gabriel-comeau / gogetopt

A Go package to parse command line options compatible with GNU getopt() style options

Gogetopt

A cli option parser for Go

Gogetopt is package which parses CLI options. It attempts to support all of the types and formats of options that getopt() does. This means both --long and -l forms, -lbx combined short options and multiple formats for values attached to options like:

• -l=foo
• --long=foo
• -l foo
• --long foo

The order which the arguments appear in the command line invocation don't matter though if you have a value attached, it needs to follow the appropriate option before another option appears.

To install the package:

go get github.com/gabriel-comeau/gogetopt

Here's a small example program which uses the package. The program prints each argument it gets to its own line. If it gets the allcaps option, the output will be in all caps. If it gets the appendstring option, it will add a space and then the string to each argument. If it gets the help flag, it will print the generated usage text and then quit.

package main

import (
	"fmt"
	"os"
	"strings"

	"github.com/gabriel-comeau/gogetopt"
)

// First register the three options and then run Parse()
func init() {
	var regErr error

	// Boolean opts
	regErr = gogetopt.RegisterOpt("allcaps", "caps", "c", true, false, "Switch output to ANGRY")
	if regErr != nil {
		fmt.Println("Gogetopt option registration error: " + regErr.Error())
		os.Exit(1)
	}

	regErr = gogetopt.RegisterOpt("help", "help", "h", true, false, "Prints help message")
	if regErr != nil {
		fmt.Println("Gogetopt option registration error: " + regErr.Error())
		os.Exit(1)
	}

	// String opts
	regErr = gogetopt.RegisterOpt("appendstring", "append", "a", false, false, "String to be appended to each line of ouput")
	if regErr != nil {
		fmt.Println("Gogetopt option registration error: " + regErr.Error())
		os.Exit(1)
	}

	// Parse the options
	gogetopt.Parse()

	if gogetopt.HasError() {
		printHelpAndDie(gogetopt.GetError())
	}

}

// Now, based on which options came in, run the program
func main() {

	if gogetopt.GetBool("help") {
		printHelpAndDie(nil)
	}

	extraArgs := gogetopt.GetArgs()
	for _, str := range extraArgs {
		out := str

		// gogetopt.GetString("key") returns "" if the option wasn't set
		if gogetopt.GetString("appendstring") != "" {
			out += " " + gogetopt.GetString("appendstring")
		}

		if gogetopt.GetBool("allcaps") {
			out = strings.ToUpper(out)
		}

		fmt.Println(out)
	}
}

func printHelpAndDie(err error) {
	if err != nil {
		fmt.Printf("Error during getopt parse: %v\n", err.Error())
	}
	fmt.Println(gogetopt.GetUsage())
	os.Exit(1)
}

The package is MIT licensed, details can be found in the included "COPYING" file.