How to embed a hash, tag or branch name?

How do I embed a hash, tag or branch name into source code managed by git?

I've tried searching the net, git manuals etc but haven't found a replacement for the old '$Id: $' strings from svn. What I need is a way to map compiled binaries and flash images to git tree heads, tags and branches.

Thanks,

-Mikko

Mikko Rapeli <mikko.rapeli@iki.fi> writes:

You can embed SHA-1 of a _file contents_ (blob) using '$Id: $' keyword with `ident` attribute - see gitattributes manpage.

The correct solution of embedding version number is to do it at _build time_, using e.g. script similar to GIT-VERSION-GEN used by Git itself and by Linux kernel. It helps if you tag your releases.

If you really, really, really need it, you can embed tag or branch name into source code using `filter` attribute and custom clean/smudge filters to do keyword un-expansion and keyword expansion. But please think twice about what you want to achive with keyword expansion, and whether keyword expansion is a best solution...

On Fri, Jul 31, 2009 at 02:27:50AM -0700, Jakub Narebski wrote:

Great, thanks!

This would help, but I'm on cygwin/msysgit and compiling with a microcontroller IDE MPLAB and PICC-18 compiler, so I really don't want to dig deeper into build time integration at the moment.

Btw, I don't know how didn't notice that this is a FAQ: http://git.or.cz/gitwiki/GitFaq#Doesgithavekeywordexpansion.3F

-Mikko

Am 31.07.2009 11:52 schrieb Mikko Rapeli:

Hi Mikko,

I don't know whether you want to use the "ident" command on your final binary. With Git, that's pointless, as all source files will have the same $Id$. So it's perfectly sufficient to have only ONE file enriched with Git's SHA1.

Suggestion: During build time, compile (and link in) a file (e.g.
version.c) with "-DVERSION=\"$(git describe)\"". My version.c looks like
this:

----------------------------------
char const * version()
{
     return VERSION;
}
----------------------------------

The function then returns sth. like "foo12004-26-gc6c9273", which means that you're 26 commits ahead of the annotated tag "foo12004" and your commit has SHA1 "c6c9273". Then make your application somehow return that version string when asked (or deliver a version.txt together with it). This way you know that your binary was built using commit "c6c9273". You can further refine the VERSION by adding a "-dirty" if the working tree was dirty at build time. Then you'll know that your binary was based on c6c9273 "with some changes".

Make sure that version.c is the ONLY file that compiles with that -DVERSION switch. Otherwise all files get re-compiled when $(git describe) changes. That's not what you want.

     HTH, Dirk

On Sat, 1 August 2009, Dirk Süsserott wrote:

You are wrong. In Git $Id$ / $Id: $ expands to SHA-1 id of _blob_ (i.e. of file *contents*), not SHA-1 id of a commit. This way when switching branches or rewinding branch using git-reset we don't have to pay huge performance penalty because of `ident`, as we would have because every file would have to be changed if $Id$ was about commit id (or if there was $Revision$ or $Author$ implemented).

GIT-VERSION-GEN and various tricks in Makefile do just that, not only for compiled parts, but also for scripts.

[...]

Am 01.08.2009 15:13 schrieb Jakub Narebski:

Ok, sorry about that. Actually I haven't read the concerning docs *that* well when I figured out that keyword expansion with Git is not exactly a good idea.

Right, but my explanation shows the overall intention of that. So, Mikko, have a look at GIT-VERSION-GEN and my suggestion and use some kind of summary of them.