確認日をcalコマンドに入力せずに、このスクリプトの最後で私が何を間違っているのか疑問に思います。

#Purpose: Validate a date
#Usage: chkdate year month day
#
if [ $# -eq 0 ]; then
        echo Usage: chkdate year month day
        exit 0
fi
year=$1; month=$2; day=$3; extra=$4
if [[ "$extra" != "" ]]; then
        # Too much data!
        echo Usage: chkdate year month day
        exit 1
fi
if [[ "$year" == "" || "$month" == "" || "$day" == "" ]]; then
        # Not enough data!
        echo Usage: chkdate year month day
        exit 2
fi
if [[ ! ( $year =~ ^[0-9]+$ && $month =~ ^[0-9]+$ && $day =~ ^[0-9]+$ ) ]]; then
        # Date not numeric!
        echo Usage: chkdate year month day
        exit 3
fi
#Remove leading zeros if any
year=$(echo "$year" | bc)
month=$(echo "$month" | bc)
day=$(echo "$day" | bc)
if [[ $year -lt 1 || $year -gt 9999 || $month -lt 1 || $month -gt 12 || $day -lt 1 || $day -gt 31 ]]; then
        # Date out of range!
        echo Usage: chkdate year month day
        exit 4
fi
if [[ ( $month == 1 || $month == 3 || $month == 5 || $month == 7 || $month == 8 || $month == 10 || $month == 12 ) && $day -gt 31 ]]; then
        # Invalid day!
        echo Usage: chkdate year month day
        exit 5
fi
if [[ ( $month == 4 || $month == 6 || $month == 9 || $month == 11 ) && $day -gt 30 ]]; then
        # Invalid day!
        echo Usage: chkdate year month day
        exit 6
fi
if [[ $month == 2 && $(($year%100)) == 0 ]]; then
        if [[ $(($year%400)) == 0 ]]; then
                isLeapYear=1
        else
                isNotLeapYear=1
        fi
elif [[ $month == 2 && $(($year%4)) == 0 ]]; then
        isLeapYear=1
else
        isNotLeapYear=1
fi
if [[ $month == 2 && $day -gt 28 && $isNotLeapYear ]]; then
        # Not Leap year!
        echo Usage: chkdate year month day
        exit 7
fi
if [[ $month == 2 && $day -gt 29 && $isLeapYear ]]; then
        # Invalid day!
        echo Usage: chkdate year month day
        exit 8
fi
while [[ $# -ne [1-8] ]]; do
cal << ( $year $month $day )
fi
echo $year $month $day is valid date