1. Can you think of why we use `fork/execvp` instead of just calling `execvp` directly? What value do you think the `fork` provides?
> **Answer**: Because execvp substitutes a new program for the existing process image, we utilize fork/execvp.
The shell would be replaced and we would be unable to process user instructions if we ran execvp straight in our shell.
While the parent process (our shell) stays open to take input, the fork generates a new process that can execute the external command on its own.
Because of this isolation, the shell can continue to operate even in the event that the external command fails or ends.
2. What happens if the fork() system call fails? How does your implementation handle this scenario?
> **Answer**: Fork() returns -1 if it fails, indicating that no child process is formed. We verify the fork's
return value in our implementation. To keep the shell from crashing when a negative result is returned, we use perror()
to emit the relevant error message before continuing (or maybe ending the loop). This guarantees that the shell gracefully
manages system problems or resource constraints.
3. How does execvp() find the command to execute? What system environment variable plays a role in this process?
> **Answer**: In order to find the command, execvp() looks through every directory specified in the PATH environment variable.
In each of these folders, it searches for an executable file with the name supplied as the command.
execvp() runs the command if it is located in one of the PATH directories; if not, it returns an error.
4. What is the purpose of calling wait() in the parent process after forking? What would happen if we didn’t call it?
> **Answer**: The parent process suspends execution until the child process ends when it calls wait() (or waitpid()).
In addition to preventing the generation of zombie processes—which happen when a child has completed execution but its
exit status is not collected—this enables the shell to get the child's exit status. Without using wait(), the parent process
could keep running without thoroughly cleaning up the child, which might eventually cause resource leaks and process table depletion.
5. In the referenced demo code we used WEXITSTATUS(). What information does this provide, and why is it important?
> **Answer**: The exit code is extracted by WEXITSTATUS() from the status value that wait() or waitpid() returns.
This exit code shows whether the child process experienced a problem (nonzero exit code) or finished successfully (often an exit value of 0).
It's crucial because it gives the shell (or script) a means of figuring out if the command that was performed was successful and,
if not, of taking appropriate action or reporting problems.
6. Describe how your implementation of build_cmd_buff() handles quoted arguments. Why is this necessary?
> **Answer**: When a token starts with a double quotation in build_cmd_buff(), the function handles all characters up to the following
double quote as a single parameter, even if they contain spaces. This keeps the quoted string's literal content intact.
Because users frequently need to give arguments that contain spaces (such file names or messages), handling quoted arguments is essential.
In the absence of this, the shell would divide these parameters into several tokens, resulting in improper operation.
7. What changes did you make to your parsing logic compared to the previous assignment? Were there any unexpected challenges in refactoring your old code?
> **Answer**: The parsing mechanism was improved over the last assignment to handle quoted texts correctly, remove duplicate spaces,
and reduce leading and trailing spaces. This necessitated interpreting the contained content as a single token and identifying the
beginning and closing quotations. Making sure that quotations matched accurately and that no extra spaces or unexpected characters were
added or deleted was an unforeseen issue. The code became more complicated as a result of balancing these instances, but the command
parser became more reliable and intuitive.
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