Launch a fork every N seconds

[Sergi]

Hi everyone, I have this assignment in which I need to run "ls" every N seconds. We're not allowed to use signals, we can only use the command sleep, but via an exec function, we can't use "system".

This is the code I have:

main()
{
    int N=5;
    int i;
    pid_t pid;
    pid = fork();
    if (pid==0) {
        for (i=0; i<N; i++) {
            if (fork()==0)
                execl("/bin/ls", "ls", NULL);
        }
    }
    else if (pid>0) {
        wait(NULL);
    }
    else
        perror("fork failed");
}

I've tried many things, but the problem is I have to run an execl (or execvp) with sleep in it. Being mandatory, it erases the rest of the program.
My teachers insists it can be done with execs, forks and waits. I still can't see how.

[john.c]

Your attempt makes no sense. You say you want to launch ls every N seconds, but instead you launch N copies of ls.

As for executing sleep with exec, it's pretty simple. You need to turn your N int into a string, which you can do with sprintf. Below I've called the string nstr.

    switch (fork()) {
    case -1:
        perror("fork");
        exit(EXIT_FAILURE);
    case 0:
        execl("/bin/sleep", "sleep", nstr, (const char*)NULL);
        exit(0); // child exits
    }
    wait(NULL);  // parent waits for child