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    <p>Note that '<code>dup(p[1])</code>' means you have two file descriptors pointing to the same file. It does not close <code>p[1]</code>; you should do that explicitly. Likewise with '<code>dup(p[0])</code>'. Note that a file descriptor reading from a pipe only returns zero bytes (EOF) when there are no open write file descriptors for the pipe; until the last write descriptor is closed, the reading process will hang indefinitely. If you <code>dup()</code> the write end, there are two open file descriptors to the write end, and both must be closed before the reading process gets EOF.</p> <p>You also do not need or want the <code>wait()</code> call in your code. If the <code>ls</code> listing is bigger than a pipe can hold, your processes will deadlock, with the child waiting for <code>ls</code> to complete and <code>ls</code> waiting for the child to get on with reading the data it has written.</p> <p>When the redundant material is stripped out, the working code becomes:</p> <pre><code>#include &lt;unistd.h&gt; int main(void) { int p[2]; pid_t ret; pipe(p); ret = fork(); if (ret == 0) { close(1); dup(p[1]); close(p[0]); close(p[1]); execlp("ls", "ls", "-l", (char *) 0); } else if (ret &gt; 0) { close(0); dup(p[0]); close(p[0]); close(p[1]); execlp("wc", "wc", "-l", (char *) 0); } return(-1); } </code></pre> <p>On Solaris 10, this compiles without warning with:</p> <pre><code>Black JL: gcc -Wall -Werror -Wmissing-prototypes -Wstrict-prototypes -o x x.c Black JL: ./x 77 Black JL: </code></pre>
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    1. POA doubt on pipes in Unix
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    1. USJonathan Leffler
    1. USJonathan Leffler
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    1. COI got it. I have one more doubt. When 2 file descripters are pointing to the same file and I call close() on one. Does the other remain accesible? Beacuse they share the same entry in the file table. So after calling close on Ist , that entry must be removed.
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    2. COYes, close() only closes the file descriptor; it doesn't clean up the file table entry if there's another file descriptor also referring to it. The file table entry is only removed when all file descriptors referring to it are closed.
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    3. COThanks a lot, a lot of doubts have been cleares now.
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