Finding what branch a Git commit came from

Question

Is there a way to find out what branch a commit comes from given its SHA-1 hash value?

Bonus points if you can tell me how to accomplish this using Ruby Grit.

Answer 1

TL;DR:

Use the below if you care about shell exit statuses:

• branch-current - the current branch's name
• branch-names - clean branch names (one per line)
• branch-name - Ensure that only one branch is returned from branch-names

Both branch-name and branch-names accept a commit as the argument, and default to HEAD if none is given.

---

Aliases useful in scripting

branch-current = "symbolic-ref --short HEAD"  # https://stackoverflow.com/a/19585361/5353461
branch-names = !"[ -z \"$1\" ] && git branch-current 2>/dev/null || git branch --format='%(refname:short)' --contains \"${1:-HEAD}\" #"  # https://stackoverflow.com/a/19585361/5353461
branch-name = !"br=$(git branch-names \"$1\") && case \"$br\" in *$'\\n'*) printf \"Multiple branches:\\n%s\" \"$br\">&2; exit 1;; esac; echo \"$br\" #"

---

Commit only reachable from only one branch

% git branch-name eae13ea
master
% echo $?
0

• Output is to STDOUT
• Exit value is 0.

---

Commit reachable from multiple branches

% git branch-name 4bc6188
Multiple branches:
attempt-extract
master%
% echo $?
1

• Output is to STDERR
• The exit value is 1.

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Because of the exit status, these can be safely built upon. For example, to get the remote used for fetching:

remote-fetch = !"branch=$(git branch-name \"$1\") && git config branch.\"$branch\".remote || echo origin #"