shell 清空指定大小的日志文件

#!/bin/bash
# 当/var/log/syslog大于68B时
if ! [ -f /var/log/syslog ]
then
echo "file not exist!"
exit
fi
if [ `ls -l /var/log/syslog|awk '{print $5}'` -gt $(68) ]
then
cat /var/log/syslog >> ~/log/history # 将日志备份
echo >> ~/log/history # 增加一个空行
date >> ~/log/history # 记录时间
echo "-------------------------------------" >> ~/log/history
echo > /var/log/syslog # 清空
fi