bash - Check if image:tag combination already exists on docker hub

Question

As part of a bash script, I want to check if a particularly docker image:tag combination exists on docker hub. Also, it will be a private repository.

i.e. the pseudocode would be like:

tag = something
if image:tag already exists on docker hub:
    Do nothing
else
    Build and push docker image with that tag

Answer 1

Update: Docker-Free solution see below

Using Docker

This is the solution I use with gitlab using the docker:stable image.

Login

docker login -u $USER -p $PASSWORD $REGISTRY

Check whether it's there:

docker manifest inspect $IMGNAME:$IMGTAG > /dev/null ; echo $?

docker will return 0 on success or 1 on failure.

If you get a warning: Update Docker or enable experimental client-features:

Set the environment variable DOCKER_CLI_EXPERIMENTAL to enabled (See Matěj's answer below)

Alternatively adjust the config (original answer):

echo '{"experimental": "enabled"}' > ~/.docker/config.json

This will also overwrite your config. If that is not an option you need to do that manually or use jq, sed or whatever you have available.

Update: If you don't have access to a docker-daemon, e.g. because you are building a docker image using kaniko within a docker, you can use the registry-api scripts provided by harbor. Note that they are python2.