Determine the default branch on an upstream repo

Question

Is there a way to determine what the default branch is on an upstream repo when the local repo had the default branch changed to something different than the upstream repo?

Answer 1

There is no notation of "default branch" in Git. There is only HEAD in local and remote repository. You move HEAD locally quite often so there almost always be difference between upstream HEAD and local HEAD.

Answer 2

Solution 1: git rev-parse (Recommended)

Just do this:

git rev-parse --abbrev-ref refs/remotes/origin/HEAD

That should print out HEAD branch of the remote, which for a hosted repo should be the default branch, whether that may be origin/main, origin/master, origin/develop, origin/stable, whatever. (If the remote is actually another working copy, the remote HEAD is the checked-out branch.)

Your local Git repository caches this information, as the ref refs/remotes/origin/HEAD (replace origin by whatever the remote may be named.) Usually this gets set automatically by git clone, but if your local repository has a slightly unusual history (such as if your local repo began its life before the remote repo did), that local ref may be missing. In which case, this will generally recreate it:

git remote set-head origin --auto

That will contact the remote, check what its actual HEAD branch is, and update the local Git repository's refs/remotes/origin/HEAD ref.

Since this is locally cached information, it is possible for it to become outdated, if the remote repository changes its default branch. git fetch will not detect that change, but git remote set-head origin --auto will check what the remote HEAD is and update this local ref to match. So you may need to run that command manually after any such change in a remote repo.

In summary:

git rev-parse --abbrev-ref refs/remotes/origin/HEAD

gives you the answer quickly, but has a small chance of failing or being wrong;

git remote set-head origin --auto && 
  git rev-parse --abbrev-ref refs/remotes/origin/HEAD

is always going to be correct, but is slower.

Solution 2: git ls-remote

git ls-remote --symref origin HEAD

Example output:

ref: refs/heads/main    HEAD
bbac5bc097f944b3ad94e723364c5513d27b1910    HEAD

You could even do something like this:

git ls-remote --symref origin HEAD |
    egrep '^ref: refs/heads/.*\tHEAD$' |
    cut -d/ -f3- |
    cut $'-d\t' -f1

That will just print main (or master, or whatever).

I recommend solution 1 instead, because it is simpler, and I don't think this solution has any real advantages over it.

Solution 3: GitHub CLI

If the remote happens to be GitHub or GitHub Enterprise, you can also use the GitHub CLI:

gh repo view  --json defaultBranchRef --jq .defaultBranchRef.name

That will print main, or master, or whatever the remote default branch name may be.

I don't recommend this solution either, because solutions 1 and 2 will work for any Git host (GitHub, GitLab, BitBucket, Gitea, whatever). Plus it requires you to install and configure another CLI tool.