15.7.c

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

#define MAXLINE 1024

int main(void)
{
    char    line[MAXLINE];
    FILE    *fpin;

    if ((fpin = popen("./15.6", "r")) == NULL) {
        printf("popen error\n");
        exit(-1);
    }

    for ( ; ; ) {
        fputs("prompt> ", stdout);
        fflush(stdout);
        
        if (fgets(line, MAXLINE, fpin) == NULL) {
            break;
        }

        if (fputs(line, stdout) == EOF) {
            printf("fputs error to pipe");
            exit(-1);
        }
    }

    if (pclose(fpin) == -1) {
        printf("pclose error\n");
        exit(-1);
    }

    putchar("\n");
    return 0;
}