Core (Tunneling)

local fuelLevel = turtle.getFuelLevel()
local totalRuns = 0
local runsToDo = 5
local fuelUsedPer = 100
local estimateFuelUsage = fuelUsedPer * runsToDo

-- check fuel level
function checkFuelLevel()
    fuelLevel = turtle.getFuelLevel()
    if fuelLevel <= estimateFuelUsage then
        os.error("Insufficient fuel!")
    end
end

-- move over and get ready for next run
function prepNextRun()
    turtle.turnRight()
    turtle.dig()
    turtle.forward()
    turtle.turnLeft()
end

print("Starting program...")
os.sleep(0.5)
print("Checking fuel levels...")
checkFuelLevel()
os.sleep(0.5)
print("Sufficient fuel in tank.")
print("Current fuel level: " .. fuelLevel)

for i = 1, runsToDo, 1 do
    print("Starting run #" .. i)
    shell.run("tunnel")
    print("Completed run #" .. i)
    print("Runs left: " .. runsToDo - i)
    os.sleep(1)
    print("Preparing for next run...")
    prepNextRun()
end

print("Finishing up program...")
print("Calculating fuel used...")
print("Fuel Used: " .. fuelLevel - turtle.getFuelLevel())