// gcc -Wall -Wextra -o client client.c

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>

#define FIFO_PATH "/tmp/myfifo"

int
main(int argc, char *argv[])
{
    int fd = -1;

    fd = open(FIFO_PATH, O_WRONLY);
    printf("fd = %d\n", fd);

    if (fd < 0) {
        fprintf(stderr, "Could not open fifo %s: %s\n", FIFO_PATH, strerror(errno));
        return -1;
    }

    int flags = fcntl(fd, F_GETFL);
    if (flags == -1)
        fprintf(stderr, "fcntl F_GETFL: %s\n", strerror(errno));
    printf("flags = 0%o\n", flags);

    if (argc > 1) {
        write(fd, argv[1], strlen(argv[1]) );
    } else {
        write(fd, &"What ho!", 9);
    }
    // note: printf "What ho" > /tmp/myfifo from bash, would close the file descriptor.

    printf("Closing ... fd = %d\n", fd);
    close(fd); // EOF

    return 0;
}

//=====