15.9.c

#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <string.h>
#include <unistd.h>

#define MAXLINE 1024

static void sig_pipe(int);

int main(void)
{
    int     n, fd1[2], fd2[2];
    pid_t   pid;
    char    line[MAXLINE];

    if (signal(SIGPIPE, sig_pipe) == SIG_ERR) {
        printf("signal error\n");
        exit(-1);
    }

    if (pipe(fd1) < 0 || pipe(fd2) < 0) {
        printf("pipe error\n");
        exit(-1);
    }

    if ((pid = fork()) < 0) {
        printf("fork error\n");
        exit(-1);
    } else if (pid > 0) {
        close(fd1[0]);
        close(fd2[1]);

        while (fgets(line, MAXLINE, stdin) != NULL) {
            n = strlen(line);

            if (write(fd1[1], line, n) != n) {
                printf("write error to pipe\n");
                exit(-1);
            }

            if ((n = read(fd2[0], line, MAXLINE)) < 0) {
                printf("read error to pipe\n");
                exit(-1);
            }

            if (0 == n) {
                printf("child closed pipe\n");
                break;
            }

            line[0] = 0;
            if (fputs(line, stdout) == EOF) {
                printf("fputs error\n");
                exit(-1);
            }
        }

        if (ferror(stdin)) {
            printf("fgets error to stdin\n");
            exit(-1);
        }

        return 0;
    } else {
        close(fd1[1]);
        close(fd2[0]);

        if (fd1[0] != STDIN_FILENO) {
            if (dup2(fd1[0], STDIN_FILENO) != STDIN_FILENO) {
                printf("dup2 error to stdin");
                exit(-1);
            }

            close(fd1[0]);
        }

        if (fd2[1] != STDOUT_FILENO) {
            if (dup2(fd2[1], STDOUT_FILENO) != STDOUT_FILENO) {
                printf("dup2 error to stdin");
                exit(-1);
            }

            close(fd2[1]);
        }

        if (execl("./15.8" "15.8", (char *)0) < 0) {
            printf("execl error\n");
            exit(-1);
        }

        return 0;
    }
}

static void sig_pipe(int signo)
{
    printf("SIGPIPE caught\n");
    exit(1);
}