Grabbing Requested URL Variable

I'm trying to make a PHP script that grabs any variables followed by the php script... i.e. http://www.mydomain.com/script.php?user105 and when someone visits that script it would grab "user105" and save to a text file on the host. Or something that grabs the requested url and saves it to a text file.

 

Another approach:

http://www.mydomain.com/script.php?var=user105

Then to get the variable is by

if (isset($_GET['var'])) $content = $_GET['var'];
else $content = null;

PHP:

 

If your URL format is http://www.mydomain.com/script.php?user105

You can grab the "user105" by :
$grab = $_SERVER['QUERY_STRING'];