Adding Environment Variables

One of the more painful things in our introductory example was handling environment variables, and I promised Viper would make this easier.

Viper actually has a feature called AutomaticEnv which will automatically read your configuration keys and look for a standardized environment variable string that matches.

The docs go into more detail about the semantics of working with environment variables, but suffice to say that AutomaticEnv will take a key logLevel and look for the equivalent LOGLEVEL from the environment.

Let's enable AutomaticEnv by adding it to our init() function.

func init() {
	viper.AddConfigPath(".")
	viper.SetConfigName("config")
	viper.SetConfigType("yaml")
	viper.AutomaticEnv()
}

The run your code while overridding the debug value for LOGLEVEL with info.

$ LOGLEVEL=info go run .
The log level is set to: info

However, it's possible (and almost likely) for another application to also expect the LOGLEVEL environment variable, so you can add a prefix to your environment variables to disambiguate them from others.

func init() {
    // ... unchanged ...
	viper.SetEnvPrefix("cp")
	viper.AutomaticEnv()
}

Now our environment variables must have the CP_ prefix, e.g. CP_LOGLEVEL.

$ CP_LOGLEVEL=info go run .
The log level is set to: info
...

Without the prefix, the value is ignored.
$ LOGLEVEL=info go run .
The log level is set to: debug
...