Part 1 - Creating a Child Process
The first task is to modify the main() function from the sample code provided so that a child process is forked and executes the command specified by the user. This will require parsing what the user has entered into separate tokens and storing the tokens in an array of character strings (args in the code provided). For example if the user enters the command ps -ael at th osh> prompt, the values stored in the args array are:
• args[0] = "ps"
• args[1] = "-ael"
• args[2] =NULL
This args array will be passed to the execvp() function, which has the following prototype: execvp(char *command, char *params[]);
Here, command represents the command to be performed and params stores the parameters to this command. For this project, the execvp() function should be invoked as execvp(args[0], args). Be sure to check whether the user included an & to determine whether or not the parent process is to wait for the child to exit.
Part 2 - Creating a History Feature
The next task is to modify the shell interface program so that is 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 command will be numbered 26-35. The user will be able to list the command history by entering the command "history" at the osh> prompt. As an example:
Your program should support two techniques for retrieving commands from the command history:
1. When the user enters !!, the most recent command in the history is executed.
2. When the user enters a single ! followed by an integer N, the Nth command in the history is executed.
The program should also manage basic error handling. If there are no commands in the history, entering !! should result in a message "No commands in history." If there is no command corresponding to the number entered with the single !, the program should output "No such command in history."