provide name each robots with ROS_NAMESPACE

edit

I buy three turtlebot3 burger. I want to control them at the same time.

I know e-manual.This site say that we can control three robots with three terminal.

$ ROS_NAMESPACE=tb3_0 rosrun turtlebot3_teleop turtlebot3_teleop_key
$ ROS_NAMESPACE=tb3_1 rosrun turtlebot3_teleop turtlebot3_teleop_key
$ ROS_NAMESPACE=tb3_2 rosrun turtlebot3_teleop turtlebot3_teleop_key

But I want to control with only one terminal. So,I think that I provide to name with namespace in program「turtlebot3 teleop_key」. But I don't know how to use. I want to Know.