shell计算uptime的日志的最后一列
日志格式：
18:41:58 up 1 day, 10:02, 2 users, load average: 1.12, 0.99, 1.02 18:41:59 up 1 day, 10:02, 2 users, load average: 1.11, 0.99, 1.02 18:42:00 up 1 day, 10:02, 2 users, load average: 1.11, 0.99, 1.02 18:42:01 up 1 day, 10:02, 2 users, load average: 1.11, 0.99, 1.02 18:42:02 up 1 day, 10:02, 2 users, load average: 1.11, 0.99, 1.02 18:42:03 up 1 day, 10:02, 2 users, load average: 1.11, 0.99, 1.02 18:42:04 up 1 day, 10:02, 2 users, load average: 1.10, 0.99, 1.02 18:42:05 up 1 day, 10:02, 2 users, load average: 1.10, 0.99, 1.02 18:42:06 up 1 day, 10:02, 2 users, load average: 1.10, 0.99, 1.02
代码如下：
//拼接字符串
str=`echo \`awk '{print $12}' /tmp/a.log |grep -v -|tr '\n' '+'\``
//得到的字符串后边多一个“+”
//去掉末尾的“+”
str2=`echo ${str%+}`
//交给bc计算
echo $str2|bc