Is there a good reason why you're using symbolic refs?

You can almost always use a hash in any place where symbolic refs are used -- and the hash is almost always better form. Plus in this case, a hash would resolve the problem that Joost mentions about setting the sort vars $a and $b.

Update: I use the word "almost" just to cover myself. My real belief is that using a hash is ALWAYS the best choice, but I know someone would come up with an argument. :)

Update 2: This will set up a hash of letters for ya, although it's not really clear from your post how you plan to use the values.

my %letters = map {$_,1} (a..z);