I personally believe that to expand a little bit on the subject, I may mention that that code may be cast in the form of two nested greps:

  my @good = grep {
    my $yes = $_;
    !grep $_ == $yes, @notgood; 
} @goodarray;
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One minor inconvenience, with the inner one, is that it scans all of @notgood also when it has already found one matching element: of course we're generally not manic about this because we don't care premature optimization; but I somewhat psychologically feel uneasy with it. Then List::Util's first() comes to the rescue:

my @good = grep {
    my $yes = $_;
    !first {$_ == $yes} @notgood;
} @goodarray;
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Too bad it's not a builtin in the first place. But then 5.10 can do even better, with its smart match operator:

my @good = grep { not @notgood ~~ $_ } @goodarray;
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And that's it!