main.rb

require 'turtle'

turtles = [Turtle.new, Turtle.new, Turtle.new]

while true
  # get the command
	print "Enter a command: "
	s = gets.chomp

	# exit?
	if s == 'exit' then
		break
	end

	# parse and route the command
	turtle_num, t_cmd = s.split(" ", 2)
	turtles[turtle_num.to_i].parse_command t_cmd
end

turtle.rb

class Turtle

  module Directions
		UP = 0
		RIGHT = 1
		DOWN = 2
		LEFT = 3
	end
	
	MAPSIZE = 20
	attr_accessor :x_pos, :y_pos, :is_pen_down, :direction, :the_map
	
	def initialize
		@x_pos = 0
		@y_pos = 0
		@the_map = Array.new(MAPSIZE) { Array.new(MAPSIZE) { 0 } }
		@the_map[0][0] = 1
		@is_pen_down = false
		@direction = Directions::RIGHT
	end

	def draw_map
		i = 0

		while i < MAPSIZE
			print "\n"
			@the_map.each do |sub|
				print "#{sub[i]} "
			end
			i += 1
		end

		print "\n"
	end

	def move spaces
		x_mod = 1 
		y_mod = 1

		case @direction
		when Directions::UP
			if @y_pos - spaces < 0 then
				return
			else
				x_mod = 0
				y_mod = -1
			end
		when Directions::RIGHT
			if @x_pos + spaces > MAPSIZE - 1 then
				return
			else
				x_mod = 1
				y_mod = 0
			end
		when Directions::DOWN
			if @y_pos + spaces > MAPSIZE - 1 then
				return
			else
				x_mod = 0
				y_mod = 1
			end
		when Directions::LEFT
			if @x_pos - spaces < 0 then
				return
			else 
				x_mod = -1
				y_mod = 0
			end
		else 
			return
		end

		while spaces > 0
			@x_pos += x_mod 
			@y_pos += y_mod
			if is_pen_down == true
				@the_map[@x_pos][@y_pos] = 1
			end
			
			spaces -= 1
		end
	end

	def put_pen_down
		@is_pen_down = true
	end

	def pick_pen_up
		@is_pen_down = false
	end

	def turn_left
		@direction = @direction > 0 ? @direction - 1 : @direction = 3
	end

	def turn_right
		@direction = @direction < 3 ? @direction + 1 : @direction = 0
	end

	def status
		print "position: <#{@x_pos}, #{@y_pos}>, direction: #{@direction}, pen status: #{@is_pen_down}\n"
	end

	def parse_command command
		commands = command.split
		case commands[0]
			when "1"
				self.pick_pen_up
			when "2"
				self.put_pen_down
			when "3"
				self.turn_right
			when "4"
				self.turn_left
			when "5"
				spaces = commands[1].to_i
				if spaces == 0
					print "Invalid command set: '#{command}'\n"
					return
				end
				self.move spaces
			when "6"
				self.draw_map
			when "9"
				exit
			else
				print "Invalid command set: '#{command}'\n"
		end
	end
end