root/pipe4.c

DEFINITIONS

1. main

#include<unistd.h>
#include<stdio.h>

#ifdef SYSVR4
#define PIPE(a) pipe(a)
#else
#include<sys/socket.h>
#define PIPE(a) socketpair(AF_UNIX, SOCK_STREAM,PF_UNIX,(a))
#endif

int main() {

        int p,i;
        int fd[2];
        char *messages[]={"3+4\n","5*6\n","10+100-(4*4)\n"};
        char result[100];

        PIPE(fd);
        if (p=fork()) {
                close(fd[1]);
                dup2(fd[0],0);
                dup2(fd[0],2);
                for (i=0;i<3;i++) {
                        fprintf(stderr,messages[i]);
                        fflush(stderr);
                        if (gets(result)) {
                                printf("%s\n",result);
                        }
                }

        } else {
                close(fd[0]);
                dup2(fd[1],1);
                dup2(fd[1],0);
                execl("/usr/bin/bc","bc","-q",(char *)0);
        }

        return 0;
}