use strict;
use warnings;
use Data::Dumper;

sub set_hash
{
   my $href = shift;
   my $val  = shift;
   my @key  = @_;
   $href->{$key[0]}{$key[1]}{$key[2]} = $val;
}

my %h;
set_hash(\%h, 42, 'a', 'b', 'c');
set_hash(\%h, 69, 'x', 'y', 'z');
print Dumper(\%h);