A derived version that doesn't load the full file list in memory:

use strict;
use warnings;
use File::Find::Rule;

my ($n, @dirs) = @ARGV;
$n ||= 20;
@dirs = '.' unless @dirs;

sub top {
    my $file_sizes = shift;
    my @big = (sort { $file_sizes->{$b} <=> $file_sizes->{$a} } keys %
+$file_sizes)[0..$n-1];
    my %big = map { $_ => $file_sizes->{$_} } @big;
    return \%big
}

my $rule = File::Find::Rule->file->readable;
my $file_sizes = {};

$rule->start(@dirs);
while (defined (my $image = $rule->match) ) {
    my $size = (stat $image)[7];
    $file_sizes->{$image} = $size if defined $size;
    $file_sizes = top($file_sizes) if keys %$file_sizes > ($n + 10000)
+;
}
$file_sizes = top($file_sizes);

print "Biggest $n\n";
for my $file ( sort { $file_sizes->{$b} <=> $file_sizes->{$a} } keys %
+$file_sizes ){
    printf " %8dK  %s\n", $file_sizes->{$file} / 1024, $file;
}
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