Dates are easy. Either you want to find all the records relative to the current date (next 30 days, for instance), in which case you can just store a timestamp with each record and then check that timestamp against the current timestamp:

my $mtime = time();
if ($rtime < $mtime + 86400 * 30) {
    ## Do whatever processing
}
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Or you want to find all records within an exact date range, in which case you just store the dates in fixed-width, greatest significance first numerical format and test as necessary:

use strict;
use warnings;

my ($sdate, $edate, $rdate);

$sdate = sprintf('%04d%02d%02d', 2006, 11, 4);
$edate = sprintf('%04d%02d%02d', 2006, 12, 4);

while (<DATA>) {
    ($rdate) = m/(\d+)/;
    print if $sdate <= $rdate && $rdate <= $edate;
}

__DATA__
20061203 Record 1
20061204 Record 2
20061206 Record 3
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