Simple script which will pull all tagged images from given docker registry which have in repository name "library". It will remove the "library" part and push the images back to the registry.

remove-library.sh

#! /bin/bash
CREDENTIALS=""
if [ ! -z "$DOCKER_USER" ] && [ ! -z "$DOCKER_PWD" ]; then
    CREDENTIALS="$DOCKER_USER:$DOCKER_PWD@"
fi

if [ ! -z "$CREDENTIALS" ]; then
    docker login -u "$DOCKER_USER" -p "$DOCKER_PWD" -e "test@email.my" "$DOCKER_REGISTRY"
fi

if [ -z "$DOCKER_REGISTRY" ]; then
    echo "MISSING DOCKER_REGISTRY env variable."
    exit 1
fi
REGISTRY_URL="https://$CREDENTIALS$DOCKER_REGISTRY"

REPOS=$(curl -fs "${REGISTRY_URL}/v2/_catalog" | jq -r '.repositories|.[]')

for r in ${REPOS}
do
    if [[ "$r" == library* ]]; then
        IMAGE_TAGS=$(curl -fs "${REGISTRY_URL}/v2/$r/tags/list" | jq -r '.tags|.[]')
        for tag in ${IMAGE_TAGS}
        do
            IMAGE="$DOCKER_REGISTRY/$r:$tag"
            (docker pull ${IMAGE} && echo -e "OK Successfully pulled ${IMAGE}\n")
            NEW_IMAGE="${IMAGE//library\/}" # remove the "library/" repository from the image name
            (docker tag ${IMAGE} ${NEW_IMAGE})
            (docker push ${NEW_IMAGE} && echo -e "OK Successfully pushed ${NEW_IMAGE}\n")
        done
    else
        echo "Repository [$r] is not a library repository, skipping"
    fi
done