my ( @buffer, %source, %dest )

$source{key1} = "value1";
$source{key2} = "value2";

push (@buffer, \%source); # beachte den "\"

$source{key1} = "value3";
$source{key2} = "value4";

push (@buffer, \%source); # beachte den "\"

#(...)

%source = %{ pop(@buffer) }; # und hier das %{ }

print $source{key1};