Just one comment more.
In perlfaq4 you have a chunk of code to evaluate union, intersection a difference from two arrays.
"How do I compute the difference of two arrays? How do I compute the intersection of two arrays?"
You can see question/answer here

perldoc -q intersection
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Hopes

perl -le '$_=$,=q,\,@4O,,s,^$,$\,,s,s,^,b9,s,$_^=q,$\^-]!,,print'
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