#!/usr/bin/perl -w

use strict;
use Calendar::Simple qw(calendar);
use POSIX qw(strftime);

my $today = strftime '%Y-%m-%d', localtime;
my ($year, $month) = split /-/, shift || $today;

printf "\n%04d-%02d\n\n", $year, $month;
print "Mon Tue Wed Thu Fri Sat Sun\n";

for (calendar $month, $year, 1) {
    for (@$_) {
        no warnings;
        $_ = sprintf '%3s', $_ || '';
    }
    print "@$_\n";
}
print "\n";