As you don't care how many times the items are in array 1, I'd use a hash rather than multiple greps. A hash will make it an O(M + N) algorithm, the greps are an O(M x N) solution. Of course, this will use more memory too and you should take that into consideration when choosing which to use.

my %seen; 
@seen{@array_1} = (0) x @array_1; 
exists( $seen{$_} ) and $seen{$_}++ for @array_2;
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-sauoq
"My two cents aren't worth a dime.";