#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>

int main(void)
{
        const char *cmd[]={"ls", "tac", "less", NULL};
        int curpipe[2]={-1, -1}, lastpipe=-1, n;
        pid_t pids[64];

        for(n=0; cmd[n] != NULL; n++)
        {
                // If this isn't the last in the chain,
                // make a pipe for cmd[n] to write into.
                if(cmd[n+1] != NULL) pipe(curpipe);

                switch(pids[n]=fork())
                {
                case -1:
                        perror("couldn't fork");
                        break;
                default:// parent code

                        // Our latest child has a copy of the writing
                        // end, we don't need it anymore.
                        if(curpipe[1] >= 0) close(curpipe[1]);

                        // ...but we'll need the reading end next time.
                        // and we should close the last loop's reading end.
                        if(lastpipe >= 0) close(lastpipe);
                        lastpipe=curpipe[0];

                        // don't use those FD's again.
                        curpipe[1]=-1;  curpipe[0]=-1;
                        break;

                case 0: // child code

                        // If we have a reading end, use it.
                        if(lastpipe >= 0)
                        {
                                dup2(lastpipe, 0);
                                close(lastpipe);
                        }

                        // if we have a writing end, use it.
                        if(curpipe[1] >= 0)
                        {
                                // make a copy.
                                dup2(curpipe[1], 1);
                                // close both ends.
                                close(curpipe[1]);
                                close(curpipe[0]);
                        }

                        execlp(cmd[n], cmd[n], NULL);
                        perror("couldn't exec");
                        exit(1);
                        break;
                }
        }

        for(n=0; cmd[n] != NULL; n++)
        {
                int status;
                wait(&status);
        }
}