Regex plus vs star difference?
PhpRegexPhp Problem Overview
What is the difference between:
(.+?)
and
(.*?)
when I use it in my php preg_match regex?
Php Solutions
Solution 1 - Php
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
Solution 2 - Php
The first (+) is one or more characters. The second (*) is zero or more characters. Both are non-greedy (?) and match anything (.).
Solution 3 - Php
+ matches at least one character
* matches any number (including 0) of characters
The ? indicates a lazy expression, so it will match as few characters as possible.
Solution 4 - Php
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
Solution 5 - Php
A + matches one or more instances of the preceding pattern. A * matches zero or more instances of the preceding pattern.
So basically, if you use a + there must be at least one instance of the pattern, if you use * it will still match if there are no instances of it.
Solution 6 - Php
Consider below is the string to match.
ab
The pattern (ab.*) will return a match for capture group with result of ab
While the pattern (ab.+) will not match and not returning anything.
But if you change the string to following, it will return aba for pattern (ab.+)
aba
Solution 7 - Php
+ is minimal one, * can be zero as well.
Solution 8 - Php
A star is very similar to a plus, the only difference is that while the plus matches 1 or more of the preceding character/group, the star matches 0 or more.
Solution 9 - Php
I think the previous answers fail to highlight a simple example:
for example we have an array:
numbers = [5, 15]
The following regex expression ^[0-9]+ matches: 15 only.
However, ^[0-9]* matches both 5 and 15. The difference is that the + operator requires at least one duplicate of the preceding regex expression