container

<?php

// YourCommand.php
use Symfony\Component\DependencyInjection\ContainerInterface;

private $container;

public function __construct(ContainerInterface $container)
{
    parent::__construct();
    $this->container = $container;
}

protected function execute(InputInterface $input, OutputInterface $output)
{
    $em = $this->container->get('doctrine')->getManager();

    // do stuff...
}