my $arg = "10FFFF"; # for instance

# simpler way?
eval { use warnings FATAL => qw(all);
  my ($fh, $string);
  open($fh, ">", \$string) || die "open(string) failed: $!";
  binmode($fh, ":utf8");
  print $fh chr(hex("$arg"));
};

die "good, caught it from eval: $@" if $@;

# don't want to get here
binmode(STDOUT, ":utf8");
print chr(hex($arg));