`rbenv install` not appearing with ruby-build package install, but command works

From https://github.com/sstephenson/ruby-build:

Installing ruby-build as an rbenv plugin will give you access to the rbenv install command.

Installing ruby-build as a standalone program will give you access to the ruby-build command for precise control over Ruby version installation. If you have rbenv installed, you will also be able to use the rbenv install command.

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Interestingly enough, installing ruby-build as a plugin in a user's ~/.rbenv gives them access to more rubies (instead of messing with /usr/share/ruby-build), but the command is still not available in rbenv's help.

It seems like it would be ideal for new users to see the `install` and `uninstall` plugin options.

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Suggestions:

- get command completion in before LTS hits - that's reason enough to install from git for me

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Notes:

lsb_release -rd
Description: Ubuntu 13.10
Release: 13.10

death@badwolf:/usr/share/ruby-build$ apt-cache policy rbenv
rbenv:
  Installed: 0.3.0-1
  Candidate: 0.3.0-1
  Version table:
 *** 0.3.0-1 0
        500 http://us.archive.ubuntu.com/ubuntu/ saucy/universe amd64 Packages
        100 /var/lib/dpkg/status
death@badwolf:/usr/share/ruby-build$ apt-cache policy ruby-build
ruby-build:
  Installed: 20120524-1
  Candidate: 20120524-1
  Version table:
 *** 20120524-1 0
        500 http://us.archive.ubuntu.com/ubuntu/ saucy/universe amd64 Packages
        100 /var/lib/dpkg/status

death@badwolf:/usr/share/ruby-build$ rbenv install
usage: rbenv install VERSION
       rbenv install /path/to/definition

Available versions:
  1.8.6-p383
  1.8.6-p420
  1.8.7-p249
  1.8.7-p302
  1.8.7-p334
  1.8.7-p352
  1.8.7-p357
  1.8.7-p358
  1.9.1-p378
  1.9.2-p180
  1.9.2-p290
  1.9.2-p318
  1.9.2-p320
  1.9.3-dev
  1.9.3-p0
  1.9.3-p125
  1.9.3-p194
  1.9.3-p448
  1.9.3-preview1
  1.9.3-rc1
  2.0.0-dev
  jruby-1.6.3
  jruby-1.6.4
  jruby-1.6.5
  jruby-1.6.5.1
  jruby-1.6.6
  jruby-1.6.7
  jruby-1.6.7.2
  jruby-1.7.0-preview1
  maglev-1.0.0
  rbx-1.2.4
  rbx-2.0.0-dev
  ree-1.8.6-2009.06
  ree-1.8.7-2009.09
  ree-1.8.7-2009.10
  ree-1.8.7-2010.01
  ree-1.8.7-2010.02
  ree-1.8.7-2011.03
  ree-1.8.7-2011.12
  ree-1.8.7-2012.01
  ree-1.8.7-2012.02

death@badwolf:/usr/share/ruby-build$ rbenv
rbenv 0.3.0
usage: rbenv <command> [<args>]

Some useful rbenv commands are:
   commands List all rbenv commands
   rehash Rehash rbenv shims (run this after installing binaries)
   global Set or show the global Ruby version
   local Set or show the local directory-specific Ruby version
   shell Set or show the shell-specific Ruby version
   version Show the current Ruby version
   versions List all Ruby versions known by rbenv
   which Show the full path for the given Ruby command
   whence List all Ruby versions with the given command

See 'rbenv help <command>' for information on a specific command.
For full documentation, see: https://github.com/sstephenson/rbenv#readme

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a fully git-installed rbenv + ruby-build environment:

rbenv@badwolf:~$ rbenv
rbenv 0.4.0-67-g3300587
Usage: rbenv <command> [<args>]

Some useful rbenv commands are:
   commands List all available rbenv commands
   local Set or show the local application-specific Ruby version
   global Set or show the global Ruby version
   shell Set or show the shell-specific Ruby version
   install Install a Ruby version using the ruby-build plugin
   uninstall Uninstall a specific Ruby version
   rehash Rehash rbenv shims (run this after installing executables)
   version Show the current Ruby version and its origin
   versions List all Ruby versions available to rbenv
   which Display the full path to an executable
   whence List all Ruby versions that contain the given executable

See `rbenv help <command>' for information on a specific command.
For full documentation, see: https://github.com/sstephenson/rbenv#readme