Let's establish some ground rules.

Provide a function that takes two arrayrefs, combines them and returns an array containing all the elements in the previous two arrays, bu no duplicates.

As I don't know them, you can't use commandline opts. *grins*

my @arr1 = (1, 2, 3, 4, 5);
my @arr2 = (4, 5, 6, 7, 8);

my @arr3 = f(\@arr1, \@arr2);

sub f {
#234567890#234567890#234567890
@h{map{@$_}@_}=1;keys%h
}
[download]

23 characters, and I know I can do better.

Update: 22 chars

@h{map@$_,@_}=1;keys%h
[download]

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Don't go borrowing trouble. For programmers, this means Worry only about what you need to implement.