use strict;
use warnings;

my %foo = ( one => 1, two => 2 );
my %bar = ( three => 3, four => 4 );
my %baz = ( five => 5, six => 6 );

dump_keys( $_ ) for \%foo, \%bar, \%baz;

sub dump_keys { print "$_\n" for keys %{+shift} }