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#!/usr/bin/perl

...
3
4
5

$ perl  doubly_linked.pl
Current: 0      Previous:       Next: 1
...
Current: 2      Previous: 1     Next: 3
Current: 3      Previous: 2     Next: 4
Current: 4      Previous: 3     Next: 5

$VAR1 = {
          'next' => {
...
          'prev' => undef,
          'data' => 0
        };