Need help printing a reference to a hash of hashes

[numberwhun]

Hello all!

I am working on trying to figure out how to print out a hash of hashes. How the hash in the code is defined below is very similar to how the hash is defined in the script I am working with. (Yes, this is for work so I cannot share the actual code, sorry).

I was using this web page as a reference for figuring this out as it has been of great assistance before, but for some reason, the code below prints out NOTHING.

Why? I am not sure but I am hopeful that someone can tell me why and what I am doing wrong.

use strict;
use warnings;

my %hash1;
my $hash2;


$hash2 = 1;

$hash1{$hash2}{key1} = 1;
$hash1{$hash2}{key2} = 2;
$hash1{$hash2}{key3} = 3;

for my $keys1 (keys %$hash1){
	for my $keys2 (keys %{hash1->{$keys1}}){
		print "The value of hash1->$keys1->$keys2 is:  $hash1->{$keys1}{$keys2}\n"
	}
}

Thanks in advance for any and all help!

Best regards,

Jeff

[eWish]

I am certain that Kevin will enlighten us both, but here is one that I have done in the past.

	# Print each of the categories
	foreach my $category ( sort { keys %{ $product_data{$b} } <=> keys %{ $product_data{$a} } } keys %product_data ) {
		print qq~<ul><li>$category</li>~;
			
			# Print each of the sub-categories (1 level deep only)
			for my $sub_category ( sort { $_{$a} <=> $_{$b} }  keys %{ $product_data{$category} } )  {
				print qq~<ul><li>$sub_category</li><ul>~; 
				
				# Print each of the product names of the sub-categories
				for my $product_name(@{$product_data{$category}{$sub_category}}) {
					print qq~<li>$product_name</li>~;
				}
				print qq~</ul></ul>~;
	 		}
 			print qq~</ul>~;
	}

--Kevin

[KevinADC]

Hello all!

I am working on trying to figure out how to print out a hash of hashes. How the hash in the code is defined below is very similar to how the hash is defined in the script I am working with. (Yes, this is for work so I cannot share the actual code, sorry).

I was using this web page as a reference for figuring this out as it has been of great assistance before, but for some reason, the code below prints out NOTHING.

Why? I am not sure but I am hopeful that someone can tell me why and what I am doing wrong.

use strict;
use warnings;

my %hash1;
my $hash2;


$hash2 = 1;

$hash1{$hash2}{key1} = 1;
$hash1{$hash2}{key2} = 2;
$hash1{$hash2}{key3} = 3;

for my $keys1 (keys %$hash1){
	for my $keys2 (keys %{hash1->{$keys1}}){
	}
}

Thanks in advance for any and all help!

Best regards,

Jeff

Did you run the code with "strict" on? It should produce these errors:

Global symbol "$hash1" requires explicit package name at script line 14.
Can't use bareword ("hash1") as a HASH ref while "strict refs" in use at script line 15.


The biggest problem is that %hash1 is not a reference to a hash, it is a hash (of hashes). Line 15 also has a syntax error, "hash1" should be "$hash1".

Here is the code corrected:

use strict;
use warnings;

my %hash1;
my $hash2;


$hash2 = 1;

$hash1{$hash2}{key1} = 1;
$hash1{$hash2}{key2} = 2;
$hash1{$hash2}{key3} = 3;

for my $keys1 (keys %hash1){
	for my $keys2 ( keys %{ $hash1{$keys1} } ){
		print "The value of hash1->$keys1->$keys2 is:  $hash1{$keys1}{$keys2}\n"
	}
}

The "print" line could also be written with the arrow operator but its not necessary:

print "The value of hash1->$keys1->$keys2 is:  $hash1{$keys1}->{$keys2}\n"

This is really what the original code was trying to do:

use strict;
use warnings;

my $hash1;
my $hash2;


$hash2 = 1;

$hash1->{$hash2}->{key1} = 1;
$hash1->{$hash2}->{key2} = 2;
$hash1->{$hash2}->{key3} = 3;



for my $keys1 (keys %{$hash1}){
	for my $keys2 ( keys %{ $hash1->{$keys1} } ){
		print "The value of hash1->$keys1->$keys2 is:  $hash1->{$keys1}->{$keys2}\n"
	}
}

Now $hash1 is a reference to a hash of hashes and not a hash of hashes.

[numberwhun]

Did you run the code with "strict" on? It should produce these errors:

Global symbol "$hash1" requires explicit package name at script line 14.
Can't use bareword ("hash1") as a HASH ref while "strict refs" in use at script line 15.


The biggest problem is that %hash1 is not a reference to a hash, it is a hash (of hashes). Line 15 also has a syntax error, "hash1" should be "$hash1".

Here is the code corrected:

use strict;
use warnings;

my %hash1;
my $hash2;


$hash2 = 1;

$hash1{$hash2}{key1} = 1;
$hash1{$hash2}{key2} = 2;
$hash1{$hash2}{key3} = 3;

for my $keys1 (keys %hash1){
	for my $keys2 ( keys %{ $hash1{$keys1} } ){
		print "The value of hash1->$keys1->$keys2 is:  $hash1{$keys1}{$keys2}\n"
	}
}

The "print" line could also be written with the arrow operator but its not necessary:

print "The value of hash1->$keys1->$keys2 is:  $hash1{$keys1}->{$keys2}\n"

This is really what the original code was trying to do:

use strict;
use warnings;

my $hash1;
my $hash2;


$hash2 = 1;

$hash1->{$hash2}->{key1} = 1;
$hash1->{$hash2}->{key2} = 2;
$hash1->{$hash2}->{key3} = 3;



for my $keys1 (keys %{$hash1}){
	for my $keys2 ( keys %{ $hash1->{$keys1} } ){
		print "The value of hash1->$keys1->$keys2 is:  $hash1->{$keys1}->{$keys2}\n"
	}
}

Now $hash1 is a reference to a hash of hashes and not a hash of hashes.

Interesting. Gotta practice up with these. Thanks Kevin, it worked!

Regards,

Jeff

[KevinADC]

It seems to be a common source of confusion. Just keep in mind if you decalre a hash like this:

%hash = (key => 'value');

or:

$hash{key} = 'value';

it is just a regular hash regardless of whatever is in the hash. Same is true with an array. Now the data stored in the hash/array could be references to other things, but the main hash/array is not.

These would be references to hashes or arrays:

$hash = {foo => 'bar'};
$array = [qw(foo bar)];

The difference is of course using a scalar on the left side and the respective brackets on the right side.

[chiku1523]

Jeff,

You can print hash of hash easily using Dumper.
Data::Dumper is one module


-Chiku

[KevinADC]

Jeff,

You can print hash of hash easily using Dumper.
Data::Dumper is one module


-Chiku

This is true, and Jeff is aware of that, he could have used it maybe to pin point the problems in his own code. Good suggestion to use Data::Dumper.

[numberwhun]

This is true, and Jeff is aware of that, he could have used it maybe to pin point the problems in his own code. Good suggestion to use Data::Dumper.

I do know that I can print it using Data::Dumper, but unfortunately the situation does not allow for the inclusion of new modules (that situation being that this is work related).

See, the software I am working with is distributed to the field machines only after they have been converted to executable binaries using perl2exe. It was already setup to include a specific set of modules.

Sure, modules can be added, but it not something I want to undertake at this time when I can do it without it. Thanks for the suggestion though, as Kevin said, it was definitely a good one.

Regards,

Jeff