Q: How to tag individual files

The crash course at: http://git.or.cz/course/svn.html says:

I've done a bit of searching, and I can't for the life of me figure out how to tag an individual file. Help from the group would be much appreciated. Thanks.

-- Poojan Wagh http://www.circuitdesign.info

Poojan Wagh <poojanwagh@gmail.com> wrote:

You don't tag individual files. Git is snapshot based. You tag the entire project at once.

The comment you quoted was talking about tagging a single listing of blobs (a tree) or a single blob (stream of bytes). This can be handy in rare cases. In the linux kernel for example the prior history was stored by tagging the tree of that prior history, as there was no git based history preceeding that snapshot, so there were no commits to tag. In git.git Junio publishes his GnuPG public key as a tagged blob, making it available to validate signed tag objects.

So you can't tag individual files. The comment is a bit misleading and gets far too low-level for an otherwise high-level conversion guide.

Thanks, Shawn, for the clarification. Your explanation--together with http://www.kernel.org/pub/software/scm/git/docs/user-manual.html#the-object-database-- makes it clear.

So, to summarize (with the intent of fixing any misunderstanding on my 
part): You can tag the contents of files (blobs), but not files per se, 
because:
1. Git doesn't store files as an object as such. It stores the contents 
of files ("blobs")
2. Git stores directories (which define their constituent file names and 
contents=>blobs) as "tree" objects. So, the association between a file's 
name and a its contents occurs in a tree object.

One thing I notice about this structure is that a tree object can at least theoretically give me what I want: the ability to have files organized with labels (a la gmail) rather than folders--I would like to be able to have a single file show up under many different labels rather than mutually exclusive folders/directories. I know that this won't happen automatically, but it's nice to know that I *could* do it if I wanted to.

Thanks!

P.S. I also found http://www.gitcasts.com/posts/browsing-git-objects useful for as illustration of all the object structure.

Shawn O. Pearce wrote:

  Hi,

On Sun, Jul 13, 2008 at 05:35:37AM +0000, Shawn O. Pearce wrote:

..snip..

  I have tried to make this less misleading, thanks for noticing. I kept
the mention, though, because I think people should not be misled to
thinking that only commits are tagged, and then get confused when they
first meet v2.6.11.