does not actually store the reference to the %h hash in any way, all it does is add an element to the %g hash with 1 as the value and the string representation of the %h hash ("HASH(0x90fcc70)") as the key. If you really want to use this string representation as the key (not a good idea IMO) you'd do

use strict;

my %h = ("foo" => 1,
         "bar" => 2);

my %g = ();
$g{\%h} = \%h;

my @k = keys %g;
my $hashref = $k[0];
my %tmp = %{$g{$hashref}};
print $tmp{"foo"}
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I think you should use something more useful as the hash key, or, if you just want to store hash references in a data structure without meaningful keys, use an array instead:

use strict;

my %h = ("foo" => 1,
         "bar" => 2);

push (my @g,\%h);
my $hashref = $g[0];
print $hashref->{foo};
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Also, consider using more descriptive variable names (unless this is just an example and not your actual code).