我有一个 shell 脚本，使用 set -e 递增变量，如下例所示：
$ var=0; echo $?
0
$ ((var++)); echo $?
1
$ ((var++)); echo $?
0
$ ((var++)); echo $?
0
$ echo $var; echo $?
3
0
$ bash --version
GNU bash, version 4.2.46(1)-release (x86_64-redhat-linux-gnu)
Copyright (C) 2011 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software; you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
$ …