svn: /phpdoc/en/trunk/reference/pcre/ pattern.syntax.xml

degeberg Wed, 28 Jul 2010 08:06:25 +0000 Revision: http://svn.php.net/viewvc?view=revision&revision=301646 Log: Documented the (?| syntax in PCRE. Changed paths: U phpdoc/en/trunk/reference/pcre/pattern.syntax.xml Modified: phpdoc/en/trunk/reference/pcre/pattern.syntax.xml =================================================================== --- phpdoc/en/trunk/reference/pcre/pattern.syntax.xml 2010-07-28 07:54:29 UTC (rev 301645) +++ phpdoc/en/trunk/reference/pcre/pattern.syntax.xml 2010-07-28 08:06:25 UTC (rev 301646) @@ -1285,6 +1285,39 @@ also by name. PHP 5.2.2 introduced two alternative syntaxes <literal>(?&lt;name&gt;pattern)</literal> and <literal>(?'name'pattern)</literal>. </para> + + <para> + Sometimes it is necessary to have multiple matching, but alternating + subgroups in a regular expression. Normally, each of these would be given + their own backreference number even though only one of them would ever + possibly match. To overcome this, the <literal>(?|</literal> syntax allows + having duplicate numbers. Consider the following regex matched against the + string <literal>Sunday</literal>: + </para> + + <informalexample> + <programlisting> +<![CDATA[(?:(Sat)ur|(Sun))day]]> + </programlisting> + </informalexample> + + <para> + Here <literal>Sun</literal> is stored in backreference 2, while + backreference 1 is empty. Matching yields <literal>Sat</literal> in + backreference 1 while backreference 2 does not exist. Changing the pattern + to use the <literal>(?|</literal> fixes this problem: + </para> + + <informalexample> + <programlisting> +<![CDATA[(?|(Sat)ur|(Sun))day]]> + </programlisting> + </informalexample> + + <para> + Using this pattern, both <literal>Sun</literal> and <literal>Sat</literal> + would be stored in backreference 1. + </para> </section> <section xml:id="regexp.reference.repetition">