Config file in Go which uses environment variables and falls back on a default value

config.go

package config

import (
    "os"
)

type GitHubConfig struct {
    Username string
    APIKey   string
}

type Config struct {
    GitHub GitHubConfig
}

// New returns a new Config struct
func New() *Config {
    return &Config{
        GitHub: GitHubConfig{
	    Username: getEnv("GITHUB_USERNAME", ""),
	    APIKey: getEnv("GITHUB_API_KEY", ""),
	},
    }
}

// Simple helper function to read an environment or return a default value
func getEnv(key string, defaultVal string) string {
    if value, exists := os.LookupEnv(key); exists {
	return value
    }

    return defaultVal
}