shell脚本监控Linux系统的登录情况

#!/bin/bash
while true
do
sleep 2
a=`stat -c %Y /var/log/login.log`
b=`date +%s`
if [ $(($b-$a)) -le 10 ];
then
echo "somebody login in!!!do something!!!"
`执行命令`
fi
echo "every thing goes well, no login operate..."
done