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

 int main()
 {
   int fd[2];

   /* create pipe */
   pipe(fd);

   /* create child process */
   switch (fork())
   {
     case -1:/* error */
             perror("fork - can't create process");
             break;
     case 0 :/* child process */
             close(1);     //close standard output
             close(fd[0]); //write-only pipe
             dup(fd[1]);   //duplicate fd[1]

             /* execute ls command */
             if (!fork()) execlp("ls", "ls", NULL);
             else
             {
               wait();
               close(fd[1]);
             }
             break;
     default:/* parent process */
             close(0);     //close standard input
             close(fd[1]); //read-only pipe
             dup(fd[0]);   //dupliactate fd[0]

             /* execute wc command */
             if (!fork()) execlp("wc", "wc", NULL);
             else
             {
               wait();
               close(fd[0]);
             }
   }
 }

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

 int main()
 {
   int fd;

   /* make named pipe (FIFO) */
   mkfifo("fifo", 0600);

   /* create child process */
   switch (fork())
   {
     case -1:/* error */
             perror("fork - can't create process");
             break;
     case 0 :/* child process */
             close(1);                    //close standard output
             fd = open("fifo", O_WRONLY); //open named pipe (FIFO)
             dup(fd);                     //duplicate fd

             /* execute ls command */
             if (!fork()) execlp("ls", "ls", NULL);
             else
             {
               wait();
               close(fd);
             }
             break;
     default:/* parent process */
             close(0);                    //close standard input
             fd = open("fifo", O_RDONLY); //open named pipe (FIFO)
             dup(fd);                     //dupliactate fd

             /* execute wc command */
             if (!fork()) execlp("wc", "wc", NULL);
             else
             {
               wait();
               close(fd);
               unlink("fifo");
             }
   }
 }