Positive look-behind assertion (?<=...)


What is a positive look-behind assertion? How to use it?

How to write a regular expression to find words ending with 'oo' in text like: ?

✍: FYIcenter.com


A positive look-behind assertion is a zero-width assertion that allows you to match a subpattern left to the current position (look-behind) without moving the matching position. Positive look-behind assertion is expressed as (?<=pattern). For example:

(?<=\t)\w+   - matches a word that follows a tab

The regular expression to match find words ending with 'oo' is: Note that:

 *          - skip space characters
(\w+)       - capture the word
(?<=oo)     - is the word ending with '00'?

Click the button to test this regular expression here online:

2013-01-31, 2692👍, 0💬