<?xml version="1.0" encoding="iso-8859-1"?>
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<refentry id="function.preg-replace-callback">
 <refnamediv>
  <refname>preg_replace_callback</refname>
  <refpurpose>Perform a regular expression search and replace using a callback</refpurpose>
 </refnamediv>
 <refsect1>
  <title>Description</title>
  <methodsynopsis>
   <type>mixed</type><methodname>preg_replace_callback</methodname>
   <methodparam><type>mixed</type><parameter>pattern</parameter></methodparam>
   <methodparam><type>callback</type><parameter>callback</parameter></methodparam>
   <methodparam><type>mixed</type><parameter>subject</parameter></methodparam>
   <methodparam choice="opt"><type>int</type><parameter>limit</parameter></methodparam>
   <methodparam choice="opt"><type>int</type><parameter role="reference">count</parameter></methodparam>
  </methodsynopsis>
  <para>
   The behavior of this function is almost identical to
   <function>preg_replace</function>, except for the fact that instead of
   <parameter>replacement</parameter> parameter, one should specify a
   <parameter>callback</parameter> that will be called and passed an array of
   matched elements in the subject string. The callback should return the
   replacement string.
   See <function>preg_replace</function> for description of other parameters.
  </para>
  <example>
   <title><function>preg_replace_callback</function> example</title>
   <programlisting role='php'>
<![CDATA[
<?php
// this text was used in 2002
// we want to get this up to date for 2003
$text = "April fools day is 04/01/2002\n";
$text.= "Last christmas was 12/24/2001\n";
// the callback function
function next_year($matches) 
{
  // as usual: $matches[0] is the complete match
  // $matches[1] the match for the first subpattern
  // enclosed in '(...)' and so on
  return $matches[1].($matches[2]+1);
}
echo preg_replace_callback(
            "|(\d{2}/\d{2}/)(\d{4})|",
            "next_year",
            $text);
// result is:
// April fools day is 04/01/2003
// Last christmas was 12/24/2002
?>
]]>
   </programlisting>
  </example>
  <para>
   You'll often need the <parameter>callback</parameter> function
   for a <function>preg_replace_callback</function> in just one place.
   In this case you can use <function>create_function</function> to
   declare an anonymous function as callback within the call to
   <function>preg_replace_callback</function>. By doing it this way
   you have all information for the call in one place and do not
   clutter the function namespace with a callback functions name
   not used anywhere else.
  </para>
  <example>
   <title><function>preg_replace_callback</function> and <function>create_function</function></title>
   <programlisting role='php'>
<![CDATA[
<?php
/* a unix-style command line filter to convert uppercase
 * letters at the beginning of paragraphs to lowercase */
$fp = fopen("php://stdin", "r") or die("can't read stdin");
while (!feof($fp)) {
    $line = fgets($fp);
    $line = preg_replace_callback(
        '|<p>\s*\w|',
        create_function(
            // single quotes are essential here,
            // or alternative escape all $ as \$
            '$matches',
            'return strtolower($matches[0]);'
        ),
        $line
    );
    echo $line;
}
fclose($fp);
?>
]]>
   </programlisting>
  </example>
  <example>
   <title><function>preg_replace_callback</function> using recursive structure
    to handle encapsulated BB code</title>
   <programlisting role='php'>
<![CDATA[
<?php
$input = "plain [indent] deep [indent] deeper [/indent] deep [/indent] plain"; 

function parseTagsRecursive($input) 
{
    
    $regex = '#\[indent]((?:[^[]|\[(?!/?indent])|(?R))+)\[/indent]#';

    if (is_array($input)) {
        $input = '<div style="margin-left: 10px">'.$input[1].'</div>';
    }

    return preg_replace_callback($regex, 'parseTagsRecursive', $input);
}

$output = parseTagsRecursive($input);

echo $output;
?>
]]>
   </programlisting>
  </example>
  <note>
   <para>
    <parameter>count</parameter> parameter is available since PHP 5.1.0.
   </para>
  </note>
  <para>
   See also <function>preg_replace</function>,
   <function>create_function</function>,
   &listendand; &seealso.callback;.
  </para>
 </refsect1>
</refentry>

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