env

A library for loading environment variables

Loading configuration from environment variables with os.Getenv can get tedious. This package provides an interface to specify expected environment variables and takes care of loading the values and producing good error messages if a variable is missing or has the wrong format. It can also generate documentation and it has a way to define groups of variables with a common prefix.

Usage

You first create an env.Env and call its methods to set expected environment variables:

var config struct{
	name    string
	port    int
	verbose bool
}
e := env.New()
e.String("NAME", &config.name, "a short name for the service")
e.OptionalInt("PORT", &config.port, 8080, "the port number to listen on (default: 8080)")
e.Bool("VERBOSE", &config.verbose, "produce verbose error messages")

Then, Load actually loads the variables:

err := e.Load()
if err != nil {
	fmt.Printf("error: %s", err)
}

The Help method produces documentation in this format:

NAME -- a short name for the service
PORT -- the port number to listen on
VERBOSE -- produce verbose error messages

The FromMap function let you hard-code an environment, which can be useful for testing.

Finally, the Prefix method lets you define a set of variables with a common prefix. It returns a new Env instance that can be passed around, so you can move the configuration code closer to where the configuration is needed.