How to get current branch within github actions

I added a separate step for extracting branch name from $GITHUB_REF and set it to the step output

- name: Extract branch name
  shell: bash
  run: echo "##[set-output name=branch;]$(echo ${GITHUB_REF#refs/heads/})"
  id: extract_branch

after that, I can use it in the next steps with

- name: Push to ECR
  id: ecr
  uses: jwalton/gh-ecr-push@master
  with:
    access-key-id: ${{ secrets.AWS_ACCESS_KEY_ID }}
    secret-access-key: ${{ secrets.AWS_SECRET_ACCESS_KEY }}
    region: us-west-2
    image: eng:${{ steps.extract_branch.outputs.branch }}

I believe GITHUB_REF is the only environment variable that includes the branch name.

You can extract just the branch name from the rest of that string like this:

${GITHUB_REF##*/}

Example:

$ GITHUB_REF=refs/heads/feature-branch-1
$ echo ${GITHUB_REF##*/}
feature-branch-1

---

Update: Added a complete workflow example.

Workflow

name: CI
on: push
jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - name: Git checkout
        uses: actions/checkout@v1
      - name: Branch name
        run: echo running on branch ${GITHUB_REF##*/}
      - name: Build
        run: docker build -t tedmiston/tag-example:${GITHUB_REF##*/} .

Source: https://github.com/tedmiston/x/blob/master/.github/workflows/workflow.yml

Sample output - master branch

Run docker build -t tedmiston/tag-example:${GITHUB_REF##*/} .
  docker build -t tedmiston/tag-example:${GITHUB_REF##*/} .
  shell: /bin/bash -e {0}
Sending build context to Docker daemon  146.9kB

Step 1/1 : FROM alpine
latest: Pulling from library/alpine
9d48c3bd43c5: Pulling fs layer
9d48c3bd43c5: Verifying Checksum
9d48c3bd43c5: Download complete
9d48c3bd43c5: Pull complete
Digest: sha256:72c42ed48c3a2db31b7dafe17d275b634664a708d901ec9fd57b1529280f01fb
Status: Downloaded newer image for alpine:latest
 ---> 961769676411
Successfully built 961769676411
Successfully tagged tedmiston/tag-example:master

Log: https://github.com/tedmiston/x/commit/cdcc58a908e41d3d90c39ab3bf6fef1ad2c4238a/checks#step:4:16

Sample output - non-master branch

Run docker build -t tedmiston/tag-example:${GITHUB_REF##*/} .
  docker build -t tedmiston/tag-example:${GITHUB_REF##*/} .
  shell: /bin/bash -e {0}
Sending build context to Docker daemon  144.9kB

Step 1/1 : FROM alpine
latest: Pulling from library/alpine
9d48c3bd43c5: Pulling fs layer
9d48c3bd43c5: Verifying Checksum
9d48c3bd43c5: Download complete
9d48c3bd43c5: Pull complete
Digest: sha256:72c42ed48c3a2db31b7dafe17d275b634664a708d901ec9fd57b1529280f01fb
Status: Downloaded newer image for alpine:latest
 ---> 961769676411
Successfully built 961769676411
Successfully tagged tedmiston/tag-example:branch-name-test

Log: https://github.com/tedmiston/x/commit/4e8d31259f861aaa2c30375756fc081c3659bddf/checks#step:4:16

---

See this answer for more on parameter expansion syntax.

For reference the page Virtual environments for GitHub Actions lists all of the environment variables available in the execution environment.

Be aware that if you are executing your GitHub action on pull request trigger, then GITHUB_REF variable will contain something like refs/pull/421/merge so if you will try to git push to that name it will most likely fail.

What you can use though are references on the GitHub context in your YAML. Something like: ${{ github.head_ref }}

https://help.github.com/en/actions/automating-your-workflow-with-github-actions/contexts-and-expression-syntax-for-github-actions#github-context