Switch to stdio for output. It's simpler

[overonion] / reverse.c

#include "reverse_lib.h"

#include <err.h>
#include <stdio.h>
#include <sysexits.h>

int main(int argc, char** argv) {
  if (argc != 2) {
    errx(EX_USAGE, "Usage: reverse filename");
  }

  reverse_file(argv[1], stdout);

  return 0;
}