Creating a composite action

Introduction

In this guide, you'll learn about the basic components needed to create and use a packaged composite action. To focus this guide on the components needed to package the action, the functionality of the action's code is minimal. The action prints "Hello World" and then "Goodbye", or if you provide a custom name, it prints "Hello [who-to-greet]" and then "Goodbye". The action also maps a random number to the random-number output variable, and runs a script named goodbye.sh.

Once you complete this project, you should understand how to build your own composite action and test it in a workflow.

Composite actions and reusable workflows

Composite actions allow you to collect a series of workflow job steps into a single action which you can then run as a single job step in multiple workflows. Reusable workflows provide another way of avoiding duplication, by allowing you to run a complete workflow from within other workflows. For more information, see Avoiding duplication.

Prerequisites

Before you begin, you'll create a repository on GitHub.

1. Create a new public repository on GitHub. You can choose any repository name, or use the following hello-world-composite-action example. You can add these files after your project has been pushed to GitHub. For more information, see Creating a new repository.

2. Clone your repository to your computer. For more information, see Cloning a repository.

3. From your terminal, change directories into your new repository.

   Shell

   cd hello-world-composite-action
   

4. In the hello-world-composite-action repository, create a new file called goodbye.sh with example code:

   Shell

   echo "echo Goodbye" > goodbye.sh
   

5. From your terminal, make goodbye.sh executable.

   Shell

   chmod +x goodbye.sh
   

   Shell

   chmod +x goodbye.sh
   

   Shell

   git add --chmod=+x -- goodbye.sh
   

6. From your terminal, check in your goodbye.sh file.

   Shell

   git add goodbye.sh
   git commit -m "Add goodbye script"
   git push
   

   Shell

   git add goodbye.sh
   git commit -m "Add goodbye script"
   git push
   

   Shell

   git commit -m "Add goodbye script"
   git push
   

Creating an action metadata file

1. In the hello-world-composite-action repository, create a new file called action.yml and add the following example code. For more information about this syntax, see Metadata syntax for GitHub Actions.

   YAML

   name: 'Hello World'
   description: 'Greet someone'
   inputs:
     who-to-greet:  # id of input
       description: 'Who to greet'
       required: true
       default: 'World'
   outputs:
     random-number:
       description: "Random number"
       value: ${{ steps.random-number-generator.outputs.random-number }}
   runs:
     using: "composite"
     steps:
       - name: Set Greeting
         run: echo "Hello $INPUT_WHO_TO_GREET."
         shell: bash
         env:
           INPUT_WHO_TO_GREET: ${{ inputs.who-to-greet }}
   
       - name: Random Number Generator
         id: random-number-generator
         run: echo "random-number=$(echo $RANDOM)" >> $GITHUB_OUTPUT
         shell: bash
   
       - name: Set GitHub Path
         run: echo "$GITHUB_ACTION_PATH" >> $GITHUB_PATH
         shell: bash
         env:
           GITHUB_ACTION_PATH: ${{ github.action_path }}
   
       - name: Run goodbye.sh
         run: goodbye.sh
         shell: bash
   
   

   This file defines the who-to-greet input, maps the random generated number to the random-number output variable, adds the action's path to the runner system path (to locate the goodbye.sh script during execution), and runs the goodbye.sh script.

   For more information about managing outputs, see Metadata syntax for GitHub Actions.

   For more information about how to use github.action_path, see Accessing contextual information about workflow runs.

2. From your terminal, check in your action.yml file.

   Shell

   git add action.yml
   git commit -m "Add action"
   git push
   

3. From your terminal, add a tag. This example uses a tag called v1. For more information, see About custom actions.

   Shell

   git tag -a -m "Description of this release" v1
   git push --follow-tags
   

Testing out your action in a workflow

The following workflow code uses the completed hello world action that you made in Creating a composite action.

Copy the workflow code into a .github/workflows/main.yml file in another repository, replacing OWNER and SHA with the repository owner and the SHA of the commit you want to use, respectively. You can also replace the who-to-greet input with your name.

on: [push]

jobs:
  hello_world_job:
    runs-on: ubuntu-latest
    name: A job to say hello
    steps:
      - uses: actions/checkout@v4
      - id: foo
        uses: OWNER/hello-world-composite-action@SHA
        with:
          who-to-greet: 'Mona the Octocat'
      - run: echo random-number "$RANDOM_NUMBER"
        shell: bash
        env:
          RANDOM_NUMBER: ${{ steps.foo.outputs.random-number }}

on: [push]

jobs:
  hello_world_job:
    runs-on: ubuntu-latest
    name: A job to say hello
    steps:
      - uses: actions/checkout@v4
      - id: foo
        uses: OWNER/hello-world-composite-action@SHA
        with:
          who-to-greet: 'Mona the Octocat'
      - run: echo random-number "$RANDOM_NUMBER"
        shell: bash
        env:
          RANDOM_NUMBER: ${{ steps.foo.outputs.random-number }}

From your repository, click the Actions tab, and select the latest workflow run. The output should include: "Hello Mona the Octocat", the result of the "Goodbye" script, and a random number.

Example composite actions on GitHub

You can find many examples of composite actions on GitHub.

• microsoft/action-python
• microsoft/gpt-review
• tailscale/github-action