Use hash and count the elements occurs in the array as follow.

use strict;
use warnings;
use Data::Dumper;

my %count;
grep { ++$count{$_} } qw(a b a c d d e f g f h h);
print Dumper \%count;
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$VAR1 = {
          'e' => 1,
          'a' => 2,
          'd' => 2,
          'c' => 1,
          'h' => 2,
          'b' => 1,
          'g' => 1,
          'f' => 2
        };
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