Full API Example

Notice: This is a contrived (functioning) example meant strictly for API demonstration purposes. Use of one's imagination is encouraged.

package main

import (


func init() {
    cli.AppHelpTemplate += "\nCUSTOMIZED: you bet ur muffins\n"
    cli.CommandHelpTemplate += "\nYMMV\n"
    cli.SubcommandHelpTemplate += "\nor something\n"

    cli.HelpFlag = &cli.BoolFlag{Name: "halp"}
    cli.VersionFlag = &cli.BoolFlag{Name: "print-version", Aliases: []string{"V"}}

    cli.HelpPrinter = func(w io.Writer, templ string, data interface{}) {
        fmt.Fprintf(w, "best of luck to you\n")
    cli.VersionPrinter = func(cCtx *cli.Context) {
        fmt.Fprintf(cCtx.App.Writer, "version=%s\n", cCtx.App.Version)
    cli.OsExiter = func(cCtx int) {
        fmt.Fprintf(cli.ErrWriter, "refusing to exit %d\n", cCtx)
    cli.ErrWriter = io.Discard
    cli.FlagStringer = func(fl cli.Flag) string {
        return fmt.Sprintf("\t\t%s", fl.Names()[0])

type hexWriter struct{}

func (w *hexWriter) Write(p []byte) (int, error) {
    for _, b := range p {
        fmt.Printf("%x", b)

    return len(p), nil

type genericType struct {
    s string

func (g *genericType) Set(value string) error {
    g.s = value
    return nil

func (g *genericType) String() string {
    return g.s

func main() {
    app := &cli.App{
        Name:     "kənˈtrīv",
        Version:  "v19.99.0",
        Compiled: time.Now(),
        Authors: []*cli.Author{
                Name:  "Example Human",
                Email: "human@example.com",
        Copyright: "(c) 1999 Serious Enterprise",
        HelpName:  "contrive",
        Usage:     "demonstrate available API",
        UsageText: "contrive - demonstrating the available API",
        ArgsUsage: "[args and such]",
        Commands: []*cli.Command{
                Name:        "doo",
                Aliases:     []string{"do"},
                Category:    "motion",
                Usage:       "do the doo",
                UsageText:   "doo - does the dooing",
                Description: "no really, there is a lot of dooing to be done",
                ArgsUsage:   "[arrgh]",
                Flags: []cli.Flag{
                    &cli.BoolFlag{Name: "forever", Aliases: []string{"forevvarr"}},
                Subcommands: []*cli.Command{
                        Name:   "wop",
                        Action: wopAction,
                SkipFlagParsing: false,
                HideHelp:        false,
                Hidden:          false,
                HelpName:        "doo!",
                BashComplete: func(cCtx *cli.Context) {
                    fmt.Fprintf(cCtx.App.Writer, "--better\n")
                Before: func(cCtx *cli.Context) error {
                    fmt.Fprintf(cCtx.App.Writer, "brace for impact\n")
                    return nil
                After: func(cCtx *cli.Context) error {
                    fmt.Fprintf(cCtx.App.Writer, "did we lose anyone?\n")
                    return nil
                Action: func(cCtx *cli.Context) error {
                    fmt.Fprintf(cCtx.App.Writer, "dodododododoodododddooooododododooo\n")
                    if cCtx.Bool("forever") {
                    return nil
                OnUsageError: func(cCtx *cli.Context, err error, isSubcommand bool) error {
                    fmt.Fprintf(cCtx.App.Writer, "for shame\n")
                    return err
        Flags: []cli.Flag{
            &cli.BoolFlag{Name: "fancy"},
            &cli.BoolFlag{Value: true, Name: "fancier"},
            &cli.DurationFlag{Name: "howlong", Aliases: []string{"H"}, Value: time.Second * 3},
            &cli.Float64Flag{Name: "howmuch"},
            &cli.GenericFlag{Name: "wat", Value: &genericType{}},
            &cli.Int64Flag{Name: "longdistance"},
            &cli.Int64SliceFlag{Name: "intervals"},
            &cli.IntFlag{Name: "distance"},
            &cli.IntSliceFlag{Name: "times"},
            &cli.StringFlag{Name: "dance-move", Aliases: []string{"d"}},
            &cli.StringSliceFlag{Name: "names", Aliases: []string{"N"}},
            &cli.UintFlag{Name: "age"},
            &cli.Uint64Flag{Name: "bigage"},
        EnableBashCompletion: true,
        HideHelp:             false,
        HideVersion:          false,
        BashComplete: func(cCtx *cli.Context) {
            fmt.Fprintf(cCtx.App.Writer, "lipstick\nkiss\nme\nlipstick\nringo\n")
        Before: func(cCtx *cli.Context) error {
            fmt.Fprintf(cCtx.App.Writer, "HEEEERE GOES\n")
            return nil
        After: func(cCtx *cli.Context) error {
            fmt.Fprintf(cCtx.App.Writer, "Phew!\n")
            return nil
        CommandNotFound: func(cCtx *cli.Context, command string) {
            fmt.Fprintf(cCtx.App.Writer, "Thar be no %q here.\n", command)
        OnUsageError: func(cCtx *cli.Context, err error, isSubcommand bool) error {
            if isSubcommand {
                return err

