while (my $client = $server->accept()) {
    if (fork() == 0) { # child (Kindprozesse kümmern sich um die einzelnen Clients)
        $client->autoflush(1);
        print $client "Welcome to $0. Please log in.\n";
        while (<$client>) {
            if (...) {} # prüfen was der client schickt...
            elsif (/quit|exit/i) { close $client; last; }
        }
    } # end if fork() == 0
}

my $server = IO::Socket::INET->new(Proto => 'tcp',
                                                        LocalPort => $port,
                                                        Listen => 5,
                                                        Reuse => 1) || die "Socket: $!";

my $select = IO::Select->new($server);

while (my @ready = $select->can_read()) {
    foreach my $handle (@ready) {
        if ($handle == $server) {
            my $newclient = $server->accept();
            $newclient->autoflush();
            $select->add($newclient);
            print $newclient "Hallo, bitte logge dich ein\n";
        }
        else {
            if (defined (my $line = <$handle>)) { # hier steht was der client geschickt hat und dann halt entsprechend reagieren...
            }
        }
    }

}