# git grep -P is multiline for negative lookahead/behind 4 messages from 2016-08-01 to 2016-08-04. Participants: Michael Giuffrida, Junio C Hamano. Thread: https://gitlist.dev/t/42983 ## Michael Giuffrida, 2016-08-01 09:09 Subject: git grep -P is multiline for negative lookahead/behind Message-ID: URL: https://gitlist.dev/e/CACi5S_0QGEgnijGyaBeZxOSobdwfA%2Bd-wa-jrHs64Va097mnRQ%40mail.gmail.com ``` Negative lookahead/lookbehind with `git grep -P` considers the surrounding lines of an otherwise positive match. This differs from `grep -P` behavior. It does not repro for *positive* lookahead/lookbehind. Example: $ echo -e 'Bar\nBar Baz\nBat' > test.txt && git add test.txt $ git grep -P 'Bar(?!\sB)' test.txt # Find 'Bar' not followed by '\sB' With regular grep, this works: $ grep -P 'Bar(?!\sB)' test.txt Bar Because \s includes \n, the negative lookahead unexpectedly finds the B on line 2, and therefore line 1 fails to match the full expression. Positive lookahead works like `grep -P`, in that it isn't unexpectedly multiline: $ git grep -P 'Bar(?=\sB)' test.txt # Find 'Bar' followed by '\sB' test.txt:Bar Baz $ grep -P 'Bar(?=\sB)' test.txt Bar Baz Is this expected behavior, and if so, why/where is this documented? git: git version 2.8.0.rc3.226.g39d4020, also 2.9.2.517.gf8f7adc, both with libpcre grep: grep (GNU grep) 2.16 ``` ## Junio C Hamano, 2016-08-01 21:35 Subject: Re: git grep -P is multiline for negative lookahead/behind Message-ID: URL: https://gitlist.dev/e/xmqqr3a8goka.fsf%40gitster.mtv.corp.google.com In-Reply-To: ``` Michael Giuffrida writes: > Is this expected behavior, and if so, why/where is this documented? I do not think "git grep" was designed to do multi-line anything, with or without lookahead. If you imagine that the implementation attempts its matches line-by-line, does that explain the observed symptom? ``` ## Michael Giuffrida, 2016-08-04 18:54 Subject: Re: git grep -P is multiline for negative lookahead/behind Message-ID: URL: https://gitlist.dev/e/CACi5S_2j%2BPXFwE755CSiE01%3DsYALx-17Hk1k8zJOR9_Fj7y9Pg%40mail.gmail.com In-Reply-To: ``` On Mon, Aug 1, 2016 at 2:35 PM, Junio C Hamano wrote: > Michael Giuffrida writes: > >> Is this expected behavior, and if so, why/where is this documented? > > I do not think "git grep" was designed to do multi-line anything, > with or without lookahead. If you imagine that the implementation > attempts its matches line-by-line, does that explain the observed > symptom? No. If it worked line-by-line, it would produce more results. It is not producing the expected matches because it *is* considering the previous line in negative lookbehind, when I don't want or expect it to. Thus it throws out results that should match. ``` ## Junio C Hamano, 2016-08-04 22:09 Subject: Re: git grep -P is multiline for negative lookahead/behind Message-ID: URL: https://gitlist.dev/e/CAPc5daVPpeCTLbo4t7gRbKbP%3DBMnhHHtE68uXjanQDS2nKc4dw%40mail.gmail.com In-Reply-To: ``` On Thu, Aug 4, 2016 at 11:54 AM, Michael Giuffrida wrote: > On Mon, Aug 1, 2016 at 2:35 PM, Junio C Hamano wrote: >> I do not think "git grep" was designed to do multi-line anything, >> with or without lookahead. If you imagine that the implementation >> attempts its matches line-by-line, does that explain the observed >> symptom? > > No. If it worked line-by-line, it would produce more results. It is > not producing the expected matches because it *is* considering the > previous line in negative lookbehind, when I don't want or expect it > to. Thus it throws out results that should match. If that is the case I do not know what is going on; perhaps somebody more familiar with the pcre codepath can help. Sorry. ```