How can I tell if I'm logged in to a private Docker registry from a script?

Question

How can I tell whether or not I\'m logged in to a private Docker registry server from a script? In other words, has docker login some.registry.com been run success

Answer 1

This is a bit hacky, but it works in most of the cases for me:

if ! grep -q "my.private.registry.com" ~/.docker/config.json ; then
    docker login "my.private.registry.com"
fi

Basically, you search if there is a record of "my.private.registry.com" in ~/.docker/config.json. However, if the session is expired, this check won't catch it.