rbenv: [binary-name]: command not found

This happened to me with Vagrant, but the issue isn't specific to that gem.

I was using an older version of Vagrant which was installed via a gem which provided a binary. I was using rbenv. The Vagrant maintainer depreciated the gem and provided an installer. I uninstalled all my Vagrant gems and ran the installer. Then this happened:

jd at James in ~
><((°> vagrant --version
rbenv: vagrant: command not found

jd at James in ~
[127] ><((ˣ> echo $PATH
/usr/local/share/npm/bin /usr/local/share/python /usr/local/bin /Users/jd/.rbenv/shims /Users/jd/bin /usr/bin /bin /usr/sbin /sbin

jd at James in ~
><((°> /usr/bin/vagrant --version
Vagrant version 1.1.5

What's going on?!

It turns out that rbenv installs shims for all binaries, which auto-switch to the appropriate ruby version before invoking the real binary. To fix all that mess, run the following:

rbenv rehash

Definitely rather surprising. Postmodern (who resolved this issue for me) suggested chruby as a potential solution you never want to think about this again.