使用BASH:

#!/bin/bash
# home/victoria/test.sh

START=$(date +"%s")                                     ## seconds since Epoch
for i in $(seq 1 10)
do
  sleep 1.5
  END=$(date +"%s")                                     ## integer
  TIME=$((END - START))                                 ## integer
  AVG_TIME=$(python -c "print(float($TIME/$i))")        ## int to float
  printf 'i: %i | elapsed time: %0.1f sec | avg. time: %0.3f\n' $i $TIME $AVG_TIME
  ((i++))                                               ## increment $i
done

输出

$ ./test.sh 
i: 1 | elapsed time: 1.0 sec | avg. time: 1.000
i: 2 | elapsed time: 3.0 sec | avg. time: 1.500
i: 3 | elapsed time: 5.0 sec | avg. time: 1.667
i: 4 | elapsed time: 6.0 sec | avg. time: 1.500
i: 5 | elapsed time: 8.0 sec | avg. time: 1.600
i: 6 | elapsed time: 9.0 sec | avg. time: 1.500
i: 7 | elapsed time: 11.0 sec | avg. time: 1.571
i: 8 | elapsed time: 12.0 sec | avg. time: 1.500
i: 9 | elapsed time: 14.0 sec | avg. time: 1.556
i: 10 | elapsed time: 15.0 sec | avg. time: 1.500
$

获取当前时间，以秒为单位，自纪元的Linux, Bash

试试这个Bash语法，而不是尝试使用外部程序expr:

count=$((FIRSTV-SECONDV))

顺便说一句，使用expr的正确语法是:

count=$(expr $FIRSTV - $SECONDV)

但是请记住，使用expr将比我上面提供的内部Bash语法慢。

你可以使用:

((count = FIRSTV - SECONDV))

为了避免调用一个单独的流程，如下面的记录:

pax:~$ FIRSTV=7
pax:~$ SECONDV=2
pax:~$ ((count = FIRSTV - SECONDV))
pax:~$ echo $count
5

空格很重要，expr期望它的操作数和操作符作为单独的参数。您还必须捕获输出。是这样的:

COUNT=$(expr $FIRSTV - $SECONDV)

但更常见的是使用内置算术展开:

COUNT=$((FIRSTV - SECONDV))

你只需要在负号和反勾号周围多留一些空白:

COUNT=`expr $FIRSTV - $SECONDV`

注意退出状态:

当表达式不为空或0时，退出状态为0;当表达式为空或0时，退出状态为1。

在bash脚本中与set -e结合使用表达式时，请记住这一点，如果命令以非零状态退出，set -e将立即退出。

使用BASH:

#!/bin/bash
# home/victoria/test.sh

START=$(date +"%s")                                     ## seconds since Epoch
for i in $(seq 1 10)
do
  sleep 1.5
  END=$(date +"%s")                                     ## integer
  TIME=$((END - START))                                 ## integer
  AVG_TIME=$(python -c "print(float($TIME/$i))")        ## int to float
  printf 'i: %i | elapsed time: %0.1f sec | avg. time: %0.3f\n' $i $TIME $AVG_TIME
  ((i++))                                               ## increment $i
done

输出

$ ./test.sh 
i: 1 | elapsed time: 1.0 sec | avg. time: 1.000
i: 2 | elapsed time: 3.0 sec | avg. time: 1.500
i: 3 | elapsed time: 5.0 sec | avg. time: 1.667
i: 4 | elapsed time: 6.0 sec | avg. time: 1.500
i: 5 | elapsed time: 8.0 sec | avg. time: 1.600
i: 6 | elapsed time: 9.0 sec | avg. time: 1.500
i: 7 | elapsed time: 11.0 sec | avg. time: 1.571
i: 8 | elapsed time: 12.0 sec | avg. time: 1.500
i: 9 | elapsed time: 14.0 sec | avg. time: 1.556
i: 10 | elapsed time: 15.0 sec | avg. time: 1.500
$

获取当前时间，以秒为单位，自纪元的Linux, Bash