`vvagrant` command which reads an environment variable `$VAGRANT_VERSION` (or command argument) to determine which version of vagrant to use. Useful for having both 1.0.x and 1.2.x installed at the same time.

vvagrant README

## Make a directory like this for each version you want
vv% ls -l ~/local/share/rbenv/gemsets
total 0
drwxr-xr-x  8 hunner  staff  272 Apr 22 15:06 vagrant_1.0.7/
drwxr-xr-x  8 hunner  staff  272 Apr 22 15:12 vagrant_1.2.2/

## Put this in vagrant_*/Gemfile
vv% cat vagrant_1.2.1/Gemfile
source 'https://rubygems.org'
gem 'vagrant', :path => File.expand_path('vagrant', File.dirname(__FILE__))

## Clone the vagrant repo for each version you want and install gemsets
vv% git clone https://github.com/mitchellh/vagrant.git ~/local/share/rbenv/gemsets/vagrant_1.2.2/vagrant
vv% cd !$
vv% git checkout v1.2.2
vv% bundle update

## Use `vvagrant` (see script below)
vv% vvagrant 1.2.2 box list
CentOS-6.4-x86_64-v20130309       (virtualbox)
centos-6.3-x86_64-minimal-pe2.7.2 (virtualbox)
debian-70rc1-x64-vbox4210         (virtualbox)
vv% export VAGRANT_VERSION=1.0.7
vv% vvagrant box list
CentOS-6.4-x86_64-v20130309
centos-6.3-x86_64-minimal-pe2.7.2
centos-64-x64-vbox4210
debian-607-x64-vbox4210

vvagrant.sh

#!/bin/bash

if [[ $1 =~ [0-9]\.[0-9]\.[0-9] ]] ; then
  vversion=$1
  vargs=${@:2}
elif [[ ! -z $VAGRANT_VERSION ]] ; then
  vversion=$VAGRANT_VERSION
  vargs=$@
else
  echo "$0: version argument missing"
  exit 1
fi

gem_bin='vagrant'
gemset="vagrant_${vversion}"

gemset_root="${HOME}/local/share/rbenv/gemsets/${gemset}"

gem_path="${gemset_root}/vagrant/bin/${gem_bin}"
gemfile="${gemset_root}/Gemfile"


if [ -e "$gem_path" ]; then
  export VAGRANT_HOME="${gemset_root}/vagrant.d"
  export VAGRANT_INSTALLER_ENV=bugmenot #disable warning message
  export BUNDLE_GEMFILE="$gemfile"
  exec bundle exec "${gem_path}" $vargs
else
  echo "Unable to execute $0; backing executable '${gem_path}' missing or not executable" >&2
  exit 255
fi