# here's the hash
%s = (   "substring1" => 'string1',
         "substring2" => 'string2',
         "substring3" => 'string3'
     );

# get the current keys
@keys = keys(%s);

# go through each key and sway the key/value
foreach $key (@keys) {
    $s{$key} = $key;

    # print out the swapped hash value
    print "$s{$key}\n";
}

Output
----------------------------------
substring1
substring2
substring3