Net::FTP supports the size command so you can get the bytes just from calling size but this only works if remote host supports it so you will probably want to check to see if size is supported. If size is not supported then you would probably want to roll your own at that point. Here is how I do it..

if ($self->supported(size)) {
    my $ret=$self->size($file);
    print "\t$ret bytes transferred\n";
}
else {
    #see earlier example  
}
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