HoleDig.lua

local count = 0
turtle.digDown()

while turtle.down() do
    count = count+1
    turtle.digDown()
    turtle.dig()
    turtle.place()
    if turtle.getItemCount() == 0 then
    turtle.select(turtle.getSelectedSlot()+1)
    end
end

for i=1,count do
    turtle.up()
end
turtle.select(1)
turtle.placeDown()