我已经在ubuntu 18.04成功安装了ROS melodic和gazebo9。在安装后设置环境时，
如果我再次重新开始环境设置，我会错误地键入echo "source /opt/ros/indigo/setup.bash" >> ~/.bashrc而不是现在echo "source /opt/ros/melodic/setup.bash" >> ~/.bashrc
echo "source /opt/ros/melodic/setup.bash" >> ~/.bashrc
source ~/.bashrc
它抛出一个错误bash: /opt/ros/indigo/setup.bash: No such file or directory
我该如何解决这个问题？