mine

--The local postition tracker, dont have any refrence to real world
local posx = 0
local posy = 0
local posz = 0
--The local direction set at start, 1 forward, 2 right, 3 back, 4 left
local direction = 1

-- Move and update position
function move()
    if direction == 1 then
        posx = posx + 1
    elseif direction == 2 then
        posz = posz + 1
    elseif direction == 3 then
        posx = posx - 1
    elseif direction == 4 then
        posz = posz - 1
    end
    turtle.forward()
end

-- Turn and change direction
function turnRight()
    direction = direction + 1
    turtle.turnRight()
end
-- Turn and change diretction
function turnLeft()
    direction = direction - 1
    turtle.turnLeft()
end

-- make a 3 high tunnel forward
function tunnelForward()
    if turtle.detect() then
        turtle.dig()
    end
    move()
    if turtle.detectUp() then
        turtle.digUp()
    end
    if turtle.detectDown() then
        turtle.digDown()
    end
end

-- Make the robot go to the startingposition
function goHome()
    if posx > 0 then
        while(direction ~= 3) do
            turnRight()
        end
        for k=1,math.abs(posx),1 do
            move()
        end
    elseif posx < 0 then
        while(direction ~= 1) do
            turnRight()
        end
        for k=1,math.abs(posx),1 do
            move()
        end
    end
    if posz > 0 then
        while(direction ~= 4) do
            turnRight()
        end
        for k=1,math.abs(posz),1 do
            move()
        end
    elseif posz < 0 then
        while(direction ~= 2) do
            turnRight()
        end
        for k=1,math.abs(posz),1 do
            move()
        end
    end
end



-----Main funtion-----
print("Dig v101 by Coffedahl")
sleep(10)
print("Please have some chests in slot 1 and fuel in slot 2")
--get size of tunnel
print("Please enter length of tunnel:")
local length = io.read()
print("Please enter width of tunnel:")
local width = io.read()
print("Starting dig")
--Refuel
turtle.select(2)
turtle.refuel()
turtle.select(1)

local dig_direction = 1
for i=1,width,1 do
    for o=1,length,1 do
        tunnelForward()
        if turtle.getItemCount(16) > 0 then
            turtle.select(1)
            turtle.placeDown()
            for e=2,16,1 do
                turtle.select(e)
                turtle.dropDown()
            end
            turtle.select(1)
        end
    end
    if dig_direction == 1 then
        turnRight()
        tunnelForward()
        turnRight()
        dig_direction = 2
    elseif dig_direction == 2 then
        turnLeft()
        tunnelForward()
        turnLeft()
        dig_direction = 1
    end
    if i == width - 1 then
        dig_direction = 0
    end
end
goHome()
print("Done")