dev.go

package main

import (
	"fmt"
	"gopkg.in/alecthomas/kingpin.v2"
)

type DevCommand struct {
	debug bool
}

func (d *DevCommand) run(c *kingpin.ParseContext) error {
	fmt.Println("running dev, debug? ", d.debug)

	return nil
}

func configureDevCommand(app *kingpin.Application) {
	cmd := &DevCommand{}
	d := app.Command("dev", "Runs dev").Action(cmd.run)
	d.Flag("debug", "use debug").BoolVar(&cmd.debug)
}

go.mod

module github.com/bkono/clier

go 1.12

require (
	github.com/alecthomas/template v0.0.0-20160405071501-a0175ee3bccc // indirect
	github.com/alecthomas/units v0.0.0-20151022065526-2efee857e7cf // indirect
	github.com/stretchr/testify v1.3.0 // indirect
	gopkg.in/alecthomas/kingpin.v2 v2.2.6
)

main.go

package main

import (
	"fmt"
	"gopkg.in/alecthomas/kingpin.v2"
	"os"
)

func parseConfig(c *kingpin.ParseContext) error {
	fmt.Printf("parse config with context: %+v\n", c)
	return nil
}

func main() {
	kingpin.HelpFlag.Short('h')
	app := kingpin.New("modular", "My modular application.").Action(parseConfig)
	configureServerCommand(app)
	configureDevCommand(app)
	kingpin.MustParse(app.Parse(os.Args[1:]))
}

server.go

package main

import (
	"fmt"
	"gopkg.in/alecthomas/kingpin.v2"
)

type ServerCommand struct {
	port string
}

func (s *ServerCommand) run(c *kingpin.ParseContext) error {
	fmt.Println("running server on port ", s.port)

	return nil
}

func configureServerCommand(app *kingpin.Application) {
	cmd := &ServerCommand{}
	s := app.Command("server", "Runs a server").Action(cmd.run).Default()
	s.Flag("port", "port to listen on").Short('p').Default("4000").StringVar(&cmd.port)
}