my $num_ent_chars = "()";  # add other characters as needed, but ^ - [ ] are special
$data =~ s/([$num_ent_chars])/sprintf("&#x%4x;",ord($1))/ge;


##</code><code>##

perl -le '$_="me [ and ] you ^ and - him";  $c="][^-";  s/[$c]/xxx/g;  print'