Your code doesn't compile. Please make always sure to post functional code.
The \1 wouldn't work here, at least I can't think how to use it between different regex calls ala / /g where you apply one regex several times. \1 can be used inside one regex to refer to an already matched part, but you actually don't do this here.
There is the experimental (?{ code }) construct which allows you to execute code inside the regex where you maybe could check if it already matched.

One better way would be to first match all patterns multiple times and then filter the list using a hash: 

use strict;
use warnings;

my $word = "zezl";
my $dictword = "zezezl";

my @pairs = $word =~ /(?=(..))/g;

my $matcher = qr/(?=(@{[join "|", @pairs]}))/;


my %seen;
my $matches = 0;
my @matches;
foreach my $match ($dictword =~ /$matcher/g) {
    if (not exists $seen{$match}) {
        $matches ++;
        push @matches, $match;
    }
    $seen{$match} = 1;
}

print "Matches: @matches\n";
print "$matches $dictword \n";

[download]
Here we iterate over the results and mark all matches as seen, but only count them the first time. In addition when you need the list of real matches you can push the first matches in an array like shown above.

In reply to Re: force regular expression to match every item only once by mscharrer
in thread force regular expression to match every item only once by hiddenOx

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