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