$timeout=5;
eval {
    local $SIG{ALRM} = sub { die "alarm\n" }; # NB: \n required
    alarm $timeout;
    $nread = system('F:\perl1.pl');
    alarm 0;
};
if ($@) {
    die unless $@ eq "alarm\n";   # propagate unexpected errors
    print "process terminated\n";}
else {
    # didn't
}