}
		exe = fields[0]
		if !strings.ContainsAny(exe, `/\`) {
			if lp, err := cfg.LookPath(exe); err == nil {
				exe = lp
			}
		}
		id, err = buildid.ReadFile(exe)
		if err != nil {
			return "", "", err
		}

		// If we can't find a build ID, use a hash.
		if id == "" {
			id = b.fileHash(exe)
		}
	}

	b.id.Lock()
	b.toolIDCache[key] = id

	flag.Usage = usage
	flag.Parse()
	telemetry.Inc("buildid/invocations")
	telemetry.CountFlags("buildid/flag:", *flag.CommandLine)
	if flag.NArg() != 1 {
		usage()
	}

	file := flag.Arg(0)
	id, err := buildid.ReadFile(file)
	if err != nil {
		log.Fatal(err)
	}
	if !*wflag {
		fmt.Printf("%s\n", id)
		return
	}

	// Keep in sync with src/cmd/go/internal/work/buildid.go:updateBuildID

	f, err := os.Open(file)