Eehmm.. It's usually best to copy & paste actual running code :-) 
#!/usr/bin/perl -w
use strict;
use Data::Dumper;
my %hash = ();
my $hashref = \%hash;
%hash = (
    key1 => {
        key1_1 => ["value1_1","value1_2"],
        key1_2 => "w00t!",
    },
    key2 => {
        key2_1 => "wakkawak!",
        key2_2 => $hashref->{key1}, # update!
    },
);

print Dumper($hashref);

[download]

I think the problem is that the whole %hash = ( ... ) thing is a single statement, and the actual assignment would be done after all the rest of the statement is resolved, (so after $hashref->{key2}{key1_1} is resolved).

You need to split this up in two statements: 

#!/usr/bin/perl -w
use strict;
use Data::Dumper;
my %hash = ();
my $hashref = \%hash;
%hash = (
    key1 => { 
        key1_1 => ["value1_1","value1_2"],
        key1_2 => "w00t!",
    },
    key2 => { 
        key2_1 => "wakkawak!", 
    },
);

$hash{key2}{key2_2} =  $hashref->{key1}; #update!

print Dumper($hashref);

[download]
updated: $hashref->{key1_1} is always undef, ofcourse.

"What should it profit a man, if he should win a flame war, yet lose his cool?"

In reply to Re: Populating a nested hash with itself? by Joost
in thread Populating a nested hash with itself? by jkva

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