回声＆QUOT;＃＆QUOT！;失败 - ＆QUOT;事件未发现＆QUOT;
问题描述：
以下失败，我不明白为什么：
The following fails and I don't understand why:
$ echo "#!"
下面还失败，相同的错误消息：
the following also fails with the same error message:
$ echo "\#!"
错误消息：
-bash: !": event not found
为什么会失败？应如何回声来代替呢？
答
的！字符用于 CSH 风格历史扩展。
The ! character is used for csh-style history expansion.
如果您不使用此功能，设置+ O histexpand （又名设置+ H ）关闭此行为。它是关闭的脚本，但往往启用交互使用。
If you do not use this feature, set +o histexpand (aka set +H) turns off this behavior. It is turned off for scripts, but often enabled for interactive use.
作为一种变通方法，您可以使用单引号代替双引号的。
As a workaround, you can use single quotes instead of double quotes.