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revision 207 by ph10, Tue Jun 19 13:39:46 2007 UTC revision 208 by ph10, Mon Aug 6 15:23:29 2007 UTC
# Line 4  PCRE - Perl-compatible regular expressio Line 4  PCRE - Perl-compatible regular expressio
4  .SH "PCRE REGULAR EXPRESSION DETAILS"  .SH "PCRE REGULAR EXPRESSION DETAILS"
5  .rs  .rs
6  .sp  .sp
7  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
8  described below. Regular expressions are also described in the Perl  are described in detail below. There is a quick-reference syntax summary in the
9  documentation and in a number of books, some of which have copious examples.  .\" HREF
10  Jeffrey Friedl's "Mastering Regular Expressions", published by O'Reilly, covers  \fBpcresyntax\fP
11  regular expressions in great detail. This description of PCRE's regular  .\"
12  expressions is intended as reference material.  page. Perl's regular expressions are described in its own documentation, and
13    regular expressions in general are covered in a number of books, some of which
14    have copious examples. Jeffrey Friedl's "Mastering Regular Expressions",
15    published by O'Reilly, covers regular expressions in great detail. This
16    description of PCRE's regular expressions is intended as reference material.
17  .P  .P
18  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,
19  there is now also support for UTF-8 character strings. To use this, you must  there is now also support for UTF-8 character strings. To use this, you must
# Line 240  meanings Line 244  meanings
244  .SS "Absolute and relative back references"  .SS "Absolute and relative back references"
245  .rs  .rs
246  .sp  .sp
247  The sequence \eg followed by a positive or negative number, optionally enclosed  The sequence \eg followed by an unsigned or a negative number, optionally
248  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
249  can be coded as \eg{name}. Back references are discussed  reference can be coded as \eg{name}. Back references are discussed
250  .\" HTML <a href="#backreferences">  .\" HTML <a href="#backreferences">
251  .\" </a>  .\" </a>
252  later,  later,
# Line 1290  previous example can be rewritten as Line 1294  previous example can be rewritten as
1294  .sp  .sp
1295    \ed++foo    \ed++foo
1296  .sp  .sp
1297    Note that a possessive quantifier can be used with an entire group, for
1298    example:
1299    .sp
1300      (abc|xyz){2,3}+
1301    .sp
1302  Possessive quantifiers are always greedy; the setting of the PCRE_UNGREEDY  Possessive quantifiers are always greedy; the setting of the PCRE_UNGREEDY
1303  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
1304  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 1364  subpattern is possible using named paren Line 1373  subpattern is possible using named paren
1373  .P  .P
1374  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
1375  backslash is to use the \eg escape sequence, which is a feature introduced in  backslash is to use the \eg escape sequence, which is a feature introduced in
1376  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
1377  optionally enclosed in braces. These examples are all identical:  number, optionally enclosed in braces. These examples are all identical:
1378  .sp  .sp
1379    (ring), \e1    (ring), \e1
1380    (ring), \eg1    (ring), \eg1
1381    (ring), \eg{1}    (ring), \eg{1}
1382  .sp  .sp
1383  A positive number specifies an absolute reference without the ambiguity that is  An unsigned number specifies an absolute reference without the ambiguity that
1384  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
1385  reference. A negative number is a relative reference. Consider this example:  the reference. A negative number is a relative reference. Consider this
1386    example:
1387  .sp  .sp
1388    (abc(def)ghi)\eg{-1}    (abc(def)ghi)\eg{-1}
1389  .sp  .sp
# Line 1976  Cambridge CB2 3QH, England. Line 1986  Cambridge CB2 3QH, England.
1986  .rs  .rs
1987  .sp  .sp
1988  .nf  .nf
1989  Last updated: 19 June 2007  Last updated: 06 August 2007
1990  Copyright (c) 1997-2007 University of Cambridge.  Copyright (c) 1997-2007 University of Cambridge.
1991  .fi  .fi

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