See also:
How can I see which Git branches are tracking which remote / upstream branch?
How can I find out which remote branch a local branch is tracking?
Do I need to parse git config output, or is there a command that would do this for me?
Update: Well, it's been several years since I posted this! For my specific purpose of comparing HEAD to upstream, I now use @{u}, which is a shortcut that refers to the HEAD of the upstream tracking branch. (See https://git-scm.com/docs/gitrevisions#Documentation/gitrevisions.txt-emltbranchnamegtupstreamemegemmasterupstreamememuem ).
Original answer: I've run across this problem as well. I often use multiple remotes in a single repository, and it's easy to forget which one your current branch is tracking against. And sometimes it's handy to know that, such as when you want to look at your local commits via git log remotename/branchname..HEAD.
All this stuff is stored in git config variables, but you don't have to parse the git config output. If you invoke git config followed by the name of a variable, it will just print the value of that variable, no parsing required. With that in mind, here are some commands to get info about your current branch's tracking setup:
LOCAL_BRANCH=`git name-rev --name-only HEAD`
TRACKING_BRANCH=`git config branch.$LOCAL_BRANCH.merge`
TRACKING_REMOTE=`git config branch.$LOCAL_BRANCH.remote`
REMOTE_URL=`git config remote.$TRACKING_REMOTE.url`
In my case, since I'm only interested in finding out the name of my current remote, I do this:
git config branch.$(git name-rev --name-only HEAD).remote