Perl Data Dumper Specifiers Explanation

Question

Observing the output of Data::Dumper, the specifiers ($VAR1, "", ;) are not explained in the CPAN documentation.

Here is my output:

$VAR1 = "Snow";
$VAR1 = "Rain";
$VAR1 = "Sunny";
$VAR1 = "";

They're explained [right at the beginning of the documentation](https://perldoc.pl/Data::Dumper#DESCRIPTION). — melpomene, Sep 27 '18 at 20:16
Note that you can change the name of the variable used by setting `$Data::Dumper::Varname` (defaults to VAR), and remove those variables and semicolons entirely by setting `$Data::Dumper::Terse` to 1, if you don't care about being able to string-eval the result (most people don't). — Grinnz, Sep 27 '18 at 20:27
@Grinnz this is the type of information I was looking for when talking about the data dumper. Many people want to score this question down, but they really don't understand exactly the data dumper module. — Minimalist, Sep 27 '18 at 23:54
@Grinnz another point I asked this question to get more a practitioner point-of-view when using this module. Thanks for your input. — Minimalist, Sep 28 '18 at 00:13

score 3 · Answer 1 · answered Sep 27 '18 at 19:36

The specifiers are described in the second paragraph of the DESCRIPTION:

The return value can be "eval"ed to get back an identical copy of the original reference structure.

So, you can take the string returned by Dumper and run

my $x = eval $dumped_string;

score -1 · Accepted Answer · answered Sep 27 '18 at 20:20

Looks like you have an array:

my @arr = ('Snow','Rain','Sunny');
print Dumper(@arr);

When you pass the array, Dumper thinks you passed 3 separate variables. That is why you get:

$VAR1 = 'Snow';
$VAR2 = 'Rain';
$VAR3 = 'Sunny';

In order to see the array as data structure, you need to pass the reference to the array:

print Dumper(\@arr);

This will produce:

$VAR1 = [
          'Snow',
          'Rain',
          'Sunny'
        ];

The output says that you passed the reference to array with 3 elements.

OP's output says `$VAR1` everywhere, indicating that it's from multiple `Dumper` calls. — melpomene, Sep 27 '18 at 20:21

2 Answers2