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

if docker login worked, you will find a .docker folder on your home directory (~/.docker/), with a config.json file with credentials in it.

otherwise you would get an error login in.

Note: docker determine what credentials to use by looking at the registry name:

if you do

docker pull myregistry.com/myimage:tag

docker will look if you're logged in, and if not will check if you have the credentials for the registry myregistry.com and login with those.

If not you will get a permission error