I had some good old fashion fun today on the shell today. I stumbled across this “gem” of an expression:

yes xargs | xargs yes

This expression can be repeated infinitely (mostly) many times without changing the output and without loosing symmetry when joining on the yes’s. In other words, the last expression is equivalent (in regards to output and symmetry):

yes xargs | xargs yes xargs | xargs yes xargs | xargs yes xargs | xargs yes xargs | xargs yes xargs | xargs yes xargs | xargs yes xargs | xargs yes xargs | xargs yes xargs | xargs yes xargs | xargs yes xargs | xargs yes

You can throw some rot13s (with care), cats, and a few other commands in there with the same effect. I am not sure exactly how it functions; it seems to work different on different OSes. I have tried in on Linux, Mac OS X, Solaris, and OpenBSD, and all seem to be a bit different. They seem to run a bit differently, and the output is different. It’s all very fun.

Update: I thought I should clarify that last little bit. The way pipes are treated seems to vary some; the actual functionality is trivial.