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

main(int argc, char *args[])
{
  int fd, n;
  char buffer[1024];
  struct stat st;

  if(argc > 3)
  {
    fprintf(stderr, "Usage: %s [inputfile [outputfile]]", args[0]);
    exit(1);
  }
  if(argc >= 2 && strcmp(args[1], "-") )
  {
    if( ((fd = open(args[1], O_RDONLY)) == -1) || (dup2(fd, STDIN_FILENO) == -1) )
    {
      fprintf(stderr, "%s: Unable to open %s for input.\n", args[0], args[2]);
      exit(1);
    }
    close(fd);
    fstat(STDIN_FILENO, &st);
  } else
    st.st_mode = S_IRUSR | S_IWUSR;

  if(argc == 3 && strcmp(args[2], "-") )
  {
    if( ((fd = open(args[2], O_WRONLY | O_CREAT | O_TRUNC, st.st_mode)) == -1) || (dup2(fd, STDOUT_FILENO) == -1))
    {
      fprintf(stderr, "%s: Unable to open %s for output.\n", args[0], args[2]);
      exit(1);
    }
    close(fd);
  }

  while( (n = read(STDIN_FILENO, buffer, 1024)) > 0)
  {
    if(write(STDOUT_FILENO, buffer, n) != n)
    {
      fprintf(stderr, "%s: Error writing.\n", args[0]);
      exit(1);
    }
  }
}