How to find git branch name from commit hash?

Question

I have a bash script that accepts a branch name string (like "master" or "feature / foo") or commit hashes (like "1234abcd").

I have a repository and I can call git.

What is the best way to determine if a string is a branch name or a commit hash?

#!/bin/bash commit_or_branch="$1" cd /path/to/my_repo git fetch if <is_branch $commit_or_branch> then echo "it a branch" else echo "it a commit" fi 

Answer 1

You can use git show-ref :

 git show-ref --head | grep refs 

If it is empty, it is SHA1 (or an invalid object, which is not very good).
If not, this is the name of the branch.

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The best method comes from Validate if commit exists "using git merge-base :

The branch name will lead to another line (SHA1)

 C:\Users\vonc\prog\b2d>git merge-base master master de4accfd28c5f25fcc057d56996b83450be5dc60 

SHA1 will produce the same result (or at least start with the same result ):

 C:\Users\vonc\prog\b2d>git merge-base 03949c3d3f88a378c6a08e57daa97059b52813f1 03949c3d3f88a378c6a08e57daa97059b52813f1 03949c3d3f88a378c6a08e57daa97059b52813f1 

foobar will fail:

 C:\Users\vonc\prog\b2d>git merge-base xxx xxx fatal: Not a valid object name xxx 

This means something like:

 if [[ git merge-base $string $string ]]; then if [[ $(git merge-base $string $string) == $string* ]]; then echo "SHA1" else echo "branch" fi else echo "Not a valid object name '$string'" fi 

Answer 2

If you want a reliable mechanism to specify relative names (for example, you may be one of SHA1 commits a named branch), you can use git name-rev to resolve it.

Examples:

 $ git config remote.upstream.url https://github.com/RobotLocomotion/drake.git $ git log --oneline -n 5 7530a95 Merge pull request #5743 from soonho-tri/pr-reformat-mathematical_program ebc8f25 Suppresses console output of speed_bump.obj genrule. (#5726) d8b9a0b Merge pull request #5735 from david-german-tri/namespaces 79e10e8 Remove redundant 'symbolic::' prefix from mathematical_program code b68b590 Clean up mathematical_program code by adding using std::* $ git name-rev HEAD HEAD master $ git name-rev 79e10e8 79e10e8 master^2 $ git name-rev HEAD~20 HEAD~20 remotes/origin/issue/5646_return_binding~3 

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Link: Git Tips

Answer 3

Imo you cannot verify this reliably since the hash is also a valid branch name. Try:

 git checkout -b 0c8158f47d7dda89226d4e816fee1fb9ac6c1204 

This means that there may be a situation where there is a branch with this name, as well as a commit.

Since you can pass the branch name or commit to most git commands, you do not need to distinguish between them.

Answer 4

As mentioned in @VonC and @ hek2mgl, this may not be one or the other test. You can slightly change your script to something like this (borrowed from this SO answer :

 #!/bin/bash commit_or_branch="$1" cd /path/to/my_repo git fetch if git branch | grep $commit_or_branch 2> /dev/null then echo "it a branch" fi if git cat-file -e $commit_or_branch 2> /dev/null then echo "it a commit" fi 

Please note that these are only tests for local branches .. see this post if you are interested in remote branches.