code: func (dpkg) getPackageVersion(packageName string) (string, error) {
  	output, err := exec.Command("dpkg-query", "--show", "--showformat='${Version}'", packageName).Output()
  	if err != nil {
  		return "", errors.Wrap(err, "dpkg-query failed")
  	}
  	version := extractUpstreamVersion(string(output))
  	if version == "" {
  		return "", errors.New("no version information")
  	}
  	return version, nil
  }
docs: // getPackageVersion returns the upstream package version for the package given
  // the packageName, and an error if no such package exists.