# Parsing diff --git lines 4 messages from 2008-03-09 to 2008-03-09. Participants: Simon Fraser, Linus Torvalds, Jakub Narebski, Johannes Schindelin. Thread: https://gitlist.dev/t/12598 ## Simon Fraser, 2008-03-09 01:48 Subject: Parsing diff --git lines Message-ID: URL: https://gitlist.dev/e/F4D3B820-CCF4-4212-BF32-700EFD448143%40mac.com ``` I'm working on a GUI for git, and I'd like to be able to provide some diff navigation tools. That requires that I can find the file chunks in a diff, and parse out the file names. However, I don't see a reliable way to identify the two files from a "diff --git" line. Here's a (deliberately pathological) example: diff --git a/a / b/file with spaces.txt b/a / b/file with spaces.txt In this case, the repository contains directories called "a " and " b" and the file names have spaces in. What would make this possible would be either to always quote file paths containing spaces, or use a character other than a space (e.g. a \t) between the two file names. Thanks Simon ``` ## Linus Torvalds, 2008-03-09 04:04 Subject: Re: Parsing diff --git lines Message-ID: URL: https://gitlist.dev/e/alpine.LFD.1.00.0803081955110.5896%40woody.linux-foundation.org In-Reply-To: ``` On Sat, 8 Mar 2008, Simon Fraser wrote: > > However, I don't see a reliable way to identify the two files > from a "diff --git" line. Here's a (deliberately pathological) > example: See how "git-apply" does it. The rule is: - if the filenames are different, you should ignore the filenames on the "diff --git" line, and trust the ones on the "renamed from/to" ones (which are unambiguous because they only have one filename per line) - if the filenames aren't different, then you can unambiguously know how to parse it by simply making sure they are the same. So to take your example: > diff --git a/a / b/file with spaces.txt b/a / b/file with spaces.txt Here, you can *know* that the filename is "a / b/file with spaces.txt", because it must match the pattern "a/$filename b/$filename", and no other split at a space would ever do that! See in particular "git_header_name()" in builtin-apply.c. See the comments both at the top of the function and there in the middle to reflect the above rule: /* * This is to extract the same name that appears on "diff --git" * line. We do not find and return anything if it is a rename * patch, and it is OK because we will find the name elsewhere. * We need to reliably find name only when it is mode-change only, * creation or deletion of an empty file. In any of these cases, * both sides are the same name under a/ and b/ respectively. */ ... /* * Accept a name only if it shows up twice, exactly the same * form. */ > What would make this possible would be either to always quote > file paths containing spaces, or use a character other than > a space (e.g. a \t) between the two file names. Well, git didn't originally ever quote filenames at all, and I actually wanted the "diff --git" line to look as much like a regular "diff -urN" line as possible (which has spaces between the names) These days, we could quote, but hey, anybody who parses diff lines needs to be able to handle the non-quoted form *anyway*, so quoting doesn't really help anybody in the end. Linus ``` ## Jakub Narebski, 2008-03-09 08:25 Subject: Re: Parsing diff --git lines Message-ID: URL: https://gitlist.dev/e/m3r6ekfgnw.fsf%40localhost.localdomain In-Reply-To: ``` Linus Torvalds writes: > On Sat, 8 Mar 2008, Simon Fraser wrote: > > > > However, I don't see a reliable way to identify the two files > > from a "diff --git" line. Here's a (deliberately pathological) > > example: > > See how "git-apply" does it. > > The rule is: > > - if the filenames are different, you should ignore the filenames on the > "diff --git" line, and trust the ones on the "renamed from/to" ones > (which are unambiguous because they only have one filename per line) > > - if the filenames aren't different, then you can unambiguously know how > to parse it by simply making sure they are the same. By the way, the default pre-commit hook behaves a bit strangely on files which contain spaces[*1*] in filename (due to GNU-diff-uism): * * You have some suspicious patch lines: * * In b * trailing whitespace (line 1) b:1:++ b/ b Foootnote: ========== [*1*] If file has '"', '\' or control character in filename, it is quoted. -- Jakub Narebski Poland ShadeHawk on #git ``` ## Johannes Schindelin, 2008-03-09 20:45 Subject: Re: Parsing diff --git lines Message-ID: URL: https://gitlist.dev/e/alpine.LSU.1.00.0803092144150.3975%40racer.site In-Reply-To: ``` Hi, On Sun, 9 Mar 2008, Jakub Narebski wrote: > Foootnote: Alternatively, you can write "Bigfootnote" or "Sasquatchnote". Ciao, Dscho ```