            fmt.Fprintf(cCtx.App.Writer, "WRONG: %#v\n", err)
            return nil
        Action: func(cCtx *cli.Context) error {
            cli.HandleExitCoder(errors.New("not an exit coder, though"))
            cli.ShowCommandCompletions(cCtx, "nope")
            cli.ShowCommandHelp(cCtx, "also-nope")

            fmt.Printf("%#v\n", cCtx.App.Command("doo"))
            if cCtx.Bool("infinite") {
                cCtx.App.Run([]string{"app", "doo", "wop"})

            if cCtx.Bool("forevar") {
            fmt.Printf("%#v\n", cCtx.App.VisibleCategories())
            fmt.Printf("%#v\n", cCtx.App.VisibleCommands())
            fmt.Printf("%#v\n", cCtx.App.VisibleFlags())

            fmt.Printf("%#v\n", cCtx.Args().First())
            if cCtx.Args().Len() > 0 {
                fmt.Printf("%#v\n", cCtx.Args().Get(1))
            fmt.Printf("%#v\n", cCtx.Args().Present())
            fmt.Printf("%#v\n", cCtx.Args().Tail())

            set := flag.NewFlagSet("contrive", 0)
            nc := cli.NewContext(cCtx.App, set, cCtx)

            fmt.Printf("%#v\n", nc.Args())
            fmt.Printf("%#v\n", nc.Bool("nope"))
            fmt.Printf("%#v\n", !nc.Bool("nerp"))
            fmt.Printf("%#v\n", nc.Duration("howlong"))
            fmt.Printf("%#v\n", nc.Float64("hay"))
            fmt.Printf("%#v\n", nc.Generic("bloop"))
            fmt.Printf("%#v\n", nc.Int64("bonk"))
            fmt.Printf("%#v\n", nc.Int64Slice("burnks"))
            fmt.Printf("%#v\n", nc.Int("bips"))
            fmt.Printf("%#v\n", nc.IntSlice("blups"))
            fmt.Printf("%#v\n", nc.String("snurt"))
            fmt.Printf("%#v\n", nc.StringSlice("snurkles"))
            fmt.Printf("%#v\n", nc.Uint("flub"))
            fmt.Printf("%#v\n", nc.Uint64("florb"))

            fmt.Printf("%#v\n", nc.FlagNames())
            fmt.Printf("%#v\n", nc.IsSet("wat"))
            fmt.Printf("%#v\n", nc.Set("wat", "nope"))
            fmt.Printf("%#v\n", nc.NArg())
            fmt.Printf("%#v\n", nc.NumFlags())
            fmt.Printf("%#v\n", nc.Lineage()[1])
            nc.Set("wat", "also-nope")

            ec := cli.Exit("ohwell", 86)
            fmt.Fprintf(cCtx.App.Writer, "%d", ec.ExitCode())
            fmt.Printf("made it!\n")
            return ec
        Metadata: map[string]interface{}{
            "layers":          "many",
            "explicable":      false,
            "whatever-values": 19.99,

    if os.Getenv("HEXY") != "" {
        app.Writer = &hexWriter{}
        app.ErrWriter = &hexWriter{}


func wopAction(cCtx *cli.Context) error {
    fmt.Fprintf(cCtx.App.Writer, ":wave: over here, eh\n")
    return nil

Last update: February 1, 2023