If set to true, the user is not prompted and a Yes response is assumed in all cases.`
	filenameFlagHelpStr = `Path to file containing IstioOperator custom resource
This flag can be specified multiple times to overlay multiple files. Multiple files are overlaid in left to right order.`
	installationCompleteStr            = `Installation complete`

	}

	// Allow users to override some variables through $HOME/.istioctl/config.yaml
	// and environment variables.
	viper.SetEnvPrefix("ISTIOCTL")
	viper.AutomaticEnv()
	viper.AllowEmptyEnv(true) // So we can say ISTIOCTL_CERT_DIR="" to suppress certs
	viper.SetConfigName(configName)
	viper.SetConfigType(configType)
	viper.AddConfigPath(configPath)
	viper.SetEnvKeyReplacer(strings.NewReplacer("-", "_"))
	err := viper.ReadInConfig()

	envName := strings.Replace(strings.ToUpper(name), "-", "_", -1)
	// Note: we do not rely on istio env package to retrieve configuration. We relies on viper.
	// This is just to make sure the reference doc tool can generate doc with these vars as env variable at istio.io.
	env.Register(envName, defaultValue, usage)
	bindViper(name)
}

func bindViper(name string) {