UNIX Shell and History Feature
1.The first task is to modify the main() function in Figure 3.36 so that a child process is forked and executes the command specified by the user.
The next task is to modify the shell interface program so that it provides a history feature that allows the user to access the most recently entered commands. The user will be able to access up to 10 commands by using the feature. The commands will be consecutively numbered starting at 1, and the numbering will continue past 10. For example, if the user has entered 35 commands, the 10 most recent commands will be numbered 26 to 35. The user will be able to list the command history by entering the command history at the osh> prompt.
