Turtle - Move up

-- I name the file "u" to
-- minimize typing :)
-- Usage: u 3
-- Moves the turtle up 3, and
-- digs if anything is in the way.
-- If you just type "u", it moves 1.

arg = (...)
arg = tonumber(arg) or 1
x = 0

while x < arg do
    if turtle.up() == true then
    x = x + 1
    else
    turtle.digUp()
    end
end