ref: 56f45bb8a89dfcb3c87d3a2d7663bb03130dce87
dir: /lua/test/env.lua/
-- read environment variables as if they were global variables
local f=function (t,i) return os.getenv(i) end
setmetatable(getfenv(),{__index=f})
-- an example
print(a,USER,PATH)