I am trying to implement a shell in C. I can execute simple commands just fine with a simple execvp() but one of the requirements is to manage commands like this: "ls -l | head | tail -4" with a 'for' loop and only one 'pipe()' statement redirecting stdin and stdout. Now after days I'm a bit lost.

N = Number of simple commands (3 in the example: ls, head, tail) commands = a list of structs with the commands, like this:

commands[0].argv[0]: ls
commands[0].argv[1]: -l
commands[1].argv[0]: head
commands[2].argv[0]: tail
commands[2].argv[1]: -4

So, I made the for loop, and started to redirect stdin and stdout in order to connect all the commands with pipes, but...I'm just clueless why it doesn't work.

for (i=0; i < n; i++){

pipe(pipe);
if(fork()==0){  // CHILD

    close(pipe[0]);
    close(1);
    dup(pipe[1]);
    close(pipe[1]);

    execvp(commands[i].argv[0], &commands[i].argv[0]);
    perror("ERROR: ");
    exit(-1);

}else{      // FATHER

    close(pipe[1]);
    close(0);
    dup(pipe[0]);
    close(pipe[0]);

}
}

What I want to create is a 'line' of childed processes:

[ls -l] ----pipe----> [head] ----pipe----> [tail -4]

All this processes have a root (the process runing my shell) so, the first father is also a child of the shell process, I'm a bit exhausted already, can anyone help me here please?

I'm not even sure if the childs should be the ones executing the commands.

Thanks guys !!

c shell posix pipe
Edit
Report