/[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 575 by ph10, Sun Nov 21 12:55:42 2010 UTC revision 678 by ph10, Sun Aug 28 15:23:03 2011 UTC
# Line 32  Starting a pattern with this sequence is Line 32  Starting a pattern with this sequence is
32  option. This feature is not Perl-compatible. How setting UTF-8 mode affects  option. This feature is not Perl-compatible. How setting UTF-8 mode affects
33  pattern matching is mentioned in several places below. There is also a summary  pattern matching is mentioned in several places below. There is also a summary
34  of UTF-8 features in the  of UTF-8 features in the
 .\" HTML <a href="pcre.html#utf8support">  
 .\" </a>  
 section on UTF-8 support  
 .\"  
 in the main  
35  .\" HREF  .\" HREF
36  \fBpcre\fP  \fBpcreunicode\fP
37  .\"  .\"
38  page.  page.
39  .P  .P
# Line 52  such as \ed and \ew to use Unicode prope Line 47  such as \ed and \ew to use Unicode prope
47  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
48  table.  table.
49  .P  .P
50    If a pattern starts with (*NO_START_OPT), it has the same effect as setting the
51    PCRE_NO_START_OPTIMIZE option either at compile or matching time. There are
52    also some more of these special sequences that are concerned with the handling
53    of newlines; they are described below.
54    .P
55  The remainder of this document discusses the patterns that are supported by  The remainder of this document discusses the patterns that are supported by
56  PCRE when its main matching function, \fBpcre_exec()\fP, is used.  PCRE when its main matching function, \fBpcre_exec()\fP, is used.
57  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 184  The following sections describe the use
184  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
185  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
186  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
187  both inside and outside character classes.  both inside and outside character classes.
188  .P  .P
189  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.
190  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 193  non-alphanumeric with backslash to speci
193  particular, if you want to match a backslash, you write \e\e.  particular, if you want to match a backslash, you write \e\e.
194  .P  .P
195  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
196  backslash. All other characters (in particular, those whose codepoints are  backslash. All other characters (in particular, those whose codepoints are
197  greater than 127) are treated as literals.  greater than 127) are treated as literals.
198  .P  .P
199  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 215  Perl, $ and @ cause variable interpolati
215    \eQabc\eE\e$\eQxyz\eE   abc$xyz        abc$xyz    \eQabc\eE\e$\eQxyz\eE   abc$xyz        abc$xyz
216  .sp  .sp
217  The \eQ...\eE sequence is recognized both inside and outside character classes.  The \eQ...\eE sequence is recognized both inside and outside character classes.
218  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
219    by \eE later in the pattern, the literal interpretation continues to the end of
220    the pattern (that is, \eE is assumed at the end). If the isolated \eQ is inside
221    a character class, this causes an error, because the character class is not
222    terminated.
223  .  .
224  .  .
225  .\" HTML <a name="digitsafterbackslash"></a>  .\" HTML <a name="digitsafterbackslash"></a>
# Line 242  one of the following escape sequences th Line 246  one of the following escape sequences th
246  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
247  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.
248  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
249  \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
250  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
251  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
252  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
253  0xc0 bits are flipped.)  0xc0 bits are flipped.)
254  .P  .P
255  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 436  any Unicode letter, and underscore. Note
436  \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
437  is noticeably slower when PCRE_UCP is set.  is noticeably slower when PCRE_UCP is set.
438  .P  .P
439  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
440  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
441  characters by default, these always match certain high-valued codepoints in  characters by default, these always match certain high-valued codepoints in
442  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 752  Characters with the "mark" property are
752  preceding character. None of them have codepoints less than 256, so in  preceding character. None of them have codepoints less than 256, so in
753  non-UTF-8 mode \eX matches any one character.  non-UTF-8 mode \eX matches any one character.
754  .P  .P
755    Note that recent versions of Perl have changed \eX to match what Unicode calls
756    an "extended grapheme cluster", which has a more complicated definition.
757    .P
758  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
759  a structure that contains data for over fifteen thousand characters. That is  a structure that contains data for over fifteen thousand characters. That is
760  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 962  The handling of dot is entirely independ
962  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
963  special meaning in a character class.  special meaning in a character class.
964  .P  .P
965  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
966  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
967  that signifies the end of a line.  that signifies the end of a line.
968  .  .
# Line 1071  default, but cause an error if the PCRE_ Line 1078  default, but cause an error if the PCRE_
1078  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
1079  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.
1080  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,
1081  whereas [\ew] includes underscore. A positive character class should be read as  whereas [\ew] includes underscore. A positive character class should be read as
1082  "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
1083  something AND NOT ...".  something AND NOT ...".
1084  .P  .P
1085  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 1433  items:
1433    an escape such as \ed or \epL that matches a single character    an escape such as \ed or \epL that matches a single character
1434    a character class    a character class
1435    a back reference (see next section)    a back reference (see next section)
1436    a parenthesized subpattern (unless it is an assertion)    a parenthesized subpattern (including assertions)
1437    a recursive or "subroutine" call to a subpattern    a recursive or "subroutine" call to a subpattern
1438  .sp  .sp
1439  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 1824  those that look ahead of the current pos
1824  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,
1825  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.
1826  .P  .P
1827  Assertion subpatterns are not capturing subpatterns, and may not be repeated,  Assertion subpatterns are not capturing subpatterns. If such an assertion
1828  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
1829  of assertion contains capturing subpatterns within it, these are counted for  numbering the capturing subpatterns in the whole pattern. However, substring
1830  the purposes of numbering the capturing subpatterns in the whole pattern.  capturing is carried out only for positive assertions, because it does not make
1831  However, substring capturing is carried out only for positive assertions,  sense for negative assertions.
1832  because it does not make sense for negative assertions.  .P
1833    For compatibility with Perl, assertion subpatterns may be repeated; though
1834    it makes no sense to assert the same thing several times, the side effect of
1835    capturing parentheses may occasionally be useful. In practice, there only three
1836    cases:
1837    .sp
1838    (1) If the quantifier is {0}, the assertion is never obeyed during matching.
