Sudo gem install rails not working because of problem with alias_method and is_file

I had downloaded ruby, rails, and rubygems previously on my hard drive
when I ran Windows. I just downloaded Ubuntu and tried to use RoR but it
wasn’t working, so I figured I had to follow the installation procedure
listed here http://guides.rubyonrails.org/getting_started.html to get it
working. When I type in

sudo gem install rails

I get the following error message

/usr/local/lib/site_ruby/1.9.1/rubygems/package.rb:383:in
alias_method': undefined methodis_file’ for class
Gem::Package::TarReader::Entry' (NameError) from /usr/local/lib/site_ruby/1.9.1/rubygems/package.rb:383:inclass:Entry
from /usr/local/lib/site_ruby/1.9.1/rubygems/package.rb:319:in
<class:TarReader>' from /usr/local/lib/site_ruby/1.9.1/rubygems/package.rb:311:inmodule:Package
from /usr/local/lib/site_ruby/1.9.1/rubygems/package.rb:46:in
<module:Gem>' from /usr/local/lib/site_ruby/1.9.1/rubygems/package.rb:18:in<top
(required)>’
from /usr/local/lib/site_ruby/1.9.1/rubygems/custom_require.rb:21:in
require' from /usr/local/lib/site_ruby/1.9.1/rubygems/custom_require.rb:21:inrequire’
from /usr/local/lib/site_ruby/1.9.1/rubygems/builder.rb:1:in <top (required)>' from /usr/local/lib/site_ruby/1.9.1/rubygems/custom_require.rb:21:inrequire’
from /usr/local/lib/site_ruby/1.9.1/rubygems/custom_require.rb:21:in
require' from /usr/local/lib/site_ruby/1.9.1/rubygems.rb:61:inmanage_gems’
from /usr/bin/gem:4:in `’

I have no idea how to solve this. At this point I just want to delete
everything having to do with rails and ruby and start over again. How do
I do this?

On 13 January 2013 02:29, Alex M. [email protected] wrote:

I had downloaded ruby, rails, and rubygems previously on my hard drive
when I ran Windows. I just downloaded Ubuntu and tried to use RoR but it
wasn’t working, so I figured I had to follow the installation procedure
listed here http://guides.rubyonrails.org/getting_started.html to get it
working. When I type in

sudo gem install rails

I strongly advise using rvm to install Ruby and Rails in Ubuntu

Colin