删除三天前重命名的文件夹

#!/bin/sh
for i in `ls /vm/vm/ |grep -P 'drop$'`
do
now=$(date +%s)
droptime=$(date -d "$(echo $i | awk -F . '{print $2 " " $3}')" +%s)
n=$(($now - $droptime))
if [ "$n" -ge "259200" ];then
rm -rf /vm/vm/$i
fi
done

ls /vm/vm

S140112.2013-05-29.12:10:36.drop  S140112.2013-06-21.12:10:36.drop  S140112.2013-06-24.12:10:36.drop  S987602

S010730.2013-06-05.13:43:26.drop  S140112.2013-06-19.12:10:36.drop  S140112.2013-06-22.12:10:36.drop  S140112.2013-06-25.12:10:36.drop  S987620
S140112                           S140112.2013-06-20.12:10:36.drop  S140112.2013-06-23.12:10:36.drop  S231232

删除时间大于三天的文件夹。