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

Diff of /code/trunk/doc/html/pcrepattern.html

Parent Directory | Revision Log | View Patch Patch

-revision 243 by ph10,
Thu Sep 13 09:28:14 2007 UTC
+revision 416 by ph10,
Sat Apr 11 14:34:02 2009 UTC
 Line 35 
 man page, in case the conversion went wr
  <li><a name="TOC20" href="#SEC20">COMMENTS</a>
  <li><a name="TOC21" href="#SEC21">RECURSIVE PATTERNS</a>
  <li><a name="TOC22" href="#SEC22">SUBPATTERNS AS SUBROUTINES</a>
- <li><a name="TOC23" href="#SEC23">CALLOUTS</a>
+ <li><a name="TOC23" href="#SEC23">ONIGURUMA SUBROUTINE SYNTAX</a>
- <li><a name="TOC24" href="#SEC24">BACKTRACKING CONTROL</a>
+ <li><a name="TOC24" href="#SEC24">CALLOUTS</a>
- <li><a name="TOC25" href="#SEC25">SEE ALSO</a>
+ <li><a name="TOC25" href="#SEC25">BACKTRACKING CONTROL</a>
- <li><a name="TOC26" href="#SEC26">AUTHOR</a>
+ <li><a name="TOC26" href="#SEC26">SEE ALSO</a>
- <li><a name="TOC27" href="#SEC27">REVISION</a>
+ <li><a name="TOC27" href="#SEC27">AUTHOR</a>
+ <li><a name="TOC28" href="#SEC28">REVISION</a>
  </ul>
  <br><a name="SEC1" href="#TOC1">PCRE REGULAR EXPRESSION DETAILS</a><br>
  <P>
  The syntax and semantics of the regular expressions that are supported by PCRE
  are described in detail below. There is a quick-reference syntax summary in the
  <a href="pcresyntax.html"><b>pcresyntax</b></a>
- 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>
+ <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 56 
 description of PCRE's regular expression
+Line 63 
 description of PCRE's regular expression
  The original operation of PCRE was on strings of one-byte characters. However,
  there is now also support for UTF-8 character strings. To use this, you must
  build PCRE to include UTF-8 support, and then call <b>pcre_compile()</b> with
- the PCRE_UTF8 option. How this affects pattern matching is mentioned in several
+ the PCRE_UTF8 option. There is also a special sequence that can be given at the
- places below. There is also a summary of UTF-8 features in the
+ start of a pattern:
+ <pre>
+   (*UTF8)
+ </pre>
+ Starting a pattern with this sequence is equivalent to setting the PCRE_UTF8
+ option. This feature is not Perl-compatible. How setting UTF-8 mode affects
+ pattern matching is mentioned in several places below. There is also a summary
+ of UTF-8 features in the
  <a href="pcre.html#utf8support">section on UTF-8 support</a>
  in the main
  <a href="pcre.html"><b>pcre</b></a>
-Line 113 
 The newline convention does not affect w
+Line 127 
 The newline convention does not affect w
  default, this is any Unicode newline sequence, for Perl compatibility. However,
  this can be changed; see the description of \R in the section entitled
  <a href="#newlineseq">"Newline sequences"</a>
- below.
+ below. A change of \R setting can be combined with a change of newline
+ convention.
  </P>
  <br><a name="SEC3" href="#TOC1">CHARACTERS AND METACHARACTERS</a><br>
  <P>
-Line 311 
 following the discussion of
+Line 326 
 following the discussion of
  <a href="#subpattern">parenthesized subpatterns.</a>
  </P>
  <br><b>
+ Absolute and relative subroutine calls
+ </b><br>
+ <P>
+ For compatibility with Oniguruma, the non-Perl syntax \g 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
+ <a href="#onigurumasubroutines">later.</a>
+ Note that \g{...} (Perl syntax) and \g&#60;...&#62; (Oniguruma syntax) are <i>not</i>
+ synonymous. The former is a back reference; the latter is a subroutine call.
+ </P>
+ <br><b>
  Generic character types
  </b><br>
  <P>
-Line 349 
 In UTF-8 mode, characters with values gr
+Line 375 
 In UTF-8 mode, characters with values gr
  \w, and always match \D, \S, and \W. 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 \b, because it is defined in terms of \w
+ and \W.
  </P>
  <P>
  The sequences \h, \H, \v, and \V are Perl 5.10 features. In contrast to the
