#!/usr/bin/perl ---
use strict;
use warnings;
use Data::Dumper qw' Dumper ';
Main( @ARGV );
exit( 0 );
sub Main {
    my $variable = 'String';
    my %Hash = ( $variable => 'Hello' );
    my $Ref = \%Hash;
    $Ref->{STRING} = 'STRING';
    $Ref->{'s'.'t'.'r'.'i'.'NG'} = 'striNG';
    $Hash { $Ref->{$variable} } = 'World!';
    print Dumper( \%Hash ), "\n\n";
}
__END__
$VAR1 = {
          'String' => 'Hello',
          'Hello' => 'World!',
          'striNG' => 'striNG',
          'STRING' => 'STRING'
        };
[download]

I suggest reading through perlintro and References quick reference