# Update a hash by adding or replacing mappings. Hash references
# stored in the top level hash can be updated recursively, if desired.
# Params:
#   %h      = The hash to modify
#   $depth = Recursion depth.
#   @kv     = New key value pairs.
sub hpush(\%$@);
sub hpush(\%$@) {
    my ($h, $depth, @kv) = @_;
    
    while (@kv) {
        my ($k, $v) = splice @kv, 0, 2;
        
        if ($depth > 0 and ref($h->{$k}) eq 'HASH' and ref($v) eq 'HASH') {
            hpush %{$h->{$k}}, $depth - 1, %{$v};
        }
        else {
            $h->{$k} = $v;
        }
    }
}

use Data::Dumper;

my %h = (
  foo => 42,
  bar => {
    x => {
      u => 1,
      v => 2
    },
    y => 'blubb'
  }
);

print Dumper \%h;

hpush %h, 1, (
  baz => 23,
  bar => {
    x => {
      w => 3
    },
    z => 'blargh'
  }
);


print Dumper \%h;