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Piping output between processes. C.

Hello everyone. I have a problem.
I have to write a peace of code in C that will simulate a simple shell and in that shell only commands that are listed in specification file are allowed. However, that is not a problem, because I got it working already for single command entries. What I'm struggling with is geting output piped from one command to another like:
# ls -l | grep stuff
given that both ls and grep are permitted.
Any idea how to approach it?
I use fork() and execvp() to execute commands.
Many thanks in advance.

I am so sorry.
I should have searched this forum before posting my question.
This problem can easily be solved by using popen() like it was suggested in thread below.
Sort of:

Code:

/*****************************************************************************

 Excerpt from "Linux Programmer's Guide - Chapter 6"

 (C)opyright 1994-1995, Scott Burkett

 ***************************************************************************** 

 MODULE: popen2.c

 *****************************************************************************/



#include <stdio.h>



int main(void)

{

        FILE *pipein_fp, *pipeout_fp;

        char readbuf[80];



        /* Create one way pipe line with call to popen() */

        if (( pipein_fp = popen("ls", "r")) == NULL)

        {

                perror("popen");

                exit(1);

        }



        /* Create one way pipe line with call to popen() */

        if (( pipeout_fp = popen("sort", "w")) == NULL)

        {

                perror("popen");

                exit(1);

        }



        /* Processing loop */

        while(fgets(readbuf, 80, pipein_fp))

                fputs(readbuf, pipeout_fp);



        /* Close the pipes */

        pclose(pipein_fp);

        pclose(pipeout_fp);



        return(0);

}

Sorry ones again.