php - Regex plus vs star difference?

Question

What is the difference between:

(.+?)

and

(.*?)

when I use it in my php preg_match regex?

question from:https://stackoverflow.com/questions/65892071/why-the-second-group-include-a-slash-in-this-regex

Answer 1

They are called quantifiers.

* 0 or more of the preceding expression

+ 1 or more of the preceding expression

Per default a quantifier is greedy, that means it matches as many characters as possible.

The ? after a quantifier changes the behaviour to make this quantifier "ungreedy", means it will match as little as possible.

Example greedy/ungreedy

For example on the string "abab"

a.*b will match "abab" (preg_match_all will return one match, the "abab")

while a.*?b will match only the starting "ab" (preg_match_all will return two matches, "ab")

You can test your regexes online e.g. on Regexr, see the greedy example here