Regex Quantifiers: What's the Difference Between ` ` and `*`?

Quantifiers: Understanding the Difference Between and * in Regex

Regex, a powerful tool for text matching and manipulation, utilizes quantifiers to specify the number of occurrences of a pattern in a string. The difference between the and * quantifiers lies in their greedy vs. ungreedy matching behavior.

The quantifier means that the preceding expression must appear one or more times, while the * quantifier allows it to appear zero or more times.

By default, quantifiers are greedy, meaning they match as many characters as possible. However, appending a ? after the quantifier changes the behavior to "ungreedy," making it match as few characters as possible.

Example: Greedy vs. Ungreedy Matching

Consider the string "abab" and the regular expressions:

• a.*b: Matches the entire string "abab" (preg_match_all would return one match)
• a.*?b: Matches only the starting "ab" (preg_match_all would return two matches)

The greedy quantifier in the first example matches as many characters as possible, while the ungreedy quantifier in the second example matches only the essential characters to satisfy the expression.

Application:

The ungreedy quantifier can be beneficial when you want to capture specific substrings or avoid matching unwanted characters. For instance, when parsing HTML tags, the greedy quantifier could overmatch a tag, including its contents, while the ungreedy quantifier ensures that it matches only the tag itself.

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