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POPersistent execvp on pipe?
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copied!<p>I am working on an assignment for my Operating System class (Posix & C), building a mini-shell, and I don't know how to solve the following problem:</p> <p>My mini-shell has to accept two commands, for example <code>ls | grep a</code>. For that I create a pipe of size two and a child. The child closes all that it has to close and opens all that it has to open (standard/pipe's in & out). It then executes "ls," using execvp. I am sure this works well. After that, the parent shuts and opens inputs and outputs (I am sure I do it well), and then executes <code>grep a</code>.</p> <p>Now, the problem is that the process <code>grep a</code> never finishes. Same for <code>tail -1</code>, e.g.. Yet it does work for <code>head -1</code>. I think that happens because <code>grep</code> and <code>tail</code>, which are executed by the parent, wait for more input, even though the child has finished its operation. <code>ls | grep a</code> produces the right output, displayed on the console (The pipe's output is set as default output), but, as I've said, <code>grep a</code> does not finish. </p> <p>So, my question is: how can I inform the parent that the pipe has finished writing, so it can finish the execution of <code>grep a</code> for example?</p> <p>Thank you.</p> <p>Here's the code:</p> <p>[fd is the pipe, it is initialized previously in the code. If you can see any incongruous thing, please let me know; I've cleaned the code a bit, and this is only the problematic part, as you can see.]</p> <pre><code> int fd[2]; pipe(fd); if ((pid = fork()) != -1){ if(pid == 0){ /*Child executing */ close(fd[0]); close(1); dup(fd[1]); close(fd[1]); execvp(argvv[0][0], argvv[0]); /* Here's stored the first instruction */ } else{ /* Parent executing */ wait(&status); close(fd[1]); close(0); dup(fd[0]); close(fd[0]); execvp(argvv[1][0], argvv[1]); /* Here's stored the second instruction */ } } </code></pre>

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