Use the code below to say matched element count also, this will tell you the possible matches not only twice.

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

my %hash_count;
my @array =  ( "54321", "54312" ,    "5999" ,    "54352" ,    "12345" 
+   );

  my @original =    ( "12345" ,    "54321" ,    "12355", "54321"    );

    foreach my $string(@array)
    {
        foreach my $string2(@original)
        {
            if ($string eq $string2) {
                $hash_count{$string}++;
            }
            else
            {
                unless (exists $hash_count{$string})
                {
                    $hash_count{$string} = 0;
                }
            }

        }
    }

print Dumper \%hash_count;

foreach (keys %hash_count)
{        
    unless ($hash_count{$_}) {
            print "$_ Not found\n";
    }   
    else
    {   
            print "$_ found $hash_count{$_} times\n" ;
    }
}
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