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POMultiprogramming in Unix
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  1. POMultiprogramming in Unix
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    copied!<p>I have some problems trying to make a simple program using execlp, fork and pipes. The program at hand is supossed to do "last |head -5| sort" but it doesn't work. Here is the code.</p> <pre><code>#include &lt;string.h&gt; #include &lt;fcntl.h&gt; #include &lt;stdio.h&gt; #include &lt;errno.h&gt; #include &lt;sys/types.h&gt; #include &lt;sys/stat.h&gt; //last |head -5| sort int main(int argc, char* argv[]){ int buzon[2]; int buzon2[2]; if(pipe(buzon) &lt; 0) error("error de pipe"); switch(fork()){ case -1: error("error de fork"); case 0: if(close(1) &lt; 0) error("error de close"); if(dup(buzon[1]) &lt; 0) error("error de dup"); if(close(buzon[0]) &lt; 0) error("error de close"); if(close(buzon[1]) &lt; 0) error("error de close"); execlp("last", "last", NULL); error("error de execlp"); } switch(fork()){ case -1: error("error de fork"); case 0: if(close(0) &lt; 0) error("error de close"); if(close(1) &lt; 0) error("error de close"); if(dup(buzon[0]) &lt; 0) error("error de dup"); if(dup(buzon[1]) &lt; 0) error("error de dup"); if(close(buzon[0]) &lt; 0) error("error de close"); if(close(buzon[1]) &lt; 0) error("error de close"); execlp("head", "head", "-n 5", NULL); error("error de execlp"); } switch(fork()){ case -1: error("error de fork"); case 0: if(close(0)&lt;0) error("error de close"); if(dup(buzon[0]) != 1) error("error de dup"); if(close(buzon[0]) &lt; 0) error("error de close"); if(close(buzon[1]) &lt; 0) error("error de close"); execlp("sort", "sort", NULL); error("error de execlp"); } if(close(buzon[0]) &lt; 0) error("error de close"); if(close(buzon[1]) &lt; 0) error("error de close"); while(wait(NULL) != -1); } </code></pre> <p>Any idea of what fails. The problem is when I use 2 pipes. If I make a program which only uses 1 pipe, it works.</p>
 

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