# You use push so you must want an array
push @{ $provisions{$person} }, $1; 

# You use hash of hash addressing so you must want a hash
$total_bytes{$source}{$destination} += $bytes;

##</code><code>##

perl -MData::Dumper -le'$t{x}{y}[2]{foo}[3]{bar}=1; print Dumper \%t'
$VAR1 = {
          'x' => {
                   'y' => [
                            undef,
                            undef,
                            {
                              'foo' => [
                                         undef,
                                         undef,
                                         undef,
                                         {
                                           'bar' => 1
                                         }
                                       ]
                            }
                          ]
                 }
        };