my %hash;       
$hash{'name'} = "Doraemon";
$hash{'age'} = "1000";

#... some code
# oh! my birthday, i'm getting older
$hash{'ege'} = "1001";   # oops, i just add new key

##</code><code>##

$k_name = 'name';
$k_age = 'age';

$hash{$k_ege} = "Do";   # warning, gotcha!