You need a few more steps in there to make that work. Here's an example:
var test = 5
var test2 = 5
var temp = get("test")
temp += test2
That said, I'd ask why you need to access variables via their string names? As you can imagine, the above isn't very efficient (or easy to understand). Based on what the underlying need is, there's likely a better way to design whatever you're doing.