file/find.go
func ContainString(filename, s string) (bool, error) {
	f, err := os.Open(filename)
	if err != nil {
		return false, fmt.Errorf("ContainString: %s", err)
	}
	defer f.Close()

	buf := bufio.NewReader(f)

	for {
		line, err := buf.ReadString('\n')
		if err == io.EOF {
			break
		}
		if strings.Contains(line, s) {
			return true, nil
		}
	}
	return false, nil
}
func ContainString(filename, s string) (bool, error) {
	f, err := os.Open(filename)
	if err != nil {
		return false, fmt.Errorf("ContainString: %s", err)
	}
	defer f.Close()

	buf := bufio.NewReader(f)

	for {
		line, err := buf.ReadString('\n')
		if err == io.EOF {
			break
		}
		if strings.Contains(line, s) {
			return true, nil
		}
	}
	return false, nil
}
// ContainString returns whether the named file contains the string s. The
// return value is a boolean.