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Version Flag

The default version flag (-v/--version) is defined as cli.VersionFlag, which is checked by the cli internals in order to print the App.Version via cli.VersionPrinter and break execution.

Customization

The default flag may be customized to something other than -v/--version by setting cli.VersionFlag, e.g.:

package main

import (
  "log"
  "os"

  "github.com/urfave/cli"
)

func main() {
  cli.VersionFlag = cli.BoolFlag{
    Name: "print-version, V",
    Usage: "print only the version",
  }

  app := cli.NewApp()
  app.Name = "partay"
  app.Version = "19.99.0"
  err := app.Run(os.Args)
  if err != nil {
    log.Fatal(err)
  }
}

Alternatively, the version printer at cli.VersionPrinter may be overridden, e.g.:

package main

import (
  "fmt"
  "log"
  "os"

  "github.com/urfave/cli"
)

var (
  Revision = "fafafaf"
)

func main() {
  cli.VersionPrinter = func(c *cli.Context) {
    fmt.Printf("version=%s revision=%s\n", c.App.Version, Revision)
  }

  app := cli.NewApp()
  app.Name = "partay"
  app.Version = "19.99.0"
  err := app.Run(os.Args)
  if err != nil {
    log.Fatal(err)
  }
}

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 (
  "errors"
  "flag"
  "fmt"
  "io"
  "os"
  "time"

  "github.com/urfave/cli"
)

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.BashCompletionFlag = cli.BoolFlag{Name: "compgen", Hidden: true}
  cli.VersionFlag = cli.BoolFlag{Name: "print-version, V"}

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

type hexWriter struct{}

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

  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.NewApp()
  app.Name = "kənˈtrīv"
  app.Version = "19.99.0"
  app.Compiled = time.Now()
  app.Authors = []cli.Author{
    cli.Author{
      Name:  "Example Human",
      Email: "human@example.com",
    },
  }
  app.Copyright = "(c) 1999 Serious Enterprise"
  app.HelpName = "contrive"
  app.Usage = "demonstrate available API"
  app.UsageText = "contrive - demonstrating the available API"
  app.ArgsUsage = "[args and such]"
  app.Commands = []cli.Command{
    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, forevvarr"},
      },
      Subcommands: cli.Commands{
        cli.Command{
          Name:   "wop",
          Action: wopAction,
        },
      },
      SkipFlagParsing: false,
      HideHelp:        false,
      Hidden:          false,
      HelpName:        "doo!",
      BashComplete: func(c *cli.Context) {
        fmt.Fprintf(c.App.Writer, "--better\n")
      },
      Before: func(c *cli.Context) error {
        fmt.Fprintf(c.App.Writer, "brace for impact\n")
        return nil
      },
      After: func(c *cli.Context) error {
        fmt.Fprintf(c.App.Writer, "did we lose anyone?\n")
        return nil
      },
      Action: func(c *cli.Context) error {
        c.Command.FullName()
        c.Command.HasName("wop")
        c.Command.Names()
        c.Command.VisibleFlags()
        fmt.Fprintf(c.App.Writer, "dodododododoodododddooooododododooo\n")
        if c.Bool("forever") {
          c.Command.Run(c)
        }
        return nil
      },
      OnUsageError: func(c *cli.Context, err error, isSubcommand bool) error {
        fmt.Fprintf(c.App.Writer, "for shame\n")
        return err
      },
    },
  }
  app.Flags = []cli.Flag{
    cli.BoolFlag{Name: "fancy"},
    cli.BoolTFlag{Name: "fancier"},
    cli.DurationFlag{Name: "howlong, 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, d"},
    cli.StringSliceFlag{Name: "names, N"},
    cli.UintFlag{Name: "age"},
    cli.Uint64Flag{Name: "bigage"},
  }
  app.EnableBashCompletion = true
  app.UseShortOptionHandling = true
  app.HideHelp = false
  app.HideVersion = false
  app.BashComplete = func(c *cli.Context) {
    fmt.Fprintf(c.App.Writer, "lipstick\nkiss\nme\nlipstick\nringo\n")
  }
  app.Before = func(c *cli.Context) error {
    fmt.Fprintf(c.App.Writer, "HEEEERE GOES\n")
    return nil
  }
  app.After = func(c *cli.Context) error {
    fmt.Fprintf(c.App.Writer, "Phew!\n")
    return nil
  }
  app.CommandNotFound = func(c *cli.Context, command string) {
    fmt.Fprintf(c.App.Writer, "Thar be no %q here.\n", command)
  }
  app.OnUsageError = func(c *cli.Context, err error, isSubcommand bool) error {
    if isSubcommand {
      return err
    }

