use Set::Scalar;

my @filenames = ( 'name1.txt', 'name2.txt' );
my @sets = map {
    read_file_to_set( $_ )
} @filenames;

my $intersection = $sets[0]->intersection( $sets[1] );

print "$intersection\n";

sub read_file_to_set {
    my ($filename) = @_;

    open my $fh, '<', $filename
        or die "Cannot open '$filename' for reading: $!\n";

    chomp( my @lines = <$fh> );

    close $fh;

    return Set::Scalar->new( @lines );
}