You're asking where/how $file is being read: If you read the CGI.pm docs, CGI.pm saves the uploaded file to a temp file and returns $file as a filehandle to that temp file. The docs also say that if you use $file as a scalar, it returns the filename of the original file. Which is why you should be able to pull out the filename to $fileName, and then continue to use $file when you read the file, assuming the filehandle is being created and passed correctly.

question, which may or may not be related: are you accessing this subroutine from within the your module or from outside your module? if from within, how are you calling this function? I'm just wondering why you need to pass the object (i.e. my $self=shift;) if you never need $self. Unless, of course, this is the routine you are accessing from outside the module. It's just that I think that perl writing convention recommends that a subroutine with a name that begins with an underscore (i.e. "_file_upload") indicates an internal routine. Just a convention, though, not a rule. But it may confuse people who are used to the convention, plus I'm just trying to make sure you're not unexpectedly chopping off the first parameter you pass to this routine (depending on how you are calling it).

Doesn't answer your question, but I was hoping to help with the insight.