local length = 20

def getDepth()
    write("The desired tunnel length? Default is 20")
    length = read()
end

def digColumn()
    dig()
    turtle.up()
    dig()
    turtle.left()
    dig()
    turtle.down()
    dig()
    turtle.down()
    dig()
    turtle.right()
    dig()
    turtle.right()
    dig()
end

def dig()
    if turtle.detect() then
        turtle.dig()
    end
end

digColumn()