Disclaimer: This example is designed to demonstrate basic concepts of Swift Configuration and is not production-ready code. It lacks comprehensive error handling, testing, and other features required for production use.

Overview

This example demonstrates the fundamental concepts of Swift Configuration through a simple command-line interface that prints a personalized greeting message. The application showcases how to:

• Set up multiple configuration providers in a hierarchy.
• Use environment variables and command-line arguments as configuration sources.
• Read configuration values with type safety and default fallbacks.

What it does

The CLI application reads a greetedName configuration value from multiple sources and prints "Hello, {name}!". The configuration sources are prioritized as follows:

1. Command-line arguments (highest priority)
2. Environment variables (lower priority)
3. Default value ("World" - used when no other source provides the value)

Step-by-step instructions

Step 1: Build the example

Navigate to the example directory and build the executable:

cd Examples/hello-world-cli-example
swift build

Step 2: Run with default value

Run the application without any configuration to see the default behavior:

swift run CLI

Expected output:

Hello, World!

Step 3: Run with environment variable

Set the GREETED_NAME environment variable and run the application:

GREETED_NAME="Swift" swift run CLI

Expected output:

Hello, Swift!

Step 4: Run with command-line argument

Provide the configuration via command-line argument:

swift run CLI --greeted-name "Developer"

Expected output:

Hello, Developer!

Step 5: Demonstrate provider priority

Show how command-line arguments override environment variables by providing both:

GREETED_NAME="EnvValue" swift run CLI --greeted-name "CLIValue"

Expected output:

Hello, CLIValue!

This demonstrates that command-line arguments take precedence over environment variables in the provider hierarchy.