The UNIX Shell

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于 2004-11-09 01:13:00 发布

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分类专栏： Oprating Systems Principles 文章标签： shell unix keyboard system interface command

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Shell是用户与操作系统间的文本接口，作为命令解释器，可接受用户通过键盘等设备输入的命令。典型多用户系统需提供执行和管理程序等命令。Shell还能成为强大编程语言，这一理念源于UNIX系统，文中给出简单shell脚本代码。

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A shell is a text-based interface between the user and the OS, which is a command interpreter that accepts statements (commands) issued by the user through the keyboard, mouse or other devices. A typical multiuser system should provide commands to the tasks which excute and manage programs, manipulate files and obtain system information.
A shell could also be turned to a powerful programming language. This idea was pioneered in the UNIX OS. The following is the code of a simple shell script (OSP by Bic & Shaw) :

COUNT = 'who|wc -l'
if test $COUNT -lt 8
then echo $COUNT users logged in
else echo too many users
fi