piper.c

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

int main(int argc, char *argv[]) {
  int pfd0[2], pfd1[2];
  pid_t ls_pid, wc_pid,	wc1_pid;

  pipe(pfd0);
  pipe(pfd1);

  if ((ls_pid = fork()) == 0) {
    dup2(pfd0[1],STDOUT_FILENO);

    close(pfd0[0]);
    close(pfd1[0]);
    close(pfd1[1]);

    execl("/bin/ls", "ls","-al", NULL);
    perror("exec ls failed");
    exit(EXIT_FAILURE);
  }

  if ((wc_pid = fork()) == 0) {
    dup2(pfd0[0], STDIN_FILENO);
    dup2(pfd1[1], STDOUT_FILENO);

    close(pfd0[1]);
    close(pfd1[0]);

    execl("/usr/bin/wc", "wc", NULL);
    perror("exec wc failed");
    exit(EXIT_FAILURE);
  }

  if ((wc1_pid = fork()) == 0) {
    dup2(pfd1[0], STDIN_FILENO);

    close(pfd0[0]);
    close(pfd0[1]);
    close(pfd1[1]);

    execl("/usr/bin/wc", "wc", NULL);
    perror("exec wc failed");
    exit(EXIT_FAILURE);
  }

  close(pfd0[0]);
  close(pfd0[1]);
  close(pfd1[0]);
  close(pfd1[1]);

  waitpid(ls_pid, NULL, 0);
  waitpid(wc_pid, NULL, 0);
  waitpid(wc1_pid, NULL, 0);

  return EXIT_SUCCESS;
}