gistfile1.txt

22:40:31 /Users/jasonn/source/ruby_koans $ irb
>> begin
?> nil.some_method_nil_doesnt_know_about
>> rescue Exception => ex
>> puts ex.class
>> puts ex.message
>> end
NoMethodError
undefined method `some_method_nil_doesnt_know_about' for nil:NilClass
=> nil
>> 

Line 2 is the begin block. The begin keyword to Ruby tells Ruby that you're going to execute some code that may throw an exception. Line 3 does in fact throw an exception.

Line 4 is the rescue block. This line tells Ruby that if an exception of type "Exception" is thrown, catch that exception and store it in the variable ex.

Line 5 and 6 calls two methods on the Exception (ex) that was thrown. Line 5 prints out what type/class the exception was, Line 6 prints out the corresponding error message.

Line 7 ends the program.

After typing end into irb, it executes the code. It runs line 3, which raises a "NoMethodError" exception, which our rescue block catches. Our rescue block tells it to print out the type (output line 8) and the error message (output line 9).