ref: ab21f2b775066b8158ac5d90c0dba6a99c7aa2e7
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)