启动命令：
roslaunch beginner_tutorials turtlemimic.launch arg1:=3.0
查询命令：
rosparam get /param1
可以看到param1不是默认的5.0，而是3.0
launch文件如下
注意："$(arg arg1)"必须加双引号
<launch>
<arg name="arg1" default="5.0"/>
<param name="param1" value="$(arg arg1)" />
<group ns="turtlesim1">
<node pkg="turtlesim" name="sim" type="turtlesim_node">
</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>
原文：https://www.cnblogs.com/xbit/p/11519463.html