Thanks for you answers.
All my test where done on a Centos 7 box and I successfully started a container with
podman based on this image.
So I'm sure bash was successfully installed and running.
I forgot to mention that I also tested with the '--format docker' as suggested by
Tow Sweeney without any success.
How can I check with buildah if the image has been build with the docker image-spec
instead of the OCI?