Re: how to track the history of a line in a file

From: Jeff King <peff@peff.net>
Date: Jan 2, 2009, 21:26 UTC
Message-ID: <20090102212655.GA24082@coredump.intra.peff.net>
In-Reply-To: <alpine.DEB.1.10.0901021405460.21567@asgard.lang.hm>

On Fri, Jan 02, 2009 at 02:13:32PM -0800, david@lang.hm wrote:

> I have a need to setup a repository where I'm storing config files, and I  
> need to be able to search the history of a particular line, not just when  
> the last edit of the line was (which is what I see from git blame)

As you figured out, the "manual" way is to just keep reblaming from the parent of each blame. Recent versions of "git gui blame" have a "reblame from parent" option in the context menu which makes this a lot less painful.

> 57f8f7b6 (Linus Torvalds 2008-10-23 20:06:52 -0700 3) SUBLEVEL = 28
>
> what I would want it to show would be a list of the commits that have  
> changed this line.

The tricky thing here is what is "this line"? Using the line number isn't right, since it will change based on other content coming in and out of the file. You can keep drilling down by reblaming parent commits, but remember that each time you do that you are manually looking at the content and saying "Oh, this is the line I am still interested in." So I a script would have to correlate the old version and new version of the line and realize how to follow the "interesting" thing.

In your case, I think you want to see any commit in Makefile which changed a line with SUBLEVEL in it. Which is maybe easiest done as:

  git log -z -p Makefile |
    perl -0ne 'print if /\n[+-]SUBLEVEL/' |
    tr '\0' '\n'

and is pretty fast. But obviously we're leveraging some content-specific knowledge about what's in the Makefile.

-Peff