It takes url's in a plain text and turn it to html link.

gistfile1.php

<?php 

function formatUrlsInText($strInput){
    $strInput = ereg_replace( "www\.", "http://www.", $strInput );
    $strInput = ereg_replace( "http://http://www\.", "http://www.", $strInput );
    $strInput = ereg_replace( "https://http://www\.", "https://www.", $strInput );
    $reg_exUrl = "/(http|https|ftp|ftps)\:\/\/[a-zA-Z0-9\-\.]+\.[a-zA-Z]{2,3}(\/\S*)?/";
    preg_match_all($reg_exUrl, $strInput, $matches);
    $usedPatterns = array();
    foreach($matches[0] as $pattern){
        if(!array_key_exists($pattern, $usedPatterns)){
            $usedPatterns[$pattern]=true;
            $strInput = str_replace  ($pattern, '<a href=' . $pattern . ' target="_blank">' . $pattern .'</a> ', $strInput);
        }
    }
    return $strInput;
} 

?>