Then the solution above may be simplified to:

#!/usr/bin/perl -l

use strict;
use warnings;

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

my %saw;
$saw{$_}++ for @file1, @file2;

print <<"EOT"
\@file1 only: (@{[ grep $saw{$_}==1, @file1 ]})
\@file2 only: (@{[ grep $saw{$_}==1, @file2 ]})
common: (@{[ grep $saw{$_}==2, @file2 ]})
EOT

__END__
[download]

or even, using modulo-2 math, but more obscurely:

#!/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, @file2;

print <<"EOT"
\@file1 only: (@{[ grep $saw{$_}, @file1 ]})
\@file2 only: (@{[ grep $saw{$_}, @file2 ]})
common: (@{[ grep !$saw{$_}, @file2 ]})
EOT

__END__
[download]

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