Wednesday 15 May 2019
regex - What do 'lazy' and 'greedy' mean in the context of regular expressions?
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Could someone explain these two terms in an understandable way?
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Greedy will consume as much as possible. From http://www.regular-expressions.info/repeat.html we see the example of trying to match HTML tags with <.+>. Suppose you have the following:
Hello World
You may think that <.+> (. means any non newline character and + means one or more) would only match the and the , when in reality it will be very greedy, and go from the first < to the last >. This means it will match Hello World instead of what you wanted.
Making it lazy (<.+?>) will prevent this. By adding the ? after the +, we tell it to repeat as few times as possible, so the first > it comes across, is where we want to stop the matching.
I'd encourage you to download RegExr, a great tool that will help you explore Regular Expressions - I use it all the time.
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