pushHandler(new StreamHandler('logs/app.log', Logger::WARNING)); $log->warning('This is a warning message'); $log->error('This is an error message'); ?>This example shows how to use the Monolog library to log messages to a file. The `Logger` class is used to create a logger instance, which is configured to write only warning and error messages to a file using the `StreamHandler` class. Finally, two messages are logged to the file using the `warning()` and `error()` methods of the logger instance. Package Library: Monolog Library