#include <stdio.h>

#define DATA "Bright star, would I were steadfast as thou art . . ."

/*
 * This program creates a pipe, then forks. The child communicates to the
 * parent over the pipe. Notice that a pipe is a one-way communications
 * device.  I can write to the output socket (sockets[1], the second socket
 * of the array returned by pipe()) and read from the input socket
 * (sockets[0]), but not vice versa.
 */

main()
{
     int sockets[2], child;

     /* Create a pipe */
     if (pipe(sockets) < 0) {
          perror("opening stream socket pair");
          exit(10);
     }

     if ((child = fork()) == -1)
          perror("fork");
     else if (child) {
          char buf[1024];

          /* This is still the parent. It reads the child's message. */
          close(sockets[1]);
          if (read(sockets[0], buf, 1024) < 0)
               perror("reading message");
          printf("-->%s\n", buf);
          close(sockets[0]);
     } else {
          /* This is the child. It writes a message to its parent. */
          close(sockets[0]);
          if (write(sockets[1], DATA, sizeof(DATA)) < 0)
               perror("writing message");
          close(sockets[1]);
     }
}