or download this
$ perl -MEncode=_utf8_on -e'$s = "\xF1\xF4"; _utf8_on($s); "" =~ /$s/'
Malformed UTF-8 character (unexpected non-continuation byte 0xf4, imme
+diately after start byte 0xf1) in regexp compilation at -e line 1.
...
$ perl -MEncode=_utf8_on -e'$s = "\xF1\xF4"; "" =~ /$s/'
$