/[pcre]/code/trunk/doc/pcrepattern.3

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-revision 259 by ph10,
Wed Sep 19 09:52:44 2007 UTC
+revision 394 by ph10,
Wed Mar 18 16:38:23 2009 UTC
 Line 9 
 are described in detail below. There is
  .\" HREF
  \fBpcresyntax\fP
  .\"
- page. Perl's regular expressions are described in its own documentation, and
+ page. PCRE tries to match Perl syntax and semantics as closely as it can. PCRE
+ also supports some alternative regular expression syntax (which does not
+ conflict with the Perl syntax) in order to provide some compatibility with
+ regular expressions in Python, .NET, and Oniguruma.
+ .P
+ Perl's regular expressions are described in its own documentation, and
  regular expressions in general are covered in a number of books, some of which
  have copious examples. Jeffrey Friedl's "Mastering Regular Expressions",
  published by O'Reilly, covers regular expressions in great detail. This
-Line 310 
 parenthesized subpatterns.
+Line 315 
 parenthesized subpatterns.
  .\"
  .
  .
+ .SS "Absolute and relative subroutine calls"
+ .rs
+ .sp
+ For compatibility with Oniguruma, the non-Perl syntax \eg followed by a name or
+ a number enclosed either in angle brackets or single quotes, is an alternative
+ syntax for referencing a subpattern as a "subroutine". Details are discussed
+ .\" HTML <a href="#onigurumasubroutines">
+ .\" </a>
+ later.
+ .\"
+ Note that \eg{...} (Perl syntax) and \eg<...> (Oniguruma syntax) are \fInot\fP
+ synonymous. The former is a back reference; the latter is a subroutine call.
+ .
+ .
  .SS "Generic character types"
  .rs
  .sp
-Line 345 
 In UTF-8 mode, characters with values gr
+Line 364 
 In UTF-8 mode, characters with values gr
  \ew, and always match \eD, \eS, and \eW. This is true even when Unicode
  character property support is available. These sequences retain their original
  meanings from before UTF-8 support was available, mainly for efficiency
- reasons.
+ reasons. Note that this also affects \eb, because it is defined in terms of \ew
+ and \eW.
  .P
  The sequences \eh, \eH, \ev, and \eV are Perl 5.10 features. In contrast to the
  other sequences, these do match certain high-valued codepoints in UTF-8 mode.
-Line 1192 
 details of the interfaces for handling n
+Line 1212 
 details of the interfaces for handling n
  \fBpcreapi\fP
  .\"
  documentation.
+ .P
+ \fBWarning:\fP You cannot use different names to distinguish between two
+ subpatterns with the same number (see the previous section) because PCRE uses
+ only the numbers when matching.
  .
  .
  .SH REPETITION
-Line 1240 
 support is available, \eX{3} matches thr
+Line 1264 
 support is available, \eX{3} matches thr
  which may be several bytes long (and they may be of different lengths).
  .P
  The quantifier {0} is permitted, causing the expression to behave as if the
- previous item and the quantifier were not present.
+ previous item and the quantifier were not present. This may be useful for
+ subpatterns that are referenced as
+ .\" HTML <a href="#subpatternsassubroutines">
+ .\" </a>
+ subroutines
+ .\"
+ from elsewhere in the pattern. Items other than subpatterns that have a {0}
+ quantifier are omitted from the compiled pattern.
  .P
  For convenience, the three most common quantifiers have single-character
  abbreviations:
-Line 2023 
 It matches "abcabc". It does not match "
+Line 2054 
 It matches "abcabc". It does not match "
  processing option does not affect the called subpattern.
  .
  .
+ .\" HTML <a name="onigurumasubroutines"></a>
+ .SH "ONIGURUMA SUBROUTINE SYNTAX"
+ .rs
+ .sp
+ For compatibility with Oniguruma, the non-Perl syntax \eg followed by a name or
+ a number enclosed either in angle brackets or single quotes, is an alternative
+ syntax for referencing a subpattern as a subroutine, possibly recursively. Here
+ are two of the examples used above, rewritten using this syntax:
+ .sp
+   (?<pn> \e( ( (?>[^()]+) | \eg<pn> )* \e) )
+   (sens|respons)e and \eg'1'ibility
+ .sp
+ PCRE supports an extension to Oniguruma: if a number is preceded by a
+ plus or a minus sign it is taken as a relative reference. For example:
+ .sp
+   (abc)(?i:\eg<-1>)
+ .sp
+ Note that \eg{...} (Perl syntax) and \eg<...> (Oniguruma syntax) are \fInot\fP
+ synonymous. The former is a back reference; the latter is a subroutine call.
+ .
+ .
  .SH CALLOUTS
  .rs
  .sp
-Line 2068 
 or removal in a future version of Perl".
+Line 2120 
 or removal in a future version of Perl".
  production code should be noted to avoid problems during upgrades." The same
  remarks apply to the PCRE features described in this section.
  .P
- Since these verbs are specifically related to backtracking, they can be used
+ Since these verbs are specifically related to backtracking, most of them can be
- only when the pattern is to be matched using \fBpcre_exec()\fP, which uses a
+ used only when the pattern is to be matched using \fBpcre_exec()\fP, which uses
- backtracking algorithm. They cause an error if encountered by
+ a backtracking algorithm. With the exception of (*FAIL), which behaves like a
+ failing negative assertion, they cause an error if encountered by
  \fBpcre_dfa_exec()\fP.
  .P
  The new verbs make use of what was previously invalid syntax: an opening
-Line 2192 
 Cambridge CB2 3QH, England.
+Line 2245 
 Cambridge CB2 3QH, England.
  .rs
  .sp
  .nf
- Last updated: 17 September 2007
+ Last updated: 18 March 2009
- Copyright (c) 1997-2007 University of Cambridge.
+ Copyright (c) 1997-2009 University of Cambridge.
  .fi

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