Btukfyl

I am trying to learn monolog and I am following this tutorial: https://stackify.com/php-monolog-tutorial/

It says

First, when you create a logger, channel name should be included, so that you can distinguish your list of loggers.

$logger = new MonologLogger('channel-name');
$app->container->logger = $logger;

In the example above, ‘channel-name’ should be included in every log entry. This way you can easily look up and filter the entries; create another channel for each component. Examples of these channels might include ‘database’, ‘security’, ’business’, and others.

So what exactly are channels and how should I use them?

The "channel" here is not a generic PHP concept, it's just a term that monolog uses for a category of messages which you want to log.

From the monolog usage documentation:

You can create many Loggers, each defining a channel (e.g.: db, request, router, ..) and each of them combining various handlers, which can be shared or not. The channel is reflected in the logs and allows you to easily see or filter records.

Further down that page, there is another section on using channels:

Channels are a great way to identify to which part of the application a record is related. This is useful in big applications (and is leveraged by MonologBundle in Symfony).

Picture two loggers sharing a handler that writes to a single log file. Channels would allow you to identify the logger that issued every record. You can easily grep through the log files filtering this or that channel.

In simple words, you can define a channel as a separate log file.

Generally you might need to classify your log files for different services or modules.

For this purpose, Monolog allows you to create different channels, where each can log separately to different file and allow you to configure your log per channel.

In the line you are referring to

 $logger = new MonologLogger('channel-name'); 

 $app->container->logger = $logger;

You are specifying the channel in the constructor of Monologger.

Anytime you use this $logger object it will be writing to the file you specified when you configured the channel. Below is an example from the Symfony docs for a channel config

https://symfony.com/doc/current/logging/channels_handlers.html#switching-a-channel-to-a-different-handler

   monolog:

      handlers:

          security:

             # log all messages (since debug is the lowest level)

             level:    debug

             type:     stream

             path:     '%kernel.logs_dir%/security.log'

             channels: [security]

In which case you would do that in your code to use the channel

 $logger = new MonologLogger('security');

And then you will be logging to "security.log" with type "stream" errors of level "debug".