flip-flop

I have heard and read about flip-flops with regular expressions in Perl and Ruby recently, but I was unable to find how they really work and what the common use cases are. Can anyone explain this in a language-agnostic manner? Now that I understand what it is, and how it works, I would rephrase the question to be simply: What is a flip-flop operator? The flip-flop operator in Perl evaluates to true when the left operand is true, and keeps evaluating to true until the right operand is true. The left and right operand could be any kind of expression, but most often it is used with regexes. With

I think I understand how a flip-flop works thanks to a tutorial, but the example there is contrived just for teaching. Can anyone give an example of how you have actually used or would use a flip-flop? I'm looking for a real-world application, not just another demonstration. What problems can this tool solve? The link used to be http://vision-media.ca/resources/ruby/ruby-flip-flop-or-range-operators , but seems to be spam this days. James Thompson Here's an example (taken from a rubycentral.com article ) where you print out only certain lines from a file: file = File.open("ordinal") while file