This controller checks CodeIgniter 3.0 class filename.
Starting with CodeIgniter 3.0, all class filenames (libraries, drivers, controllers and models) must be named in a Ucfirst-like manner or in other words - they must start with a capital letter. CodeIgniter User Guide
Install controllers/Check.php into your CodeIgniter 3.0 application/controllers folder.
Access to http://your-server/check/filename.
Or you can run via CLI:
$ php index.php check filename
If you want to fix filename:
$ php index.php check filename fix