ej_pipe.c

#include <sys/types.h>
#include <sys/wait.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>

int
main(int argc, char *argv[])
{
   int pipefd[2];
   pid_t cpid;
   char buf;

   if (argc != 2) {
       fprintf(stderr, "Usage: %s <string>\n", argv[0]);
       exit(EXIT_FAILURE);
   }

   if (pipe(pipefd) == -1) {
       perror("pipe");
       exit(EXIT_FAILURE);
   }

   cpid = fork();
   if (cpid == -1) {
       perror("fork");
       exit(EXIT_FAILURE);
   }

   if (cpid == 0) {    /* Child reads from pipe */
       close(pipefd[1]);          /* Close unused write end */

       while (read(pipefd[0], &buf, 1) > 0)
           write(STDOUT_FILENO, &buf, 1);

       write(STDOUT_FILENO, "\n", 1);
       close(pipefd[0]);
       _exit(EXIT_SUCCESS);

   } else {            /* Parent writes argv[1] to pipe */
       close(pipefd[0]);          /* Close unused read end */
       write(pipefd[1], argv[1], strlen(argv[1]));
       close(pipefd[1]);          /* Reader will see EOF */
       wait(NULL);                /* Wait for child */
       exit(EXIT_SUCCESS);
   }
}