Using Events

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The Application class of the Console component allows you to optionally hook into the lifecycle of a console application via events. Instead of reinventing the wheel, it uses the Symfony EventDispatcher component to do the work:

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use Symfony\Component\Console\Application;
use Symfony\Component\EventDispatcher\EventDispatcher;

$dispatcher = new EventDispatcher();

$application = new Application();
$application->setDispatcher($dispatcher);
$application->run();

Warning

Console events are only triggered by the main command being executed. Commands called by the main command will not trigger any event, unless run by the application itself, see How to Call Other Commands.

The ConsoleEvents::COMMAND Event

Typical Purposes: Doing something before any command is run (like logging which command is going to be executed), or displaying something about the event to be executed.

Just before executing any command, the ConsoleEvents::COMMAND event is dispatched. Listeners receive a ConsoleCommandEvent event:

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use Symfony\Component\Console\ConsoleEvents;
use Symfony\Component\Console\Event\ConsoleCommandEvent;

$dispatcher->addListener(ConsoleEvents::COMMAND, function (ConsoleCommandEvent $event): void {
    // gets the input instance
    $input = $event->getInput();

    // gets the output instance
    $output = $event->getOutput();

    // gets the command to be executed
    $command = $event->getCommand();

    // writes something about the command
    $output->writeln(sprintf('Before running command <info>%s</info>', $command->getName()));

    // gets the application
    $application = $command->getApplication();
});

Disable Commands inside Listeners

Using the disableCommand() method, you can disable a command inside a listener. The application will then not execute the command, but instead will return the code 113 (defined in ConsoleCommandEvent::RETURN_CODE_DISABLED). This code is one of the reserved exit codes for console commands that conform with the C/C++ standard:

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use Symfony\Component\Console\ConsoleEvents;
use Symfony\Component\Console\Event\ConsoleCommandEvent;

$dispatcher->addListener(ConsoleEvents::COMMAND, function (ConsoleCommandEvent $event): void {
    // gets the command to be executed
    $command = $event->getCommand();

    // ... check if the command can be executed

    // disables the command, this will result in the command being skipped
    // and code 113 being returned from the Application
    $event->disableCommand();

    // it is possible to enable the command in a later listener
    if (!$event->commandShouldRun()) {
        $event->enableCommand();
    }
});

The ConsoleEvents::ERROR Event

Typical Purposes: Handle exceptions thrown during the execution of a command.

Whenever an exception is thrown by a command, including those triggered from event listeners, the ConsoleEvents::ERROR event is dispatched. A listener can wrap or change the exception or do anything useful before the exception is thrown by the application.

Listeners receive a ConsoleErrorEvent event:

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use Symfony\Component\Console\ConsoleEvents;
use Symfony\Component\Console\Event\ConsoleErrorEvent;

$dispatcher->addListener(ConsoleEvents::ERROR, function (ConsoleErrorEvent $event): void {
    $output = $event->getOutput();

    $command = $event->getCommand();

    $output->writeln(sprintf('Oops, exception thrown while running command <info>%s</info>', $command->getName()));

    // gets the current exit code (the exception code)
    $exitCode = $event->getExitCode();

    // changes the exception to another one
    $event->setError(new \LogicException('Caught exception', $exitCode, $event->getError()));
});

The ConsoleEvents::TERMINATE Event

Typical Purposes: To perform some cleanup actions after the command has been executed.

After the command has been executed, the ConsoleEvents::TERMINATE event is dispatched. It can be used to do any actions that need to be executed for all commands or to cleanup what you initiated in a ConsoleEvents::COMMAND listener (like sending logs, closing a database connection, sending emails, ...). A listener might also change the exit code.

Listeners receive a ConsoleTerminateEvent event:

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use Symfony\Component\Console\ConsoleEvents;
use Symfony\Component\Console\Event\ConsoleTerminateEvent;

$dispatcher->addListener(ConsoleEvents::TERMINATE, function (ConsoleTerminateEvent $event): void {
    // gets the output
    $output = $event->getOutput();

    // gets the command that has been executed
    $command = $event->getCommand();

    // displays the given content
    $output->writeln(sprintf('After running command <info>%s</info>', $command->getName()));

    // changes the exit code
    $event->setExitCode(128);
});

Tip

This event is also dispatched when an exception is thrown by the command. It is then dispatched just after the ConsoleEvents::ERROR event. The exit code received in this case is the exception code.

Additionally, the event is dispatched when the command is being exited on a signal. You can learn more about signals in the the dedicated section.

The ConsoleEvents::SIGNAL Event

Typical Purposes: To perform some actions after the command execution was interrupted.

Signals are asynchronous notifications sent to a process in order to notify it of an event that occurred. For example, when you press Ctrl + C in a command, the operating system sends the SIGINT signal to it.

When a command is interrupted, Symfony dispatches the ConsoleEvents::SIGNAL event. Listen to this event so you can perform some actions (e.g. logging some results, cleaning some temporary files, etc.) before finishing the command execution.

Listeners receive a ConsoleSignalEvent event:

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use Symfony\Component\Console\ConsoleEvents;
use Symfony\Component\Console\Event\ConsoleSignalEvent;

$dispatcher->addListener(ConsoleEvents::SIGNAL, function (ConsoleSignalEvent $event): void {

    // gets the signal number
    $signal = $event->getHandlingSignal();

    // sets the exit code
    $event->setExitCode(0);

    if (\SIGINT === $signal) {
        echo "bye bye!";
    }
});

It is also possible to abort the exit if you want the command to continue its execution even after the event has been dispatched, thanks to the abortExit() method:

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use Symfony\Component\Console\ConsoleEvents;
use Symfony\Component\Console\Event\ConsoleSignalEvent;

$dispatcher->addListener(ConsoleEvents::SIGNAL, function (ConsoleSignalEvent $event) {
    $event->abortExit();
});

Tip

All the available signals (SIGINT, SIGQUIT, etc.) are defined as constants of the PCNTL PHP extension. The extension has to be installed for these constants to be available.

If you use the Console component inside a Symfony application, commands can handle signals themselves. To do so, implement the SignalableCommandInterface and subscribe to one or more signals:

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// src/Command/SomeCommand.php
namespace App\Command;

use Symfony\Component\Console\Command\Command;
use Symfony\Component\Console\Command\SignalableCommandInterface;

class SomeCommand extends Command implements SignalableCommandInterface
{
    // ...

    public function getSubscribedSignals(): array
    {
        // return here any of the constants defined by PCNTL extension
        return [\SIGINT, \SIGTERM];
    }

    public function handleSignal(int $signal): int|false
    {
        if (\SIGINT === $signal) {
            // ...
        }

        // ...

        // return an integer to set the exit code, or
        // false to continue normal execution
        return 0;
    }
}

Symfony doesn't handle any signal received by the command (not even SIGKILL, SIGTERM, etc). This behavior is intended, as it gives you the flexibility to handle all signals e.g. to do some tasks before terminating the command.

Tip

If you need to fetch the signal name from its integer value (e.g. for logging), you can use the getSignalName() method.

This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.
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