features from POSIX conventions

1. I couldn’t find how to enable support of -tls equivalence to -l -s -t. i.e. grouping of flags after a hyphen.
2. How to specify parsing of [FILE] part in example below? Or should I parse it from args before passing args to CommandLineUtils?

$>ls --help
Usage: ls [OPTION]... [FILE]...
List information about the FILEs (the current directory by default).
Sort entries alphabetically if none of -cftuvSUX nor --sort is specified.

Mandatory arguments to long options are mandatory for short options too.
  -a, --all                  do not ignore entries starting with .
  -A, --almost-all           do not list implied . and ..
      --author               with -l, print the author of each file
  -b, --escape               print C-style escapes for nongraphic characters

So if points above are not possible now, please consider implementing them.

See POSIX Conventions for Command Line Arguments

[natemcmaster]

Implemented in f00244246a3323743440119cabd521c5fae9e00c. You can try nightlies by using this feed: https://www.myget.org/gallery/natemcmaster/. This behavior will be enabled by default in 2.3.0 unless we detect there would be issues due to the app having short options with multiple characters. In 3.0, I’ll make short options with multiple characters an error unless you disable clustering explicitly.

[natemcmaster]

Multi-character short options are not supported in clustered groups. POSIX clustering requires single letter options only. By default (i.e. you haven’t called ParserSettings.ClusterOptions = true), clustering is will be enabled if and only if there are no multi-character short option name. If you’ve explicitly enabled clustering and add a multi-character option, the library with throw an error.

Re: the -v, -vv, -vvv options. CLU will keep track of how many times NoValue options are specified. If you wanted to take advantage of clustering, you could do this instead:

var optVerbose = app.Option("-v", "Set the logging to verbose. Specify `-v` multiple times for even more verbosity", CommandOptionType.NoValue);
app.OnExecute(() => 
{
   var verboseLevel = optVerbose.HasValue()
      ? optVerbose.Values.Count
      : 0;
});