Edit Question - KnowledgeHub

Title Body

I'm having trouble understanding the finer details of negative lookahead regular expressions. After reading Regex lookahead, lookbehind and atomic groups , I thought I had a good summary of negative lookaheads when I found this description: (?!REGEX_1)REGEX_2 Match only if REGEX_1 does not match; after checking REGEX_1 , the search for REGEX_2 starts at the same position. Hoping I understood the algorithm, I cooked up a two-sentence test insult; I wanted to find the sentence without a certain word. Specifically... Insult: 'Yomama is ugly. And, she smells like a wet dog.' Requirements : Test 1: Return a sentence without 'ugly'. Test 2: Return a sentence without 'looks'. Test 3: Return a sentence without 'smells'. I assigned the test words to $arg , and I used (?:(?![A-Z].*?$arg.*?\.))([A-Z].*?\.) to implement the test. (?![A-Z].*?$arg.*?\.) is a negative lookahead to reject a sentence with the test word ([A-Z].*?\.) matches at least one sentence. The critical piece seems to be in understanding where the regex engine starts matching after processing the negative lookahead. Expected Results : Test 1 ($arg = "ugly"): "And, she smells like a wet dog." Test 2 ($arg = "looks"): "Yomama is ugly." Test 3 ($arg = "smells"): "Yomama is ugly." Actual Results : Test 1 ($arg = "ugly"): "And, she smells like a wet dog." (Success) Test 2 ($arg

Tags (comma-separated) Cancel