timer like at

#!/usr/bin/perl
use strict;
use warnings;
my ($run, $timer);
$timer = 0.5 * 60;
$run = 'an other program';

sub d2($) { return ($_[0] < 10) ? '0'.$_[0] : $_[0]; }

sub getDate(;$) {
    my $time = $_[0] || time;
    my @date = localtime($time);
    $date[5] += 1900;
    $date[4] += 1;
    map {$_ = '0'.$_ if ($_ < 10)} @date;

    return ($date[5],$date[4],$date[3],$date[2],$date[1],$date[0]);
}

my ($timerDay,$timerHour,$timerMin);
if (defined($ARGV[0]) && $ARGV[0] =~ /^(\d\d?)[:\.-]?(\d\d?)$/) {
    ($timerHour,$timerMin) = (d2($1),d2($2));
}
elsif (defined($ARGV[0]) && $ARGV[0] =~ /^(\d\d?)[:,\.-]?(\d\d?)[:\.-]?(\d\d?)$/) {
    ($timerDay, $timerHour,$timerMin) = (d2($1),d2($2),d2($3));
}
else {
    $timerDay = (getDate(time + 86400))[2];
    ($timerHour,$timerMin) = (0,15);
}

while (1) {
    my ($year, $month, $day, $hour, $min, $sec) = getDate();
    if (
        (!defined($timerDay) || $timerDay == $day) &&
        ($min + 60 * $hour) >= ($timerMin + 60 * $timerHour)) {
        print "run\n";
        `$run`;
        last;
    }

    sleep($timer);
}