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revision 185 by ph10, Tue Jun 19 13:39:46 2007 UTC revision 208 by ph10, Mon Aug 6 15:23:29 2007 UTC
# Line 41  man page, in case the conversion went wr Line 41  man page, in case the conversion went wr
41  </ul>  </ul>
42  <br><a name="SEC1" href="#TOC1">PCRE REGULAR EXPRESSION DETAILS</a><br>  <br><a name="SEC1" href="#TOC1">PCRE REGULAR EXPRESSION DETAILS</a><br>
43  <P>  <P>
44  The syntax and semantics of the regular expressions supported by PCRE are  The syntax and semantics of the regular expressions that are supported by PCRE
45  described below. Regular expressions are also described in the Perl  are described in detail below. There is a quick-reference syntax summary in the
46  documentation and in a number of books, some of which have copious examples.  <a href="pcresyntax.html"><b>pcresyntax</b></a>
47  Jeffrey Friedl's "Mastering Regular Expressions", published by O'Reilly, covers  page. Perl's regular expressions are described in its own documentation, and
48  regular expressions in great detail. This description of PCRE's regular  regular expressions in general are covered in a number of books, some of which
49  expressions is intended as reference material.  have copious examples. Jeffrey Friedl's "Mastering Regular Expressions",
50    published by O'Reilly, covers regular expressions in great detail. This
51    description of PCRE's regular expressions is intended as reference material.
52  </P>  </P>
53  <P>  <P>
54  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,
# Line 255  meanings Line 257  meanings
257  Absolute and relative back references  Absolute and relative back references
258  </b><br>  </b><br>
259  <P>  <P>
260  The sequence \g followed by a positive or negative number, optionally enclosed  The sequence \g followed by an unsigned or a negative number, optionally
261  in braces, is an absolute or relative back reference. A named back reference  enclosed in braces, is an absolute or relative back reference. A named back
262  can be coded as \g{name}. Back references are discussed  reference can be coded as \g{name}. Back references are discussed
263  <a href="#backreferences">later,</a>  <a href="#backreferences">later,</a>
264  following the discussion of  following the discussion of
265  <a href="#subpattern">parenthesized subpatterns.</a>  <a href="#subpattern">parenthesized subpatterns.</a>
# Line 1303  previous example can be rewritten as Line 1305  previous example can be rewritten as
1305  <pre>  <pre>
1306    \d++foo    \d++foo
1307  </pre>  </pre>
1308    Note that a possessive quantifier can be used with an entire group, for
1309    example:
1310    <pre>
1311      (abc|xyz){2,3}+
1312    </pre>
1313  Possessive quantifiers are always greedy; the setting of the PCRE_UNGREEDY  Possessive quantifiers are always greedy; the setting of the PCRE_UNGREEDY
1314  option is ignored. They are a convenient notation for the simpler forms of  option is ignored. They are a convenient notation for the simpler forms of
1315  atomic group. However, there is no difference in the meaning of a possessive  atomic group. However, there is no difference in the meaning of a possessive
# Line 1377  subpattern is possible using named paren Line 1384  subpattern is possible using named paren
1384  <P>  <P>
1385  Another way of avoiding the ambiguity inherent in the use of digits following a  Another way of avoiding the ambiguity inherent in the use of digits following a
1386  backslash is to use the \g escape sequence, which is a feature introduced in  backslash is to use the \g escape sequence, which is a feature introduced in
1387  Perl 5.10. This escape must be followed by a positive or a negative number,  Perl 5.10. This escape must be followed by an unsigned number or a negative
1388  optionally enclosed in braces. These examples are all identical:  number, optionally enclosed in braces. These examples are all identical:
1389  <pre>  <pre>
1390    (ring), \1    (ring), \1
1391    (ring), \g1    (ring), \g1
1392    (ring), \g{1}    (ring), \g{1}
1393  </pre>  </pre>
1394  A positive number specifies an absolute reference without the ambiguity that is  An unsigned number specifies an absolute reference without the ambiguity that
1395  present in the older syntax. It is also useful when literal digits follow the  is present in the older syntax. It is also useful when literal digits follow
1396  reference. A negative number is a relative reference. Consider this example:  the reference. A negative number is a relative reference. Consider this
1397    example:
1398  <pre>  <pre>
1399    (abc(def)ghi)\g{-1}    (abc(def)ghi)\g{-1}
1400  </pre>  </pre>
# Line 1990  Cambridge CB2 3QH, England. Line 1998  Cambridge CB2 3QH, England.
1998  </P>  </P>
1999  <br><a name="SEC25" href="#TOC1">REVISION</a><br>  <br><a name="SEC25" href="#TOC1">REVISION</a><br>
2000  <P>  <P>
2001  Last updated: 19 June 2007  Last updated: 06 August 2007
2002  <br>  <br>
2003  Copyright &copy; 1997-2007 University of Cambridge.  Copyright &copy; 1997-2007 University of Cambridge.
2004  <br>  <br>

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