converting text urls to clickable links

today i came across a challenge that i am surprise i have not faced before but it seemed worthy to make a post about. i have been working on a social networking tool for a company and they wanted all urls to automatically be parsed into clickable links regardless of the syntax (ie http://www.site.com, site.com, www.site.com). the solution was extremely simple: write a regular expression to match any url and use to make a comparison. heres the code:

<?php
$pattern = "@\b(https?://)?(([0-9a-zA-Z_!~*'().&=+$%-]+:)?[0-9a-zA-Z_!~*'().&=+$%-]+\@)?(([0-9]{1,3}\.){3}[0-9]{1,3}|([0-9a-zA-Z_!~*'()-]+\.)*([0-9a-zA-Z][0-9a-zA-Z-]{0,61})?[0-9a-zA-Z]\.[a-zA-Z]{2,6})(:[0-9]{1,4})?((/[0-9a-zA-Z_!~*'().;?:\@&=+$,%#-]+)*/?)@";
$new_text = preg_replace($pattern, '<a href="\0">\0</a>', $old_text);
?>

thats it, simple and effective. this is similar to how Facebook converts any url into a link in a status update. with the url in tack you could then use that url to capture a screenshop of the website and make it display along with the link.