In Hudson, how do I get the current build's git commit sha?

We are using Hudson with git. We have a build/test server which compiles our project and then a QA server to which we need to deploy.

We want to get the current built git commit sha and use it to pull the appropriate commit for deployment on our QA server.

Unfortunately it seems that the hudon git plugin does not set the git commit sha in the environment variables (as the svn plugin does in SVN_REVISION for example). How do we get around this?

Pointer/ examples will be helpful as I am a hudson noob.

Thanks