Example of evaluating untrusted code in Lua

load-example.lua

local oldprint = print

print = function(a)
    oldprint("load print: " .. a)
end

a = 1
local f = load "print(a)"
f() -- this will print 'load print: 1'

--
-- the code below would get a 'attempt to call a nil value':
--
--     local f = load "oldprint(a)"
--     f()
--
-- this happens because loaded code can only access globals. override all
-- dangerous functions and combine this with pcall and ya get a simple way of
-- running untrusted code
--