commands

how can i do /hi <player> and send the message to the player given?

 

PHP:

public function onCommand(CommandSender $sender, Command $cmd, $label, array $args)
{
    if($cmd->getName() === "hi") // checks that the command is /hi
    {
        if(isset($args[0])) // check that <player> was given
        {
            $sendTo = $this->getServer()->getPlayer($args[0])
            if($sendTo !== null && $sendTo->isOnline()) // check that the given player is online
            {
                $sendTo->sendMessage("your message goes here")
            } else
            {
                $sender->sendMessage(TextFormat::WHITE. $args[0] .TextFormat::RED." is not online!")
            }
        } else
        {
            $sender->sendMessage(TextFormat::RED."Please specify a player!")
        }
    }
}

In the future, please show what you've tried to do, because it won't help you if we just give you code and you don't try