/[pcre]/code/trunk/doc/pcrepattern.3
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revision 171 by ph10, Mon Jun 4 14:28:58 2007 UTC revision 172 by ph10, Tue Jun 5 10:40:13 2007 UTC
# Line 30  The remainder of this document discusses Line 30  The remainder of this document discusses
30  PCRE when its main matching function, \fBpcre_exec()\fP, is used.  PCRE when its main matching function, \fBpcre_exec()\fP, is used.
31  From release 6.0, PCRE offers a second matching function,  From release 6.0, PCRE offers a second matching function,
32  \fBpcre_dfa_exec()\fP, which matches using a different algorithm that is not  \fBpcre_dfa_exec()\fP, which matches using a different algorithm that is not
33  Perl-compatible. Some of the features discussed below are not available when  Perl-compatible. Some of the features discussed below are not available when
34  \fBpcre_dfa_exec()\fP is used. The advantages and disadvantages of the  \fBpcre_dfa_exec()\fP is used. The advantages and disadvantages of the
35  alternative function, and how it differs from the normal function, are  alternative function, and how it differs from the normal function, are
36  discussed in the  discussed in the
# Line 241  meanings Line 241  meanings
241  .rs  .rs
242  .sp  .sp
243  The sequence \eg followed by a positive or negative number, optionally enclosed  The sequence \eg followed by a positive or negative number, optionally enclosed
244  in braces, is an absolute or relative back reference. A named back reference  in braces, is an absolute or relative back reference. A named back reference
245  can be coded as \eg{name}. Back references are discussed  can be coded as \eg{name}. Back references are discussed
246  .\" HTML <a href="#backreferences">  .\" HTML <a href="#backreferences">
247  .\" </a>  .\" </a>
# Line 525  properties in PCRE. Line 525  properties in PCRE.
525  .SS "Resetting the match start"  .SS "Resetting the match start"
526  .rs  .rs
527  .sp  .sp
528  The escape sequence \eK, which is a Perl 5.10 feature, causes any previously  The escape sequence \eK, which is a Perl 5.10 feature, causes any previously
529  matched characters not to be included in the final matched sequence. For  matched characters not to be included in the final matched sequence. For
530  example, the pattern:  example, the pattern:
531  .sp  .sp
532    foo\eKbar    foo\eKbar
533  .sp  .sp
534  matches "foobar", but reports that it has matched "bar". This feature is  matches "foobar", but reports that it has matched "bar". This feature is
535  similar to a lookbehind assertion  similar to a lookbehind assertion
536  .\" HTML <a href="#lookbehind">  .\" HTML <a href="#lookbehind">
537  .\" </a>  .\" </a>
538  (described below).  (described below).
539  .\"  .\"
540  However, in this case, the part of the subject before the real match does not  However, in this case, the part of the subject before the real match does not
541  have to be of fixed length, as lookbehind assertions do. The use of \eK does  have to be of fixed length, as lookbehind assertions do. The use of \eK does
542  not interfere with the setting of  not interfere with the setting of
543  .\" HTML <a href="#subpattern">  .\" HTML <a href="#subpattern">
544  .\" </a>  .\" </a>
545  captured substrings.  captured substrings.
546  .\"  .\"
547  For example, when the pattern  For example, when the pattern
548  .sp  .sp
549    (foo)\eKbar    (foo)\eKbar
550  .sp  .sp
551  matches "foobar", the first substring is still set to "foo".  matches "foobar", the first substring is still set to "foo".
552  .  .
553  .  .
