sub pushhash (\%@) {
  my $hash = shift;
  my $key;
  $$hash{$key} = shift while defined($key = shift);
}

my %a;

$a{cow} = "COW1";
$a{dog} = "DOG1";

pushhash %a, cow => "COW2", bull => "Terrier";

for (sort keys %a) {
  print "$_ => $a{$_}\n";
}