You could use AJAX programming to value check and insert the values into the database, or whatever other action, asynchronously, meaning no page reload. Hooray.
Perhaps the simplest way, and the way I would do it, is using a $_POST variable.
<input type="text" name="uniquename" />
on the next page, you would access the variable as such
Alternatively you could use $_GET and place the user value in to the browser request URI, but $_POST is more secure and when possible should be first choice.