PATH=/bin:/usr/bin

if test $# -ne 3
then
    echo usage: zeller year month day >&2
    exit 1
fi

# Zeller algorithm part one:  adjust so that March is month zero
newmonth=`expr $2 - 3`  # -1 to convert to zero-origin, then -2 for zeller algo
newyear=$1
if test $newmonth -lt 0
then
    newyear=`expr $newyear - 1`
    newmonth=`expr $newmonth + 12`
fi

# Zeller algorithm part two:  the big formula
weekday=`echo \
	    26 $newmonth 1 + \* 2 - 10 /  \
	    $3 +  \
	    $newyear 100 % +  \
	    $newyear 100 % 4 / +  \
	    $newyear 400 / +  \
	    2 $newyear 100 / \* -  \
	    7777 +  \
	7 % p | dc`

# turn that into a day name
day0=Sunday
day1=Monday
day2=Tuesday
day3=Wednesday
day4=Thursday
day5=Friday
day6=Saturday
eval echo \$day$weekday