HW2
released: 09/21, 22:00
due: 09/28, 13:00

Study 09/21's lecture handout (https://naizhengtan.github.io/21fall/notes/handout_3a.pdf)
and answer the following questions.
Submit your answers to Canvas assignments. There is an entry for this homework.


Question 1: Describe what happens when line 21 is executed.
[hint: read "$ man 2 execve"]


Question 2: Compile and run the code below.
    """
    #include <unistd.h>
    int main() {
        // We used to have a bug here (can you see why?)
        //   the line was: char * argv[] = {"ls", "-a"}
        char * argv[] = {"ls", "-a", NULL};
        int ret = execve("/bin/ls", argv, 0);
    }
    """
Write down the output of this program and what you think happened.

  [open question: "ls" is part of the arguments ({"ls", "-a"}). why?
  what if you replace "ls" with something else? do you expect this outcome? and
  what do you think of this consequence (of replacing "ls" with something else)?]


Question 3: Describe what happens when line 23 is executed.
[hint: read "$ man 2 wait"]


Question 4: In line 23, what does "0" mean in "wait(0)"?
[hint: read "$ man 2 wait"]


Question 5: Describe what happens when line 69-71 are executed.
[hint: read "$ man 2 pipe"]


Question 6: Read "6. Commentary" (starting line 153). And answer the
question---have you read "6. Commentary"?