}

func (f *exitCodeFilter) Finish() (int, error) {
	// f.buf could be empty, contain a partial match of exitRe, or
	// contain a full match.
	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))
	}