What's the Difference Between the ` ` and `*` Quantifiers in Regular Expressions?

Understanding the Difference between Regular Expression Plus ( ) and Star (*) Quantifiers

In PHP's preg_match function, regular expressions use quantifiers, such as plus ( ) and star (*), to specify how many occurrences of a given pattern should be matched. The difference between these two quantifiers lies in their behavior and the resulting matches they produce.

Plus ( ) Quantifier:

• Matches one or more occurrences of the preceding expression.
• Is greedy by default, meaning it matches as many characters as possible.

Star (*) Quantifier:

• Matches zero or more occurrences of the preceding expression.
• Is also greedy by default, but can be made "ungreedy" by adding a question mark (?) after the quantifier.

Example: Greedy vs. Ungreedy Quantifiers

Consider the following example with the string "abab":

• a.*b: Greedy match will match "abab" as a whole string.
• a.*?b: Ungreedy match will only match the first "ab" portion of the string, resulting in two matches.

Making Quantifiers Ungreedy

Adding a question mark (?) after a quantifier changes its behavior from greedy to ungreedy. Ungreedy quantifiers match as few characters as possible, leading to different results compared to greedy quantifiers. This can be useful in certain scenarios where matching the minimum possible characters is desired.

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