1839    However, it may contain internal capturing parenthesized groups that are called
1840    from elsewhere via the
1841    .\" HTML <a href="#subpatternsassubroutines">
1842    .\" </a>
1843    subroutine mechanism.
1844    .\"
1845    .sp
1846    (2) If quantifier is {0,n} where n is greater than zero, it is treated as if it
1847    were {0,1}. At run time, the rest of the pattern match is tried with and
1848    without the assertion, the order depending on the greediness of the quantifier.
1849    .sp
1850    (3) If the minimum repetition is greater than zero, the quantifier is ignored.
1851    The assertion is obeyed just once when encountered during matching.
1852  .  .
1853  .  .
1854  .SS "Lookahead assertions"  .SS "Lookahead assertions"
# Line 1992  already been matched. The two possible f Line 2018  already been matched. The two possible f
2018  If the condition is satisfied, the yes-pattern is used; otherwise the  If the condition is satisfied, the yes-pattern is used; otherwise the
2019  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
2020  subpattern, a compile-time error occurs. Each of the two alternatives may  subpattern, a compile-time error occurs. Each of the two alternatives may
2021  itself contain nested subpatterns of any form, including conditional  itself contain nested subpatterns of any form, including conditional
2022  subpatterns; the restriction to two alternatives applies only at the level of  subpatterns; the restriction to two alternatives applies only at the level of
2023  the condition. This pattern fragment is an example where the alternatives are  the condition. This pattern fragment is an example where the alternatives are
2024  complex:  complex:
2025  .sp  .sp
2026    (?(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 2045  the condition is true if any of them hav
2045  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
2046  number is relative rather than absolute. The most recently opened parentheses  number is relative rather than absolute. The most recently opened parentheses
2047  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
2048  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
2049  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
2050  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.)
2051  .P  .P
# Line 2139  dd-aaa-dd or dd-dd-dd, where aaa are let Line 2165  dd-aaa-dd or dd-dd-dd, where aaa are let
2165  .SH COMMENTS  .SH COMMENTS
2166  .rs  .rs
2167  .sp  .sp
2168  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
2169  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,
2170  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
2171  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 2189  default newline convention is in force:
2189  .sp  .sp
2190    abc #comment \en still comment    abc #comment \en still comment
2191  .sp  .sp
2192  On encountering the # character, \fBpcre_compile()\fP skips along, looking for  On encountering the # character, \fBpcre_compile()\fP skips along, looking for
2193  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
2194  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
2195  0x0a (the default newline) does so.  0x0a (the default newline) does so.
# Line 2480  failing negative assertion, they cause a Line 2506  failing negative assertion, they cause a
2506  .P  .P
2507  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
2508  (including recursive subpatterns), their effect is confined to that subpattern;  (including recursive subpatterns), their effect is confined to that subpattern;
2509  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
2510  processed as anchored at the point where they are tested.  is encountered in a positive assertion \fIis\fP passed back (compare capturing
2511    parentheses in assertions). Note that such subpatterns are processed as
2512    anchored at the point where they are tested.
2513  .P  .P
2514  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
2515  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 2525  minimum length of matching subject, or t
2525  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
2526  included backtracking verbs will not, of course, be processed. You can suppress  included backtracking verbs will not, of course, be processed. You can suppress
2527  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
2528  when calling \fBpcre_exec()\fP.  when calling \fBpcre_compile()\fP or \fBpcre_exec()\fP, or by starting the
2529    pattern with (*NO_START_OPT).
2530  .  .
2531  .  .
2532  .SS "Verbs that act immediately"  .SS "Verbs that act immediately"
# Line 2571  indicates which of the two alternatives Line 2600  indicates which of the two alternatives
2600  of obtaining this information than putting each alternative in its own  of obtaining this information than putting each alternative in its own
2601  capturing parentheses.  capturing parentheses.
2602  .P  .P
2603    If (*MARK) is encountered in a positive assertion, its name is recorded and
2604    passed back if it is the last-encountered. This does not happen for negative
2605    assetions.
2606    .P
2607  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
2608  pattern involves (*MARK). However, unless (*MARK) used in conjunction with  pattern involves (*MARK). However, unless (*MARK) used in conjunction with
2609  (*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 2721  matching name is found, normal "bumpalon
2721  .sp  .sp
2722    (*THEN) or (*THEN:NAME)    (*THEN) or (*THEN:NAME)
2723  .sp  .sp
2724  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
2725  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
2726  backtracking, but only within the current alternation. Its name comes from the  backtracking, but only within the current alternation. Its name comes from the
2727  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 2736  overall match fails. If (*THEN) is not d
2736  like (*PRUNE).  like (*PRUNE).
2737  .  .
2738  .P  .P
2739  The above verbs provide four different "strengths" of control when subsequent  The above verbs provide four different "strengths" of control when subsequent
2740  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
2741  alternation. (*PRUNE) comes next, failing the match at the current starting  alternation. (*PRUNE) comes next, failing the match at the current starting
2742  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 2775  Cambridge CB2 3QH, England.
2775  .rs  .rs
2776  .sp  .sp
2777  .nf  .nf
2778  Last updated: 21 November 2010  Last updated: 24 August 2011
2779  Copyright (c) 1997-2010 University of Cambridge.  Copyright (c) 1997-2011 University of Cambridge.
2780  .fi  .fi

Legend:
Removed from v.575  
changed lines
  Added in v.678

  ViewVC Help
Powered by ViewVC 1.1.5