Nested viper and unmarshal into config

main.go

package main

import (
    "fmt"
    "strings"
    viper "github.com/spf13/viper"
)

type Config struct {
    Stripe Stripe
    TestKey string
    DefaultKey string `mapstructure:"default_key"`
}

type Stripe struct {
    SecretKey string `mapstructure:"secret_key"`
}

func main() {
    viper.SetConfigName("config")
    viper.SetConfigType("yaml")
    viper.AddConfigPath(".")
    viper.SetEnvKeyReplacer(strings.NewReplacer(".", "_"))
    viper.AutomaticEnv()
    _ = viper.ReadInConfig()

    viper.BindEnv("DEFAULT_KEY");
    viper.BindEnv("STRIPE.SECRET_KEY");

    var config Config
    _ = viper.Unmarshal(&config)


    fmt.Println("stripe key:",config.Stripe.SecretKey)
    fmt.Println("default key:",config.DefaultKey)
}

// $ STRIPE_SECRET_KEY=test DEFAULT_KEY=123 go run .
// stripe key: test
// default key: 123