Format Go Flag Into Human Readable Output

go_flag_usage.go

flag.Usage = func() {
	w := tabwriter.NewWriter(os.Stdout, 0, 0, 2, ' ', 0)
	fmt.Fprintf(w, "%v [FLAGS]\n", os.Args[0])
	fmt.Fprintln(w, "Flag\tDefault\tDescription")
	nl, dl, ul := 4, 7, 11
	out := ""
	flag.VisitAll(func(f *flag.Flag) {
		out += fmt.Sprintf("-%s\t%s\t%s\n", f.Name, f.DefValue, f.Usage)
		if len(f.Name)+1 > nl {
			nl = len(f.Name) + 1
		}
		if len(f.DefValue) > dl {
			dl = len(f.DefValue)
		}
		if len(f.Usage) > ul {
			ul = len(f.Usage)
		}
	})
	fmt.Fprintf(w, "%v\t%v\t%v\n", strings.Repeat("-", nl), strings.Repeat("-", dl), strings.Repeat("-", ul))
	fmt.Fprintln(w, out)
	w.Flush()
}