<?xml version="1.0" encoding="iso-8859-1"?>
<!-- $Revision: 1.26 $ -->
<refentry xml:id="function.preg-match" xmlns="http://docbook.org/ns/docbook">
 <refnamediv>
  <refname>preg_match</refname>
  <refpurpose>Perform a regular expression match</refpurpose>
 </refnamediv>

 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <type>int</type><methodname>preg_match</methodname>
   <methodparam><type>string</type><parameter>pattern</parameter></methodparam>
   <methodparam><type>string</type><parameter>subject</parameter></methodparam>
   <methodparam choice="opt"><type>array</type><parameter role="reference">matches</parameter></methodparam>
   <methodparam choice="opt"><type>int</type><parameter>flags</parameter></methodparam>
   <methodparam choice="opt"><type>int</type><parameter>offset</parameter></methodparam>
  </methodsynopsis>
  <para>
   Searches <parameter>subject</parameter> for a match to the regular
   expression given in <parameter>pattern</parameter>.
  </para>
 </refsect1>

 <refsect1 role="parameters">
  &reftitle.parameters;
  <para>
   <variablelist>
    <varlistentry>
     <term><parameter>pattern</parameter></term>
     <listitem>
      <para>
       The pattern to search for, as a string.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>subject</parameter></term>
     <listitem>
      <para>
       The input string.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>matches</parameter></term>
     <listitem>
      <para>
       If <parameter>matches</parameter> is provided, then it is filled with
       the results of search. <varname>$matches[0]</varname> will contain the
       text that matched the full pattern, <varname>$matches[1]</varname>
       will have the text that matched the first captured parenthesized
       subpattern, and so on.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>flags</parameter></term>
     <listitem>
      <para>
       <parameter>flags</parameter> can be the following flag:
       <variablelist>
        <varlistentry>
         <term><constant>PREG_OFFSET_CAPTURE</constant></term>
         <listitem>
          <simpara>
           If this flag is passed, for every occurring match the appendant string
           offset will also be returned. Note that this changes the return value
           in an array where every element is an array consisting of the matched
           string at index <literal>0</literal> and its string offset into
           <parameter>subject</parameter> at index <literal>1</literal>.
          </simpara>
         </listitem>
        </varlistentry>
       </variablelist>
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>offset</parameter></term>
     <listitem>
      <para>
       Normally, the search starts from the beginning of the subject string.
       The optional parameter <parameter>offset</parameter> can be used to
       specify the alternate place from which to start the search (in bytes).
      </para>
      <note>
       <para>
        Using <parameter>offset</parameter> is not equivalent to passing 
        <literal>substr($subject, $offset)</literal> to
        <function>preg_match</function> in place of the subject string,
        because <parameter>pattern</parameter> can contain assertions such as
        <emphasis>^</emphasis>, <emphasis>$</emphasis> or
        <emphasis>(?&lt;=x)</emphasis>. Compare:
        <informalexample>
         <programlisting role="php">
<![CDATA[
<?php
$subject = "abcdef";
$pattern = '/^def/';
preg_match($pattern, $subject, $matches, PREG_OFFSET_CAPTURE, 3);
print_r($matches);
?>
]]>
         </programlisting>
         &example.outputs;
         <screen>
<![CDATA[
Array
(
)
]]>
         </screen>
         <para>
          while this example
         </para>
         <programlisting role="php">
<![CDATA[
<?php
$subject = "abcdef";
$pattern = '/^def/';
preg_match($pattern, substr($subject,3), $matches, PREG_OFFSET_CAPTURE);
print_r($matches);
?>
]]>
         </programlisting>
         <para>
          will produce
         </para>
         <screen>
<![CDATA[
Array
(
    [0] => Array
        (
            [0] => def
            [1] => 0
        )

)
]]>
         </screen>
        </informalexample>
       </para>
      </note>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   <function>preg_match</function> returns the number of times
   <parameter>pattern</parameter> matches. That will be either 0 times
   (no match) or 1 time because <function>preg_match</function> will stop
   searching after the first match. <function>preg_match_all</function>
   on the contrary will continue until it reaches the end of
   <parameter>subject</parameter>.
   <function>preg_match</function> returns &false; if an error occurred.
  </para>
 </refsect1>

