Welcome Plugin, developed for Scriptcraft Minecraft Server Plugin. Perfect example getting commands/options/arguments.

welcome.js

// Welcome Plugin
// 1.0
// Sean Loper
// Displays a message on player join with custom setting to change it to another message.

var VERSION = '1.0';
var COLOR = '\u00A79';
var WELCOME_MSG = 'Welcome To The Server!';

function myPlayerJoinHook( event ){
  var player = event.player;
  echo( player, WELCOME_MSG);
}
events.playerJoin( myPlayerJoinHook );

function myPlayerCommandHook( event ){
	var player = event.player;
	var msg = event.message.substring(1, event.message.length);
	var commands = msg.split(" ");
	if(commands.length > 0)
		var cmd = commands[0].toLowerCase();
	if(commands.length > 1)
		var option = commands[1].toLowerCase();
	if(commands.length > 2)
		var arg = event.message.substring((3 + cmd.length + option.length), event.message.length);
	if(cmd == 'welcome') {
		if(commands.length == 1) {
			echo(player, COLOR + 'Type /Welcome Help. For a list of commands.');
		}
		if(commands.length == 2) {
			if(option == 'version')
  				echo(player, COLOR + 'Version: ' + VERSION);
			if(option == 'help')
  				echo(player, COLOR + 'COMMANDS\n/Welcome Version - Displays the current Version of this Plugin.\n/Welcome Set <Message> - Sets the current message players see when they join.');
		}
  		if(commands.length >= 3)
  		{
  			if(option == 'set') {
  				if(isOp(player)) {
  					WELCOME_MSG = arg;
  					echo(player, COLOR + 'Player Join Message Set.');
  				} else {
  					echo(player, COLOR + 'You must be OP to use this.');
  				}
  			}
  		}
  	}
}
// Canary Version Below, uncomment and comment the one beneath it for Canary.
// events.playerCommand( myPlayerCommandHook );
events.playerCommandPreprocess( myPlayerCommandHook );