$myhash = \%myhash;

mergetwohashes($myhash, \%b);

sub mergetwohashes {
    #my($a)=$_[0];
    my($b)=$_[1];
    $_[0] = { %{$_[0]},  %{$b} };
}

##</code><code>##

sub mergetwohashes {
    my($a)=$_[0];
    my($b)=$_[1];
    %{$a} = ( %{$a},  %{$b} );
}