bash shell中的数学运算

cat test7:

#!/bin/bash
# An example of using the expr command
var1=
var2=
var3=`expr $var2 / $var1`
echo The result is $var3

添加可执行权限:chmod u+x test7

运行:./test7 结果如下:

The result is 
05-22 17:06