Load Configuration from Environment Variables with Defaults

#!/bin/bash

# --- Configuration Variables ---
# Each variable attempts to read from an environment variable first,
# then falls back to a default value if the environment variable is not set.

# Database Host
# Example: export DB_HOST="prod.database.com"
DB_HOST=${DB_HOST:-"localhost"}

# Database Port
# Example: export DB_PORT="5432"
DB_PORT=${DB_PORT:-"3306"} # Default for MySQL

# Database Name
# Example: export DB_NAME="my_production_db"
DB_NAME=${DB_NAME:-"default_app_db"}

# Application Environment
# Example: export APP_ENV="production"
APP_ENV=${APP_ENV:-"development"}

# API Key (Sensitive - use secure methods in production)
# Example: export MY_API_KEY="super_secret_key"
MY_API_KEY=${MY_API_KEY:-"fallback_api_key_for_dev"}

# Debug Mode
# Example: export DEBUG_MODE="true"
DEBUG_MODE=${DEBUG_MODE:-"false"}


# --- Display Loaded Configuration ---
echo "--- Application Configuration ---"
echo "Database Host: $DB_HOST"
echo "Database Port: $DB_PORT"
echo "Database Name: $DB_NAME"
echo "App Environment: $APP_ENV"
echo "API Key: $([[ "$MY_API_KEY" != "fallback_api_key_for_dev" ]] && echo "********" || echo "Using fallback key")" # Mask sensitive info
echo "Debug Mode: $DEBUG_MODE"
echo "---------------------------------"

# --- Script Logic based on Config ---
if [ "$APP_ENV" = "production" ]; then
    echo "Running in PRODUCTION environment."
    # Add production-specific logic here (e.g., specific logging, disable debug)
    DEBUG_MODE="false" # Ensure debug is off in production
else
    echo "Running in $APP_ENV environment."
    if [ "$DEBUG_MODE" = "true" ]; then
        echo "Debug mode is ON."
    fi
fi

# Example of using a config value
echo "Connecting to database at $DB_HOST:$DB_PORT/$DB_NAME..."
# Placeholder for actual connection logic