MyCommand.php

<?php

namespace App\Command;

use Symfony\Component\Console\Command\Command;
use Symfony\Component\Console\Input\InputArgument;
use Symfony\Component\Console\Input\InputInterface;
use Symfony\Component\Console\Input\InputOption;
use Symfony\Component\Console\Output\OutputInterface;
use Symfony\Component\Console\Style\SymfonyStyle;

class MyCommand extends Command
{
    protected static $defaultName = 'MyCommand';

    protected function configure()
    {
        $this
            ->setName('app:mycommand')
            ->setDescription('Add a short description for your command')
            ->addArgument('arg1', InputArgument::OPTIONAL, 'Argument description')
            ->addOption('option1', null, InputOption::VALUE_NONE, 'Option description')
        ;
    }

    protected function execute(InputInterface $input, OutputInterface $output)
    {
        $io = new SymfonyStyle($input, $output);
        $argument = $input->getArgument('arg1');

        if ($input->getOption('option1')) {
            // ...
        }

        $io->success('You have a new command! Now make it your own! Pass --help to see your options.');
    }
}

services.yaml

# Put parameters here that don't need to change on each machine where the app is deployed
# https://symfony.com/doc/current/best_practices/configuration.html#application-related-configuration
parameters:

services:
    # default configuration for services in *this* file
    _defaults:
        autowire: true      # Automatically injects dependencies in your services.
        autoconfigure: true # Automatically registers your services as commands, event subscribers, etc.
        public: false       # Allows optimizing the container by removing unused services; this also means
                            # fetching services directly from the container via $container->get() won't work.
                            # The best practice is to be explicit about your dependencies anyway.

    # makes classes in src/ available to be used as services
    # this creates a service per class whose id is the fully-qualified class name
    App\:
        resource: '../src/*'
        exclude: '../src/{Entity,Migrations,Tests}'

    # controllers are imported separately to make sure services can be injected
    # as action arguments even if you don't extend any base controller class
    App\Controller\:
        resource: '../src/Controller'
        tags: ['controller.service_arguments']

    # add more service definitions when explicit configuration is needed
    # please note that last definitions always *replace* previous ones