codeigniter $_FILES upload

In Codeigniter syntax for normal PHP code $_POST['name'] is $this->input->post('name'). Does anyone knows what is syntax in CI for $_FILES['file']?

I don't want to upload, I want to catch file and make some action before uploading. In upload helper is only this: $this->upload->do_upload('file') - and that is uploading. I want to manage file before this step.

Thanks in advance