Bridge

-- Programmed:  17 May 2014
-- by Skyler James
--
-- Builds a bridge <length>
-- blocks long, 1 block wide
--
-- The blocks to be used in
-- the bridge MUST be placed
-- in slot 9. There is error
-- checking to ensure this.
--
-- Turtle will NOT break any
-- blocks in its way

local tArgs = { ... }
if #tArgs ~= 1 then
    print( "Usage: bridge <length>" )
    return
end

-- Set length with user input
local length = tonumber( tArgs[1] )
if length < 1 then
    print( "Bridge length must be positive" )
    return
end

-- Check that there are <length>
-- blocks provided in slot 9
local numblocks = turtle.getItemCount(9)
if numblocks < length
    print("Please place at least "..length.." building blocks in slot 9")
    return
end

-- Place a block underneath
-- the turtle to build bridge
function putblockdown()
    if not (turtle.detectDown()) then
        turtle.select(9)
        turtle.placeDown()
    end
end

-- Move forward <length> times
-- and build a bridge with
-- blocks provided in slot 9
local i = 0
for i,length,1 do
    if (turtle.detect()) then
        break
    else
        putblockdown()
        turtle.forward()
    end
end

-- That's all, folks!
print("Built a bridge "..i.." blocks long")
return