#include <ctype.h>
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
int main(int argc, char **argv) {
  if (argc != 2) {
    fprintf(stderr, "Wrong argument count!\n");
    return 1;
  }

  int reader = open(argv[1], O_RDONLY);
  if (reader == -1) {
    perror("Opening the file for reading failed");
    return 1;
  }

  int writer = open(argv[1], O_WRONLY);
  if (writer == -1) {
    perror("Opening the file for writing failed");
    close(reader);
    return 1;
  }

  while (1) {
    char buf[256];
    int cnt = read(reader, buf, 256);
    if (cnt <= 0)
      break;

    for (int i = 0; i < cnt; ++i)
      buf[i] = toupper(buf[i]);


    write(writer, buf, cnt);
  }
  
  close(reader);
  close(writer);
  return 0;
}