这些事件可以是诸如计时器，信号，文件描述符上预备读取的数据，等等。

These events can be things like timers, signals, data ready for reading on a file descriptor, and so on.

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到这时，用户可以编写shell脚本，在变量中存储信息和导出信息，控制文件描述符，控制信号处理，使用for循环和case语句，以及其他大量功能。

Now, users could write shell scripts; store and export information in variables; control file descriptors; control signal handling, for loops, and case statements; and so much more.

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