这是因为远程命令的标准输入和标准输出都绑定到了您的键盘和显示器，这正是SSH的神奇之处。
Because the standard input and the standard output of the remote command are tied to your keyboard and display, albeit through the magic of SSH.
PHP最初不是设计用于与用户直接的键盘输入或文本输出结合使用。
PHP wasn't originally designed to be used with direct keyboard input or text output to the user.
默认情况下，标准输入是从键盘处获取它的内容的，不过，就像标准输出那样，标准输入也是可以被重定向的。
By default, standard input gets its contents from the keyboard, but like standard output, it can be redirected.
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