Simplified golang implementation of tree - the recursive directory listing program that produces a depth indented listing of files

mytree.go

package main

import (
	"flag"
	"fmt"
	"io"
	"io/ioutil"
	"os"
	"path"
)

type TaskConfig struct {
	DirOnly bool
	Dirname string
	Level int64
	Writer io.Writer
}

func main() {
	dirOnly := flag.Bool("d", false, "List directories only.")
	level := flag.Int64("L", 0, "Max display depth of the directory tree.")
	outfile := flag.String("o", "", "Send output to filename.")
	usageInfo := flag.Bool("h", false, "Prints usage information")

	flag.Usage = func() {
		fmt.Fprintf(os.Stderr, "Usage: %s [options] [<dir>]\nOptions are:\n", os.Args[0])
		flag.PrintDefaults()
	}

	flag.Parse()
	if *usageInfo == true {
		flag.Usage()
		os.Exit(0)
	}
	tc := TaskConfig{
		DirOnly:*dirOnly,
		Level:*level,
	}
	if flag.NArg() == 0 {
		tc.Dirname, _ = os.Getwd()
	} else {
		tc.Dirname = flag.Arg(0)
	}
	if *outfile != "" {
		f, err := os.Create(*outfile)
		check(err)
		defer f.Close()
		tc.Writer = f
	} else {
		tc.Writer = os.Stdout
	}
	tc.nestedList(1, tc.Dirname)
}

func (tc TaskConfig) nestedList(cl int64, cd string) {
	if cl == 1 {
		_, err := fmt.Fprintf(tc.Writer, "%s\n", cd)
		check(err)
	}
	files, err := ioutil.ReadDir(cd)
	check(err)
	for _, f := range files {
		if tc.DirOnly == false || f.IsDir() == true {
			_, err := fmt.Fprintf(tc.Writer, "%s%s\n", spaces(cl*2), f.Name())
			check(err)
		}
		if f.IsDir() && (tc.Level == 0 || tc.Level > cl) {
			tc.nestedList(cl+1, path.Join(cd, f.Name()))
		}
	}
}

func spaces(n int64) string {
	b := make([]byte, n)
	for i := range b {
		b[i] = ' '
	}
	return string(b)
}

func check(err error) {
	if err != nil {
		fmt.Fprintf(os.Stderr, "Error: %v\n", err)
		os.Exit(1)
	}
}