For a specific case, you can just use the snippet you showed, of course: $hash{a}{b}{c}='some value'; When you specify nested references like that, Perl will autovivify the references that don't already point to something. (See perlref for more on autovivification.)

If you're looking to do this with an arbitrary list, here's a subroutine that shows one way to do it: 

#!/usr/local/bin/perl -w

use strict;

sub set_nested_value {
  my($href, $keys, $value) = @_;
  my $last_key = pop @$keys;

  for my $key (@$keys) {
    $href = $href->{$key} ||= {};
  }

  $href->{$last_key} = $value;
}

my %hash;

set_nested_value(\%hash, ['a' .. 'c'], 'some value');
set_nested_value(\%hash, ['a', 'b', 'd'], 'other value');

use Data::Dumper;

print Dumper \%hash;

[download]
The for loop descends through the nested hashes. With the ||= operator, when there isn't already a hash reference at that level, it creates a new anonymous hash. $href is then reassigned to the next level in the nested hash.

Note that this code assumes that each key will either point to a hash reference or to a value. If you set a value first, and then try to use it as a nested hash, you'll get an error from use strict. If you set a nested hash first, and then set a value at the same level, you'll delete the entire nested hash. Error checking could be added to the sub to handle those situations gracefully.

In reply to Re: A hash slice but not.. by chipmunk
in thread A hash slice but not.. by smferris

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