Checking the current branch programatically

The git branch Porcelain command, when run without any argument, lists the local branches, and shows the current branch prefixed with an asterisk, like this:

$ git branch
* master
  next
$ git checkout master^0
$ git branch
* (no branch)
  master
  next

The second one with (no branch) is shown when you are not on any branch at all. It often is used when you are sightseeing the tree of a tagged version, e.g. after running git checkout v1.8.3 or something like that.

To find out what the current branch is, casual/careless users may have scripted around git branch, which is wrong. We actively discourage against use of any Porcelain command, including git branch, in scripts, because the output from the command is subject to change to help human consumption use case.

And in fact, since release 1.8.3, the output when you are not on any branch, has become something like this:
$ git checkout v1.8.3
$ git branch
* (detached from v1.8.3)
  master
  next

in order to give you (as a human consumer) a better information. If your script depended on the exact phrasing from git branch, e.g.

branch=$(git branch | sed -ne 's/^\* \(.*\/\1/p')
case "$branch" in
'('?*')') echo not on any branch ;;
*) echo on branch $branch ;;
esac

your script will break.

The right way to programatically find the name of the current branch, if any, is not to use the Porcelain command git branch that is meant for the human consumption, but to use a plumbing command git symbolic-ref instead:

if branch=$(git symbolic-ref --short -q HEAD)
then
  echo on branch $branch
else
  echo not on any branch
fi