用exec C shell程序实现管道

Question

尝试实现shell程序我遇到了以下情况。

我想实现至少一个级别的管道（不链接） 例 我希望我的shell可以执行以下命令

ls | less

这是我的片段

int main()
{
    pid_t pid;
    int fd[2];
    char buffer[1024];      

    pipe(fd);
    pid=fork();


    if(pid==0){

        close(fd[0]);
        dup2(fd[1],1);
        close(fd[1]);

        execlp( "ls","ls",NULL);
        exit(0);

    }else{

        //parent
        wait(NULL);
        close(fd[1]);
        read(fd[0],buffer,sizeof(buffer));  // the parent reads the output of the last command 
                                        // from stdout 
        //printf("Recived:: %s\n",buffer); //for debugging --- and it works(got the output of the last command printed)!

        pid=fork();
        if(!pid){

            //printf("In new  child ::%s\n",buffer);// this line stil works

            **/**   !! HERE IS THE ISSUE **/**
            // I want to pass the a filename as an argument to the next command 
            // in this case for less 
            // someting like this execlp("less","less",filename.ext,NULL);

            // my question is how can I get file name in this situation

            //I tried to get file struct from the file discriptor and the tried to get
            // file name from that file , but faild!
            //FILE * file=fdopen(fd[0],"r+");
            //file->name;

            execlp("less","less",buffer ,NULL);

        }


    }

    return 0;
}