use Symbol;

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

##</code><code>##

use File::CounterFile;

  # ...

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