If you prefer map you could:

my @test = ("camel","aplaca","peguin","aplaca","monkey","camel","camel
+");
my (%duplicate,%test,@redundant);

map{exists$test{$_}?$duplicate{$_}=1:$test{$_}=1}@test;

@redundant = keys %duplicate;
print "@redundant\n";
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tachyon