git equivalent of svn r-number

[Matthew Seaman]

On 03/01/2021 12:54, Robert Huff wrote:
> 
> 	(I think this may have already been asnwered, but I can't find
> the thread.)
> 	What is it?
> 	Where is it stored?
> 	How do I get git to report it?

There is no exact equivalent of the repository wide unique and 
monotonically increasing SVN revision number in git, simply because of 
the difference in the way git works, with a large number of distrubuted 
repositories rather than one central one.

Instead, there is a vaguely similar concept which is the SHA-1 hash of a 
commit. You can find these by using `git log` or `git reflog` -- so with 
this, git can tell you if the branch you are on contains a particular 
commit, which is almost, but not quite, usable for the much the same 
purposes as the SVN revision number.

There's also `git describe` which gives you some combination of the 
latest tag on your timeline, how many commits there have been on that 
branch since then and the hash of the latest commit, like so:

```
codling:/usr/src:% git describe HEAD
release/8.1.0-103892-g84eaf2ccc6aa
```

Note: the hash is the hex string at the end -- this is actually the 
unambiguous prefix of the SHA-1 hash of the latest commit on your 
timeline (preceeded by a 'g' for 'git' -- g obviously isn't a 
hexadecimal digit):

```
codling:/usr/src:% git log HEAD^1..HEAD
commit 84eaf2ccc6aa05da7b7389991d3023698b756e3f (HEAD -> main, freebsd/main)
Author: Konstantin Belousov <kib at FreeBSD.org>
Date:   Mon Dec 21 19:02:31 2020 +0200

     x86: stop punishing VMs with low priority for TSC timecounter

     I suspect that virtualization techniques improved from the time when we
     have to effectively disable TSC use in VM.  For instance, it was 
reported
     (complained) in https://github.com/JuliaLang/julia/issues/38877 that
     FreeBSD is groundlessly slow on AWS with some loads.

     Remove the check and start watching for complaints.

     Reviewed by:    emaste, grehan
     Discussed with: cperciva
     Sponsored by:   The FreeBSD Foundation
     Differential Revision:  https://reviews.freebsd.org/D27629
```

You can also access the SVN r-numbers from before the cut-over via git 
notes -- see Warner's collection of documentation at 
https://github.com/bsdimp/freebsd-git-docs/ for a description of how 
that works and much more besides --- these docs will be polished up and 
added to the handbook eventually.

	Cheers,

	Matthew





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