Defining Independent FlagSets in GoLang

Question

The Go documentation (http://golang.org/pkg/flag/) says:

The FlagSet type allows one to define independent sets of flags, such as to implement subcommands in a command-line interface.

I need this functionality but I can't figure out how to persuade the flag pkg to do it. When I define two FlagSets, parsing one of them will give me errors and warnings if the commandline has flags that are meant for the second one. Example:

f1 := flag.NewFlagSet("f1", flag.ContinueOnError)
apply := f1.Bool("apply", false, "")
silent := f1.Bool("silent", false, "")
if err := f1.Parse(os.Args[1:]); err == nil {
    fmt.Println(*apply, *silent)
}
f2 := flag.NewFlagSet("f2", flag.ContinueOnError)
reset := f2.Bool("reset", false, "")
if err := f2.Parse(os.Args[1:]); err == nil {
    fmt.Println(*reset)
}

I get all sorts of warnings if I try to do cmd -apply OR cmd -reset. I want to keep these FlagSets separate because I want to only have -silent work for -apply.

What am I missing?

Answer 1

You are meant to distinguish between subcommands first, and then call Parse on the right FlagSet.

f1 := flag.NewFlagSet("f1", flag.ContinueOnError)
silent := f1.Bool("silent", false, "")
f2 := flag.NewFlagSet("f2", flag.ContinueOnError)
loud := f2.Bool("loud", false, "")

switch os.Args[1] {
  case "apply":
    if err := f1.Parse(os.Args[2:]); err == nil {
      fmt.Println("apply", *silent)
    }
  case "reset":
    if err := f2.Parse(os.Args[2:]); err == nil {
      fmt.Println("reset", *loud)
    }
}

http://play.golang.org/p/eaEEx_EReX