How to find out which of 'master' or 'main' branches exists in a repository?

Question

I'm working on a Bash script that does some Git repository maintenance. Some of repositories use 'master' as the main branch while others use 'main'. What Git command can I use to return the first branch of these which exists?

P.S. I want to check local branches of a repo, since there will always be a local 'master' or 'main' branch.

You'd have to define "the first which exists". If you meant the first which has been created, git doesn't keep that kind of branch metadata. But you might want to check `git config --get init.defaultbranch` on recent enough git repos. — Romain Valeri, Jun 22 '21 at 15:07
@RomainValeri that would only tell you which would be the default branch when initializing a new repo, not of the current one — Marcus Müller, Jun 22 '21 at 15:09
Not the first which has been created, just the first from the list which exists. I assume there will be one of these. BTW, `git config --get init.defaultbranch` doesn't return anything for me. — planetp, Jun 22 '21 at 15:10
@MarcusMüller As I said, there will always be just one of them. Why would you need to have both? — planetp, Jun 22 '21 at 15:29
@planetp for example, a medium-sized FOSS project I work closely with migrated to `main`. But they couldn't just waltz in and immediately delete `master`, because there's people (and projects) whose automation depends on the name of branches, so `master` and `main` both exist, but `master` simply sees no further updates. — Marcus Müller, Jun 22 '21 at 15:30

Eugene Yarmash · Answer 1 · 2021-09-20T09:29:00.853

9

To find out which of the two local branches exists, you can use git branch with the -l/--list argument:

git branch -l master main  # outputs 'master' or 'main', provided only one exists

Git also marks the current branch with an asterisk, so you could use sed to strip it:

git branch -l master main | sed 's/^* //'

edited Sep 20 '21 at 09:29

answered Jun 23 '21 at 10:35

Eugene Yarmash

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Better use `git branch -l master main | sed -r 's/^[* ] //' | head -n 1`: removes the first double space or space star according to the current branch state, then remove any other result line which could corrupt the variable content. – jbaptperez Jul 01 '22 at 14:54

score 4 · Answer 2 · answered Jun 22 '21 at 19:04

To find out what some other Git repository's HEAD is, use git ls-remote:

$ git ls-remote --symref origin HEAD
ref: refs/heads/master  HEAD
670b81a890388c60b7032a4f5b879f2ece8c4558    HEAD

This assumes both your Git, and the remote's Git, are not so old that they do not support --symref (it must be supported on both sides). Note that this command can be run outside any repository by using a URL directly, instead of a remote name like origin.

To find out what branch names exist in some other Git repository, either clone it and inspect the resulting remote-tracking names, or use git ls-remote. Note that you can specify just refs/heads to limit the output to branch names only, or omit it entirely to get everything (all branch and tag names and any other names they choose to expose).

Paul Hodges · Answer 3 · 2022-07-18T13:29:54.573

What Git command can I use to return the first branch of these which exists?

git branch -r returns a list of remotes.
grep origin/ma will match main and master.
If you need to be pickier, use grep -E 'origin/(main|master)'

Assigning the list returned to an array should work, but be wary of names with spaces &c because the array elements are delimited by whitespace and the whole thing can blow up.

b=( $(git branch -r | grep origin/ma ) ) # all matches
git checkout "${b[0]##*/}"               # first hit

If you want to be a little more careful,

for n in main master; do 
  b="$(git branch -r -l "origin/$n")"
  if [[ -n "$b" ]]; then
    git checkout "${b[0]##*/}"
    break # keep the first success
  fi 
done

Marcus Müller · Answer 4 · 2021-06-22T15:45:32.477

1

Well, "default branch" has no meaning locally; it only makes sense if your repo is a remote to someone else, or in terms of a remote that someone else hosts. (Also, in terms of "what branch do I pull by default when I pull from this local branch, but if you knew that, you wouldn't be asking this.)

git fetch
git branch -r --list 'origin/HEAD' | grep '>'

edited Jun 22 '21 at 15:45

answered Jun 22 '21 at 15:40

Marcus Müller

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Interestingly, this produces empty output for some (active) repos. What would that mean? – planetp Jun 22 '21 at 16:09
Interesting! What does `git branch -r --points-at origin/HEAD` tell you for these? – Marcus Müller Jun 22 '21 at 16:20
1

`error: malformed object name 'origin/HEAD'` – planetp Jun 23 '21 at 08:35
@planetp does that repository even have a remote called `origin`? – Marcus Müller Jun 23 '21 at 08:36
yes, it's otherwise a pretty 'standard' repository. – planetp Jun 23 '21 at 08:40
well without a remote, what does "default" branch even mean: hence the first sentence in my answer! – Marcus Müller Jun 23 '21 at 08:42

Greg Bray · Answer 5 · 2022-07-14T23:19:31.750

I wanted a script that worked with multiple remotes (origin fork or canonical upstream) and repositories that used main or master. Based on Paul Hodges answer I ended up with:

#Update local/fork default to match remote. Can also delete current local branch using -D (to clean up a finished feature branch)
gum(){
  REMOTES=( $(git branch -r | grep -Eo "  (origin|upstream)/(master|main)") )
  RNAME=${REMOTES[-1]%%/*}    # Prefix of last one in the list (prefer fetching from upstream over origin)
  RBRANCH=${REMOTES[-1]##*/}  # Suffix of last matching remote
  LBRANCH="$(git rev-parse --abbrev-ref HEAD)"  # Name of current checked out branch

  if [[ "$LBRANCH" != "$RBRANCH" && "$1" != "-D" ]]; then
    echo "error current branch is '$LBRANCH' not $RBRANCH and -D not specified to delete current branch"
  elif [[ ! -z $(git status -s) ]]; then
    echo "error pending changes on local branch"
  else
    # Switch to local default, delete current if requested
    if [[ "$LBRANCH" != "$RBRANCH" && "$1" == "-D" ]]; then
      git checkout $RBRANCH
      git branch -D $LBRANCH
    fi
    # fetch all and prune, then update local default
    git fetch --all -p && git merge $RNAME/$RBRANCH && if [[ "$RNAME" != "origin" ]]; then
      git push ${REMOTES[0]%%/*} $RBRANCH # also update default branch on fork
    fi
  fi
}

score 0 · Answer 6 · answered Jul 15 '22 at 00:20

I want to check local branches of a repo, since there will always be a local master or main branch

Taking that as a reliable description of your intended use-case environment, since in general use it's often enough not true,

What Git command can I use to return the first branch of these which exists?

A concise way of doing it is

if git cat-file -e refs/heads/master 2>&-; then echo master
elif git cat-file -e refs/heads/main 2>&-; then echo main
fi

but for anything even a little more elaborate you're likely to want for-each-ref,

{ git for-each-ref --format='%(refname)' refs/{heads,remotes/*}/master;
  git for-each-ref --format='%(refname)' refs/{heads,remotes/*}/main;
} | sed -E 's,(.*)/,\1 ,' | sort -usk1,1

which gives the answer for local branches and all tracked remotes without any foofaraw.

In my git repo this reports refs/remotes/origin master, for instance, and the Git project keeps both branch names in lockstep. But as someone else pointed out, some projects keep master around as a record of where it was when they switched away, and as you might have noticed I don't have a master or main branch. My make branch tracks origin/next, that's the one I run my deployments from, and there's a couple others for little projects.

To do just local branches do

{ git for-each-ref --format='%(refname:short)' refs/heads/master;
  git for-each-ref --format='%(refname:short)' refs/heads/main;
} | head -1

See the for-each-ref examples, it was built for this.

How to find out which of 'master' or 'main' branches exists in a repository?

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