I am trying to loadstring a string and run it as a function. Here is my problem:
a = "hello"
loadstring("print(a)")()
I dont want the code above to use any vars/funcs outside of it. My goal is to make the script above print nil since a isnt defined inside the loadstring.
Sorry if the question is very brief. It was hard to explain my problem.
Your variable a lives in the global environment. To keep your chunk from seeing it, you need to give it a different environment. In Lua 5.1, you'd do that like this:
a = "hello"
local chunk = loadstring("print(a)")
setfenv(chunk, {print = print})
chunk()
In Lua 5.2 or newer, you'd do that like this:
a = "hello"
load("print(a)", nil, "t", {print = print})()
It's important to note that print isn't magic. It won't be in the new environment unless you put it there explicitly, like I did.
_G and then removing what you don't want, but this is really starting to sound like an XY problem. What are you actually trying to achieve by restricting a script like this? Could you just use locals instead, like you did when you first posted the question?