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

#define INFNAME "dup.c"
#define OUTFNAME "DUP.c"

int main ()
{
   int ifd, ofd;
   char c;

   /* Open input file descriptor */
   ifd = open(INFNAME, O_RDONLY);
   if (ifd < 0) {
      fprintf(stderr, "Unable to open input file in read mode...\n");
      exit(1);
   } else {
      fprintf(stderr, "New file descriptor obtained = %d\n", ifd);
   }

   /* Open output file descriptor */
   /* The file is created in the mode rw-r--r-- (644) */
   ofd = open(OUTFNAME, O_CREAT | O_WRONLY, S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH);
   if (ofd < 0) {
      fprintf(stderr, "Unable to open output file in write mode...\n");
      exit(2);
   } else {
      fprintf(stderr, "New file descriptor obtained = %d\n", ofd);
   }

   close(0);    /* Close the file descriptor for stdin */
   close(1);    /* Close the file descriptor for stdout */

   dup(ifd);    /* Duplicate ifd at the lowest-numbered unused descriptor */
   close(ifd);  /* ifd is no longer needed */

   dup(ofd);    /* Duplicate ofd at the lowest-numbered unused descriptor */
   close(ofd);  /* ofd is no longer needed */

   /* Read from stdin and write to stdout, as if nothing has happenned */
   while (1) {
      scanf("%c", &c);  /* Reading is done from the input file */
      if (feof(stdin)) break;
      if ((c >= 'a') && (c <= 'z')) c -= 'a' - 'A';
      printf("%c", c);  /* Writing is done to the output file */
   }

   exit(0);
}