php-doc-en/reference/pcre/functions/preg-match.xml

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  <refentry id="function.preg-match">
   <refnamediv>
    <refname>preg_match</refname>
    <refpurpose>Perform a regular expression match</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
     <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>matches</parameter></methodparam>
      <methodparam choice="opt"><type>int</type><parameter>flags</parameter></methodparam>
     </methodsynopsis>
    <para>
     Searches <parameter>subject</parameter> for a match to the regular
     expression given in <parameter>pattern</parameter>.
    </para>
    <para>
     If <parameter>matches</parameter> is provided, then it is filled
     with the results of search.  $matches[0] will contain the text that
     matched the full pattern, $matches[1] will have the text that matched
     the first captured parenthesized subpattern, and so on.
    </para>
    <para>
     <parameter>flags</parameter> can be the following flag:
     <variablelist>
      <varlistentry>
       <term>PREG_OFFSET_CAPTURE</term>
       <listitem>
        <simpara>
         If this flag is set, for every occuring 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 offset <literal>0</literal> and it's string offset into
         <parameter>subject</parameter> at offset <literal>1</literal>. This
         flag is available since <literal>PHP</literal> 4.3.0 .
        </simpara>
       </listitem>
      </varlistentry>
     </variablelist>
     The <parameter>flags</parameter> parameter is available since
     <literal>PHP</literal> 4.3.0 .
    </para>

    <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 occured.
    </para>
    <note>
     <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.
     </para>
    </note>
    <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.")) {
    print "A match was found.";
} else {
    print "A match was not found.";
}
?>
]]>
      </programlisting>
     </example>
     <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.")) {
    print "A match was found.";
} else {
    print "A match was not found.";
}
if (preg_match ("/\bweb\b/i", "PHP is the website scripting language of choice.")) {
    print "A match was found.";
} else {
    print "A match was not found.";
}
?>
]]>
      </programlisting>
     </example>
     <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 = $matches[2];
// get last two segments of host name
preg_match("/[^\.\/]+\.[^\.\/]+$/",$host,$matches);
echo "domain name is: ".$matches[0]."\n";
?>
]]>
      </programlisting>
      <para>
       This example will produce:
      </para>
      <screen>
<![CDATA[
domain name is: php.net
]]>
      </screen>
     </example>
     See also <function>preg_match_all</function>, 
     <function>preg_replace</function>, and
     <function>preg_split</function>.
    </para>
   </refsect1>
  </refentry>

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