How do I set an env var with a bash expression in GitHub Actions?

Question

In GitHub Actions, I'd like to evaluate a bash expression and then assign it to an environment variable:

    - name: Tag image       env:         GITHUB_SHA_SHORT: ${{ $(echo $GITHUB_SHA | cut -c 1-6) }}       ..do other things... 

However, this naive attempt has failed. According to the docs this doesn't seem to be supported; a somewhat clean workaround would be fine.

Answer 1

The original answer to this question used the Actions runner function set-env. Due to a security vulnerability set-env is being deprecated and should no longer be used.

This is the new way to set environment variables.

name: my workflow on: push jobs:   build:     runs-on: ubuntu-latest     steps:     - uses: actions/checkout@v2     - name: Set env       run: echo "GITHUB_SHA_SHORT=$(echo $GITHUB_SHA | cut -c 1-6)" >> $GITHUB_ENV     - name: Test       run: echo $GITHUB_SHA_SHORT 

Setting an environment variable echo "{name}={value}" >> $GITHUB_ENV

Creates or updates an environment variable for any actions running next in a job. The action that creates or updates the environment variable does not have access to the new value, but all subsequent actions in a job will have access. Environment variables are case-sensitive and you can include punctuation.

(From https://help.github.com/en/actions/reference/workflow-commands-for-github-actions#setting-an-environment-variable)

Example using the output to $GITHUB_ENV method:

    echo "GITHUB_SHA_SHORT=$(echo $GITHUB_SHA | cut -c 1-6)" >> $GITHUB_ENV 

This is an alternative way to reference the environment variable in workflows.

    - name: Test       run: echo ${{ env.GITHUB_SHA_SHORT }}