554  .\" HTML <a name="smallassertions"></a>  .\" HTML <a name="smallassertions"></a>
# Line 1458  lengths, but it is acceptable if rewritt Line 1458  lengths, but it is acceptable if rewritt
1458  .sp  .sp
1459    (?<=abc|abde)    (?<=abc|abde)
1460  .sp  .sp
1461  In some cases, the Perl 5.10 escape sequence \eK  In some cases, the Perl 5.10 escape sequence \eK
1462  .\" HTML <a href="#resetmatchstart">  .\" HTML <a href="#resetmatchstart">
1463  .\" </a>  .\" </a>
1464  (see above)  (see above)
# Line 1560  recursion, a pseudo-condition called DEF Line 1560  recursion, a pseudo-condition called DEF
1560  .sp  .sp
1561  If the text between the parentheses consists of a sequence of digits, the  If the text between the parentheses consists of a sequence of digits, the
1562  condition is true if the capturing subpattern of that number has previously  condition is true if the capturing subpattern of that number has previously
1563  matched. An alternative notation is to precede the digits with a plus or minus  matched. An alternative notation is to precede the digits with a plus or minus
1564  sign. In this case, the subpattern number is relative rather than absolute.  sign. In this case, the subpattern number is relative rather than absolute.
1565  The most recently opened parentheses can be referenced by (?(-1), the next most  The most recently opened parentheses can be referenced by (?(-1), the next most
1566  recent by (?(-2), and so on. In looping constructs it can also make sense to  recent by (?(-2), and so on. In looping constructs it can also make sense to
1567  refer to subsequent groups with constructs such as (?(+2).  refer to subsequent groups with constructs such as (?(+2).
1568  .P  .P
# Line 1582  parenthesis is required. Otherwise, sinc Line 1582  parenthesis is required. Otherwise, sinc
1582  subpattern matches nothing. In other words, this pattern matches a sequence of  subpattern matches nothing. In other words, this pattern matches a sequence of
1583  non-parentheses, optionally enclosed in parentheses.  non-parentheses, optionally enclosed in parentheses.
1584  .P  .P
1585  If you were embedding this pattern in a larger one, you could use a relative  If you were embedding this pattern in a larger one, you could use a relative
1586  reference:  reference:
1587  .sp  .sp
1588    ...other stuff... ( \e( )?    [^()]+    (?(-1) \e) ) ...    ...other stuff... ( \e( )?    [^()]+    (?(-1) \e) ) ...
# Line 1730  pattern, so instead you could use this: Line 1730  pattern, so instead you could use this:
1730    ( \e( ( (?>[^()]+) | (?1) )* \e) )    ( \e( ( (?>[^()]+) | (?1) )* \e) )
1731  .sp  .sp
1732  We have put the pattern into parentheses, and caused the recursion to refer to  We have put the pattern into parentheses, and caused the recursion to refer to
1733  them instead of the whole pattern.  them instead of the whole pattern.
1734  .P  .P
1735  In a larger pattern, keeping track of parenthesis numbers can be tricky. This  In a larger pattern, keeping track of parenthesis numbers can be tricky. This
1736  is made easier by the use of relative references. (A Perl 5.10 feature.)  is made easier by the use of relative references. (A Perl 5.10 feature.)
# Line 1751  could rewrite the above example as follo Line 1751  could rewrite the above example as follo
1751    (?<pn> \e( ( (?>[^()]+) | (?&pn) )* \e) )    (?<pn> \e( ( (?>[^()]+) | (?&pn) )* \e) )
1752  .sp  .sp
1753  If there is more than one subpattern with the same name, the earliest one is  If there is more than one subpattern with the same name, the earliest one is
1754  used.  used.
1755  .P  .P
1756  This particular example pattern that we have been looking at contains nested  This particular example pattern that we have been looking at contains nested
1757  unlimited repeats, and so the use of atomic grouping for matching strings of  unlimited repeats, and so the use of atomic grouping for matching strings of
# Line 1813  relative, as in these examples: Line 1813  relative, as in these examples:
1813  .sp  .sp
1814    (...(absolute)...)...(?2)...    (...(absolute)...)...(?2)...
1815    (...(relative)...)...(?-1)...    (...(relative)...)...(?-1)...
1816    (...(?+1)...(relative)...    (...(?+1)...(relative)...
1817  .sp  .sp
1818  An earlier example pointed out that the pattern  An earlier example pointed out that the pattern
1819  .sp  .sp

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