Overkill, but........in the event that this is homework ;-), I'll let you figure out what's going on.

 $HelpMessage = "

<date/range/week> =  YYYYMMDD = individual day
                      YYYYMMDD.YYYYMMDD = series of individual days
                      YYYYMMDD-YYYYMMDD = weeklong reporting period
                     -YYYYMMDD = weeklong reporting period
";

################################################################

if (index($PERIODIN,"-") == 0) { $periodlength = "day"; }
else                           { $periodlength = "week"; }
if (!defined $InFileDir) { 
    if ($R_OR_I ne "a" && $R_OR_I ne "b") { 
        if (!(defined $Special)) { $rori = $R_OR_I; }
        else                     { $rori = $R_OR_I . "s"; }
        }
    elsif ($R_OR_I eq "a") {
        if    (defined $AggrExceptions)            { $rori = "ae"; }
        elsif (defined $Config || defined $Report) { $rori = "ap"; }
        else                                       { $rori = "ar"; }
        }
    elsif ($R_OR_I eq "b") { $rori = "b"; }
    $InFileDir = $InFileDirX{$rori,$periodlength};
    }

if (!(-d $InFileDir))
   {die "\n  Directory $InFileDir \n    does not exist\n\n";}


$MonthDay[1] = $MonthDays[3]  = $MonthDays[5]  = $MonthDays[7]=31;
$MonthDays[8] = $MonthDays[10] = $MonthDays[12] = 31;
$MonthDays[4] = $MonthDays[6]  = $MonthDays[9]  = $MonthDays[11]=30;
$MonthDays[2] = 28;

$Leap{1996} = $FakeEndFeb{19960228} = 1;
$Leap{2000} = $FakeEndFeb{20000228} = 1;
$Leap{2004} = $FakeEndFeb{20040228} = 1;
$Leap{2008} = $FakeEndFeb{20080228} = 1;
$Leap{2012} = $FakeEndFeb{20120228} = 1;

if (index($PERIODIN,".") == 0) {
    $numdates = 1;
    if (substr($PERIODIN,1,1) eq "-") {
        $begdate = $enddate = substr($PERIODIN,2);
        for (1..6) {
            $begdate = &getprevday($begdate);
            }
        $date[1] = $begdate . "-" . $enddate;
        }
    else { $date[1] = $PERIODIN; }
    }
else {
    ($begdate, $enddate, @junkjunk) = split(/\./,$PERIODIN);
    $numdates = 1;
    $date[1] = $perd = $begdate;
    while ($perd < $enddate) {
        $numdates++;
        $date[$numdates] = $perd = &getnextday($perd);
        }
    }




sub getnextday {
    local($today) = @_;
    local($nextday);
    $nyr = int($today / 10000);
    $nmo = int(($today - (10000 * $nyr)) / 100);
    $nda = $today - (10000 * $nyr) - (100 * $nmo) + 1;
    if (($nmo != 2 && $nda > $MonthDays[$nmo]) ||
        ($nmo == 2 && (!(defined $Leap{$nyr})) && $nda > 28) ||
        ($nmo == 2 &&   (defined $Leap{$nyr})  && $nda > 29)) {
        $nda = 1; 
        $nmo = $nmo + 1;
        if ($nmo > 12) {
            $nmo = 1;
            $nyr = $nyr + 1
           }
       }
    $nextday = $nyr * 10000 + $nmo * 100 + $nda;
    }

sub getprevday {
    local($today) = @_;
    local($prevday);
    $pyr = int($today / 10000);
    $pmo = int(($today - (10000 * $pyr)) / 100);
    $pda = $today - (10000 * $pyr) - (100 * $pmo) - 1;
    if ($pda == 0) {
        $pmo = $pmo - 1;
        if ($pmo == 0) {
            $pyr = $pyr - 1;
            $pmo = 12;
            }
        if ($pmo != 2)              {$pda = $MonthDays[$pmo];}
        elsif (defined $Leap{$pyr}) {$pda = 29;}
        else                        {$pda = 28;}
        }
    $prevday = $pyr * 10000 + $pmo * 100 + $pda;
    }
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