Please see comments

#!/usr/bin/perl 

my $val=0;
my @array_a = (1..8);
my @array_b = (6..10);
my %count= ();
my @all = ();
my @inter =();
my @different =();

foreach $val (@array_a, @array_b) { $count{$val}++; } #build hash 
# that counts the number of times a number is seen
# 1=>1, 2=>1, ... 6=>2, 7=>2, etc...

foreach $val (keys %count) {

    push @all, $val; # the keys have to be unique in hash %count
 
    push @{ $count{$val} > 1 ? \@inter : \@different}, $val;  # lookup
+ ternary operator
# if the $val of %count is  >1 push to @inter. if not, push to @differ
+ent
};

@all = sort {$a <=> $b} @all;    #sort
@different = sort {$a <=> $b} @different;
@inter = sort {$a <=> $b} @inter;

print "all:\n";
foreach (@all) {
    print "\t$_\n";    
};

print "Different:\n";
foreach (@different) {
    print "\t$_\n";    
};

print "Intersect:\n";
foreach (@inter) {
    print "\t$_\n";    
};
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HTH, Rob