[rot13]
Gurl'q unir gb or gbhpuvat. Abg zhpu bs n pngranel, ernyyl.

Fbeel, Qbht. Gbb rnfl. V qvq nyzbfg guvax nobhg ybbxvat sbe n sbezhyn sbe pngranevrf, gubhtu. Naq V'z fher vg'f zhpu yrff boivbhf jura erynlrq benyyl.
[/rot13]

Oh, and since it always takes me too long to remember the exact correct syntax:

tr '[a-zA-Z]' '[n-za-mN-ZA-M]'