Shell脚本判断是否是闰年

#! /bin/bash
echo -n Input year to judge if it is a leap year:
read year
let "y1=$year % 4"
let "y2=$year % 100"
let "y3=$year % 400"
if [ ! "$y1" -eq 0 ]
then
leap=0
elif [ ! "$y2" -eq 0 ]
then
leap=1
elif [ "$y3" -eq 0 ]
then
leap=1
else
leap=0
fi
if [ "$leap" -eq 1 ]
then
echo "$year is a leap year"
else
echo "$year is not a leap year"
fi

　　

[root@lenny Desktop]# ./ifrunnian.sh 
Input year to judge if it is a leap year:2003
2003 is not a leap year
[root@lenny Desktop]# ./ifrunnian.sh 
Input year to judge if it is a leap year:2005
2005 is not a leap year
[root@lenny Desktop]# ./ifrunnian.sh 
Input year to judge if it is a leap year:2008
2008 is a leap year