c程序用管道来执行“ps aux | grep firefox | tee processes.txt“

This is my first question. Hopefully it will not be dumm. Im having problems to write a program that produce "ps aux | grep firefox | tee processes.txt". I succeeded with 1 pipe like "ps aux | grep firefox ", but when I tried to generalize I have problems. My intention is to use pipes to understand them. I know that is possible with open. Any hint would be great!This is my first question. Hopefully it will no