Perl: basic question about hashmap

Question

$hash_map{$key}->{$value1} = 1;

I'm just a beginner at perl and I need help in this expression, what does this expression mean? I assume that a new key/value pair will be created but what is the meaning of 1 here?

Answer 1

What you've got here is a hash of hashes, or a two-level hash. $hash_map{$key} holds a hash reference, which points to another hash. $hash_map{$key}{$value} (the arrow can be omitted in this case) is a particular key in the second hash. The 1 is the value being assigned to that hash key.

For more on this topic, see Perl Data Structures Cookbook section on Hashes of Hashes, and also see the Perl reference tutorial for how references work.