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>