http://www.perlmonks.org?node_id=1024457


in reply to Re: change [A-Z] to U, [a-z] to L with one regex?
in thread change [A-Z] to U, [a-z] to L with one regex?

Simpler solution not limited to non-ASCII chars:

s/(\p{Lu})|\p{Ll}/ defined($1) ? 'U' : 'L' /eg;