ROS service and roslaunch
In package autoturtle, despite that two python scripts, turtlesim_move.py and turtlesim_move1.py, have different structure, their nodes do exactly the same thing, i.e., driving the turtle to move in a straight line.
For more general examples of turtlesim, see http://wiki.ros.org/turtlesim/Tutorials/Moving%20in%20a%20Straight%20Line