How to get the target branch of the GitHub pull request from an Actions?

Question

When an action is set on pull_request in Github Actions, how to get the target branch? The use case is to retrieve the PR- (and hopefully, branch)-specific comm

Answer 1

1. When you need the data in expressions (Source):

Property name	Type	Description
github.base_ref	string	The base_ref or target branch of the pull request in a workflow run. This property is only available when the event that triggers a workflow run is a pull_request.
github.head_ref	string	The head_ref or source branch of the pull request in a workflow run. This property is only available when the event that triggers a workflow run is a pull_request.

An example (modified from the documentation):

steps:
  - uses: actions/hello-world-javascript-action@v1.1
    if: ${{ github.base_ref == 'main' }}

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2. When you need the data as environment variables (Source):

Environment variable	Description
GITHUB_HEAD_REF	Only set for pull request events. The name of the head branch.
GITHUB_BASE_REF	Only set for pull request events. The name of the base branch.

An example (modified from the documentation):

steps:
  - name: Hello world
    run: echo Hello world from $GITHUB_HEAD_REF!

Answer 2

You can see all GitHub actions pull request event properties here.

Answer 3

You can access the target branch with ${{ github.event.pull_request.base.ref }}.

To know the full list of properties of the github.event object, try to run more $GITHUB_EVENT_PATH.