shell计算时间差

#!/bin/bash
current1=`date "+%Y-%m-%d %H:%M:%S"`

start_time=`date -d "$current1" +%s`

sleep 5s

current2=`date "+%Y-%m-%d %H:%M:%S"`
end_time=`date -d "$current2" +%s`

#相减算差值

time_query=`expr $end_time - $start_time`

echo $time_query