Programmatically check if HEAD is detached?

Question

I want to know whether I'm in a "HEAD detached" state in a script.

Currently I parse the output of git status but I dislike doing so because I've heard that it's a bad practice to parse Git output that's meant for human - I want a program-friendly interface to tell me whether HEAD is detached. I also don't want to manually look into .git/HEAD or parse git description or git branch.

Any ideas?

Allister

See #6976973 – Optometrist

You can try git rev-parse --symbolic-full-name HEAD, if it outputs HEAD, you're in detached mode, if it outputs a branch name, you're on that branch. – Optometrist

git rev-parse --abbrev-ref HEAD will give you a branch name if you're on a branch else will give you the detached HEAD hash – Pegpega

@Pegpega In detached HEAD state git rev-parse --abbrev-ref HEAD gives just "HEAD" string for me, not a hash. – Maris

Answer 1

The easiest command is probably:

$ git symbolic-ref -q HEAD

and check the exit status: 0 means normal; 1 is detached.

From the docs of git-symbolic-ref:

-q, --quiet
   Do not issue an error message if the <name> is not a symbolic ref
   but a detached HEAD; instead exit with non-zero status silently.

Ridings

Great solution. I'll just take this one. – Allister

Answer 2

Programmatically check requires a wrapper for Git protocol.

For example, by GitPython you're able to find out the repo detached or not repo.head.is_detached

Hydrargyrum

I didn't mention what language I'm programming in. It could be Bash where the only interface is the git binary. And that's good - Once you know how to do it in Bash you can do it in any language - by calling git binary. – Allister

@Allister git symbolic-ref HEAD may help you and just indicate the fatal error by grep command. – Hydrargyrum

Answer 3

From git 2.22, you can also use:

git branch --show-current

This prints nothing when not on a branch.

Interrelation

Answer 4

Use git branch to find a detached HEAD...

$ git branch -q
* (HEAD detached at c61a6d2)
  master

Bice

Are you sure this output is ready for consumption (i.e. text parsing)? – Allister

Sure enough to use it in my git wrapper. Could git change output? Yes, but vulnerabiity to bit-rot is common to any code you write. If you're worried, write a unit test... – Bice