How to get file size?

[Gilles Ganault <gilles.ganault@...>]

Hello

	I tried the sample at www.lua.org/pil/21.3.html but it fails with
the following error: "attempt to call method 'seek' (a nil value)"

Google didn't return much information on either that error or of other
ways to check the size of a file.

What's the correct way to do this?

Thank you.