[development] How do I send a file to the user?

[Ernst Plüss]

Hi

I want to do the following: The users fills out a form and depending
on that data an excel export is generated. The user should be prompted
to store/open the file.

The code to create the excel data is working fine.

But I don't know how to do the file sending stuff?
Is hook_file_download the right way to go? If yes, after I have the
excel file content stored in a variable how does it get to the
implementation of hook_file_download?

TIA
Ernst