getopt (forked from rsc.io/getopt)

Note

This repository is a fork of rsc's getopt. I have updated the code in various ways, and I will probably continue to do so. But the core idea (and implementation) is his rather than mine. td;dr — credit where credit is due, but all mistakes and bad ideas are my fault and not rsc's.

Introduction

Package getopt parses command lines using getopt_(3) syntax. It is a replacement for FlagSet.Parse but still expects flags themselves to be defined in package flag.

Flags defined with one-letter names are available as short flags (invoked using one dash, as in -x) and all flags are available as long flags (invoked using two dashes, as in --x or --xylophone).

To use, define a FlagSet and flags as usual with package flag. Then introduce any aliases by calling getopt.Alias:

type cfg struct {
	quiet bool
	verbose  bool
}

func main() {
	fs := getopt.NewFlagSet("awesome", flag.ContinueOnError)
	cfg := &cfg{}

	fs.BoolVar(&cfg.quiet, "quiet", false, "Print only errors")
	fs.BoolVar(&cfg.help, "v", false, "Print way too much")

	getopt.Alias("v", "verbose")
	getopt.Alias("q", "quiet")
}

Or call getopt.Aliases to define a list of aliases:

getopt.Aliases(
	"q", "quiet",
	"v", "verbose",
)

One name in each pair must already be defined in package flag (so either "q" or "quiet", and also either "v" or "verbose").

Then parse the command-line using fs.Parse().

When writing a custom flag.Usage function, call getopt.PrintDefaults instead of flag.PrintDefaults to get a usage message that includes the names of aliases in flag descriptions.