Condition to move NXT motors

edit

I've been playing with ROS+Lego NXT and after successfully playing with the sensors I got stuck trying to stop the motor when sensor touch is True. I don't know how to do it, and have no idea. I already move the motors using:

rostopic pub -1 joint_command nxt_msgs/JointCommand -- l_motor_joint XX

and

rostopic pub /joint_command nxt_msgs/JointCommand '{name: 'motor', effort: 2}'

Any ideas? thanks