .
2743  .P  .P
2744  The above verbs provide four different "strengths" of control when subsequent  The above verbs provide four different "strengths" of control when subsequent
2745  matching fails. (*THEN) is the weakest, carrying on the match at the next  matching fails. (*THEN) is the weakest, carrying on the match at the next
2746  alternation. (*PRUNE) comes next, failing the match at the current starting  alternation. (*PRUNE) comes next, failing the match at the current starting
2747  position, but allowing an advance to the next character (for an unanchored  position, but allowing an advance to the next character (for an unanchored
# Line 2742  Cambridge CB2 3QH, England. Line 2780  Cambridge CB2 3QH, England.
2780  .rs  .rs
2781  .sp  .sp
2782  .nf  .nf
2783  Last updated: 21 November 2010  Last updated: 24 July 2011
2784  Copyright (c) 1997-2010 University of Cambridge.  Copyright (c) 1997-2011 University of Cambridge.
2785  .fi  .fi
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