TIPS/sh/曜日計算

#! /bin/sh
usage () {
echo "usage: $0 <year> <month> <day> [<cent>]"
echo "          exp. : 2007/3/31 is \"$0 7 3 31\""
exit 1
}
[ $# -lt 3 ] && usage
[ -z $4 ] && H=20 || H=$4
Y=$1
M=$2
D=$3
YEAR=`expr $H \* 100`
YEAR=`expr $YEAR + $Y`
DATE=${YEAR}/${M}/${D}
echo DATE=$DATE
if [ $M -le 2 ] ; then
    Y=`expr $Y - 1`
    M=`expr $M + 12`
fi
echo 'W = y + [ y / 4 ] + [ h / 4 ] - 2h + [ 13 ( m + 1) / 5 ] + d'
tmp1=`expr $Y / 4`
#echo tmp1=$tmp1
tmp2=`expr $H / 4`
#echo tmp2=$tmp2
tmp3=`expr $H \* 2`
#echo tmp3=$tmp3
tmp4=`expr $M + 1`
tmp4=`expr $tmp4 \* 13`
tmp4=`expr $tmp4 / 5`
#echo tmp4=$tmp4
echo "W = $Y + $tmp1 + $tmp2 - $tmp3 + $tmp4 + $D"
W=`expr $Y + $tmp1 + $tmp2 - $tmp3 + $tmp4 + $D`
echo W=$W
echo "R = W % 7"
R=`expr $W % 7`
echo R=$R
echo -n "$DATE is "
case $R in
    0) echo "Saturday." ;;
    1) echo "Sunday." ;;
    2) echo "Monday." ;;
    3) echo "Tuesday." ;;
    4) echo "Wednesday." ;;
    5) echo "Thirsday." ;;
    6) echo "Friday." ;;
    *) echo "Unknown." ;;
esac
echo OK
exit 0