How to tell git branch name from commit hash?

Question

I have a bash script which accepts a string of either a branch name (e.g., \"master\", or \"feature/foo\") or a commit hash (e.g. \"1234abcd\").

I have the repository c

Answer 1

If you would like a robust mechanism to tell relative names (e.g. you SHA1 is possibly one or so commits behind 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

Reference: Git Tips (old commit)

UPDATE: As @kporter mentioned, there is also the --name-only flag (with new commits as of 2020/04/21):

$ git name-rev HEAD
HEAD tags/last_sha_with_original_matlab~313
$ git name-rev --name-only HEAD~20
tags/last_sha_with_original_matlab~333

Command-Line Reference: git name-rev