Update (April 28, 2012)
Try the new debugger gem as a replacement for ruby-debug.
Update (March 2, 2012)
Installation of linecache19 and ruby-debug-base19 can be easily done with:
bash < <(curl -L https://raw.github.com/gist/1333785)
Original answer
Have you looked at ruby-debug19 on ruby-1.9.3-preview1?
Here’s a temporary solution:
http://blog.wyeworks.com/2011/11/1/ruby-1-9-3-and-ruby-debugExcerpt from the site:
First download linecache19-0.5.13.gem and
ruby-debug-base19-0.11.26.gem from
http://rubyforge.org/frs/?group_id=8883, then …$ gem install linecache19-0.5.13.gem Building native extensions. This could take a while... Successfully installed linecache19-0.5.13 1 gem installed $ gem install ruby-debug-base19-0.11.26.gem -- --with-ruby-include=/Users/santiago/.rbenv/source/ruby-1.9.3-p0 Building native extensions. This could take a while... Successfully installed ruby-debug-base19-0.11.26 1 gem installed $ irb irb(main):001:0> require 'ruby-debug' => true