Multiple config files with different names

[mxlang]

I have a question about best practices for loading multiple configuration files with different names. First, I want to load a config file at ~/.config/demo/config.yaml and if that file doesn't exist, I want to fall back to ~/.demo.yaml. How can I solve this since I can only assign a name with viper.SetConfigName(“config”) which is loaded

[tamish560]

You can use multiple viper instances for this. Each instance manages its own config file, so you can check if the first file exists and fall back:

v := viper.New()
v.SetConfigName("config")
v.SetConfigType("yaml")
v.AddConfigPath("~/.config/demo")
v.AddConfigPath("~/.")  // fallback path

if err := v.ReadInConfig(); err != nil {
    // handle missing config
}

AddConfigPath searches paths in order, so putting ~/.config/demo first and ~/. second gives you the fallback behavior you want. The first path that contains a file named config.yaml (matching SetConfigName) wins.

If you need two completely different filenames (not just different paths), you'll need two viper instances and merge them:

v1 := viper.New()
v1.SetConfigName("config")
v1.AddConfigPath("~/.config/demo")

v2 := viper.New()
v2.SetConfigName(".demo")
v2.AddConfigPath("~/.")

if err := v1.ReadInConfig(); err != nil {
    if err := v2.ReadInConfig(); err != nil {
        return fmt.Errorf("no config found in either location")
    }
    // use v2
} else {
    // use v1
}

For merging configs from multiple files, viper.MergeConfig() and viper.MergeInConfig() let you layer them.