Set intersection and complement one-liners.

$ cat A; echo '* * * * *'; cat B
apple
cherry
carrot
lime
* * * * *
lime
orange
banana
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A ∩ B
Intersection of A and B.

$ perl -e 'open F,$ARGV[0] or die;shift;my %set = map {$_ => 1 } <>; f
+or (<F>) {print if $set{$_}};' A B
lime
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B / A
Complement of B relative to A.

$ perl -e 'open F,$ARGV[0] or die;shift;my %set = map {$_ => 1 } <>; f
+or (<F>) {print unless $set{$_}};' A B
apple
cherry
carrot
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The first argument is always set A. The union of all the other arguments is set B. Thus:

$ cat C
grape
apricot
cherry

$ perl -e 'open F,$ARGV[0] or die;shift;my %set = map {$_ => 1 } <>; f
+or (<F>) {print unless $set{$_}};' A B C
apple
carrot

$ perl -e 'open F,$ARGV[0] or die;shift;my %set = map {$_ => 1 } <>; f
+or (<F>) {print if $set{$_}};' A B C
cherry
lime
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