If I pass a reference to a hash into a sub, I keep working with the reference:

some_sub(\%some_hash);

sub some_sub {
        my $hash_ref = $_[0];

        ## Now communicate with hash using:
        ## $hash_ref->{'SOME_KEY'} returns the value for SOME_KEY
        ## or
        ## $hash_ref->{'OTHER_KEY'} = "foo" will set a key to a value
        ## etc.


        ## Or the slightly more exciting:
        ## foreach $key (keys %{$hash_ref}) {
        ##      do_something_with $hash_ref->{$key}

}
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