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POConnecting n commands with pipes in a shell?
 

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  1. POConnecting n commands with pipes in a shell?
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    <p>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.</p> <p>N = Number of simple commands (3 in the example: ls, head, tail) commands = a list of structs with the commands, like this:</p> <pre><code>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 </code></pre> <p>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.</p> <pre><code>for (i=0; i &lt; n; i++){ pipe(pipe); if(fork()==0){ // CHILD close(pipe[0]); close(1); dup(pipe[1]); close(pipe[1]); execvp(commands[i].argv[0], &amp;commands[i].argv[0]); perror("ERROR: "); exit(-1); }else{ // FATHER close(pipe[1]); close(0); dup(pipe[0]); close(pipe[0]); } } </code></pre> <p>What I want to create is a 'line' of childed processes:</p> <blockquote> <p>[ls -l] ----pipe----> [head] ----pipe----> [tail -4]</p> </blockquote> <p>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?</p> <p>I'm not even sure if the childs should be the ones executing the commands.</p> <p>Thanks guys !!</p>
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    1. COIs this homework? If not - just run `/bin/sh` with the appropriate arguments. Why reinvent the wheel?
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      1. USEd Heal
    2. COThis is only one of the requirements from a 3 pages long voluntary practice. Not exactly homework, but I'd like to know how to do this, or atleast get some clues.
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    3. COthere are numerous good posts here on S.O. that cover the background material you'll need to master this topic. Good luck.
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