#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>

main(int argc, char **argv)
{
  int p, u, f, m;

  if (argc != 4) {
    fprintf(stderr, "usage: q4 p m u\n");
    exit(1);
  }

  p = O_WRONLY;
  if (strchr(argv[1], 'a') != NULL) p |= O_APPEND;
  if (strchr(argv[1], 'c') != NULL) p |= O_CREAT;
  if (strchr(argv[1], 't') != NULL) p |= O_TRUNC;
  if (strchr(argv[1], 'x') != NULL) p |= O_EXCL;

  sscanf(argv[2], "%o", &m);
  if (sscanf(argv[3], "%o", &u) == 1) umask(u);

  f = open("f1.txt", p, m);
  write(f, "XXX\n", 4);
  close(f);

  system("ls -l f1.txt");
  chmod("f1.txt", 0644);
  system("cat f1.txt");
  exit(0);
}