added a hello world command in demo bundle

Author: Tobion

src/Acme/DemoBundle/Command/HelloWorldCommand.php

@@ -0,0 +1,48 @@
+<?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\Output\OutputInterface;
+
+/**
+ * Hello World command for demo purposes.
+ *
+ * You could also extend from Symfony\Bundle\FrameworkBundle\Command\ContainerAwareCommand
+ * to get access to the container via $this->getContainer().
+ *
+ * @author Tobias Schultze <http://tobion.de>
+ */
+class HelloWorldCommand extends Command
+{
+    /**
+     * {@inheritdoc}
+     */
+    protected function configure()
+    {
+        $this
+            ->setName('acme:hello')
+            ->setDescription('Hello World example command')
+            ->addArgument('who', InputArgument::OPTIONAL, 'Who to greet.', 'World')
+            ->setHelp(<<<EOF
+The <info>%command.name%</info> command greets somebody or everybody:
+
+<info>php %command.full_name%</info>
+
+The optional argument specifies who to greet:
+
+<info>php %command.full_name%</info> Fabien
+EOF
+            );
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    protected function execute(InputInterface $input, OutputInterface $output)
+    {
+        $output->writeln(sprintf('Hello <comment>%s</comment>!', $input->getArgument('who')));
+    }
+}