I've upgraded to Ruby 1.9 today, in preparation for attending RubyConf 
in Charlotte this weekend, and ran across some problems after upgrading.

I've written a web application in Ruby that  controls embedded media 
players over the internet. 
When I attempt to run this existing web application, I get the following 
output(s):

bash-/public$ ruby WM5.rb
/usr/lib/ruby/site_ruby/1.8/rubygems.rb:432:in `method_missing': 
undefined method `exists?' for File:Class (NoMethodError)
        from /usr/lib/ruby/site_ruby/1.8/rubygems.rb:432:in `block in 
ensure_gem_subdirectories'
        from /usr/lib/ruby/site_ruby/1.8/rubygems.rb:430:in `each'
        from /usr/lib/ruby/site_ruby/1.8/rubygems.rb:430:in 
`ensure_gem_subdirectories'
        from /usr/lib/ruby/site_ruby/1.8/rubygems.rb:355:in `set_home'
        from /usr/lib/ruby/site_ruby/1.8/rubygems.rb:121:in `dir'
        from /usr/lib/ruby/site_ruby/1.8/rubygems.rb:364:in `set_paths'
        from /usr/lib/ruby/site_ruby/1.8/rubygems.rb:131:in `path'
        from /usr/lib/ruby/site_ruby/1.8/rubygems/source_index.rb:60:in 
`installed_spec_directories'
        from /usr/lib/ruby/site_ruby/1.8/rubygems/source_index.rb:47:in 
`from_installed_gems'
        from /usr/lib/ruby/site_ruby/1.8/rubygems.rb:109:in `source_index'
        from 
/usr/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:111:in 
`init_gemspecs'
        from 
/usr/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:57:in `initialize'
        from 
/usr/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:30:in `new'
        from 
/usr/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:30:in `rescue in 
require'
        from 
/usr/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:28:in `require'
        from WM5.rb:17:in `<main>'

If this is common for Ruby 1.9 or if it is a result of some further 
setup I need to take care of, please point it out to me. The errors all 
point to rubygems, so I'd assume that others have encountered this 
problem. Questions like: "Do gems need to be reinstalled, moved or just 
pointed to some environment variable?" come to mind.
This same code runs without error(s) when I start it with Ruby 1.8.6.

Thanks for all replies and I look forward to seeing many of you this 
weekend.

-- Steve Downie