#!/usr/bin/perl

use strict;

my $string1 = "don";   # should both of these match?
my $string2 = "donk";  # (you be the judge, and choose
                       #  your regex accordingly)

my %regex = (
              complem_char_class => qr/don[^t]/,
              zwid_neg_lookahead => qr/don(?!t)/,
            );

for my $regtyp ( sort keys %regex ) {
   print "\n";
   for ( $string1, $string2 ) {
      my $result = ( /$regex{$regtyp}/ ) ? "succeeds" : "fails";
      print "For $_ : match $result based on $regtyp\n";
   }
}