The Console Component in Symfony - symfony

Question

I want to run a task using console. I checked http://symfony.com/doc/2.0/components/console/introduction.html
It asks to create GreetCommand.php.
namespace Acme\DemoBundle\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;
class GreetCommand extends Command
{
protected function configure()
{
$this
->setName('demo:greet')
->setDescription('Greet someone')
->addArgument(
'name',
InputArgument::OPTIONAL,
'Who do you want to greet?'
)
->addOption(
'yell',
null,
InputOption::VALUE_NONE,
'If set, the task will yell in uppercase letters'
)
;
}
protected function execute(InputInterface $input, OutputInterface $output)
{
$name = $input->getArgument('name');
if ($name) {
$text = 'Hello '.$name;
} else {
$text = 'Hello';
}
if ($input->getOption('yell')) {
$text = strtoupper($text);
}
$output->writeln($text);
}
}
and create another file to run the command as given below.
#!/usr/bin/env php
# app/console
<?php
use Acme\DemoBundle\Command\GreetCommand;
use Symfony\Component\Console\Application;
$application = new Application();
$application->add(new GreetCommand);
$application->run();
But the command to run it is like app/console demo:greet Fool
The thing I won't understand is that why we need to create the second file?
Sometimes, I feel Symfony is the most difficult framework to learn.

Answer 1

In first file you have defined your Command class.
Second file is needed to register/initialize instance of that command. You just tell there that your application will have GreetCommand with name "demo:greet" (name defined in command itself).
BTW When you use full-stack Symfony2 with FrameworkBundle you do not have to create second file (if we follow Symfony2 conventions) cause Command is registered automatically by FrameworkBundle Console Application using HttpKernel component