#! /bin/bash
#  Janapnese calendar (WAREKI)
#  登極令下 以降の元号カレンダ
YEAR=`date +%Y`
MONTH=`date +%m`

# usage
function usage()
{
	echo "usage: `basename $0` [-eh] [MONTH] or [YEAR MONTH]"; 
	exit 1
}

# Tsukimei 
TSUKI=(	"" "睦月" "如月" "弥生" "卯月" "皐月" "水無月"
	"文月" "葉月" "長月" "神無月" "霜月" "師走" )

# print help (-h option)
KOKI=""	# Emperor year
opt_e=0
while getopts :eh n
do
	case $n in
	e) opt_e=1 ;;
	h|*) usage ;;
	esac
done
shift $((OPTIND-1))

case $# in 
0) ;;
1) MONTH=$1;;
2) YEAR=$1; MONTH=$2;;
esac
oYEAR=$YEAR

[ $YEAR -ge 2019 ] && { GENGO="令和"; YEAR=$((YEAR-2018)); }
[ $YEAR -ge 1989 ] && { GENGO="平成"; YEAR=$((YEAR-1988)); }
[ $YEAR -ge 1926 ] && { GENGO="昭和"; YEAR=$((YEAR-1925)); }
[ $YEAR -ge 1912 ] && { GENGO="大正"; YEAR=$((YEAR-1911)); }
[ $YEAR -ge 1868 ] && { GENGO="明治"; YEAR=$((YEAR-1867)); }

if [ $opt_e -ne 0 ] ;then
echo $oYEAR
	YEAR=$((oYEAR+660))
	GENGO="  皇紀"
fi

echo "$GENGO $YEAR年 ${TSUKI[$MONTH]}" | awk '{len=length($0);feed=20-len;printf("%"feed"s\n", $0)}'
# echo " ===  $GENGO $YEAR /  $MONTH ${TSUKI[$MONTH]} === "
# echo " cal $MONTH / $YEAR "
cal $MONTH $YEAR | sed -e 1d
# =================
exit

Phase 0: 2021 / 03
Phase 1: 2021 / 03
Phase 2: 2 / 03
2 03  -->  / 令和 . [03]