Creating three children and connecting pipes between them - linux

Question

I am in need of some help of understanding how to create one parent and three children and connecting pipes between the childrens.
My task is to get the first child to run ls -l /bin/?? and send it to the second child that will run grep rwxr-xr-x and send that to the third child that will run sort.
It wil look like this if typed in to bash:
ls -l /bin/?? | grep rwxr-xr-x | sort
My code right now:
#include <sys/wait.h>
#include <sys/types.h>
#inlcude <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#define READ 0
#define WRITE 1
int main()
{
int fds[2], i;
pid_t pid;
pipe(fds);
for(i = 0; i < 3; i++)
{
pid = fork();
if(pid == (pid_t) 0)
if(i == 0)
{
/* First child */
}
else if(i == 1)
{
/* second child */
}
else if(i == 2)
{
/* Third child */
}
break;
else
{
/* This is the parent */
}
}
}
The problem is that i don't really know if this is the correct way of doing it.
Please avoid telling me to do this with threads as I am trying to learn pipes and communication between processes.

Answer 1

You are running a fork() in a loop. Every fork() will result in two processes. So total you are creating 8 processes. Need to take that fork() call out of the loop.
This is how fork works,
fork() [Process 1]
/\
/ \
[Process 1]fork() fork()[Process 2]
/\
/ \
[Process 2]fork() fork()[Process 3]
To achieve what you aspire try following code,
int main()
{
pid_t pid[3];
pid[0] = fork();
if( pid[0] == 0)
{
/* First Process */
pid[1] = fork();
if(pid[1] == 0)
{
/* First Process Continued. */
}
else
{
/* Second Process */
}
}
else
{
/* 3rd Process */
}
return 0;
}