print ${ $hash_ref }{ $key };

##</code><code>##

print ${ $hash_ref{ $key } };

##</code><code>##

sub x{ print $$_[0][1] };;

##</code><code>##

x( [['a','b'],['c','d']] );;

x( ['a','b'],['c','d'] );;

##</code><code>##

x( [['a','b'],['c','d']] );;
Use of uninitialized value in print at ...

x( ['a','b'],['c','d'] );;
Use of uninitialized value in print at ...

##</code><code>##

sub x{ print $_[0]->[1] };;

xx( [['a','b'],['c','d']] );;

xx( ['a','b'],['c','d'] );;

##</code><code>##

x( [['a','b'],['c','d']] );;
ARRAY(0x3c6e3b8)

x( ['a','b'],['c','d'] );;
b