-Line 427 
 recognized.
+Line 454 
 recognized.
  <P>
  It is possible to restrict \R to match only CR, LF, or CRLF (instead of the
  complete set of Unicode line endings) by setting the option PCRE_BSR_ANYCRLF
- either at compile time or when the pattern is matched. This can be made the
+ either at compile time or when the pattern is matched. (BSR is an abbrevation
- default when PCRE is built; if this is the case, the other behaviour can be
+ for "backslash R".) This can be made the default when PCRE is built; if this is
- requested via the PCRE_BSR_UNICODE option. It is also possible to specify these
+ the case, the other behaviour can be requested via the PCRE_BSR_UNICODE option.
- settings by starting a pattern string with one of the following sequences:
+ It is also possible to specify these settings by starting a pattern string with
+ one of the following sequences:
  <pre>
    (*BSR_ANYCRLF)   CR, LF, or CRLF only
    (*BSR_UNICODE)   any Unicode newline sequence
-Line 439 
 These override the default and the optio
+Line 467 
 These override the default and the optio
  they can be overridden by options given to <b>pcre_exec()</b>. Note that these
  special settings, which are not Perl-compatible, are recognized only at the
  very start of a pattern, and that they must be in upper case. If more than one
- of them is present, the last one is used.
+ of them is present, the last one is used. They can be combined with a change of
- </P>
+ newline convention, for example, a pattern can start with:
- <P>
+ <pre>
+   (*ANY)(*BSR_ANYCRLF)
+ </pre>
  Inside a character class, \R matches the letter "R".
  <a name="uniextseq"></a></P>
  <br><b>
-Line 1008 
 changed in the same way as the Perl-comp
+Line 1038 
 changed in the same way as the Perl-comp
  J, U and X respectively.
  </P>
  <P>
- When an option change occurs at top level (that is, not inside subpattern
+ When one of these option changes occurs at top level (that is, not inside
- parentheses), the change applies to the remainder of the pattern that follows.
+ subpattern parentheses), the change applies to the remainder of the pattern
- If the change is placed right at the start of a pattern, PCRE extracts it into
+ that follows. If the change is placed right at the start of a pattern, PCRE
- the global options (and it will therefore show up in data extracted by the
+ extracts it into the global options (and it will therefore show up in data
- <b>pcre_fullinfo()</b> function).
+ extracted by the <b>pcre_fullinfo()</b> function).
  </P>
  <P>
  An option change within a subpattern (see below for a description of
-Line 1031 
 matches "ab", "aB", "c", and "C", even t
+Line 1061 
 matches "ab", "aB", "c", and "C", even t
  branch is abandoned before the option setting. This is because the effects of
  option settings happen at compile time. There would be some very weird
  behaviour otherwise.
+ </P>
+ <P>
+ <b>Note:</b> There are other PCRE-specific options that can be set by the
+ application when the compile or match functions are called. In some cases the
+ pattern can contain special leading sequences such as (*CRLF) to override what
+ the application has set or what has been defaulted. Details are given in the
+ section entitled
+ <a href="#newlineseq">"Newline sequences"</a>
+ above. There is also the (*UTF8) leading sequence that can be used to set UTF-8
+ mode; this is equivalent to setting the PCRE_UTF8 option.
  <a name="subpattern"></a></P>
  <br><a name="SEC12" href="#TOC1">SUBPATTERNS</a><br>
  <P>
-Line 1172 
 details of the interfaces for handling n
+Line 1212 
 details of the interfaces for handling n
  <a href="pcreapi.html"><b>pcreapi</b></a>
  documentation.
  </P>
+ <P>
+ <b>Warning:</b> 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.
+ </P>
  <br><a name="SEC15" href="#TOC1">REPETITION</a><br>
  <P>
