Understanding Data::Dumper output

Simple question:

use warnings;
use XML::Simple;
use Data::Dumper;

my $file='test.osm';

my $test_data = XMLin( $file ); 

print Dumper( $test_data ); 

my @way_node_refs=$test_data->{'way'}->{'nd'};

print Dumper( @way_node_refs ); 

print( @way_node_refs[1]->{'ref'} );ere

It has the following output. The first dump is not given because it does not matter.

$VAR1 = [
      {
        'ref' => '453966480'
      },
      {
        'ref' => '453966490'
      },
      {
        'ref' => '453966482'
      },
      {
        'ref' => '453966130'
      },
      {
        'ref' => '453966143'
      },
      {
        'ref' => '453966480'
      }
    ];

How can I access the values with the key ref. I don't know how to interprete the braces kinda.

You have an array reference where the values inside the array are hash references. To access single values, use the arrow operator ->.

 print $foo->[0]->{ref};
 print $foo->[1]->{ref};

Or you can loop through them.

foreach my $elem ( @{ $foo } ) {
    print Dumper $elem;
    print $elem->{ref};
}

You could even sort them alphabetically by the values of the ref keys.

my @sorted = sort { $a->{ref} cmp $b->{ref} } @$foo; # note @sorted is an array

See perlref, perlreftut and perldsc for more details on data structures and references.