You could do: 

my @array1 = (1,2,3,4,5);
my @array2 = (4,5,6,7,8);

@union = @intersection = @difference = (); 
%count = (); 
foreach $element (@array1, @array2) { $count{$element}++ } 
foreach $element (@array1, @array2) {
    if (exists $count{$element}) {
        push @union, $element; 
        push @{ $count{$element} > 1 ? \@intersection : \@difference }
+, $element;
        delete $count{$element};
    }
}

print "Union:        @union\n";
print "Intersection: @intersection\n";
print "Difference:   @difference\n";

[download]

Output: 

Union:        1 2 3 4 5 6 7 8
Intersection: 4 5
Difference:   1 2 3 6 7 8

[download]

Update: as to the incorrect difference (as pointed out by ikegami): the OP said "it's perfect for what i need, except for ... the order", so I didn't consider it my business to redefine his/her notion of "difference", but rather just modify the code to keep the original ordering...

In reply to Re: tweaking of perldoc function (sorting/preserving order) by almut
in thread tweaking of perldoc function (sorting/preserving order) by Anonymous Monk

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