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说明：  shell 程序要求实现的shell支持以下内部命令： 1. Batch Processing 如果shell启动带有一个文件名作为参数，打开该文件并执行文件里所有命令。待所有进程全部结束退出shell。 2. Debugging 提供-v选项，shell启动时打开此选项将在运行过程中输出若干调试信息。在该模式下，shell应该显示所有被创建了的进程的PID号，通报已结束的子进程和传递给子进程的参数等。 3. Prompt (命令行提示符) 解释器打印$PS2作为提示符。 4. Background Processing 如果命令以符合&终止，在后台并发执行该程序。Shell立即等待下一命令的输入，而不等待该程序的结束。 注：所有命令和参数由空格或tab符分隔。
(shell procedures call for the support of the following internal shell commands : 1. Batch Processing If the shell startup with a file name as a parameter. Open the document and implement all the documents in order. When all the whole process from the end of the shell. 2. Debugging for-v option, shell activated this option will open in the course of operation a number of debugging output information. In the model, the shell should show all of the process of creating the PID, Bulletins have been the end of the process and the sub-transmission to the child process parameters. 3. Prompt (command line prompt) Print $ explanation for PS2 as a prompt. 4. Background Processing order to meet if)