Turtle - Dig 1 x 3 tunnel w/torches & return

-- This script digs a 1 x 3 high tunnel
-- to the length you are prompted,
-- places a torch on the side wall,
-- and returns.
-- Put torches in slot 16 (bottom right corner)
--
-- Place the turtle on the floor level of your tunnel
--------------------------------------------------------

function digIt()
  while turtle.detect() do
       turtle.dig()
       os.sleep(1.0)
  end
  turtle.forward()
  while turtle.detectDown() or turtle.detectUp() do
    turtle.digUp()
    turtle.digDown()
  end
end

function placeTorch()
  turtle.back()
  turtle.select(16)
  turtle.placeUp()
  turtle.forward()
  turtle.select(1)
end

-- this sets the initial variable values ----------------
local run = 0
local j = 0
local k = 0

term.write("Length of Branch?  ") -- You are prompted to enter a tunnel length ----------------
run = read()

----------------------------------------------------------------------------------------

-- This is the main command to dig the tunnel ----------------
turtle.up()
for i = 1, run do
  k = i - 1
  j = k % 5  -- This determines how many squares to place a torch ie: 5 ----------------
  if j == 1 then
    placeTorch()
  end
  digIt() -- this digs the tunnel length you typed in ----------------
end

-- this places a torch at the end of the tunnel, drops to the floor,
-- turns around, and returns to the start
turtle.select(16)
turtle.placeUp()
turtle.turnRight()
turtle.turnRight()
turtle.down()

for i = 1, run do -- this tells the turtle to head back the same number of squares it dug ----------------
  turtle.forward()
end