  Repetition is specified by quantifiers, which can follow any of the following
-Line 1219 
 which may be several bytes long (and the
+Line 1264 
 which may be several bytes long (and the
  </P>
  <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
+ <a href="#subpatternsassubroutines">subroutines</a>
+ from elsewhere in the pattern. Items other than subpatterns that have a {0}
+ quantifier are omitted from the compiled pattern.
  </P>
  <P>
  For convenience, the three most common quantifiers have single-character
-Line 2019 
 changed for different calls. For example
+Line 2068 
 changed for different calls. For example
  </pre>
  It matches "abcabc". It does not match "abcABC" because the change of
  processing option does not affect the called subpattern.
+ <a name="onigurumasubroutines"></a></P>
+ <br><a name="SEC23" href="#TOC1">ONIGURUMA SUBROUTINE SYNTAX</a><br>
+ <P>
+ For compatibility with Oniguruma, the non-Perl syntax \g 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:
+ <pre>
+   (?&#60;pn&#62; \( ( (?&#62;[^()]+) | \g&#60;pn&#62; )* \) )
+   (sens|respons)e and \g'1'ibility
+ </pre>
+ 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:
+ <pre>
+   (abc)(?i:\g&#60;-1&#62;)
+ </pre>
+ Note that \g{...} (Perl syntax) and \g&#60;...&#62; (Oniguruma syntax) are <i>not</i>
+ synonymous. The former is a back reference; the latter is a subroutine call.
  </P>
- <br><a name="SEC23" href="#TOC1">CALLOUTS</a><br>
+ <br><a name="SEC24" href="#TOC1">CALLOUTS</a><br>
  <P>
  Perl has a feature whereby using the sequence (?{...}) causes arbitrary Perl
  code to be obeyed in the middle of matching a regular expression. This makes it
-Line 2055 
 description of the interface to the call
+Line 2122 
 description of the interface to the call
  <a href="pcrecallout.html"><b>pcrecallout</b></a>
  documentation.
  </P>
- <br><a name="SEC24" href="#TOC1">BACKTRACKING CONTROL</a><br>
+ <br><a name="SEC25" href="#TOC1">BACKTRACKING CONTROL</a><br>
  <P>
  Perl 5.10 introduced a number of "Special Backtracking Control Verbs", which
  are described in the Perl documentation as "experimental and subject to change
-Line 2064 
 production code should be noted to avoid
+Line 2131 
 production code should be noted to avoid
  remarks apply to the PCRE features described in this section.
  </P>
  <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 <b>pcre_exec()</b>, which uses a
+ used only when the pattern is to be matched using <b>pcre_exec()</b>, 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
  <b>pcre_dfa_exec()</b>.
  </P>
  <P>
-Line 2170 
 the end of the group if FOO succeeds); o
+Line 2238 
 the end of the group if FOO succeeds); o
  second alternative and tries COND2, without backtracking into COND1. If (*THEN)
  is used outside of any alternation, it acts exactly like (*PRUNE).
  </P>
- <br><a name="SEC25" href="#TOC1">SEE ALSO</a><br>
+ <br><a name="SEC26" href="#TOC1">SEE ALSO</a><br>
  <P>
  <b>pcreapi</b>(3), <b>pcrecallout</b>(3), <b>pcrematching</b>(3), <b>pcre</b>(3).
  </P>
- <br><a name="SEC26" href="#TOC1">AUTHOR</a><br>
+ <br><a name="SEC27" href="#TOC1">AUTHOR</a><br>
  <P>
  Philip Hazel
  <br>
-Line 2183 
 University Computing Service
+Line 2251 
 University Computing Service
  Cambridge CB2 3QH, England.
  <br>
  </P>
- <br><a name="SEC27" href="#TOC1">REVISION</a><br>
+ <br><a name="SEC28" href="#TOC1">REVISION</a><br>
  <P>
- Last updated: 11 September 2007
+ Last updated: 11 April 2009
  <br>
- Copyright &copy; 1997-2007 University of Cambridge.
+ Copyright &copy; 1997-2009 University of Cambridge.
  <br>
  <p>
  Return to the <a href="index.html">PCRE index page</a>.

 Legend:



Removed from v.243
 


changed lines


 
Added in v.416
 Legend:



Removed from v.243
 


changed lines


 
Added in v.416
-Removed from v.243
+Added in v.416

webmaster@exim.org	ViewVC Help
Powered by ViewVC 1.1.12