Verbs

Verbs help delineate and separate options and values for multiple commands within a single app.

A common usage of verbs in a sample ftp program could be to provide a specific commands: upload, download, delete, etc.

A well known example of using verbs is the git version control system with multiple verbs: add, commit, push, pull, merge, etc.

To use verb commands create an option class for each verb decorated with the [Verb] attribute:

[Verb("add", HelpText = "Add file contents to the index.")]
class AddOptions { //normal options here
}
[Verb("commit", HelpText = "Record changes to the repository.")]
class CommitOptions { //normal options here
}
[Verb("clone", HelpText = "Clone a repository into a new directory.")]
class CloneOptions { //normal options here
}

A this point you have to use a proper ParserArguments<T1, T2...> overload that accepts more than one type (without using the overload with variadic arguments, the library defines versions with up to 16 type parameters):

static int Main(string[] args) {
    var result = Parser.Default.ParseArguments<AddOptions, CommitOptions, CloneOptions>(args);
}

In this case the T Value property of ParserResult<T> will be object but will contain the proper instance if parsing succeeds or NullInstance if fails.

The only change with normal parsing is the requirement to query the Parsed<object>.Value property and invoke the application logic written to handle a specific verb.

A helper extension method is provided to simplify this task:

static int Main(string[] args) {
    Parser.Default.ParseArguments<AddOptions, CommitOptions, CloneOptions>(args)
    .WithParsed<AddOptions>(opts => ...)
    .WithParsed<CommitOptions>(opts => ...)
    .WithParsed<CloneOptions>(opts => ...)
    .WithNotParsed(errs => ...)
}

Coherently with ParseArguments<T1, T2, ...>() overloads used for verbs, you can take advantage also of MapResult<T1, T2, ...>(). Like in the sample with a single target instance, here we turn the parsed verb into an exit code:

static int Main(string[] args) {
  return Parser.Default.ParseArguments<AddOptions, CommitOptions, CloneOptions>(args)
    .MapResult(
      (AddOptions opts) => RunAddAndReturnExitCode(opts),
      (CommitOptions opts) => RunCommitAndReturnExitCode(opts),
      (CloneOptions opts) => RunCloneAndReturnExitCode(opts),
      errs => 1);
}

In this scenario the parser supplies you an additional help verb that allows:

C:\> app help clone

In this way application users can display specific verb command help screen.

C:\> app help

Or will display a help screen for available verbs.