 <refsect1 role="changelog">
  &reftitle.changelog;
  <para>
   <informaltable>
    <tgroup cols="2">
     <thead>
      <row>
       <entry>&Version;</entry>
       <entry>&Description;</entry>
      </row>
     </thead>
     <tbody>
      <row>
       <entry>4.3.3</entry>
       <entry>
        The <parameter>offset</parameter> parameter was added
       </entry>
      </row>
      <row>
       <entry>4.3.0</entry>
       <entry>
        The <constant>PREG_OFFSET_CAPTURE</constant> flag was added
       </entry>
      </row>
      <row>
       <entry>4.3.0</entry>
       <entry>
        The <parameter>flags</parameter> parameter was added
       </entry>
      </row>
     </tbody>
    </tgroup>
   </informaltable>
  </para>
 </refsect1>

 <refsect1 role="examples">
  &reftitle.examples;
  <para>
   <example>
    <title>Find the string of text "php"</title>
    <programlisting role="php">
<![CDATA[
<?php
// The "i" after the pattern delimiter indicates a case-insensitive search
if (preg_match("/php/i", "PHP is the web scripting language of choice.")) {
    echo "A match was found.";
} else {
    echo "A match was not found.";
}
?>
]]>
    </programlisting>
   </example>
  </para>
  <para>
   <example>
    <title>Find the word "web"</title>
    <programlisting role="php">
<![CDATA[
<?php
/* The \b in the pattern indicates a word boundary, so only the distinct
 * word "web" is matched, and not a word partial like "webbing" or "cobweb" */
if (preg_match("/\bweb\b/i", "PHP is the web scripting language of choice.")) {
    echo "A match was found.";
} else {
    echo "A match was not found.";
}

if (preg_match("/\bweb\b/i", "PHP is the website scripting language of choice.")) {
    echo "A match was found.";
} else {
    echo "A match was not found.";
}
?>
]]>
    </programlisting>
   </example>
  </para>
  <para>
   <example>
    <title>Getting the domain name out of a URL</title>
    <programlisting role="php">
<![CDATA[
<?php
// get host name from URL
preg_match('@^(?:http://)?([^/]+)@i',
    "http://www.php.net/index.html", $matches);
$host = $matches[1];

// get last two segments of host name
preg_match('/[^.]+\.[^.]+$/', $host, $matches);
echo "domain name is: {$matches[0]}\n";
?>
]]>
    </programlisting>
    &example.outputs;
    <screen>
<![CDATA[
domain name is: php.net
]]>
    </screen>
   </example>
  </para>
 </refsect1>

 <refsect1 role="notes">
  &reftitle.notes;
  <tip>
   <para>
    Do not use <function>preg_match</function> if you only want to check if
    one string is contained in another string. Use
    <function>strpos</function> or <function>strstr</function> instead as
    they will be faster.
   </para>
  </tip>
 </refsect1>

 <refsect1 role="seealso">
  &reftitle.seealso;
  <para>
   <simplelist>
    <member><function>preg_match_all</function></member>
    <member><function>preg_replace</function></member>
    <member><function>preg_split</function></member>
   </simplelist>
  </para>
 </refsect1>

</refentry>

<!-- Keep this comment at the end of the file
Local variables:
mode: sgml
sgml-omittag:t
sgml-shorttag:t
sgml-minimize-attributes:nil
sgml-always-quote-attributes:t
sgml-indent-step:1
sgml-indent-data:t
indent-tabs-mode:nil
sgml-parent-document:nil
sgml-default-dtd-file:"../../../../manual.ced"
sgml-exposed-tags:nil
sgml-local-catalogs:nil
sgml-local-ecat-files:nil
End:
vim600: syn=xml fen fdm=syntax fdl=2 si
vim: et tw=78 syn=sgml
vi: ts=1 sw=1
-->