void update_logfile()
{
  char logfile[MAX_INPUT_LENGTH];
  sh_int filenumber=0;


  sprintf(logfile, "%s%s.%d.log", "../log/", timestamp(), filenumber);
   
  while( exists_file(logfile))
  {
    filenumber++;
    sprintf(logfile, "%s%s.%d.log", "../log/", timestamp(), filenumber);
  }

  fflush(stderr);
  freopen(logfile, "w", stderr);

  return;
}