$gotit = $PortObj->streamline;        # poll until data ready
$gotit = $PortObj->streamline($count);# block until $count chars received
    # fast alternatives to lookfor with no character processing

##</code><code>##

at the top of your code, put: $|=1: # turns off buffering for print()
sub Receive3
{
    my $gotit = $ob->streamline;
    die "got undef from streamline! $!" if (!defined ($gotit));
    return if ($gotit eq "");  # nothing to do - no chars received
    print "$gotit";            # blocking call, but "fast enough"
                               # actual code would do something with $gotit
                               # put it in a buffer and decide if it is enough for
                               # a complete command or whatever...
}