github: limit docker image builds to tags and the master branch #53

	name: release docker image
	on:
	push:
	tags:
	- '*'
	branches:
	- master
	env:
	IMAGE_NAME: "gmid"
	jobs:
	build:
	permissions: write-all
	runs-on: ubuntu-latest
	steps:
	- uses: actions/checkout@v1

	- name: build the image
	run: docker build -f contrib/Dockerfile -t gmid:alpine .

	- name: login to ghcr.io
	uses: docker/login-action@v2
	with:
	registry: ghcr.io
	username: ${{ github.actor }}
	password: ${{ secrets.GITHUB_TOKEN }}

	- name: push the image
	run: \|
	IMAGE_ID=ghcr.io/${{ github.repository_owner }}/$IMAGE_NAME
	IMAGE_ID=$(echo $IMAGE_ID \| tr A-Z a-z)
	# strip git ref prefix from version
	VERSION=$(echo "${{ github.ref }}" \| sed -e 's,./$.$,\1,')
	echo IMAGE_ID=$IMAGE_ID
	echo VERSION=$VERSION
	docker tag gmid:alpine $IMAGE_ID:$VERSION
	docker push $IMAGE_ID:$VERSION

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