Perl hash key determined by array

Question

I have an array and I am making a hash instance from it. For instance, if array is:

@folders=(temp,usr,bin);

then i want to fill in hash:

$the_path{$folders[0]}{$folders[1]}{$folders[2]}="somevalue";

But if the array is only:

@folders=(bin);

then i want the path to be:

$the_path{$folders[0]}="somevalue";

The problem is I dont know beforehand how long the array is gonna be, and I would really like to avoid making x if statements for that solution scales terribly.

How do I do this?

You've got use strict; use warnings; at the top of your file, right? That will catch many errors for you. — Ether
– Ether, Commented Jul 23, 2010 at 14:45

friedo · Accepted Answer · 2010-07-23 14:37:44Z

5

First, that's not how you define an array in Perl. You probably want to say

my @folders = ( 'temp', 'usr', 'bin' );

There's an old trick for making nested hash keys from a list:

my %the_path;
my $tmp = \%the_path;
foreach my $item( @folders ) { 
    $tmp->{$item} = { };
    $tmp = $tmp->{$item};
}

This will result in a structure like the following:

$VAR1 = {
          'temp' => {
                      'usr' => {
                                 'bin' => {}
                               }
                    }
        };

If you want to replace the empty hashref at the bottom-most level with a string, you can keep track of a count variable inside the loop.

answered Jul 23, 2010 at 14:37

friedo

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1 Comment

daxim Over a year ago

As always, we already have CPAN modules for that. Data::Diver is my favourite.

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