Question concerning ruby file access from a novice:

I have seen following code fragment from

http://www.rubycentral.com/pickaxe/tut_io.html

File.open("testfile", "r") do |aFile|
# ... process the file
end

Advantage of this notation is that file is automatically closed when do 
loop terminates -- maybe by an exception with Process.exit.

But how do I test in this notation that the file with name "testfile" 
really exits (and opening was successful). In an multi-tasking 
environment another process may delete the file just before this 
statement is executed.

Or in other words: I want to print a text like "File with filename 
"testfile" does not exist" when opening failed. 

Best regards

Stefan Salewski