Bisecting Bugs

Use binary search to rapidly hunt down the exact commit that introduced a bug.

Version Control6 min readConcept 28 of 29

The Bug Hunter

git bisect is a command that uses a binary search algorithm to efficiently find the exact commit in a project's history that introduced a bug.

Why it matters

Web developers frequently work in large codebases. When a subtle UI regression is discovered but it's unclear when it happened, git bisect drastically reduces the time needed to hunt down the exact commit.

By isolating the specific code change that caused the issue, you can understand the context and apply a fix much faster instead of blindly guessing.

How it works

You start by identifying a 'bad' commit (usually your current broken state) and a 'good' commit (an older state where the bug didn't exist).

Git checks out a commit exactly in the middle. You test it and mark it as good or bad. Git halves the remaining commits and repeats this process until the single offending commit is isolated.

Check yourself

Pick an answer to lock it in, then read why. Getting one wrong is part of how it sticks.

  1. 1What algorithm does `git bisect` use under the hood to find a bug efficiently?
  2. 2You are in the middle of a `git bisect` session, and the current commit Git checked out has a syntax error that prevents the app from running. What should you do?
  3. 3How can you fully automate a `git bisect` process so you don't have to manually test each step?

Remember this

  • Bisect uses a binary search to find bad commits fast.
  • Always start by defining a known good and known bad commit.
  • Use git bisect skip if a commit is untestable.
  • Use git bisect run to automate the search with tests.

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