- print_r: documentation ( source)
- preg_replace: documentation ( source)
<?php
$text = "http://www.google.com/\r\nhttp://www.google.com/\r\nhttp://www.google.com/";
$matches[0] = preg_replace('/(http|ftp)+(s)?:(\/\/)((\w|\.|\-)+)(\/)?(\S)+/i', '[url]\0[\4]',$text);
print_r($matches[0]);