}

	newID := id[:strings.LastIndex(id, "/")] + "/" + buildid.HashToString(hash)
	if len(newID) != len(id) {
		log.Fatalf("%s: build ID length mismatch %q vs %q", file, id, newID)
	}

	if len(matches) == 0 {
		return
	}

	f, err = os.OpenFile(file, os.O_RDWR, 0)
	if err != nil {
		log.Fatal(err)
	}
	if err := buildid.Rewrite(f, matches, newID); err != nil {
		log.Fatal(err)
	}