NDesk.Options - detect invalid arguments

Question

I am using NDesk.Options to parse command line arguments for a C# command line program. It is working fine, except I want my program to exit unsuccessfully, and show the help output, if the user includes arguments that I did not expect.

I am parsing options thusly:

var options = new OptionSet {
    { "r|reset",  "do a reset", r => _reset = r != null },
    { "f|filter=",  "add a filter", f => _filter = f },
    { "h|?|help",  "show this message and exit",  v => _showHelp = v != null },
};

try
{
    options.Parse(args);
}
catch (OptionException)
{
    _showHelp = true;
    return false;
}
return true;

With this code, if I use an argument improperly, such as specifying --filter without =myfilter after it then NDesk.Options will throw an OptionException and everything will be fine. However, I also expected an OptionException to be thrown if I pass in an argument that doesn't match my list, such as --someOtherArg. But this does not happen. The parser just ignores that and keeps on trucking.

Is there a way to detect unexpected args with NDesk.Options?

Answer 1

The OptionSet.Parse method returns the unrecognized options in a List<string>. You can use that to report unknown options.

try
{
    var unrecognized = options.Parse(args);
    if (unrecognized.Any())
    {
        foreach (var item in unrecognized) 
            Console.WriteLine("unrecognized option: {0}", item);
        _showHelp = true;
        return false;
    }
}
catch (OptionException)
{
    _showHelp = true;
    return false;
}
return true;