#!/usr/bin/perl -l

use strict;
use warnings;

my @file1=qw/foo bar baz/;
my @file2=qw/fred bar barney/;

my %saw;
$saw{$_}=1 for @file1;
$saw{$_}.=2 for @file2;
my %comm; push @{ $comm{$saw{$_}} }, $_ for keys %saw;

print <<"EOT"
\@file1 only: (@{ $comm{1} })
\@file2 only: (@{ $comm{2} })
common: (@{ $comm{12} })
EOT

__END__