#!/usr/bin/perl 
use strict;
use Digest::MD5 qw(md5);

my (@lines, %line_md5);
while (<>) {
        unless (/^\s*$/) {
                my $digest = md5($_);
                unless ( exists $line_md5{$digest} ) {
                        $line_md5{$digest} = 1;
                        push @lines, $_;
                }
        } else {
                push @lines, $_;
        }
}
print @lines;


##</code><code>##

cat file | sort | uniq