Clarification regarding Command.Arguments property

[kudla]

Hi
Guys please could you clarify the idea behind Command.Arguments property.

Actually my use case is a command with one required positional argument

app command <required-position-argument>

So without Command.Arguments declaration cmd.Args().Get(0) works well. Yet in this case there's no validation performed for argument was provided

With adding

Arguments: []cli.Argument{
  &cli.StringArgument{
       Name: "required-position-argument",
  }
}

it works the very same way (without args number validation)

While trying to extend arg declaration with

  &cli.StringArgument{
       Name: "required-position-argument",
       Min: 1,
       Max: 1,
  }

it actually starts validating against arguments number. Yet the argument value is not accessible neither through cmd.Args().Get(0) nor cmd.String("required-position-argument"). Instead it could be reached over something like cmd.Arguments[0].Values[0]

So as the examples seem not covered such a deep cases it is not clear (for v3 specifically)

• How to make in general the case of one Required argument with a single scalar string value
• What is the purpose of Argument.Name though. Are such argument values could be accessed by name somehow or is it just for help referring matter only
• What is the general case for Command.Arguments declaration

Thank you.

[dearchap]

@kudla The Argument instances should have either a Destination or Values set for example

val dest string
&cli.StringArgument{
       Name: "required-position-argument",
       Min: 1,
       Max: 1,
       Destination: &dest,
  }

val dest []string
&cli.StringArgument{
       Name: "required-position-argument",
       Min: 1,
       Max: 2,
       Values: &dest,
  }

In the first case since you need only a single string positional argument the dest will have the single value. In the second case since you could have 2 values the dest(string slice) can contain both.

[kudla]

Hi @dearchap thanks for the reply.
This pretty clarifies a usage for the cases.
Still another question is there a way to access these arguments from the context or the cmd at the action handler

func (ctx context.Context, cmd *cli.Command) error {
 // how to resolve arguments from here (by name e.g.)
 value := 
 orValues := 
}

And what the purpose for Name any way. I assume there should be the way to refer such args by name some how so? Is there?

Thnx

[bearsh]

@kudla The Argument instances should have either a Destination or Values set for example

To me, this seems quite strange. Both FlagBase and ArgumentBase have a Destination field but only for a Argument it is kind of required?

Wouldn't id be more intuitive and consistent to have a getter method to get this argument values by name?

[dearchap]

Yes we should probably add a getter method for Argument.

[punmechanic]

I've run into this behavior unexpectedly. PoC:

var rootCmd = &cli.Command{
	Name: "prtools",
	Commands: []*cli.Command{
		{
			Name:   "validate",
			Action: validate,
			Arguments: []cli.Argument{
				&cli.StringArg{Name: "filename", Max: -1},
			},
		},
	},
}

func Run(ctx context.Context, args []string) error {
	return rootCmd.Run(context.Background(), os.Args)
}

I expected to be able to access the args using .StringArgs("filename"), as I can with flags:

func validate(ctx context.Context, cmd *cli.Command) error {
	var (
		results []validationResult
		targets = cmd.Args().Slice()
	)

However, not only does an StringArgs("filename") not exist, cmd.Args().Slice() will yield an empty slice if Max is set to -1., which definitely seems like an error. If Max is set to any positive integer, this code will work as expected - but I want Max to be unbounded because I am processing a glob in a shell so I can't reasonably know how many results it'll have ahead of time.

This is confusing behavior when you consider how flags operate. I prefer being able to define my command structure in a tree at the root of the application with all flags, args, etc, so I don't use Destination/Values/global values to be passed to Actions.

[Skeeve]

Correct me if I'm wrong, but didn't you name the string argument "filename", not "name"?

[punmechanic]

Yes, typo; the actual label is immaterial because there's no way to retrieve the value of an argument using a method like this. I've corrected it :)