Shortening an if-else structure in Ruby -

i have written this, same if-else logic knew visual basic 6.0, sure there better "ruby way" of writing it.

can please show me how in ruby world?

  if params[:medication_name].nil?     med_name = 'all'   elsif params[:medication_name] == 'undefined'     med_name = 'all'   else     med_name = params[:medication_name]   end 

for case, this:

med_name = params[:medication_name]  med_name = 'all' if [nil, 'undefined'].include? med_name 

for more general long chains of if/elsif/else, @ case statements. they're overkill in case, here's example:

med_name = case params[:med_name]    when 'undefined', nil       'all'    else       params[:med_name] end