problem trying to run setup.bash on docker image

edit

I am trying to use osrf/ros:noetic-desktop-full and running into a problem. After pulling, running, and connecting to it with an interactive terminal window, I don't seem to be able to run the setup.bash script as described in basic getting started tutorial. Neither of these seem to work

# source /opt/ros/noetic/setup.bash /bin/sh: 1: source: not found

# . /opt/ros/noetic/setup.bash /bin/sh: 1: /opt/ros/noetic/setup.bash: Bad substitution /bin/sh: 7: /opt/ros/noetic/setup.bash: builtin: not found /bin/sh: 8: .: Can't open /setup.sh

I do not know what is going on, though I suspect I am not understanding something very straightforward.

Is there any getting started info specific to the osrf docker images?

Many thanks for any help or clues.