code: func (c GConfig) getStringValue(key string) string {
  	v := c.getValue(key)
  	strV := v.(string)
  	if s.HasPrefix(strV, "${") && s.HasSuffix(strV, "}") {
  		return os.ExpandEnv(strV)
  	}
  
  	return strV
  }
docs: // getStringValue returns a value for a given key as type interface which is converted
  // to actual return type by individual Get* functions.