http://qs321.pair.com?node_id=662

Current Perl documentation can be found at perldoc.perl.org.

Here is our local, out-dated (pre-5.6) version:

One alphabetic character would be /[^\W\d_]/, no matter what locale you're in. Non-alphabetics would be /[\W\d_]/ (assuming you don't consider an underscore a letter).