Question

1. Why is it necessary to implement a change directory 'cd' command in the shell? Could it be implemented by an external program instead?

3. What would happen if this program did not use the fork function, but just used execv directly? (Try it!) Try temporarily changing the code 'pid_from_fork = fork();' to 'pid_from_fork = 0;'

4. Explain what the return value of fork() means and how this program uses it..

Answer 1

1. Why is it necessary to implement a change directory 'cd' command in the shell? Could it be implemented by an external program instead?

Answer:

It's just as well that certain commands are built into the shell because it would be either difficult or impossible to implement them as separate external commands.you know that a child process inherits the current working directory from its parent as one of its environmental parameters.This inheriteance has important consequence for the cd command.

It's necessary for the cd command not to spawn a child to achieve change of directory.If it did so through a separate child process,then after cd had completed its run,control would revert to the parent and original directory would be restored.It would then be impossible to change directories.

4)Answer:

• If fork() returns a negative value, the creation of a child process was unsuccessful.
• fork() returns a zero to the newly created child process.
• fork() returns a positive value, the process ID of the child process, to the parent. The returned process ID is of type pid_t defined in sys/types.h. Normally, the process ID is an integer. Moreover, a process can use function getpid() to retrieve the process ID assigned to this process.