$pid = open3(\*CHLDIN, \*CHLDOUT, \*CHLDERR, @$cmd);
close(CHLDIN);

##</code><code>##

# timeout handling
{
    local $@ = "";
                                                                   
    eval {
        local $SIG{ALRM} = sub { die("alarm\n") }; # "\n" required
        alarm(3);

        # potentially long operation
        chomp($input = <STDIN>);

        alarm(0);
        1;
    } or do {
        die($@) unless $@ eq "alarm\n";
                                                                   
        # timed out
        warn("No answer for three seconds.\n");
        $input = "";
    }
}