An example of a GitHub Actions job that builds a Docker container image and then pushes it to to the GitHub Packages container registry associated with the same repo, using regular `docker` commands

push.yaml

# An example of a GitHub Actions job that builds a Docker container image and then pushes
# it to to the GitHub Packages container registry associated with the same repo, using
# regular `docker` commands.

# Change these to whatever you want, of course. For example, you might want to only run this workflow for
# PRs. Personally I like to check the build on every push. That said, it’s probably not necessary to publish
# an artifact (container image) for every single push; I’m personally planning to add an `if` to the push
# step that skips the `docker push` if the GitHub event is `push`.
name: Push
on:
  - push
  # un-comment this line if you also want the workflow triggered for PRs.
  # - pull_request

jobs:
  build-and-push-container-image:
    # Relevant docs: https://docs.github.com/en/actions/guides/publishing-docker-images#publishing-images-to-github-packages
    runs-on: ubuntu-20.04
    env:
      REGISTRY: ghcr.io
    steps:
      - uses: actions/checkout@v2

      - name: Set environment variables
        run: |
          echo "IMAGE_NAME=$(echo "$REGISTRY/$GITHUB_REPOSITORY" | tr '[:upper:]' '[:lower:]')" >> $GITHUB_ENV
          echo "GIT_SHA=$(echo ${{ github.sha }} | cut -c1-7)" >> $GITHUB_ENV
          echo "GIT_REF=$(git symbolic-ref -q --short HEAD || git describe --tags --exact-match)" >> $GITHUB_ENV
          echo "IMAGE_TAG=${GIT_REF}-${GIT_SHA}" >> $GITHUB_ENV

      - name: docker build
        run: docker build --tag ${IMAGE_NAME}:${IMAGE_TAG} .

      - name: docker login
        run: echo ${{ secrets.GITHUB_TOKEN }} | docker login $REGISTRY -u "${{ github.actor }}" --password-stdin

      - name: docker push
        run: docker push ${IMAGE_NAME}:${IMAGE_TAG}