Here is a solution that uses Path::Tiny. See Path::Tiny: The little module that keeps on giving for a nice introduction to Path::Tiny.

#!/usr/bin/env perl

use strict;
use warnings;

use Path::Tiny;

my $dir = shift or die 'No directory given';

my $dir_path = path($dir);

unless($dir_path->is_dir){
    die "$dir is not a directory";
}

my %files_of;

foreach my $file_path ($dir_path->children){
    my $digest = $file_path->digest; # default is SHA-256
    #my $digest = $file_path->digest('MD5'); # use this if you want MD
+5
    push @{$files_of{$digest}}, $file_path->basename;
}

foreach my $digest (keys %files_of){
    my @files = @{$files_of{$digest}};
    if( scalar @files > 1){
        print join(', ', @files), " are duplicates.\n";
    }
}

exit;
[download]