8.18.e

#include <stdio.h>
#include <errno.h>
#include <sys/wait.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

int main(int argc, char *argv[]){
// pr1 < f.dat | pr2 | pr3 > f.res

    int pid1, pid2, pid3;
    int fd1[2], fd2[1];

    if (pipe(fd1) == -1) exit(1);
    pipe(fd2);

    if ((pid1 = fork()) == -1){
        perror("fork\n");
        exit(1);
    }else if (pid1 == 0){//son1
        int fd_dat;
        if ((fd_dat = open(argv[2], O_RDONLY)) == -1){
            perror("open data\n");
            exit(1);
        }
        dup2(fd_dat, 0);
        dup2(fd1[1],1);
        close(fd1[1]);
        close(fd1[0]);
        close(fd2[0]);
        close(fd2[1]);
        //close(fd_dat);
        execlp(argv[1], argv[1], NULL);
        perror("execlp\n");
        _exit(1);
    }

    if ((pid2 = fork()) == -1){
        perror("fork\n");
        exit(1);
    }else if (pid2 == 0){//son
        if (dup2(fd1[0],0) == -1){
            perror("dup2\n");
            exit(1);
        }
        dup2(fd2[1],1);
//      close(fd1[0]);
//      close(fd1[1]);
        close(fd2[0]);
        close(fd2[1]);
        execlp(argv[3],argv[3],NULL);
        perror("execlp\n");
        _exit(1);
    }

    if ((pid3 = fork()) == -1){
        perror("fork\n");
        exit(1);
    }else if (pid3 == 0){//son
        int fd_res;
        if ((fd_res = open(argv[5], O_CREAT | O_WRONLY | O_TRUNC, 0777)) == -1){
            perror("open result\n");
            exit(1);
        }
        dup2(fd2[0],0);
        dup2(fd_res, 1);
printf("2\n");
        close(fd1[0]);
        close(fd1[1]);
        close(fd2[0]);
        close(fd2[1]);
        //close(fd_res);
        execlp(argv[4], argv[4], NULL);
        perror("execlp\n");
        _exit(1);
    }
    close(fd1[1]);
    close(fd1[0]);
    close(fd2[1]);
    close(fd2[0]);
//  close(fd_dat);
//  close(fd_res);
    wait(NULL);
    wait(NULL);
    wait(NULL);
    return 0;
}