you must decode your input, or to be more precise Perl needs to know that you are handling char-strings and not byte-strings.

For that to happen you need to convert the input's encoding format to Perl's internal text format.

from Encode

$string = decode(ENCODING, OCTETS[, CHECK])

And this can already happen in an input layer when opening.

see perluniintro#Unicode-I/O

No better help, since I don't know your input's encoding.