can't read system environment when use Unmarshal function

[lishimeng]

I want to read some value from system environment, ~ to a struct. Like this:

type Conf struct {
    OS string `mapstructure:"os"`
}
	var err error
	var c = new(Conf)
	viper.AutomaticEnv()
	err = viper.Unmarshal(&c)
	if err != nil {
		t.Fatal(err)
	}
	fmt.Println("OS: ", c.OS)

	err = viper.UnmarshalKey("os", &c)
	fmt.Println("OS: ", c.OS)
	err = viper.UnmarshalExact(&c)
	fmt.Println("OS: ", c.OS)
	os := viper.Get("os")
	fmt.Println("OS: ", os)

output:

OS:  
OS:  
OS:  
OS:  Windows_NT

(⊙o⊙)…

[github-actions]

👋 Thanks for reporting!

A maintainer will take a look at your issue shortly. 👀

In the meantime: We are working on Viper v2 and we would love to hear your thoughts about what you like or don't like about Viper, so we can improve or fix those issues.

⏰ If you have a couple minutes, please take some time and share your thoughts: https://forms.gle/R6faU74qPRPAzchZ9

📣 If you've already given us your feedback, you can still help by spreading the news,
either by sharing the above link or telling people about this on Twitter:

https://twitter.com/sagikazarmark/status/1306904078967074816

Thank you! ❤️

[sagikazarmark]

Duplicate #761

Please see the workarounds listed there.