Calling player from a command

I am wondering how do I make a command that detects or calls a player? Here is an example:
/hey <player>

Sends a hey to the selected player.

PHP:

$this->getServer()->getPlayer($playername)->sendMessage("Hey! :)");


Not really what I was looking for. Thanks tho. I looking into MassiveEconomy and saw you used args to define the player and money with the /pay <player> <amount>.
Could you show me an example command that calls the player? /poke <player>

$args is the array containing all command parameters. Each value of array is split by space.
For example if you run: /example player, $args[0] will be example and $args[1] will be player
Simply replace $playername with $args[1] and you'll get the name of the specified player

this will cause an error if $this->getServer()->getPlayer($playername) is null.
you should do this just to be safe:
if($this->getServer()->getPlayer($playername) instanceof Player){
$this->getServer()->getPlayer($playername)->sendMessage("Hey! ");
}

We don't always call it $args.

Off-topic:
Last time I got too addicted, whenever I use array_shfit() I want to put $args inside it. Since array_shift() accepts the parameter by reference, PhpStorm didn't show a warning. Eventually, it took me quite a while to find out the problem

Yeah. But usually we call the arguments array $args