3x3

print("longueur : ")
local length = io.read()

-- Function Definitions --
local function digVerticalLine()
  while turtle.detect() do
    turtle.dig()
  end
  turtle.forward()
  while turtle.detectUp() do
    turtle.digUp()
    os.sleep(0.5)
  end
  turtle.digDown()
end

local function turnAround()
  turtle.turnRight()
  turtle.turnRight()
end

local function checkForHoles()
  turtle.down()
  if not turtle.detectDown() then
    turtle.select(2)
    turtle.placeDown()
  end
  turtle.up()
end

local function digIntoWall()
  digVerticalLine()
  checkForHoles()
  turtle.turnLeft()
  digVerticalLine()
  checkForHoles()
  turnAround()
  turtle.forward()
  digVerticalLine()
  checkForHoles()
  turnAround()
  turtle.forward()
  turtle.turnRight()
end

-- Program --
turtle.up()
for i=0, length - 1 do
  digIntoWall()
  if i % 5 == 0 then
    turtle.select(1)
    turtle.placeDown()
  end
end