Introduction

In this tutorial, we will explore one of Git's powerful tools - Git Bisect. This tool assists in finding out the commit that introduced a bug in the codebase, making debugging more efficient and fast. By the end of this tutorial, you will have learned how to use Git Bisect to track down issues in your codebase.

What you will learn:

• The concept of Git Bisect
• How to use Git Bisect to debug your code

Prerequisites:

• Basic knowledge of Git
• Familiarity with command line interfaces

Step-by-Step Guide

Git Bisect is a binary search-based tool used to find the commit that introduced a bug in the code. It does this by taking a 'good' commit (where the bug did not exist) and a 'bad' commit (where the bug exists) and systematically tests the midpoint commit between them. This process continues until the exact commit that introduced the bug is found.

Steps to use Git Bisect:

1. Start the Git Bisect Session

   Run git bisect start to initiate the bisecting session. It prepares Git to begin the binary search.

2. Mark the Bad Commit

   You need to tell Git where the bug exists, which is usually the current commit. Run git bisect bad to mark the current commit as bad.

3. Mark the Good Commit

   Now, mark a commit where you're sure the bug did not exist. Run git bisect good <commit-id>. Replace <commit-id> with the id of a good commit.

4. Bisecting

   Git will now checkout a commit midway between the good and bad commits you specified. Test this commit to see if the bug exists or not. If the bug exists, mark it as bad using git bisect bad. If the bug does not exist, mark it as good using git bisect good.

5. Repeat

   Continue the process of testing and marking the commits until Git points out the first bad commit.

6. End the Git Bisect Session

   Once you have found the commit that introduced the bug, you can end the bisect session by running git bisect reset.

Code Examples

Let's consider a simple example where we have five commits in our Git history. We know that the current commit C5 is bad and the first commit C1 is good but we don't know where the bug was introduced.

# Start the bisecting session
$ git bisect start

# Mark the current commit as bad
$ git bisect bad

# Mark commit C1 as good
$ git bisect good C1

Git will now checkout a commit between C1 and C5. Let's say it checks out C3. We test C3 and find the bug exists so we mark it as bad.

$ git bisect bad

Now Git will test the commit between C1 and C3 (i.e., C2). Assume C2 does not have the bug, so we mark it as good.

$ git bisect good

Now Git will tell us that C3 is the first bad commit. We can end the bisecting session with:

$ git bisect reset

Summary

Through this tutorial, you have learned how to use Git Bisect to debug your codebase by finding the commit that introduced a bug. The next steps would be to explore other advanced Git features, such as cherry-pick, rebase, etc.

For more detailed information, you can refer to the official Git documentation here.

Practice Exercises

1. Exercise 1: Practice the Git Bisect process with a simple codebase where you intentionally introduce a bug in one of the commits.

2. Exercise 2: Try using Git Bisect on a larger project. This will give you practical experience with a more complex scenario.

Remember practice is key to mastering Git Bisect. Happy Debugging!