dig_length.lua

local length = 0
local items_to_drop = {
    "minecraft:dirt",
    "minecraft:stone",
    "minecraft:cobblestone",
    "minecraft:gravel",
    "minecraft:sand",
    "minecraft:deepslate",
}

if arg[1] ~= nil then length = tonumber(arg[1]) end

function go_back(length)
    if length == 0 then
        return 0
    end
    turtle.back()
    go_back(length - 1)
end

function start_dig(length)
    if length == 0 then
        go_back(length)
    end

    turtle.select(1)
    turtle.refuel()
    turtle.dig()
    turtle.forward()
    start_dig(length - 1)
end

start_dig(length)