Download - The Bastards Book of Regular Expressions

Laziness and greediness 100Being too greedyIn the previous chapter, we learned about the dot operator, which will match any kind of character.This seems like just what we need, right?Given the following text:The sheep says “Cowabunga!” to those who approach it.Find ".+"Replace "Hello"The result is:The sheep says “Hello” to those who approach it.However, there’s a serious problem with this solution. Given a more complicated phrase:When the sheep says “Cowabunga!”, the cow will reply, “Baa! Baa!”– when we apply the previous solution, we end up with:When the sheep says “Hello”What happened? We got burned by greediness.Let’s express the regex – ".+" – in English: Match a quotation mark and then match every characteruntil you reach another quotation mark.That seems straightforward. But consider the power of the dot: it matches any character, except fornewline characters. And “any character” includes the quotation mark.So in our example text:When the sheep says “Cowabunga!”, the cow will reply, “Baa! Baa!”There’s at least three ways that the regex engine can satisfy our pattern:It could stop at the second quotation mark:When the sheep says “Cowabunga!”, the cow will reply, “Baa! Baa!”