$ cat ~/.ssh/id_rsa.pub | pbcopy

And of course, if you’ve been following along for a week or two, you know
that this (BING!) is a Useless Use of Cat!

Rememeber, nearly all cases where you have:

cat file | some_command and its args …

you can rewrite it as:

<file some_command and its args …

http://porkmail.org/era/unix/award.html#uucaletter

;)