Check docker hub for image updates. Adapted from: https://mlohr.com/check-for-docker-image-updates/

image-check.sh

#!/bin/bash
VERBOSE=false

ec() {
    if $VERBOSE; then echo -en $1; fi
}

for IMAGE in $(docker images | grep -v '^REPOSITORY' | cut -f1 -d' ')
do
    ec "Fetching Docker Hub token...\n"
    token=$(curl --silent "https://auth.docker.io/token?scope=repository:$IMAGE:pull&service=registry.docker.io" | jq -r '.token')

    ec "Fetching remote digest...  "
    digest=$(curl --silent -H "Accept: application/vnd.docker.distribution.manifest.v2+json" \
        -H "Authorization: Bearer $token" \
        "https://registry.hub.docker.com/v2/$IMAGE/manifests/latest" | jq -r '.config.digest')
    ec "$digest\n"

    ec "Fetching local digest...  "
    local_digest=$(docker images -q --no-trunc $IMAGE:latest)
    ec "$local_digest\n"

    if [ "$digest" != "$local_digest" ] ; then
        echo "Update available for: $IMAGE"
    else
        echo "Already up to date. Nothing to do for: $IMAGE"
    fi
done