$url

The $url variable has the value of the URL to re-invoke the current script, i.e. the URL path to the Vortex executable, plus the script and any state variable information. It is set every time it is printed, to reflect the current value(s) of EXPORTed URL state variables. If no variables are being EXPORTed, or none of them are set, then $url is just a "plain" URL to invoke the script, without state information.