sub callback {
    my ( $sftp, $data, $offset, $size ) = @_;
    use Math::Pari qw( :DEFAULT PARI pari2num );
    print 'offset is a: ';
    print ref $offset;
    print "\n";
    $offset = pari2num($offset);
    print 'now offset is a: ';
    print ref $offset;
    print "\n";
    print 'size is a: ';
    print ref $size;
    print "\n";
    $size = pari2num($size);
    print 'now size is a: ';
    print ref $size;
    print "\n";
    my $percent = ($offset/$size) * 100;
    print "percent=$percent\n";
    return;
}