How to Downgrade from Ruby 1.9.2 to Ruby 1.8.7 to run Rails 2.0.2

Question

I want to downgrade the Ruby version I have installed(Ruby 1.9.2) on Ubuntu 10.04 OS so that I can use the appropriate version of Ruby 1.8.7 to run Rails 2.0.2. I am using the older version of Rails for project purpose.

If I am using Rails 2.0.2 with Ruby 1.9.2 it gives me an error saying cant convert Enumerator into an array.

I thought I could use rvm, but I am not sure if its suitable for downgrade.

I get the following in the terminal when I use the command rvm list known

mgj@pc146724-desktop:~$ rvm list known
# MRI Rubies
[ruby-]1.8.6[-p399]
[ruby-]1.8.6-head
[ruby-]1.8.7[-p302]
[ruby-]1.8.7-head
[ruby-]1.9.1-p243
[ruby-]1.9.1[-p376]
[ruby-]1.9.1-p429
[ruby-]1.9.1-head
[ruby-]1.9.2-preview1
[ruby-]1.9.2-preview3
[ruby-]1.9.2-rc1
[ruby-]1.9.2-rc2
[ruby-]1.9.2[-p0]
[ruby-]1.9.2-head
ruby-head

# JRuby
jruby-1.2.0
jruby-1.3.1
jruby-1.4.0
jruby-1.5.1
jruby-1.5.2
/home/mohnish/.rvm/config/known 

I get the following in the list of installed ruby packages on using the command dpkg -l | grep ruby

mgj@pc146724-desktop:~$ dpkg -l | grep ruby
ii  libdbm-ruby                                4.2                                             DBM interface for Ruby
ii  libdbm-ruby1.8                             1.8.7.249-2                                     DBM interface for Ruby 1.8
ii  libgdbm-ruby                               4.2                                             GDBM interface for Ruby
ii  libgdbm-ruby1.8                            1.8.7.249-2                                     GDBM interface for Ruby 1.8
ii  libopenssl-ruby                            4.2                                             OpenSSL interface for Ruby
ii  libopenssl-ruby1.8                         1.8.7.249-2                                     OpenSSL interface for Ruby 1.8
ii  libreadline-ruby                           4.2                                             Readline interface for Ruby
ii  libreadline-ruby1.8                        1.8.7.249-2                                     Readline interface for Ruby 1.8
ii  libruby1.8                                 1.8.7.249-2                                     Libraries necessary to run Ruby 1.8
ii  libtcltk-ruby                              4.2                                             Tcl/Tk interface for Ruby
ii  libtcltk-ruby1.8                           1.8.7.249-2                                     Tcl/Tk interface for Ruby 1.8
ii  rdoc                                       4.2                                             Generate documentation from ruby source file
ii  ruby                                       4.2                                             An interpreter of object-oriented scripting 
ii  ruby-elisp                                 4.2                                             Emacs-lisp ruby-mode for Ruby
ii  ruby-full                                  4.2                                             Ruby full installation
ii  ruby1.8                                    1.8.7.249-2                                     Interpreter of object-oriented scripting lan
ii  ruby1.8-dev                                1.8.7.249-2                                     Header files for compiling extension modules
ii  ruby1.8-elisp                              1.8.7.249-2                                     ruby-mode for Emacsen
mgj@pc146724-desktop:~$ ^C

Do I need to uninstall Ruby 1.9.2 and only then freshly install Ruby 1.8.7 or can I switch versions?. If I can switch versions please direct me on how to set the path from Ruby 1.9.2 to Ruby 1.8.7. Or if there is some other way please let me know.

If I have to uninstall Ruby 1.9.2 and then freshly install Ruby 1.8.7 please let me know how can I go about it. I tried the following commands to uninstall Ruby 1.9.2 but it didn't seem to find the Ruby 1.9.2 package.

sudo aptitude remove ruby

sudo aptitude remove ruby 1.9.2p0

sudo purge ruby

sudo aptitude purge ruby 1.9.2p0

When I checked for the current version of Ruby installed it shows:

mgj@pc146724-desktop:~/Downloads/rubygems_postextract/rubygems-1.4.1$ ruby -v
ruby 1.9.2p0 (2010-08-18 revision 29036) [i686-linux]

mgj@pc146724-desktop:~/Downloads/rubygems_postextract/rubygems-1.4.1$ which ruby
/home/mgj/.rvm/rubies/ruby-1.9.2-p0/bin/ruby

Thanks for your help..!!

Answer 1

Whole point of RVM is so that you can have multiple versions of Ruby and switch among them easily..

rvm install 1.8.7 #or some specific version - choose from the rvm list known
rvm use 1.8.7
rvm gemset create rails202 #create a gemset called "rails202" for Ruby 1.8.7
rvm 1.8.7@rails202 #make the gemset the current selection
gem install rails -v 2.0.2 #install rails (just for this gemset!)
#now, we have a gemset called "rails202" in Ruby 1.8.7.
#anytime we want to use it, we do:
rvm 1.8.7@rails202
#create as many gemsets needed, eg for rails 3.0.3 on Ruby 1.8.7 we can do the
#similar as above. Then to use the new gemset just do:
rvm 1.8.7@rails303
#et voila! we are now using Rails 3.0.3 on Ruby 1.8.7 !