How to get the url from a input field?

How to get the url from a input field?

I recently develop a shortener URL script, now I'm trying to add Addthis
buttons but the problem is that is sharing the current URL of the site is
on. I want the Addthis buttons share the URL that is inside of the URL
Input field anybody got some idea on how to do it?
Basically I want to add Addthis buttons and share the URL from a Input
field that got the URL shorted .