# FILE1 & FILE2 is a filehandle opened elsewhere. $read is a list of
  # filehandles we are interested in reading

  my $read = '';                    # Initialise to an empty set
                                    # (NOTE: $read=0 is very wrong)
  vec($read, fileno(FILE1), 1) = 1; # Set the appropriate bit
  vec($read, fileno(FILE2), 1) = 1; # And for another file...