%entry is a HoHoH - Hash of Hash of Hash. The first hash is keyed by name. That accesses a hash keyed by UID. That accesses a hash keyed by various parameters including the host name. In the line:

my @hosts = map {$entries{$name}{$_}{host}} keys %{$entries{$name}};

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we generate a list of the hosts associated with a particular name. The hosts are in the 'host' parameter in the hash accessed by UID.

keys %{$entries{$name}} generates a list of UIDs for a given name. Remember that hashes and arrays only store scalar values so what is stored is really a reference to a hash. So the % sigil in %{...} dereferences the hash reference to be a hash which keys then returns the list of keys for.

For each UID in the list map {$entries{$name}{$_}{host}} retreives the host name - the map generates an output list with each element from the input list replaced by the matching host name.

DWIM is Perl's answer to Gödel

In reply to Re^5: trying to decide best data structure for problem at hand. by GrandFather
in thread trying to decide best data structure for problem at hand. by mikejones

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