[: 11: y: unexpected operator问题

《私房菜》上的shell脚本问题：

转载：[: 11: y: unexpected operator问题

脚本如下：%

#!/bin/bash
# Program:
#    This program shows the user's choice
# History:
#//
PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:~/bin&
export PATH

read -p "Please input (Y/N): " yn
[ "$yn" == "Y" -o "$yn" == "y" ] &&echo "OK, continue" && exit0
[ "$yn" == "N" -o "$yn" == "n" ] &&echo "Oh, interrupt!" && exit0
echo "I don't know what your choice is"&& exit 

执行时总提示错误9

Please input (Y/N): y
[: : y: unexpected operator
[: : y: unexpected operator
I don't know what your choice is

因为ubuntu默认的sh是连接到dash的,又因为dash跟bash的不兼容所以出错了.执行时可以把sh换成bash文件名.sh来执行.成功.dash是什么东西,查了一下,应该也是一种shell,貌似用户对它的诟病颇多.
by the way修改sh默认连接到bash的一种方法：
sudo dpkg-reconfigure dash0 Q$ c+ `. U+ c2 K
选择no即可.