Directory commands

The skeleton code for your shell has a dispatcher for “built-in” commands. Every shell needs to support a number of built-in commands, which are functions in the shell itself, not external programs. For example, the exit command needs to be implemented as a built-in command, because it exits the shell itself. So far, the only two built-ins supported are ?, which brings up the help menu, and exit, which exits the shell.

Add a new built-in pwd that prints the current working directory to standard output. Then, add a new built-in cd that takes one argument, a directory path, and changes the current working directory to that directory. You may find the syscalls chdir and getcwd helpful. Check out man pages for usage details.