perl -MDigest::MD5 -ne "print if ($seen{&Digest::MD5::md5_hex($_)}.= @ARGV) =~ /10$/" fileA.txt fileB.txt > output.txt

##</code><code>##

use Tie::File;
my @content;
tie (@content, 'Tie::File', $file)
	    or die "Error: couldn't tie $file: $!\n";
# .... and treat the filecontent like an array, e.g.
print scalar(@content);
# .....
untie (@content);