The C code here is used for reference of how to pipe 3 separate children processes. It can be improved to support a dynamic amount of processes and corresponding pipes and system calls.

// This program is an example of how to run a command such as
// ps aux | grep root | grep sbin
// using C and Unix.
// pipe_example.c

#include 
#include 
#include 

int pid;
int pipe1[2];
int pipe2[2];

void exec1();
void exec2();
void exec3();

int main()
{

	// create pipe1
	if (pipe(pipe1) == -1)
	{
		perror("bad pipe1");
		exit(1);
	}

	// create pipe2
	if (pipe(pipe2) == -1)
	{
		perror("bad pipe2");
		exit(1);
	}

	// fork (ps aux)
	if ((pid = fork()) == -1)
	{
		perror("bad fork1");
		exit(1);
	}
	else if (pid == 0)
	{
		// stdin --> ps --> pipe1
		exec1();
	}
	// parent

	// fork (grep root)
	if ((pid = fork()) == -1)
	{
		perror("bad fork2");
		exit(1);
	}
	else if (pid == 0)
	{
		// pipe1 --> grep --> pipe2
		exec2();
	}
	// parent

	// close unused fds
	close(pipe1[0]);
	close(pipe1[1]);

	// fork (grep sbin)
	if ((pid = fork()) == -1)
	{
		perror("bad fork3");
		exit(1);
	}
	else if (pid == 0)
	{
		// pipe2 --> grep --> stdout
		exec3();
	}
	// parent
}

void exec1()
{
	// input from stdin (already done)
	// output to pipe1
	dup2(pipe1[1], 1);
	// close fds
	close(pipe1[0]);
	close(pipe1[1]);
	// exec
	execlp("ls", "ls", NULL);
	// exec didn't work, exit
	perror("bad exec ls");
	_exit(1);
}

void exec2()
{
	// input from pipe1
	dup2(pipe1[0], 0);
	// output to pipe2
	dup2(pipe2[1], 1);
	// close fds
	close(pipe1[0]);
	close(pipe1[1]);
	close(pipe2[0]);
	close(pipe2[1]);
	// exec
	execlp("grep", "grep", "c", NULL);
	// exec didn't work, exit
	perror("bad exec grep c");
	_exit(1);
}

void exec3()
{
	// input from pipe2
	dup2(pipe2[0], 0);
	// output to stdout (already done)
	// close fds
	close(pipe2[0]);
	close(pipe2[1]);
	// exec
	execlp("grep", "grep", "y", NULL);
	// exec didn't work, exit
	perror("bad exec grep y");
	_exit(1);
}

This code also works on Unix/Mac.
Compile with gcc pipe_example.c -o pipe_example.o
Run with ./pipe_example.o