How to list the containers attached to a given user-defined network?
The docker network inspect command produces a JSON output that can be parsed using jq to extract the relevant piece of information:

sudo docker network inspect app-bridge | jq '.[].Containers[].Name'

"app2"
"app3"
"app1"
"laughing_easley"
"database"
"thirsty_wing"


If you are already familiar with JSON processing with jq, the advantage is you can reinvest your knowledge without having to bother with Go templates. On the other hand, it relies on an external tool which may or may be not available at your site.