use strict;
use warnings;
use Data::Dumper;
use JSON;

my $son = '{    
     "trans2": [   90, 20 , 80, 33 ]
}';  # THIS IS a *STRING* 

my $r=decode_json($son);#cannot understand why I need to do
  # the 'decode' converts the string into a  a perl structure (Hash re
+f), and store in $r
print Dumper \$r; # without dumper, how can I iterate using for loop?
# Here's how to iterate ..
for my $k (sort keys %$r){
  print "Values under $k:\n";
  for my $val (@{$r->{$k}}){
     print "$val, ";
  }
  print "\n";
}
[download]

Output:

$VAR1 = \{
            'trans2' => [
                          90,
                          20,
                          80,
                          33
                        ]
          };
Values under trans2:
90, 20, 80, 33,
[download]