First off, both '@a' and '@b' are special arrays used by the 'sort' function. In this case it won't hurt anything to use them.. just something to keep in mind.

What you can do:

if (defined(@a) || defined(@b))
 {
   push(@test, @a, @b);
 }
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If either is defined it will push it into @test.. if both are defined, it pushes @a, then @b into @test.