Instead of substr you could also use regular expressions. Concatenate all your strings in the correct order with a delimiter character that is not part of the strings, eg. #. Then find the same sequence of characters to the left and right of each delimiter and remove one side. It could look like this:

my %hash = ( anee => '1', jane => '0', neen => '2', ); 
my $merge = join '#', sort { $hash{$a} <=> $hash{$b} } keys %hash;
$merge =~ s/([^#]*)#(?=\1)//g;
print "$merge\n";
[download]