Peeking over the fence with `git cherry`

If you are a Git veteran, you will likely have heard of the git cherry-pick command that lets you apply a commit or set of commits to a target branch.

But, have you heard of its sibling git cherry? While the naming is of course a bit curious, git cherry essentially lets you do the precursory work before doing git cherry-pick (or, git rebase -i). Meaning that it lets you peek over the fence and check out what commits have been made to a branch (e.g. a feature branch) as compared to a reference branch (e.g. the main branch).

So, why would we do that? Granted, it’s a niche situation. But, if you run into one of the following situations, git cherry may help you:

1. a downstream branch has some issue that doesn’t exist on the upstream branch and you need to identify probable changes/commits that may have caused it;
2. you are planning to extract some commits from a feature branch and apply them to another (for example, for git cherry-pick)

Example

set -e 
# Create a git repo
mkdir /tmp/git-cherry-example 
cd /tmp/git-cherry-example
git init .

# Create an initial set of commits on the main branch
for i in 1 2; do
  echo "main-${i}" >> "file-main-${i}.txt"
  git add .
  git commit -m "Main commit $i"
done

# a branch is forked from main and some changes are made
git checkout -b feat/thefeature
for i in 1 2; do
  echo "thefeature-${i}" >> "file-feat-${i}.txt"
  git add .
  git commit -m "Feature commit $i"
done

# meanwhile some changes happen on main
git checkout main 
for i in 3 4; do
    echo "main-$i" >> "file-main-${i}.txt"
    git add .
    git commit -m "Main commit $i"
done

# Merge the main changes into the downstream
git checkout feat/thefeature
git merge main -m "Merge branch 'main' into feat/thefeature"

git log --oneline will show the following

$ git log --oneline
193303f (HEAD -> feat/thefeature) Merge branch 'main' into feat/thefeature
077dc92 Feature commit 2
a0d38a8 (main) Main commit 4
40068af Feature commit 1
540fbce Main commit 3
0f16caa Main commit 2
30fe85f Main commit 1

Visually, we may identify the commits that only exist on feat/thefeature by running git adog (i.e. git log --all --decorate --oneline --graph):

$ git log --all --decorate --oneline --graph
*   193303f (HEAD -> feat/thefeature) Merge branch 'main' into feat/thefeature
|\
| * a0d38a8 (main) Main commit 4
| * 540fbce Main commit 3
* | 077dc92 Feature commit 2
* | 40068af Feature commit 1
|/
* 0f16caa Main commit 2
* 30fe85f Main commit 1

And git-cherry gives us the machine-readable answer (easily parseable with e.g. awk):

$ git cherry -v main feat/thefeature
+ 8f6c8f50d996cbb09d03a4969715ab757cf13439 Feature commit 1
+ 6a43e68e9ca66c1ab642da50d2fd5ebcae07ac61 Feature commit 2