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PO*Almost* Perfect C Shell Piping
 

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  1. PO*Almost* Perfect C Shell Piping
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    <p>I am writing a small linux shell in C and am so very close to being done. I take in a command from the user and store it in <strong>args</strong>, delimited by spaces. In the following example, let's say that args contains the following:</p> <p><code>args[] = {"ls", "-l", "|", "wc"};</code></p> <p>My function takes in <strong>args</strong> and also takes in how many <strong>pipes</strong> there are. I've commented my code as much as possible. Here it is:</p> <pre><code>int do_command(char **args, int pipes) { // The number of commands to run const int commands = pipes + 1; int i = 0; int pipefds[2*pipes]; for(i = 0; i &lt; pipes; i++){ if(pipe(pipefds + i*2) &lt; 0) { perror("Couldn't Pipe"); exit(EXIT_FAILURE); } } int pid; int status; int j = 0; int k = 0; int s = 1; int place; int commandStarts[10]; commandStarts[0] = 0; // This loop sets all of the pipes to NULL // And creates an array of where the next // Command starts while (args[k] != NULL){ if(!strcmp(args[k], "|")){ args[k] = NULL; // printf("args[%d] is now NULL", k); commandStarts[s] = k+1; s++; } k++; } for (i = 0; i &lt; commands; ++i) { // place is where in args the program should // start running when it gets to the execution // command place = commandStarts[i]; pid = fork(); if(pid == 0) { //if not last command if(i &lt; pipes){ if(dup2(pipefds[j + 1], 1) &lt; 0){ perror("dup2"); exit(EXIT_FAILURE); } } //if not first command&amp;&amp; j!= 2*pipes if(j != 0 ){ if(dup2(pipefds[j-2], 0) &lt; 0){ perror("dup2"); exit(EXIT_FAILURE); } } int q; for(q = 0; q &lt; 2*pipes; q++){ close(pipefds[q]); } // The commands are executed here, // but it must be doing it a bit wrong if( execvp(args[place], args) &lt; 0 ){ perror(*args); exit(EXIT_FAILURE); } } else if(pid &lt; 0){ perror("error"); exit(EXIT_FAILURE); } j+=2; } for(i = 0; i &lt; 2 * pipes; i++){ close(pipefds[i]); } for(i = 0; i &lt; pipes + 1; i++){ wait(&amp;status); } } </code></pre> <p>My problem is that while the program is <em>kind of</em> executing correctly, it is behaving strangely and I was hoping you could help me out.</p> <p>For example hen I run <strong>ls | wc</strong>, the output is that of <strong>ls | wc</strong>, but then it also prints the output of a simple <strong>ls</strong> right below it, even though it should just be the <strong>wc</strong> of the output.</p> <p>As another example, when I try <strong>ls -l | wc</strong>, the first number of <strong>wc</strong> shows up, but then the output of <strong>ls -l</strong> shows up below it, even though it should just be the <strong>wc</strong> of the output.</p> <p>Thanks in advance! :)</p>
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    1. USRick_Sch
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    1. COWorks here. Are you sure you call your function with correct arguments?
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    2. COWorks fine here too. BTW, `do_command` is not returning as it should.
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    3. COIt works?! haha. Does it work 100% correctly? Like if you type `ls -l | wc` outside of the program in the actual linux box, does it have the same output as within my code?
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