$ perl -E 'mkdir("\x{100}")'
$ perl -MB -E 'my @d= <*>; say B::perlstring($_) for @d'
"\304\200"
$ perl -E 'my ($d)= <*>; open(my $f, ">", "$d/\x{101}.txt") or die "$!"'
No such file or directory at -e line 1.