Your example suffers from being a toy example; it makes no sense to run a noninteractive command in a docker container merely to output terminal escape codes.

Your example suffers from being a toy example; it makes no sense to run a noninteractive command in a docker container merely to output terminal escape codes. If this were the norm, "docker run” would probably by default make sure to copy the TERM setting to the inner command. I would assume that if you run an interactive shell inside docker, TERM would actually be set correctly. It’s the same when you ssh somewhere else – the TERM environment variable is sent along, so that the remote program can see it and output the correct codes for your local terminal. Also, the docker image needs the terminfo database installed for “tput” to work.