Monday, June 10, 2013

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

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)

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 ;;

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)
  echo on branch $branch
  echo not on any branch


Pádraig Brady said...

Note this may be less portable given that git at least doesn't have the --short option to the symbolic-ref command.

Baruch Siach said...

I encountered the lack of --short on older git versions, and used basename to do the same:

branch=$(basename $(git symbolic-ref HEAD))