### Install PSR Log via Composer

Source: https://github.com/php-fig/log/blob/master/README.md

This command installs the PSR Log package using Composer, the dependency manager for PHP. This is the standard way to include the PSR-3 logger interface in your project.

```bash
composer require psr/log
```

--------------------------------

### Basic Logger Usage with PSR-3 Interface

Source: https://github.com/php-fig/log/blob/master/README.md

Demonstrates how to use the Psr\Log\LoggerInterface in a PHP class. It shows how to inject a logger instance and use it to log informational messages and errors, including exceptions.

```php
<?php

use Psr\Log\LoggerInterface;

class Foo
{
    private $logger;

    public function __construct(LoggerInterface $logger = null)
    {
        $this->logger = $logger;
    }

    public function doSomething()
    {
        if ($this->logger) {
            $this->logger->info('Doing work');
        }
           
        try {
            $this->doSomethingElse();
        } catch (Exception $exception) {
            $this->logger->error('Oh no!', array('exception' => $exception));
        }

        // do something useful
    }
}
```

=== COMPLETE CONTENT === This response contains all available snippets from this library. No additional content exists. Do not make further requests.