Print symbolic name for HEAD

Question

I am looking for a Git command that will print the symbolic name for HEAD. I was using this command

$ git name-rev --name-only HEAD
master
$ git checkout HEAD~2
$ git name-rev --name-only HEAD
master~2

However I noticed that it does not work on a new repository

$ git init
$ git name-rev --name-only HEAD
Could not get sha1 for HEAD. Skipping.

I found this workaround

$ git init
$ git symbolic-ref --short HEAD
master

But this does not work on older commits

$ git checkout HEAD~2
$ git symbolic-ref --short HEAD
fatal: ref HEAD is not a symbolic ref

So now I have this, which covers both new repos and older commits

$ git symbolic-ref -q --short HEAD || git name-rev --name-only HEAD
master

I was just wondering, is this the best way to do this? It feels like this should be possible with one command.

Answer 1

You write:

I am looking for a Git command that will print the symbolic name for HEAD.

The following may suffice to demonstrate that what you're asking for does not make sense in all situations, simply because HEAD may not be unambiguously associated with one reference. Read on.

What git name-rev does

In the git-name-rev man-page, you find the following description:

Given a commit, find out where it is relative to the local refs. [...]

More specifically, git name-rev checks whether <commit-ish> is reachable from any of the local references (by processing them in lexicographical order, e.g. develop before master).

Let's examine what

$ git name-rev --name-only <commit-ish>

does in different cases (the --name-only flag is incidental here, as its effects are purely cosmetic).

Case in which HEAD is not detached

If HEAD is not detached, i.o.w. if HEAD is pointing to a valid ref (let's call it myref), then there is no ambiguity: running

$ git name-rev --name-only HEAD

simply outputs

myref

because the myref reference is unambiguously associated with HEAD. So far, so good.

Case in which HEAD is detached

In that case, things are not as simple. In fact, there may be one or more references from which <commit-ish> is reachable, or there may be none at all.

Case in which there are one or more such local references

At the first such local reference found, git name-rev prints a "relative" symbolic reference, i.e. a revision of the form

<ref>~<n>

where <ref> stands for the local reference in question, and <n> stands for the generation. For example, if HEAD points directly to a commit that is a grandparent of master (master being the only local reference), then

$ git name-rev HEAD

returns

master~2

Note, however, that in case <commit-ish> is reachable from multiple references, the one returned by git name-rev is somewhat arbitrary, as it's only dictated by the lexicographical order (in which the command checks local references).

Case in which there is no such local reference

It's easy to imagine situations in which <commit-ish> is reachable from none of the local references. Actually, here is one you can reproduce at home (boilerplate stdout is omitted):

# set things up
$ mkdir test
$ cd test
$ git init

# create a commit
$ touch README.md
$ git add README.md
$ git commit -m "add README"

# detach the HEAD (make it point directly to the tip of master, instead of to master itself)
$ git checkout $(git rev-parse master)

# create a second commit (while in detached-HEAD state)
$ printf "foo\n" > README.md
$ git commit -am "write 'foo' in README"

# attempt to find a symbolic name for HEAD 
$ git name-rev --name-only HEAD
undefined

Because the commit DAG looks as follows,

A [master]
 \
  B [HEAD]

commit B is not reachable from the only reference (master); therefore, git name-rev gives up and simply returns undefined.

Conclusion

Because HEAD is not guaranteed to be unambiguously associated to one reference, what you're asking for doesn't make sense :p

Answer 2

Just want to add my solution for your case:

git symbolic-ref -q --short HEAD || git describe --all --always HEAD

This covers branches, tags, detached heads (commits) and new repositories. But tags will be returned as tags/0.1.0 for example.