TIMTOWTDI ;-)

If your program is driven by an event loop, e.g. Tk, you should use that. If it isn't, you could roll your own using alarm - or ualarm() from Time::HiRes - and use a named pipe ( see mknod(1) or makefifo(1) ) for data transfer.

use IO::File;
use Time::HiRes qw(ualarm);
use strict;

my $interval = 10000; # microseconds
{
    my ($fh, $rout, $rin);
    my $pipe = '/path/to/pipe';

    sub pipe_open {
        $fh  = IO::File->new( $pipe , O_RDONLY | O_NONBLOCK)
                 or die "Can't open $pipe: $!\n";
        $rin = '';
        vec($rin,fileno($fh),1) = 1;
    }
    pipe_open();

    sub alarm_handler {
        # look if there's input at the pipe, non-blocking mode.
        my ($nfound, $timeleft) = select($rout=$rin, undef, undef, -1)
+;
        if ($nfound) {
            print STDERR "data arrived at $pipe.\n";
            while (my $line = <$fh>) { 
                print $line;
            }
            close $fh;
            pipe_open();
        }
        ualarm($interval);
    }
}

# set up signal handler

$SIG{ALRM} = \&alarm_handler;
ualarm($interval);

# main program.

sleep while 1; # the real program certainly does something more intere
+sting
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You control the latency tweaking $interval.