Data::Dumper (and the similar Data::Dump::Streamer) are used to look at the contents of variables - generally for diagnostic purposes. They can also be used to serialise a data structure so that it can be persisted to disk (saved and restored later). Data::Dump::Streamer does a better job of handling edge cases than Data::Dumper. Consider:

use strict;
use warnings;
use Data::Dumper;
use Data::Dump::Streamer;

my %hash = (
     this => ['one', 2, 3.1],
     that => undef,
     );

print Dumper (\%hash);
Dump (\%hash);
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Prints:

$VAR1 = {
          'that' => undef,
          'this' => [
                      'one',
                      2,
                      '3.1'
                    ]
        };
$HASH1 = {
           that => undef,
           this => [
                     'one',
                     2,
                     3.1
                   ]
         };
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