Bash script to allow you to use `FROM image` in Dockerfiles even when using a private registry

local-image

#!/usr/bin/env bash

readonly _skip_examples="local-image-skip-examples"

usage() {
	local scriptname
	scriptname="$(basename "$0")"
	cat <<-EOF
	Usage: ${scriptname} command

	Commands:
	  fetch IMAGE REGISTRY		Fetch a local-tagged copy of IMAGE from REGISTRY
	  push IMAGE REGISTRY		Push IMAGE to REGISTRY
	  clean local IMAGE		Remove a local-tagged copy of IMAGE
	  clean remote IMAGE REGISTRY	Remove a REGISTRY-tagged copy of IMAGE
	  clean both IMAGE REGISTRY	Remove both local- and REGISTRY-tagged IMAGE
	EOF

	[[ "$1" == "$_skip_examples" ]] && return

	cat <<-EOF

	Examples:
	  ${scriptname} fetch company/service:2.5 docker.example.com
	        Pull docker.example.com/company/service:2.5 and tag it locally as
	        company/service:2.5.
	  ${scriptname} push company/service:2.5 docker.example.com
	        Tag company/service:2.5 as docker.example.com/company/service:2.5
	        and push it to the registry.
	  ${scriptname} clean local company/service:2.5
	        Remove company/service:2.5 from the local system.
	  ${scriptname} clean remote company/service:2.5 docker.example.com
	        Remove docker.example.com/company/service:2.5 from the local system.
	  ${scriptname} clean both company/service:2.5 docker.example.com
	        Remove docker.example.com/company/service:2.5 and company/service:2.5
	        from the local system.
	EOF
}

_retag() {
	if [[ "$#" -ne 2 ]]; then
		echo "${FUNCNAME[0]}: Expected 2 arguments, got ${#}." >&2
		return 1
	fi
	declare source="$1" dest="$2"
	echo "Tagging ${source} as ${dest}..."
	docker tag "$source" "$dest"
}

fetch() {
	if [[ "$#" -ne 2 ]]; then
		echo "${FUNCNAME[0]}: Expected 2 arguments, got ${#}." >&2
		usage "$_skip_examples"
		return 1
	fi
	declare image="$1" registry="$2"
	local remoteimage="${registry}/${image}"

	echo "Pulling ${remoteimage}..."
	docker pull "$remoteimage"

	echo

	_retag "$remoteimage" "$image"
}

push() {
	if [[ "$#" -ne 2 ]]; then
		echo "${FUNCNAME[0]}: Expected 2 arguments, got ${#}." >&2
		usage "$_skip_examples"
		return 1
	fi
	declare image="$1" registry="$2"
	local remoteimage="${registry}/${image}"

	_retag "$image" "$remoteimage"

	echo

	echo "Pushing ${remoteimage}..."
	docker push "$remoteimage"
}

clean() {
	case "$1" in
		local)	shift; _clean_local "$@";;
		remote)	shift; _clean_remote "$@";;
		both)
			shift
			_clean_local "$@"
			_clean_remote "$@"
			;;
		*)		usage;;
	esac
}

_clean_local() {
	if [[ "$#" -lt 1 ]] || [[ "$#" -gt 2 ]]; then
		echo "${FUNCNAME[0]}: Expected 1 argument, got ${#}." >&2
		usage
		return 1
	fi
	declare image="$1"
	docker rmi "$image" || true
}

_clean_remote() {
	if [[ "$#" -ne 2 ]]; then
		echo "${FUNCNAME[0]}: Expected 2 arguments, got ${#}." >&2
		usage
		return 1
	fi
	declare image="$1" registry="$2"
	local remoteimage="${registry}/${image}"
	docker rmi "$remoteimage" || true
}

main() {
	set -eo pipefail; [[ -n "$TRACE" ]] && set -x

	case "$1" in
		fetch)	shift; fetch "$@";;
		push)	shift; push "$@";;
		clean)	shift; clean "$@";;
		*)		usage;;
	esac
}

[[ "$0" == "${BASH_SOURCE[0]}" ]] && main "$@"