src/Silex/Console/EventListener/LoggerListener.php
public function onConsoleCommandException(ConsoleExceptionEvent $event)
    {
        $command = $event->getCommand();
        $command->getApplication()->getContainer()['monolog']->addError(
            sprintf(
                'Command \'%s\' execution finished with an error: \'%s\'',
                $command->getName(), $event->getException()->getMessage()
            )
        );
    }
public function onConsoleCommandException(ConsoleExceptionEvent $event)
    {
        $command = $event->getCommand();
        $command->getApplication()->getContainer()['monolog']->addError(
            sprintf(
                'Command \'%s\' execution finished with an error: \'%s\'',
                $command->getName(), $event->getException()->getMessage()
            )
        );
    }
Fires when an exception throws on command execution scope ($command->run())

@param ConsoleExceptionEvent $event ConsoleExceptionEvent instance

@return void