The hash approach is better for that, but I went ahead and re-implemented the regexp approach again anyway, just in case someone is interested in a pattern matching solution rather than an 'equal key' solution.

If you wanted to continue with the regexp approach, this solution will count the number of duplicate words. I modified the RE a little so that it would count "Antony Antony Antony" as two duplicates (Antony is repeated twice after the original). "Antony Antony Hank Antony Hank Mark" would count 3: Antony has two repeats, and Hank has one.

use warnings;
use strict;

my $string='LOCAL    Antony    17    Antony    23    1569';

my $count;
$count++ while
    $string =~ m/
                  \b([[:alpha:]]+)\b
                  (?=.*?\b\1\b)
                /xg;

print $count, "\n";
[download]