What causes "bad exit code: %v (in %q)" in golang/go?

Examine the quoted buffer in the error — it shows exactly what was captured.

bad exit code: %v (in %q)

Error message

bad exit code: %v (in %q)

What it means

Returned by exitCodeFilter.Finish (main.go:286) when the regex matched and captured an exit-code group, but strconv.Atoi failed to parse it as an integer. The captured text was present but not numeric, indicating malformed output from the device.

Source

Thrown at misc/go_android_exec/main.go:286

	b := f.buf.Bytes()
	defer f.buf.Reset()
	match := f.exitRe.FindSubmatch(b)
	if len(match) < 2 || match[1] == nil {
		// Not a full match. Flush.
		if _, err := f.w.Write(b); err != nil {
			return 0, err
		}
		return 0, fmt.Errorf("no exit code (in %q)", string(b))
	}

	// Parse the exit code.
	code, err := strconv.Atoi(string(match[1]))
	if err != nil {
		// Something is malformed. Flush.
		if _, err := f.w.Write(b); err != nil {
			return 0, err
		}
		return 0, fmt.Errorf("bad exit code: %v (in %q)", err, string(b))
	}
	return code, nil
}

// pkgPath determines the package import path of the current working directory,
// and indicates whether it is
// and returns the path to the package source relative to $GOROOT (or $GOPATH).
func pkgPath() (importPath string, isStd bool, modPath, modDir string, err error) {
	errorf := func(format string, args ...any) (string, bool, string, string, error) {
		return "", false, "", "", fmt.Errorf(format, args...)
	}
	goTool, err := goTool()
	if err != nil {
		return errorf("%w", err)
	}
	cmd := exec.Command(goTool, "list", "-e", "-f", "{{.ImportPath}}:{{.Standard}}{{with .Module}}:{{.Path}}:{{.Dir}}{{end}}", ".")
	out, err := cmd.Output()
	if err != nil {

View on GitHub (pinned to b6b368adc5)

Solutions

Examine the quoted buffer in the error — it shows exactly what was captured.
Reduce output interleaving: run with -p 1 (no parallel tests) to see if the marker stabilizes.
Ensure no test prints bytes that mimic the exit-code marker format.
If using a custom runner, make sure it emits the canonical 'exit status <int>' line.

Defensive patterns

Strategy: try-catch

Try / catch

if _, err := run.onDevice(...); err != nil {
    if strings.Contains(err.Error(), "bad exit code") {
        // output interleaving; retry with -p 1
        return rerunSerial()
    }
    return err
}

Prevention

Run tests serially (-p 1) when output interleaving corrupts the exit marker.
Ensure no test prints bytes matching the exit-code marker format.
Use the canonical 'exit status <int>' line in custom runners.

When it happens

Trigger: The exit-code regex matched text that is not a pure integer — e.g., the regex captured trailing characters, or the device/process emitted a non-numeric value where the exit code was expected. Generally points to a corrupted or partially-overwritten marker line.

Common situations: Output interleaving/concurrency garbled the exit marker line; a custom test harness prints text that matches the regex shape but with non-numeric content; terminal control sequences embedded in the captured group.

Related errors

AI-assisted analysis of golang/go@b6b368adc5 (2026-08-12). Data as JSON: /api/errors/2ea612e99c50c60e. Report an issue: GitHub.