#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
 
int main(int argc, char ** argv) {
   pid_t childpid;
   int fd[2];

   if (argc != 3)
   {
	   printf("Usage: %s command1 command2\n", argv[0]);
	   exit(1);
   }
 
   if ((pipe(fd) == -1) || ((childpid = fork()) == -1)) {
      perror("Failed to setup pipeline");
      return 1;
   }
      
   if (childpid == 0) {                                  /* ls is the child */
      if (dup2(fd[1], STDOUT_FILENO) == -1) 
         perror("Failed to redirect stdout of ls");
      else if ((close(fd[0]) == -1) || (close(fd[1]) == -1)) 
         perror("Failed to close extra pipe descriptors on ls");
      else { 
         execlp(argv[1], argv[1], NULL);
         perror("Failed to exec first command");
      }
      return 1; 
   } 
   if (dup2(fd[0], STDIN_FILENO) == -1)               /* sort is the parent */
       perror("Failed to redirect stdin of sort");
   else if ((close(fd[0]) == -1) || (close(fd[1]) == -1)) 
       perror("Failed to close extra pipe file descriptors on sort"); 
   else {
      execlp(argv[2], argv[2], NULL);
      perror("Failed to exec second command");
   }
   return 1; 
}