$SIG{ALRM} = \&timed_out;
eval {
    alarm (10);
    $buf = <>;
    alarm(0);           # Cancel the pending alarm if user responds.
};
if ($@ =~ /GOT TIRED OF WAITING/) {
    print "Timed out. Proceeding with default\n";
    ....
}

sub timed_out {
    die "GOT TIRED OF WAITING";
}