How do boolean flags work

[ThomasSchoenbeck]

Hi there,

i just tried to follow one of your examples, specifically the "ginger-crouton" example for the bool flag.

what i don't understand is why this example doesn't work for me. I could not find any other documentation on the bool flags, so right now i don't know how to figure out how to design and use bool flags.

Do you have another example or some other documentation at hand?

The code

package main

import (
  "log"
  "os"

  "github.com/urfave/cli"
)

func main() {
  app := cli.NewApp()
  app.Flags = []cli.Flag{
    cli.BoolTFlag{
      Name:  "ginger-crouton",
      Usage: "is it in the soup?",
    },
  }
  app.Action = func(ctx *cli.Context) error {
    if !ctx.Bool("ginger-crouton") {
      return cli.NewExitError("it is not in the soup", 86)
    }
    return nil
  }

  err := app.Run(os.Args)
  if err != nil {
    log.Fatal(err)
  }
}

my tests

[markwylde]

Hi @ThomasSchoenbeck

BoolTFlag is for when you want to use --whatever=true, whereas BoolFlag is for --whatever.

The following works for me:

Using BoolFlag

package main

import (
	"fmt"
	"log"
	"os"

	"github.com/urfave/cli"
)

func main() {
	app := cli.NewApp()
	app.Flags = []cli.Flag{
		cli.BoolFlag{
			Name:  "ginger-crouton",
			Usage: "is it in the soup?",
		},
	}
	app.Action = func(ctx *cli.Context) error {
		if ctx.Bool("ginger-crouton") {
			return cli.NewExitError("it is not in the soup", 86)
		}
		fmt.Println("great, it is in the soup")
		return nil
	}

	err := app.Run(os.Args)
	if err != nil {
		log.Fatal(err)
	}
}

This outputs:

mark@Marks-MacBook-Pro: $ go run testtttt.go
great, it is in the soup
mark@Marks-MacBook-Pro: $ go run testtttt.go --ginger-crouton
it is not in the soup
exit status 86

Using BoolTFlag

package main

import (
	"fmt"
	"log"
	"os"

	"github.com/urfave/cli"
)

func main() {
	app := cli.NewApp()
	app.Flags = []cli.Flag{
		cli.BoolTFlag{
			Name:  "ginger-crouton",
			Usage: "is it in the soup?",
		},
	}
	app.Action = func(ctx *cli.Context) error {
		if ctx.BoolT("ginger-crouton") {
			return cli.NewExitError("it is not in the soup", 86)
		}
		fmt.Println("great, it is in the soup")
		return nil
	}

	err := app.Run(os.Args)
	if err != nil {
		log.Fatal(err)
	}
}

This outputs:

mark@Marks-MacBook-Pro: $ go run testtttt.go
it is not in the soup
exit status 86
mark@Marks-MacBook-Pro: $ go run testtttt.go --ginger-crouton
it is not in the soup
exit status 86
mark@Marks-MacBook-Pro: $ go run testtttt.go --ginger-crouton=true
it is not in the soup
exit status 86
mark@Marks-MacBook-Pro: $ go run testtttt.go --ginger-crouton=false
great, it is in the soup

On a sidenote, if you're wondering why the BoolT defaults to true, have a look at the explanation from @jszwedko here.

👍 I agree it is a bit confusing which is why I believe it's removal in v2 will be an improvement.

It is specified in the godoc for the package (https://godoc.org/github.com/urfave/cli#BoolTFlag), but let me know if you think the documentation there could be improved (or open a PR 😄 ).

Gonna close this out, but thanks for opening this discussion!

[ThomasSchoenbeck]

thanks @markwylde for the help. really appreciate the effort.

Got it to work with the normal bool flag thanks to your example.

[talentlessguy]

I don't know why but here a flag doesn't work:

main.go

app.Commands = []cli.Command{
		{
			Name:   "build",
			Usage:  "Compile Go to WebAssembly",
			Action: CompileToWASM,
			Flags: []cli.Flag{
				cli.BoolFlag{
					Name:  "native",
					Usage: "Compile with native Go compiler",
				},
			},
		},
},

build.go

// ...
func CompileToWASM(c *cli.Context) {

	cmd := exec.Command("tinygo", "build", "-o", "build/out.wasm", "./src")

	if c.Bool("native") {
		cmd = exec.Command("go", "build", "-o", "build/out.wasm", "./src/*.go")
	}