#!/usr/bin/perl

   use strict;

   my ($hash);

   $hash->{one}{two}{three} = 'before';
   print "$hash->{one}{two}{three}\n";

   changehash($hash, [qw(one two three)], 'after');
   print "$hash->{one}{two}{three}\n";

#-----------------------------------------------------------
sub changehash {

   my ($node, $keys, $val) = @_;
   my $key;

   my $last = pop(@{$keys});

   for $key (@{$keys}) {
      if (defined ($node->{$key})) {
         $node = $node->{$key};
      }
      else {
         print STDERR "Unknown key: $key\n";
         return;
      }
   }

   if (defined ($node->{$last})) {
      $node->{$last} = $val
   }
   else {
      print STDERR "Unknown key: $last\n";
      return;
   }
}