Lab: Create and Use a Composite Action to Print a Message and Timestamp

Introduction

In this lab, you will:

1. Create a composite action that prints a custom message and the current timestamp.
2. Use this composite action in a GitHub Actions workflow.
3. Understand the structure and components of a composite action.

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Step 1: Set Up the Composite Action

Directory Structure

Ensure the following directory structure exists in your repository:

.github/
└── actions/
    └── print-message-and-time-composite-action/
        ├── action.yml

Define the Composite Action (action.yml)

Create the action.yml file in the .github/actions/print-message-and-time-composite-action directory:

name: "Print Message and Time"
description: "Prints a custom message and the current date/time"
author: "Your Name"
inputs:
  message:
    description: "The message to print"
    required: true
    default: "Hello, GitHub Actions!"
outputs:
  timestamp:
    description: "The current date and time"
runs:
  using: "composite"
  steps:
    # Step 1: Print the input message
    - name: Print the message
      run: echo "Message: $"

    # Step 2: Capture and output the current time
    - name: Get current timestamp
      id: current_time
      run: echo "timestamp=$(date)" >> $GITHUB_ENV

    # Step 3: Set the output from the timestamp
    - name: Set action output
      run: echo "timestamp=$"
      shell: bash

Key Features of the Action:

• Inputs: Accepts a message with a default value of "Hello, GitHub Actions!".
• Outputs: Returns the current timestamp (timestamp).
• Environment Variables: Uses $GITHUB_ENV to capture the timestamp for output.

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Step 2: Use the Composite Action in a Workflow

Workflow File: test-composite-action.yml

Create a workflow file in .github/workflows/test-composite-action.yml to use the composite action:

name: Test Composite Action

on:
  push:
    branches:
      - main
  workflow_dispatch:

jobs:
  test-composite-action:
    runs-on: ubuntu-latest
    steps:
      # Step 1: Checkout the repository
      - name: Checkout code
        uses: actions/checkout@v4

      # Step 2: Use the composite action
      - name: Run the custom composite action
        id: composite-action
        uses: ./github/actions/print-message-and-time-composite-action
        with:
          message: "Hello from Composite Action!"

      # Step 3: Access and display the output of the composite action
      - name: Print the timestamp
        run: echo "The timestamp is: $"

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Step 3: Verify and Test

Run the Workflow

1. Commit your changes and push them to the main branch.
2. Navigate to the Actions tab in your GitHub repository.
3. Run the workflow manually using the workflow_dispatch event or trigger it via a push event.

Expected Output

• The composite action should print the custom message (Hello from Composite Action!).
• The timestamp will be captured and displayed in the logs.

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Step 4: Explore the Details

Breakdown of Key Concepts

1. Inputs:
   • Define user-provided values (message) with a default option.
2. Outputs:
   • Use $GITHUB_ENV to capture and expose data across steps.
3. Reusable Workflows:
   • Composite actions simplify workflow reusability by encapsulating multiple steps.
4. No Docker:
   • Composite actions run directly on the runner, avoiding the need for Docker containers.

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Summary

In this lab, you:

• Created a composite action to print a message and timestamp.
• Used the action in a workflow and verified its functionality.
• Gained insight into key components like inputs, outputs, and environment variables.