// 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))
	}