Environment variables

Use an env tag when an environment variable should override a file or default value.

type Config struct {
    Port int `yaml:"port" default:"8080" env:"APP_PORT"`
}

With this field, APP_PORT has priority over port in YAML and over default:"8080".

APP_PORT=9090 go run .

Fuda converts the string 9090 into an integer before it stores the value in Port.

Add a prefix

Use WithEnvPrefix when your struct tags should contain short, reusable names.

type Config struct {
    Port int `yaml:"port" default:"8080" env:"PORT"`
}

loader, err := fuda.New().
    FromFile("config.yaml").
    WithEnvPrefix("APP_").
    Build()

Fuda now looks up APP_PORT. It joins the prefix and the env tag exactly, so include the trailing underscore in APP_ when you want one.

Empty values

Fuda treats a set environment variable as an override. For string fields, an empty value overrides a non-empty default. Unset the variable when you want to use the YAML or default value again.

Next step

Validate the final configuration before you start your application.