HelloCommand.php

<?php
namespace App\Command;

use Cake\Console\Arguments;
use Cake\Console\Command;
use Cake\Console\ConsoleIo;

/**
 * Hello command.
 */
class HelloCommand extends Command
{
    /**
     * Implement this method with your command's logic.
     *
     * @param \Cake\Console\Arguments $args The command arguments.
     * @param \Cake\Console\ConsoleIo $io The console io
     * @return null|int The exit code or null for success
     */
    public function execute(Arguments $args, ConsoleIo $io)
    {
	    $io->out('Hello world.');
    }
}