Using Monolog
=============

Installation
------------

Monolog is available on Packagist ([monolog/monolog](http://packagist.org/packages/monolog/monolog))
and as such installable via [Composer](http://getcomposer.org/).

```bash
php composer.phar require monolog/monolog
```

If you do not use Composer, you can grab the code from GitHub, and use any
PSR-0 compatible autoloader (e.g. the [Symfony2 ClassLoader component](https://github.com/symfony/ClassLoader))
to load Monolog classes.

Configuring a logger
--------------------

Here is a basic setup to log to a file and to firephp on the DEBUG level:

```php
<?php

use Monolog\Logger;
use Monolog\Handler\StreamHandler;
use Monolog\Handler\FirePHPHandler;

// Create the logger
$logger = new Logger('my_logger');
// Now add some handlers
$logger->pushHandler(new StreamHandler(__DIR__.'/my_app.log', Logger::DEBUG));
$logger->pushHandler(new FirePHPHandler());

// You can now use your logger
$logger->addInfo('My logger is now ready');
```

Let's explain it. The first step is to create the logger instance which will
be used in your code. The argument is a channel name, which is useful when
you use several loggers (see below for more details about it).

The logger itself does not know how to handle a record. It delegates it to
some handlers. The code above registers two handlers in the stack to allow
handling records in two different ways.

Note that the FirePHPHandler is called first as it is added on top of the
stack. This allows you to temporarily add a logger with bubbling disabled if
you want to override other configured loggers.

Adding extra data in the records
--------------------------------

Monolog provides two different ways to add extra informations along the simple
textual message.

### Using the logging context

The first way is the context, allowing to pass an array of data along the
record:

```php
<?php

$logger->addInfo('Adding a new user', array('username' => 'Seldaek'));
```

Simple handlers (like the StreamHandler for instance) will simply format
the array to a string but richer handlers can take advantage of the context
(FirePHP is able to display arrays in pretty way for instance).

### Using processors

The second way is to add extra data for all records by using a processor.
Processors can be any callable. They will get the record as parameter and
must return it after having eventually changed the `extra` part of it. Let's
write a processor adding some dummy data in the record:

```php
<?php

$logger->pushProcessor(function ($record) {
    $record['extra']['dummy'] = 'Hello world!';

    return $record;
});
```

Monolog provides some built-in processors that can be used in your project.
Look at the [README file](https://github.com/Seldaek/monolog/blob/master/README.mdown) for the list.

> Tip: processors can also be registered on a specific handler instead of
  the logger to apply only for this handler.

Leveraging 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 Symfony2).

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.

```php
<?php

use Monolog\Logger;
use Monolog\Handler\StreamHandler;
use Monolog\Handler\FirePHPHandler;

// Create some handlers
$stream = new StreamHandler(__DIR__.'/my_app.log', Logger::DEBUG);
$firephp = new FirePHPHandler();

// Create the main logger of the app
$logger = new Logger('my_logger');
$logger->pushHandler($stream);
$logger->pushHandler($firephp);

// Create a logger for the security-related stuff with a different channel
$securityLogger = new Logger('security');
$securityLogger->pushHandler($stream);
$securityLogger->pushHandler($firephp);
```

Customizing log format
----------------------

In Monolog it's easy to customize the format of the logs written into files,
sockets, mails, databases and other handlers. Most of the handlers use the

```php
$record['formatted']
```

value to be automatically put into the log device. This value depends on the
formatter settings. You can choose between predefined formatter classes or
write your own (e.g. a multiline text file for human-readable output).

To configure a predefined formatter class, just set it as the handler's field:

```php
// the default date format is "Y-m-d H:i:s"
$dateFormat = "Y n j, g:i a";
// the default output format is "[%datetime%] %channel%.%level_name%: %message% %context% %extra%\n"
$output = "%datetime% > %level_name% > %message% %context% %extra%\n";
// finally, create a formatter
$formatter = new LineFormatter($output, $dateFormat);

// Create a handler
$stream = new StreamHandler(__DIR__.'/my_app.log', Logger::DEBUG);
$stream->setFormatter($formatter);
// bind it to a logger object
$securityLogger = new Logger('security');
$securityLogger->pushHandler($stream);
```

You may also reuse the same formatter between multiple handlers and share those
handlers between multiple loggers.