1,切换目录：
$ roscd beginner_tutorials
2,新建launch子目录：
$ mkdir launch
3，进入子目录：
$ cd launch
4，新建launch文件
$ gedit turtlemimic.launch
5，复制下面源码到turtlemimic.launch，然后保存并退出：
<launch>
<group ns="turtlesim1">
<node pkg="turtlesim" name="sim" type="turtlesim_node"/>
</group>
<group ns="turtlesim2">
<node pkg="turtlesim" name="sim" type="turtlesim_node"/>
</group>
<node pkg="turtlesim" name="mimic" type="mimic">
<remap from="input" to="turtlesim1/turtle1"/>
<remap from="output" to="turtlesim2/turtle1"/>
</node>
</launch>
6，运行roslaunch：
$ roslaunch beginner_tutorials turtlemimic.launch
uu@uu-HP-EliteBook-6930P-Notebook-PC:~$ roscd beginner_tutorials
uu@uu-HP-EliteBook-6930P-Notebook-PC:~/catkin_ws/src/beginner_tutorials$ mkdir launch
uu@uu-HP-EliteBook-6930P-Notebook-PC:~/catkin_ws/src/beginner_tutorials$ ls
CMakeLists.txt include launch package.xml src
uu@uu-HP-EliteBook-6930P-Notebook-PC:~/catkin_ws/src/beginner_tutorials$ cd launch
uu@uu-HP-EliteBook-6930P-Notebook-PC:~/catkin_ws/src/beginner_tutorials/launch$
uu@uu-HP-EliteBook-6930P-Notebook-PC:~/catkin_ws/src/beginner_tutorials/launch$ gedit turtlemimic.launch
uu@uu-HP-EliteBook-6930P-Notebook-PC:~/catkin_ws/src/beginner_tutorials/launch$ uu@uu-HP-EliteBook-6930P-Notebook-PC:~/catkin_ws/src/beginner_tutorials/launch$ roslaunch beginner_tutorials turtlemimic.launch
... logging to /home/uu/.ros/log/f0cf7f2e-a2cd-11e8-90ab-00216a949182/roslaunch-uu-HP-EliteBook-6930P-Notebook-PC-7213.log
Checking log directory for disk usage. This may take awhile.
Press Ctrl-C to interrupt
Done checking log file disk usage. Usage is <1GB.
started roslaunch server http://uu-HP-EliteBook-6930P-Notebook-PC:33327/
SUMMARY
========
PARAMETERS
* /rosdistro: melodic
* /rosversion: 1.14.2
NODES
/
mimic (turtlesim/mimic)
/turtlesim1/
sim (turtlesim/turtlesim_node)
/turtlesim2/
sim (turtlesim/turtlesim_node)
auto-starting new master
process[master]: started with pid [7223]
ROS_MASTER_URI=http://localhost:11311
setting /run_id to f0cf7f2e-a2cd-11e8-90ab-00216a949182
process[rosout-1]: started with pid [7234]
started core service [/rosout]
process[turtlesim1/sim-2]: started with pid [7241]
process[turtlesim2/sim-3]: started with pid [7242]
process[mimic-4]: started with pid [7243]
7,打开新终端，发布运动会话：
$ rostopic pub /turtlesim1/turtle1/cmd_vel geometry_msgs/Twist -r 1 -- '[2.0, 0.0, 0.0]' '[0.0, 0.0, -1.8]'
