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perl: dereferencing a hash of hashes

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# 1  
Old 11-10-2011
perl: dereferencing a hash of hashes
Hi there, I am trying to dereference my hash of hashes but post dereferencing, it seems to lose its structure I am using Data::dumper to help me anaylise.

This is the code im using to build the HoH, (data comes from a file). I have also performed a Dumper on the data structure before and after dereferencing.



Code:
 
sub hashcreate() {
        open(IN, "/var/tmp/myrulesfile");
               while (<IN>) {
                       chomp();  # remove line feed
                       my ($rule_id,$user,$group,$access)  = split(/\|/);
                        $hashref->{ $rule_id } = {
                               rule_id => $rule_id,
                               user   => $user,
                               group  => $group,
                               access => $access,
                       };
               }
         close(IN);
  return $hashref;
}
 
 
### Run the subroutine
hashcreate();
 
### Do a Dumper on the referenced hash
print Dumper($hashref);
 
### Dereference the hash
my %hash = %$hashref;
 
### Do a Dumper on the DE-referenced hash
print Dumper(%hash);

The output for my referenced hash is fine and looks like this

Code:
 
$VAR1 = {
          '1' => {
                   'user' => 'peter',
                   'group' => 'sysadmins',
                   'rule_id' => '1',
                   'access' => 'allow'
                 },
          '0' => {
                   'user' => 'steve',
                   'group' => 'finance',
                   'rule_id' => '0',
                   'access' => 'allow'
                 },
          '2' => {
                   'user' => 'john',
                   'group' => 'dbas',
                   'rule_id' => '2',
                   'access' => 'deny'
                 },
        };

But after I dereference using

Code:
 
# Dereference the hash
my %hash = %$hashref;

my Dumper looks like this

Code:
 
$VAR1 = '1'
$VAR2 = {
                   'user' => 'peter',
                   'group' => 'sysadmins',
                   'rule_id' => '1',
                   'access' => 'allow'
                 },
$VAR3 = '0'
$VAR4 =  {
                   'user' => 'steve',
                   'group' => 'finance',
                   'rule_id' => '0',
                   'access' => 'allow'
                 },
$VAR5 = '2'
$VAR6 =  {
                   'user' => 'john',
                   'group' => 'dbas',
                   'rule_id' => '2',
                   'access' => 'deny'
                 },

It seems to have taken my hash of hashes and converted them into a series of scalars and singular hashes.

Is my dereferencing code wrong? will that only work on a singular hash as opposed to a hash of hashes?

any help would be greatly appreciated.
# 2  
Old 11-10-2011
Your dereferencing works just fine. The "problem" is how Perl thinks about hashes: a hash is basically an even sized array, with the first element being the key, and the second the associated value. Data:Smilieumper gets that data, and interprets it as an array, for which it dumps the individual elements: first the key, then the value, first a scalar, then a hash reference.
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