use Data::Alias;
use feature 'say';
$baz{'buf'} = 'Hello';
alias $foo{'bar'} = $baz{'buf'};
say $foo{'bar'};
$foo{'bar'} = 'World';
say $baz{'buf'};
$baz{'new'} = 'old';
say $foo{'old'};

__END__
Hello
World
Use of uninitialized value in say at ...