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GitHub Actions fundamentals

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4 minutes to read

Reference for Workflow syntax (YAML)

Workflow commands for GitHub Actions

Setting an environment variable

  • We can define environment variables at workflow level, job level and step level.
  • We can set environment variable with a workflow command in jobs.<job_id>.steps[*].run e.g.
  - run: |
    # literal value
    echo "action_state=yellow" >> $GITHUB_ENV
    # value from a secret
    echo "SLACK_WEBHOOK=${{ secrets.SLACK_WEBHOOK }}" >> $GITHUB_ENV

Context and expression syntax for GitHub Actions

# Expression syntax
${{ <expression> }}
if: ${{ <expression> }}
if: <expression> # You can omit {{ }}
# Read context value
${{ <context> }}
${{ env.VARIABLE_NAME }}

Useful predefined contexts

  • github.sha The commit SHA that triggered the workflow run.
  • github.ref The branch or tag ref that triggered the workflow run.

Environment variables

  • https://docs.github.com/en/actions/reference/environment-variables
  • To use the value of an environment variable in a workflow file, you should use the env context.
  • If you want to use the value of an environment variable inside a runner, you can use the runner operating system's normal method for reading environment variables. e.g. \$VARIABLE_NAME
# Use environment with GitHub `env` context and normal operation system as $ENVIRONMENT_VARIABLE
env:
  FIRST_NAME: Mona
  DAY_OF_WEEK: Mona
if: env.DAY_OF_WEEK == 'Mon'
run: echo "Hello $FIRST_NAME at ${{ env.DAY_OF_WEEK }}"

Run job on a specific repository only

jobs:
  job_id:
    name: Job name
    if: github.repository == username/repository-name

Conditional set environment variables

Ternary workflow expression

${{ github.ref == env.MAIN_BRANCH && secrets.PRO_PUBLISH_PROFILE || secrets.DEV_PUBLISH_PROFILE }}

Run a job based on a condition with if expression

Find more virtual environments

An action

  • An action is unit of code.
  • You can use an action defined in the same repository as the workflow, a public repository, or in a published Docker container image.
  • Version of the action:
    • Using the commit SHA of a released action version is the safest for stability and security.
    • Using the specific major action version allows you to receive critical fixes and security patches while still maintaining compatibility. It also assures that your workflow should still work.
    • Using the default branch of an action may be convenient, but if someone releases a new major version with a breaking change, your workflow could break.
  • More details https://docs.github.com/en/actions/reference/workflow-syntax-for-github-actions#jobsjob_idstepsuses
steps:
  # Reference the major version of a release
  - uses: actions/setup-node@v1

Known issues:

env:
  Deploy: 'false'
jobs:
  prejob:
    runs-on: ubuntu-latest
    outputs:
      envvalue: ${{ steps.setvar.outputs.envvar }}
    steps:
      - name: set value
        id: setvar
        run: |
          echo "::set-output name=envvar::$Deploy"  # get top level env and set it as output
  envcheck:
    needs: [prejob]
    if: ${{needs.prejob.outputs.envvalue=='false'}} # check env value in job level expression now.
    runs-on: [ubuntu-latest]
    steps:

You can use a step's name with step's uses

Specific branch name pattern to trigger an action

  • Match on a specific branch
on:
  push:
    branches:
      - '*'         # matches every branch that doesn't contain a '/'
      - '*/*'       # matches every branch containing a single '/'
      - '**'        # matches every branch
      - '!master'   # excludes master
  • Match all branches
on: push
on: [push, pull_request]
  • Ignore branches
on:
  push:
    branches-ignore:
      - master

Path, useful for monorepo

Retention period of GitHub Actions

Change a working directory

  • To all steps, at workflow level:
defaults:
  run:
    working-directory: ./temp
  • At job level:
jobs:
  job1:
    defaults:
      run:
        working-directory: ./temp
  • At step level:
  - name: Clean temp directory
    run: rm -rf *
    working-directory: ./temp

Yarn is already installed on Ubuntu runner

Change a default shell

  • You can use default run to set default shell to all steps
  • It can be at workflow level (defaults.run) or job level (jobs.<job_id>.defaults.run).
defaults:
  run:
    shell: powershell

How to apt-get install in a GitHub Actions workflow?

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