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 gets executed.

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. The code quickly gets verbose or dirty. For example:

use SymfonyComponentConsoleInputInputInterface;
use SymfonyComponentConsoleOutputOutputInterface;

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

    if ($output->getVerbosity() >= OutputInterface::VERBOSITY_VERBOSE) {
        $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:

use SymfonyComponentConsoleInputInputInterface;
use SymfonyComponentConsoleOutputOutputInterface;

protected function execute(InputInterface $input, OutputInterface $output)
{
    // assuming the Command extends ContainerAwareCommand...
    $logger = $this->getContainer()->get('logger');
    $logger->debug('Some info');

    $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 timestamped 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 in the Monolog configuration. This is the default in Symfony Standard Edition 2.4 too.

With the verbosity_levels option you can adapt the mapping between verbosity and log level. In the given example it will also show notices in normal verbosity mode (instead of warnings only). Additionally, it will only use messages logged with the custom my_channel channel and it changes the display style via a custom formatter (see the MonologBundle reference for more information):