#!/usr/local/bin/perl -w

use Time::Local;

($month, $year, $wday) = (localtime)[4..6];

printf "%11d/%02d\n Su Mo Tu We Th Fr Sa\n", $year + 1900, $month;

$month_data = ' ' x ((localtime timelocal(0,0,0,1,$month,$year,$wday))[6] * 3);

for (1 .. (31, ($year % 100 == 0 && $year % 400 != 0 || $year % 4 != 0)
	? 28 : 29, 31, 30, 31, 30, 31, 31, 30 ,31, 30, 31)[$month])
{
	$month_data .= sprintf(' %2d', $_);
}

print map "$_\n", unpack 'A21' x 5, $month_data;
__END__

#!/usr/local/bin/gawk -f 

BEGIN {
	year  = strftime("%Y");
	month = strftime("%m");

	printf "%11d/%02d\n Su Mo Tu We Th Fr Sa\n", year, month;

	m["02"] = (year % 100 == 0 &&
	           year % 400 != 0 ||
	           year %   4 != 0) ? 28 : 29;
	m["04"]=m["06"]=m["09"]=m["11"] = 30;
	m["01"]=m["03"]=m["05"]=m["07"]=m["08"]=m["10"]=m["12"] = 31;

	data = substr("                  ", 1, strftime("%w",
		systime() - 86400 * (strftime("%d") - 1)) * 3);

	for (i = 1; i <= m[month]; i++)
		data = sprintf("%s %2d", data, i);

	for (i = 0; i <= 5; i++)
		print substr(data, 1 + i * 21, 21);
}