Undefined method `require_gem' for main:Object

Posted on 31 January 2008

To update an old app to Rails 2.x you will need to change 'require_gem' to just 'gem'.

Otherwise you will get: Undefined method `require_gem' for main:Object

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Comments...

• I recently had this problem. I think the new version of rubygems use gem instead of require_gem. It's not necessarily a Rails 2.x issue.

  rupher at 31 Jan 08 at 07:50

• Actually, the new version of gems only requires a "require." No gem or require_gem method needed. Just do this: require 'rubygems'; require 'yourlib';

  Jeremy at 01 Feb 08 at 18:05

• gem install --remote rake

  I have been your problem before, and after i did it, it's worked well.

  Reinhart at 09 Apr 08 at 00:25

• Great. Thanks, all. I was stumbling blindly, then found this.

  ken at 10 Apr 08 at 19:35

• I had to use "gem" to get this to work:

  #!/usr/bin/env ruby

  require 'rubygems'
  gem 'multi'
  # require 'multi' # didn't work
  require 'amulti'

  multi(:fib,0){1}
  multi(:fib,1){1}
  multi(:fib,Integer){|n|fib(n-1)+fib(n-2)}

  puts fib(4)

  Rob at 05 Jun 08 at 02:00

• sorry the formatting was messed up. I pasted the code on these to pastebins:
  http://code.bulix.org/ckqjv9-66832
  http://www.pastebin.org/40737

  Rob at 05 Jun 08 at 02:22

• I am new to RoR. After getting everything installed, I ran ...
  rails sandbox

  I received the error you reported. This is what fixed the issue for me ...
  gem update rails

  jeff at 10 Jun 08 at 09:44

• Thanks!!! Saved me a million!!

  swinful at 28 Jul 08 at 19:20

• probably not because of Rails 2.0,
  but rather because of gem 1.0.1.

  "require_gem" works for gem 0.9.0
  "gem" works for both gem 0.9.0 and 1.0.1

  Heinz at 25 Aug 08 at 08:01

• Seems pretty high-handed to gratuitously break running code. And I sure can't see any pressing reason to all of a sudden drop require_gem. I guess these guys are good a developing new code and not so good at maintaining old code.

  Jon Seidel at 30 Apr 09 at 16:17

• on windows I had to create Env variable "RUBYOPT" and set to "rubygems"

  jw at 06 Jan 12 at 21:17