How do I make required options?

[koliyo]

I need some "options" to be required. This is different from the provided example in #217

Which does provide an example of an option with a required value, but the option itself is not required.

How do I make a command line "option" required?

By this I mean that if the option is not provided by the user then this is a validation error.

[nils-a]

You could set a default value on the option and then validate that the value is not the default.

But, if the option is not optional, I personally would rather use an argument and denote that as required, by using the angle-bracket-syntax like so:

[CommandArgument(0, "<firstName>")] 
public string FirstName { get; set; }

[koliyo]

For my usecase there is a multiple level nested CLI, and in this context it becomes very confusing with multiple positional arguments as well. Hard to separate command names from the input parameters. Eg compare:

program sub1 sub2 sub3 arg1 arg2 arg3

to

program sub1 sub2 sub3 --foo arg1 --bar arg2 --hej arg3

For rich CLI utilities with many subcommands I think this makes things much clearer. Think about CLI applications similar to awscli

[patriksvensson]

@koliyo Options is by its nature never required (therefore the name). You could add a custom validation step to your command such as:

public sealed class MySettings : CommandSettings
{
    [CommandOption("--foo <VALUE>")]
    public string Foo { get; set; }

    public override ValidationResult Validate()
    {
        if (string.IsNullOrWhiteSpace(Foo))
        {
            return ValidationResult.Error("Foo is required");
        }

        return base.Validate();
    }
}

[koliyo]

Yes, given that it is called CommandOption I can understand the reason to not support making these required.

However, I think it is very useful pattern to have required "options". Maybe these should be called something else in that case, like CommandParameter, or CommandNamedArgument.

To me, these fill the same purpose as named parameters in a function call, compared to only using positional parameters.

I have been able to work around this manually by using a Validate method, but I think it would be useful to have builtin support for. And it is a commonly supported pattern in many CLI environments, eg Python Click

[rhnatiuk]

End of 2024, and it seems there is still no solution for this one... :(

[patriksvensson]

@rhnatiuk There is a solution. This is by design and requires logic in the validstion step. See my answer above.

[lucasshiva]

@rhnatiuk There is a solution. This is by design and requires logic in the validstion step. See my answer above.

I'm a big fan of required options. Having one of the following would be quite nice:

[CommandOption("-f|--foo", Required = true)]
// or
[CommandOption("-f|--foo")]
[Required(true)]

System.CommandLine also supports them:

var searchTermsOption = new Option<string[]>(
    name: "--search-terms",
    description: "Strings to search for when deleting entries.")
    { IsRequired = true, AllowMultipleArgumentsPerToken = true };