http://www.perlmonks.org?node_id=438284

pglenski has asked for the wisdom of the Perl Monks concerning the following question:

Back in 04/27/01 #76296 dvergin posted a solution to finding unique occurrences in a hash. It works beautifully but I can't figure how it works.
my @ary = qw(a b c d d e b d); my %hsh; undef @hsh{@ary}; my @ary2 = keys %hsh; print "@ary2\n";
It's the line  undef @hsh{@ary} that I can't figure out. I need baby step explanations, I guess. Isn't @hsh and %hsh two completely different things? Thanks in advance. Pls refer to the what page # in the Camel book if possible.