How to get the key from the button name

Hello.

I can't seem to find any answer for this one. In many games once the player configures the input buttons the changes are reflected in the text prompts on the screen. For example if the player sets "Fire" as Mouse Button 1 or F (for example), on the screen the player will see : 'Use Mouse Button 1 to fire' or 'Use F to fire'.

I would like to this too (JS) :

 var prompt = "Use " + keySetAsFire + " to fire";
 GUIText.text = prompt;

My problem is finding the "keySetAsFire" variable. Is this possible in Unity?