find_url_make_link_txt_file.php

<?php

// The Regular Expression filter
$reg_exUrl = "/(http|https|ftp|ftps)\:\/\/[a-zA-Z0-9\-\.]+\.[a-zA-Z]{2,3}(\/\S*)?/";

// The Text you want to filter for urls
$text = "The text you want to filter goes here. http://www.google.com/";

// Check if there is a url in the text
if (preg_match($reg_exUrl, $text, $url)) {

    // make the urls hyper links
    echo preg_replace($reg_exUrl, "<a href=" . $url[0] . ">.$url[0].</a>", $text);

} else {

    // if no urls in the text just return the text
    echo $text;

}