Setting $/ to a reference to an integer, scalar
  containing an integer, or scalar that's convertable
  to an integer will attempt to read records instead
  of lines, with the maximum record size being the
  referenced integer. So this:

    $/ = \32768; # or \"32768", or \$var_containing_32768
    open(FILE, $myfile);
    $_ = <FILE>;

  will read a record of no more than 32768 bytes from
  FILE. If you're not reading from a record-oriented
  file (or your OS doesn't have record-oriented
  files), then you'll likely get a full chunk of data
  with every read. If a record is larger than the
  record size you've set, you'll get the record back
  in pieces.