/*
 * This code is identical to running
 * w | wc -w
 * in bash
 */
#include <stdio.h>
#include <unistd.h>

void child(int pfd[2]) {
    close(pfd[1]);
    dup2(pfd[0], STDIN_FILENO);
    close(pfd[0]);

    char cmd[] = "/usr/bin/wc";
    char *args[] = {"wc", "-w", NULL};
    execve(cmd, args, NULL);
}

void parent(int pfd[2]) {
    close(pfd[0]);
    dup2(pfd[1], STDOUT_FILENO);
    close(pfd[1]);

    char cmd[] = "/usr/bin/w";
    char *args[] = {"wc", NULL};
    execve(cmd, args, NULL);
}

int main (void) {
    int pfd[2];
    pipe(pfd);

    int pid = fork();

    if (pid == 0) {
        child(pfd);
    } else {
        parent(pfd);
    }
}