Lua: Executing a string and storing the output of the command in a variable

Question

I\'ve got a Lua script that receives a function call in a string. I need to execute that call and retrieve the output as a string in a variable so I can later send it somewhere.

Answer 1

I just found a way to do what I wanted, but I'd still like to know if you guys can find any flaw/better way to do it, since I'm very new to Lua:

    > s = "json.encode('{1:1, 2:3, 5:8}')"
    > s2 = "return("..s..")"
    > ret = assert(loadstring(s2))()
    > print(ret)
    "{1:1, 2:3, 5:8}"

Answer 2

You need to return the value from the loaded chunk. As it is you are telling lua you don't care about the returned value so it is throwing it away.

Note: I don't have the json module handy so I replaced the function with a function that just returns its argument for demonstration purposes:

> json = { encode = function(s) return s end }
> s = "json.encode('{1:1, 2:3, 5:8}')"
> ret = assert(loadstring("return "..s))()
> print(ret)
{1:1, 2:3, 5:8}