On Clicked, On Released GUI Button ?

GetKey sends 1 on all frames you keep pressing.

GetKeyDown sends 1 only on the frame you press, and 0 the rest of the time even if you hold down

GetKeyUp sends 1 when you release the button, and 0 any other time.

GetMouseButton and GetButton work the same way.

So I guess you are looking for

 var anyVar: boolean;

 function Start(){
    anyvar = false;
 }
 
 function Update(){
     if(Input.GetKeyDown("Jump")
         anyvar = true;
     else if(Input.GetKeyUp("Jump"))
         anyvar = false;
     }

Jump is the space bar by default, check Edit->Project Setting->Input to see what is what and change as you wish.

Or more simply:

var anyVar: boolean;

 function Start(){
    anyvar = false;
 }
 
 function Update(){
     if(Input.GetKey("Jump")
         anyvar = true;
     else
         anyvar = false;
     }

you choose.