class X < RuntimeError;end
x = [X]
begin
   raise X
rescue *x
   puts "yup"
end

---

% ruby         -v -e 'class X < RuntimeError;end; x = [X]; begin;  
raise X; rescue *x; puts "yup"; end'
ruby 1.8.6 (2007-09-24 patchlevel 111) [universal-darwin9.0]
yup

% ./runruby.rb -v -e 'class X < RuntimeError;end; x = [X]; begin;  
raise X; rescue *x; puts "yup"; end'
ruby 1.9.0 (2007-12-20 patchlevel 0) [i686-darwin9.1.0]
-e:1:in `raise': X (X)
	from -e:1:in `<main>'