Was a $_GET parameter supplied as a string?

Using PHP’s ternary operators you can test if a $_GET parameter was supplied and that it was supplied as a string by using the following one-liner:

$x = (empty($_GET['x']) or is_numeric($_GET['x'])) ? null : $_GET['x'];

That will assign null to $x if the parameter wasn’t provided, is empty or if it is numeric; otherwise it will assign the given value value to $x.