How to access a variable from another script?

Hello, I am new to Unity and programming in general. I am getting the exception:

"NullReferenceException: Object reference not set to an instance of an object ammoCount.Update () (at Assets/Standard Assets/scripts/ammoCount.js:6)"

when trying to access a variable from another script. In my case the scripts are "shoot" and "ammoCount". Shoot contains the variables ammo and mag which I want to access from ammoCount and display. I have already tried this code in ammoCount script:

 var ts : shoot;
 
 function Update () {
 var mag = ts.mag;
 var ammo = ts.ammo;
 
 guiText.text = mag + "/" + ammo;
 }

Any help would be appreciated, Thanks