run `hammer -v shell` on ruby 1.8, hit <tab> to invoke command completion and see following exception:
NoMethodError (undefined method `line_buffer' for Readline:Module)
This method is really missing for for Readline version in 1.8.
Created from redmine issue http://projects.theforeman.org/issues/4162
Upstream bug assigned to email@example.com
*** This bug has been marked as a duplicate of bug 1123478 ***