code: func File() string {
  	f := os.Getenv("CSEARCHINDEX")
  	if f != "" {
  		return f
  	}
  	var home string
  	home = os.Getenv("HOME")
  	if runtime.GOOS == "windows" && home == "" {
  		home = os.Getenv("USERPROFILE")
  	}
  	return filepath.Clean(home + "/.csearchindex")
  }
docs: // File returns the name of the index file to use.
  // It is either $CSEARCHINDEX or $HOME/.csearchindex.