    fmt.Fprintf(c.App.Writer, "WRONG: %#v\n", err)
    return nil
  }
  app.Action = func(c *cli.Context) error {
    cli.DefaultAppComplete(c)
    cli.HandleExitCoder(errors.New("not an exit coder, though"))
    cli.ShowAppHelp(c)
    cli.ShowCommandCompletions(c, "nope")
    cli.ShowCommandHelp(c, "also-nope")
    cli.ShowCompletions(c)
    cli.ShowSubcommandHelp(c)
    cli.ShowVersion(c)

    categories := c.App.Categories()
    categories.AddCommand("sounds", cli.Command{
      Name: "bloop",
    })

    for _, category := range c.App.Categories() {
      fmt.Fprintf(c.App.Writer, "%s\n", category.Name)
      fmt.Fprintf(c.App.Writer, "%#v\n", category.Commands)
      fmt.Fprintf(c.App.Writer, "%#v\n", category.VisibleCommands())
    }

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

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

    fmt.Printf("%#v\n", c.Args().First())
    if len(c.Args()) > 0 {
      fmt.Printf("%#v\n", c.Args()[1])
    }
    fmt.Printf("%#v\n", c.Args().Present())
    fmt.Printf("%#v\n", c.Args().Tail())

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

    fmt.Printf("%#v\n", nc.Args())
    fmt.Printf("%#v\n", nc.Bool("nope"))
    fmt.Printf("%#v\n", nc.BoolT("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.GlobalBool("global-nope"))
    fmt.Printf("%#v\n", nc.GlobalBoolT("global-nerp"))
    fmt.Printf("%#v\n", nc.GlobalDuration("global-howlong"))
    fmt.Printf("%#v\n", nc.GlobalFloat64("global-hay"))
    fmt.Printf("%#v\n", nc.GlobalGeneric("global-bloop"))
    fmt.Printf("%#v\n", nc.GlobalInt("global-bips"))
    fmt.Printf("%#v\n", nc.GlobalIntSlice("global-blups"))
    fmt.Printf("%#v\n", nc.GlobalString("global-snurt"))
    fmt.Printf("%#v\n", nc.GlobalStringSlice("global-snurkles"))

    fmt.Printf("%#v\n", nc.FlagNames())
    fmt.Printf("%#v\n", nc.GlobalFlagNames())
    fmt.Printf("%#v\n", nc.GlobalIsSet("wat"))
    fmt.Printf("%#v\n", nc.GlobalSet("wat", "nope"))
    fmt.Printf("%#v\n", nc.NArg())
    fmt.Printf("%#v\n", nc.NumFlags())
    fmt.Printf("%#v\n", nc.Parent())

    nc.Set("wat", "also-nope")

    ec := cli.NewExitError("ohwell", 86)
    fmt.Fprintf(c.App.Writer, "%d", ec.ExitCode())
    fmt.Printf("made it!\n")
    return nil
  }

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

  app.Metadata = map[string]interface{}{
    "layers":     "many",
    "explicable": false,
    "whatever-values": 19.99,
  }


  // ignore error so we don't exit non-zero and break gfmrun README example tests
  _ = app.Run(os.Args)
}

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

Last update: February 1, 2023