Storing a hash in a hash - perl

Question

I'm having troubles with a Perl script. I try to store a hash in a hash. The script is trivial:
use Data::Dumper;
my %h1=();
$h1{name}="parent";
my %h2=();
$h2{name}="child";
$h1{nested}=%h2; # store hash h2 in hash h1
print "h2:\n";
print Dumper(%h2); # works
print "h1{nested}:\n";
print Dumper($h1{nested}); # fails
The results:
h2:
$VAR1 = 'name';
$VAR2 = 'child';
h1{nested}:
$VAR1 = '1/8';
Why is the $h1{nested} not dumped as a hash, but as some kind of weird scalar (1/8)?
PS: even if this question sounds trivial - I searched SO but did not find that it was asked before.
PPS: my Perl is v5.10.1 (*) built for x86_64-linux-gnu-thread-multi
(with 53 registered patches, see perl -V for more detail)

Answer 1

You can only store a hashref in a hash:
$h1{nested}=\%h2;
and then you would access %h2's name by doing
$h1{nested}->{name}
In your code, %h2 is forced to scalar context, which shows you that "1/8" value, and stores that.

Answer 2

In perl the values stored in a list (hash or array) are always scalars. Given this, the only way to store a hash inside another hash is to store a reference to it.
$h1{'nested'} = \%h2;
or also
$h1{'nested'} = { 'name'=>'child' };
(the braces in the right hand side is a reference to an anonymous hash).
BTW, to not quote the literals in the keys is usually considered bad practice, see here

Answer 3

Why is the $h1{nested} not dumped as a hash, but as some kind of weird scalar (1/8)?
Because you're storing it in a scalar context!
When you do this:
$h1{nested} = %h2;
You're storing a scalar. Since %h2 is a hash, you're given the ol' fraction string. According to the Perldoc website
If you evaluate a hash in scalar context, it returns false if the hash is empty. If there are any key/value pairs, it returns true; more precisely, the value returned is a string consisting of the number of used buckets and the number of allocated buckets, separated by a slash.
That explains the 1/8 you're getting.
What you need to do is store the hash as a reference in the other hash. As others pointed out, it should be:
$h1{nested} = \%h2;
The backslash before the hash's name gives you the memory location where the hash is stored. You can use the curly braces, but I prefer the backslash notation.
Take a look at perldoc prelreftut on your computer (or on the webpage I've linked to). This will tell you how to make such things as a list of lists, hashes or hashes, lists of hashes, and hashes of lists. Just a word o` warning: If you get too complex, it'll be hard to maintain, so once you've had your fun, take a look at perldoc's Perl Object Orientation Programming Tutorial.
The perldoc command contains lots of Perl documentation including for all Perl function, Perl modules installed on your system, and even basic information about the Perl language.