Regex plus vs star difference?

Question

What is the difference between:

(.+?)

and

(.*?)

when I use it in my php preg_match regex?

Answer 1

The first (+) is one or more characters. The second (*) is zero or more characters. Both are non-greedy (?) and match anything (.).

Answer 2

In RegEx, {i,f} means "between i to f matches". Let's take a look at the following examples:

• {3,7} means between 3 to 7 matches
• {,10} means up to 10 matches with no lower limit (i.e. the low limit is 0)
• {3,} means at least 3 matches with no upper limit (i.e. the high limit is infinity)
• {,} means no upper limit or lower limit for the number of matches (i.e. the lower limit is 0 and the upper limit is infinity)
• {5} means exactly 4

Most good languages contain abbreviations, so does RegEx:

• + is the shorthand for {1,}
• * is the shorthand for {,}
• ? is the shorthand for {,1}

This means + requires at least 1 match while * accepts any number of matches or no matches at all and ? accepts no more than 1 match or zero matches.

Credit: Codecademy.com

Answer 3

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