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  1. #include <stdio.h>
  2. #include <stdlib.h>
  3. #include <unistd.h>
  4.  
  5. // pipe setup for ps -aef | grep 0 | wc -l
  6. int main()
  7. {
  8.     static const int READ = 0;
  9.     static const int WRITE = 1;
  10.     int fd[2][2] = {{0}};
  11.     int pid = 0;
  12.  
  13.     // last process first: wc -l
  14.     pipe(fd[0]);
  15.     if ((pid = fork()) == 0)
  16.     {
  17.         // setup "wc -l"
  18.         close(fd[0][WRITE]);
  19.         dup2(fd[0][READ], READ);
  20.         execlp("wc", "wc", "-l", NULL);
  21.     }
  22.     // no longer need this
  23.     close(fd[0][READ]);
  24.  
  25.     // middle process: grep 0
  26.     pipe(fd[1]);
  27.     if ((pid = fork()) == 0)
  28.     {
  29.         // setup "grep 1"
  30.         close(fd[1][WRITE]);
  31.         dup2(fd[0][WRITE], WRITE);
  32.         dup2(fd[1][READ], READ);
  33.         execlp("grep", "grep", "0", NULL);
  34.     }
  35.     // no longer need this
  36.     close(fd[0][WRITE]);
  37.     close(fd[1][READ]);
  38.  
  39.     // first process
  40.     if ((pid = fork()) == 0)
  41.     {
  42.         // setup ps -aef
  43.         dup2(fd[1][WRITE], WRITE);
  44.         execlp("ps", "ps", "-aef", NULL);
  45.     }
  46.     // no longer need his
  47.     close(fd[1][WRITE]);
  48.  
  49.     pid = wait(NULL);
  50.  
  51.     return 0;
  52. }
Success #stdin #stdout 0.01s 4460KB
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https://ideone.com/AOq1Pi
language:
C (gcc 8.3)
created:
10 years ago
visibility:
secret

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