// pipe.c example modified to use execlp()
//
// parent should really create two children and wait for them,
// otherwise output is not synchronized with the shell

// file descriptors:
//
//  0 = stdin, read using scanf()
//  1 = stdout, write using printf()
//  2 = stderr, write using fprintf( stderr, ...)
//
//  fd[0] read, input 
//  fd[1] write, output

#include <stdio.h>
#include <unistd.h>

int main( void)
{
  int fd[2]; // for pipe file descriptors

  if( pipe(fd) < 0) { perror("pipe"); return 1; }

  int pid = fork(); if( pid < 0) { perror("fork"); return 1; }

  if( pid == 0) // child
  {
    dup2( fd[0], 0); // make stdin come from pipe

    close(fd[0]); close(fd[1]); // fd no longer needed, close it
/*
    int x = 0; scanf("%d",&x); // read from parent
    printf( "x = %d\n", x);
*/
    execlp( "rev", "rev", NULL); // should not return
    perror( "rev");
  }
  else // parent
  {
    dup2( fd[1], 1); // make stdout go to pipe

    close(fd[0]); close(fd[1]); // fd no longer needed, close it
/*
    printf( "%d", 123); // write to child
*/
    execlp( "date", "date", NULL);
    perror( "date");
  }

  return 0;
} 

/* sample run:

$ make
gcc -Wall -o pipe pipe.c
$ ./pipe
$ 2202 TDE 54:30:80 7  peS deW

*/