Invoke rbenv alias <name> <version> to make a symbolic link from <name> to
<version> in the rbenv versions directory, effectively creating an
alias. The cool part is that if you pass in a point release as the name, you
can give --auto to link to the latest installed patch level. For example,
rbenv alias 1.8.7 --auto will automatically create an alias from 1.8.7 to
1.8.7-p371 (or whatever the most recent version you have installed is).
Plus, if you're using ruby-build, rbenv install A.B.C-pXXX automatically
invokes rbenv alias A.B.C --auto, so you'll always have up to date aliases
for point releases.
Whether it's a good idea to use these aliases in a .ruby-version file, I
cannot say. I created this plugin to find out. If your only concern is
having to reinstall gems every time you install a new patch release, check out
rbenv-communal-gems.
mkdir -p ~/.rbenv/plugins
git clone git://github.com/tpope/rbenv-aliases.git \
~/.rbenv/plugins/rbenv-aliases
rbenv alias --auto