Cherry-pick, Bisect and Reflog

Introduction

Three tools solve problems that confuse many developers: getting one fix onto another branch, finding exactly when something broke, and recovering from "I just deleted my work".

Cherry-pick: copy one commit

Sometimes you need a single commit from another branch, for example a bug fix that must also go into a release branch.

git switch release-1.0
git cherry-pick a1b2c3d

Git applies the changes of that commit as a new commit on your current branch, with a new hash. If it conflicts, resolve, git add, then git cherry-pick --continue.

Use it sparingly. Copying commits creates duplicates in history, and many cherry-picks suggest your branching needs rethinking.

Bisect: find the commit that broke it

Imagine the app worked last month and is broken now, with hundreds of commits in between. Bisect performs a binary search through history, so you test only a few commits.

git bisect start
git bisect bad               # the current commit is broken
git bisect good v1.2.0       # this old tag worked

Git checks out a commit in the middle. You test it, then tell Git:

git bisect good    # or: git bisect bad

Git halves the range again and again. After about log2(N) steps, it names the first bad commit. For 1,000 commits, that is about 10 tests. When finished:

git bisect reset

You can automate it with a script that exits 0 for good and non-zero for bad:

git bisect run ./test.sh

This works best when each commit builds and runs, which is another reason for clean history.

Reflog: the safety net

Git records every place HEAD has pointed. Even after a hard reset or a deleted branch, the commits usually remain for a while (often months), but are no longer reachable by name.

git reflog

a1b2c3d HEAD@{0}: reset: moving to HEAD~3
e4f5a6b HEAD@{1}: commit: Add search feature

To get the lost work back, point a branch at it:

git branch recovered e4f5a6b

The reflog is local to your computer. It is not sent to remotes. Unreachable commits are eventually removed by garbage collection.

Try it yourself

Create a repository with 8 commits where a bug appears in commit 5, with a small test script. Use git bisect run to find it. Then make a hard reset back a few commits and recover them with the reflog.

Summary

• git cherry-pick copies one commit onto the current branch.
• git bisect finds the commit that introduced a bug with a binary search.
• git reflog lists where HEAD has been, so lost commits can be recovered.