use strict;
use warnings;
use Data::Dumper;
my %hash = (
  a => 1,
);
print Dumper \%hash;

$hash{b} = 2;
print Dumper \%hash;

%hash = (
  c => 3,
);
print Dumper \%hash;

# ausgabe
__END__
$VAR1 = {
          'a' => 1
        };

$VAR1 = {
          'a' => 1,
          'b' => 2
        };

$VAR1 = {
          'c' => 3
        };