I'd like to see radical changes [...], not some small syntax adjustments

Ah, but "some small syntax adjustments" are all that's between your code working on pre 5.6 install and not.

use Symbol;

sub Counter ($) {
    local $/ = "\n";
    my             $fh = gensym();
    open           $fh, "+< $_[0]" or
    open           $fh, ">  $_[0]" or return undef;
      # ...
}
[download]

But the way I'd do it ...

use File::CounterFile;

  # ...

my $count = File::CounterFile->new($counter,$def_value)->inc;
[download]

    --k.