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Greediness Regular Expressions (Regexp)

Let's look at the concepts of greedy and lazy quantification.

We'll start by writing a regular expression that will highlight all the tags in our string. To do this, enter the opening and closing characters of the tag: < and >, and put any character inside:


/<.*>/

<a href="https://www.yahoo.com">google</a>


Despite the fact that there are two tags in the string – opening and closing – a match was found for the whole strong. This behavior is called greedy behavior. This means that the quantifier is repeated as many times as possible. Quantification is greedy by default in regular expressions, so we've captured the longest possible substring. The entire string corresponds to our regular expression; everything inside < and > counts as tag content.

To avoid greedy behavior, we can specify any character inside the tag instead of any character except the closing one. And then the two tags are matched separately:


/<[^>]*>/

<a href="https://www.yahoo.com">google</a>


Despite the effectiveness of such a solution, it's only an escape from the problem. That way you can avoid the consequences of greedy behavior, but not the behavior itself.

To turn a greedy quantization into a lazy one, you have to use a special symbol, ?:


/<.*?>/

<a href="https://www.yahoo.com">google</a>


Keep in mind that many special characters behave differently in regular expressions, depending on where they are. If ? were placed after the dot, it would be treated simply as a “no character or one character” quantifier:


/<.?>/

<p><a href=" www.yahoo.com ">google</a></p>


But when ? comes right after a quantifier, it's treated by regex as a special character that turns greedy quantifiers into lazy ones.


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