How to Configure Monolog to Display Console Messages

It is possible to use the console to print messages for certain verbosity levels using the OutputInterface instance that is passed when a command is run.

When a lot of logging has to happen, it's cumbersome to print information depending on the verbosity settings (-v, -vv, -vvv) because the calls need to be wrapped in conditions. For example:

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use Symfony\Component\Console\Input\InputInterface;
use Symfony\Component\Console\Output\OutputInterface;

protected function execute(InputInterface $input, OutputInterface $output)
{
    if ($output->isDebug()) {
        $output->writeln('Some info');
    }

    if ($output->isVerbose()) {
        $output->writeln('Some more info');
    }
}

Instead of using these semantic methods to test for each of the verbosity levels, the MonologBridge provides a ConsoleHandler that listens to console events and writes log messages to the console output depending on the current log level and the console verbosity.

The example above could then be rewritten as:

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

use Psr\Log\LoggerInterface;
use Symfony\Component\Console\Command\Command;
use Symfony\Component\Console\Input\InputInterface;
use Symfony\Component\Console\Output\OutputInterface;

class YourCommand extends Command
{
    public function __construct(
        private LoggerInterface $logger,
    ) {
    }

    protected function execute(InputInterface $input, OutputInterface $output)
    {
        $this->logger->debug('Some info');
        $this->logger->notice('Some more info');
    }
}

Depending on the verbosity level that the command is run in and the user's configuration (see below), these messages may or may not be displayed to the console. If they are displayed, they are time-stamped and colored appropriately. Additionally, error logs are written to the error output (php://stderr). There is no need to conditionally handle the verbosity settings anymore.

The Monolog console handler is enabled by default:

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# config/packages/dev/monolog.yaml
monolog:
    handlers:
        # ...
        console:
            type:   console
            process_psr_3_messages: false
            channels: ['!event', '!doctrine', '!console']

            # optionally configure the mapping between verbosity levels and log levels
            # verbosity_levels:
            #     VERBOSITY_NORMAL: NOTICE

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<!-- config/packages/dev/monolog.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:monolog="http://symfony.com/schema/dic/monolog"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd">

    <monolog:config>
        <!-- ... -->

        <monolog:handler name="console" type="console" process-psr-3-messages="false">
            <monolog:channels>
                <monolog:channel>!event</monolog:channel>
                <monolog:channel>!doctrine</monolog:channel>
                <monolog:channel>!console</monolog:channel>
            </monolog:channels>
        </monolog:handler>
    </monolog:config>
</container>

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// config/packages/dev/monolog.php
use Symfony\Config\MonologConfig;

return static function (MonologConfig $monolog) {
    $monolog->handler('console')
        ->type('console')
        ->processPsr3Messages(false)
        ->channels()->elements(['!event', '!doctrine', '!console'])
    ;
};

Now, log messages will be shown on the console based on the log levels and verbosity. By default (normal verbosity level), warnings and higher will be shown. But in full verbosity mode, all messages will be shown.