IO::Select seems like a good choice, but unfortunately it does not work. i.e. if the whois server is unavailable, I get no output.

open my $WHOIS, "jwhois x.x.x.x 2>&1 |";
my $s = IO::Select->new($WHOIS);

while (my @ready = $s->can_read) {
    for my $fh (@ready) {
        if ($fh == $WHOIS) {
            my $buf = <$fh>;
            if ($buf) {
                print $buf;
            }
            else {
               close($fh);
            }
        }
    }
}
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Note that this works great, if the server sends some output and then closes the connection, but not for servers which send some output and then hang.