Implementing pipe in C

Question

I am trying to implement pipe in C. eg - $ ls | wc | wc

I have written the following code -

#include
#include

        

Answer 1

This does virtually no error checking, but why so complicated?

int main (int argc, char ** argv) {
    int i;

    for( i=1; i<argc-1; i++)
    {
        int pd[2];
        pipe(pd);

        if (!fork()) {
            dup2(pd[1], 1); // remap output back to parent
            execlp(argv[i], argv[i], NULL);
            perror("exec");
            abort();
        }

        // remap output from previous child to input
        dup2(pd[0], 0);
        close(pd[1]);
    }

    execlp(argv[i], argv[i], NULL);
    perror("exec");
    abort();
}

Answer 2

If your are still interested in why your source didn't work (Sergey's solution is better anyway):

The problem is not closing the write side of fd_1 in the parent process. Thus both argv[1] and parent have been writers to that pipe and that caused the confusion. Please don't ask for more details (esp. why the prob doesn't occur if you use only one pipe) but your original source will run with tree processes if you just add a close( fd_1[1] ); after the first call of run_cmd()