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

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

    int pipe_ends [2];
    if (pipe(pipe_ends) == -1)
        perror("pipe"), exit(1);

    pid_t child = fork();
    if (child == -1)
        perror("fork"), exit(1);

    if (child == 0) {
        // the child

        char msg [] = { "Hi\n" };

        close(pipe_ends[0]);
        
        if (write(pipe_ends[1], msg, sizeof msg - 1) == -1)
            perror("write");
        
    } else {
        // the parent
    
        char pipe_buf[128];

        close(pipe_ends[1]);
        
        size_t n;
        while ((n = read(pipe_ends[0], pipe_buf, sizeof pipe_buf)) > 0)
            if (write(1, pipe_buf, n) != n)
                perror("write");
    }
}