#include <stdio.h>
#include <errno.h>
#include <fcntl.h>
#include <stdlib.h>
#include <unistd.h>

int main() {
        int pdesk[2][2];

        pipe(pdesk[0]);

        if(fork() == 0) {
        //dziecko 1
                //write to first pipe
                close(pdesk[0][0]);
                dup2(pdesk[0][1], STDOUT_FILENO);       //kopia deskryptora pliku
                close(pdesk[0][1]);
                execlp("who", "who", NULL);
        }
        pipe(pdesk[1]);
        if(fork() == 0) {
        //dziecko 2
                //read from first pipe
                close(pdesk[0][1]);
                dup2(pdesk[0][0], STDIN_FILENO);
                close(pdesk[0][0]);
                //write to second pipe
                close(pdesk[1][0]);
                dup2(pdesk[1][1], STDOUT_FILENO);
                close(pdesk[1][1]);
                execlp("head", "head", NULL);
        }
        //rodzic
        //close first pipe
        close(pdesk[0][0]);
        close(pdesk[0][1]);
        //read from second pipe
        close(pdesk[1][1]);
        dup2(pdesk[1][0], STDIN_FILENO);
        return 0;
}