#!/usr/bin/perl
use strict ;
use warnings ;
use CGI ;
use Net::FTP;

my $cgi = CGI->new();

...

my $file_name = $cgi->param( 'doc' ) || '';
$cgi->upload( 'doc_upload' );

# Can I alter where the file is temporally written here?
my $tmp_file = $cgi->tmpFileName( $file_name );