sh := b.BackgroundShell()
	out, err := sh.runOut(".", nil, "swig", "-version")
	if err != nil {
		return err
	}
	re := regexp.MustCompile(`[vV]ersion +(\d+)([.]\d+)?([.]\d+)?`)
	matches := re.FindSubmatch(out)
	if matches == nil {
		// Can't find version number; hope for the best.
		return nil
	}

	major, err := strconv.Atoi(string(matches[1]))
	if err != nil {