I've been learning LUA and want to clear console

I’ve been tiring to clear my console to make it neater, I’ve tried os.execute("clear") (which is similar to what I use in python)
this is the whole program:

    while( true )
    do
        local opacity
        print("What do you want the opacity to be? (invisible is 1, solid is 0)")
        opacity = io.read()
        opacity = tonumber(opacity)
        if opacity >1 then
            print("Thats not correct, try again")
            os.execute("clear")
            elseif opacity <=1 then
            print(opacity)
        end
    end

>Solution :

On Windows:

os.execute("cls")

On Unix:

os.execute("clear")