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.com.

1. Create a new public repository on GitHub.com. 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 " Contexts ".

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, but replace actions/hello-world-composite-action@v1 with the repository and tag you created. 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: actions/hello-world-composite-action@v1
        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:
 actions/hello-world-composite-action@v1

        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.com

You can find many examples of composite actions on GitHub.com.

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