Changelog:

  • 22 March 2023: add pointer to readings

  1. Possibly working with a partner, write a single file my_system.c that defines the my_system function specified below. You may include helper functions in the file, but it should not contain main.

  2. In a separate file, write a main to test your my_system function and make sure it works as intended.

  3. Show your working function to a TA or submit your .c files to the submission site.

1 int my_system(const char *command)

This is a simplified version of the system standard library function (see man 3 system for details). You should handle all aspects of the function as described in the manual page except

  1. you do not need to ignore or block any signals
  2. you do not need to check if a shell is available for NULL commands

You must not use system in your implementation. You should use fork; wait or waitpid; and either execve or one of its front-ends (execl, execlp, execle, execv, execvp, or execvpe).

In addition to manpages for the above functions, you may find it useful to refer to the lecture slides and/or the threads reading.

Note that the wait status that my_system should return can be retrieved using wait or waitpid.

Because my_system needs to be thread-safe, do not use any global variables.

The following main function

int main(int argc, const char *argv[]) {
    int a1 = my_system("sleep 1; echo hi");
    int a2 = my_system("echo bye");
    int a3 = my_system("flibbertigibbet 23");
    printf("%d %d %d\n", 
        WEXITSTATUS(a1), WEXITSTATUS(a2), WEXITSTATUS(a3));
}

should print

hi
bye
sh: 1: flibbertigibbet: not found
0 0 127

(note: the details of the not found line will vary based on the version of sh installed on the computer)

The following main function

int main(int argc, const char *argv[]) {
    my_system("echo -n 'type something: ';"
        " read got;"
        " echo Thanks for typing \\\"\"$got\"\\\"");
}

should prompt for user input, wait until it is provided, and then repeat what they typed, as e.g.

type something: this is a test
Thanks for typing "this is a test"