envdecode is a Go package for populating structs from environment variables.

envdecode uses struct tags to map environment variables to fields, allowing you you use any names you want for environment variables. envdecode will recurse into nested structs, including pointers to nested structs, but it will not allocate new pointers to structs.

Full API docs are available on godoc.org.

Define a struct with env struct tags:

type Config struct {
    Hostname  string `env:"SERVER_HOSTNAME,default=localhost"`
    Port      uint16 `env:"SERVER_PORT,default=8080"`

    AWS struct {
        ID        string   `env:"AWS_ACCESS_KEY_ID"`
        Secret    string   `env:"AWS_SECRET_ACCESS_KEY,required"`
        SnsTopics []string `env:"AWS_SNS_TOPICS"`
    }

    Timeout time.Duration `env:"TIMEOUT,default=1m"`
}

Fields must be exported (i.e. begin with a capital letter) in order for envdecode to work with them. An error will be returned if a struct with no exported fields is decoded (including one that contains no env tags at all).

Then call envdecode.Decode:

var cfg Config
err := envdecode.Decode(&cfg)

• Structs (and pointer to structs)
• Slices of below defined types, separated by semicolon
• bool
• float32, float64
• int, int8, int16, int32, int64
• uint, uint8, uint16, uint32, uint64
• string
• time.Duration, using the time.ParseDuration() format
• *url.URL, using url.Parse()