GitHub Actions to use variables set from shell

Question

Goal:

In GitHub Actions, to define my commit message dynamically from shell:

      - name: Commit changes
        uses: EndBug/add-and-commit@v7
        with:
          message: "added on $(date -I)"

However, it seems that I have to define a environment variable then use it. I'm following How do I set an env var with a bash expression in GitHub Actions? and other help files like this, but still cannot tell how to make use of such environment variable that I've define previously. This is what I tried but failed:

      - name: Checkout repo
        uses: actions/checkout@v2
      - run: |
          touch sample.js
          echo "today=$(date -I)" >> $GITHUB_ENV

      - name: Commit changes
        uses: EndBug/add-and-commit@v7
        with:
          message: "added on ${today}"

How to make it work?

Answer 1

If you want to reference an environment variable set using the $GITHUB_ENV environment file in the arguments to another task, you'll need to use workflow syntax to access the appropriate key of the top level env key, like this:

- name: Commit changes
  uses: EndBug/add-and-commit@v7
  with:
    message: "added on ${{env.today}}"

You can access it as a standard environment from inside of a running task, for example:

- name: Show an environment variable
  run: |
      echo "today is $today"

In that example, the expression $today is expanded by the shell, which looks up the environment variable named today. You could also write:

- name: Show an environment variable
  run: |
      echo "today is ${{env.today}}"

In this case, the expansion would be performed by github's workflow engine before the run commands execute, so the shell would see a literal command that looks like echo "today is 2021-07-14".

---

You can accomplish something similar using output parameters, like this:

- name: "Set an output parameter"
  id: set_today
  run: |
    echo "::set-output name=today::$(date -I)"

- name: Commit changes
  uses: EndBug/add-and-commit@v7
  with:
    message: "added on ${{steps.set_today.outputs.today}}"

Using output parameters is a little more granular (because they are qualified by the step id), and they won't show up in the environment of processes started by your tasks.