oclif-command-type

static args = [
  {
    name: 'file',               // name of arg to show in help and reference with args[name]
    required: false,            // make the arg required with `required: true`
    description: 'output file', // help description
    hidden: true,               // hide this arg from help
    parse: input => 'output',   // instead of the user input, return a different value
    default: 'world',           // default value if no arg input
    options: ['a', 'b'],        // only allow input to be from a discrete set
  }
]