Why it is necessary to source the environmental setup files (e.g., /opt/ros/noetic/setup.bash or ~/catkin_ws/devel/setup.bash)?

Question

Why it is necessary to source the environmental setup files (e.g.,  /opt/ros/noetic/setup.bash  or  ~/catkin_ws/devel/setup.bash )?

Accepted Answer

To ROS be able to find resources that have been installed or built to that location.

Answer

To push sources to a git repository.

Answer

To build the developed source code.

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