Git Bisect

One of the challenges in software development is tracking down elusive bugs that mysteriously appear in your codebase. Git bisect is a powerful tool designed to help you pinpoint the commit where a bug was introduced. In this blog post, we'll explore various ways to use the git bisect command, providing you with a comprehensive guide to efficiently and systematically identify the commit responsible for a bug.

1. Initializing Git Bisect:

To start using Git bisect, first, ensure you are in a clean state with no uncommitted changes:

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git bisect start

This initializes the bisect process.

2. Marking Good and Bad Revisions:

You need to mark a known good and bad revision to guide Git in its search. Use:

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git bisect good <good-commit>
git bisect bad <bad-commit>

Replace <good-commit> and <bad-commit> with commit hashes or references.

3. Automating the Bisect Process:

If you have a script that can determine whether the bug is present, you can automate the bisect process:

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git bisect start <good-commit> <bad-commit>
git bisect run <test-script>

This automatically performs a binary search to find the offending commit using the provided test script.

4. Manually Testing Commits:

If automation is not feasible, manually test commits using:

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git bisect good

or

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git bisect bad

These commands guide Git to the next commit to test. Repeat until Git identifies the problematic commit.

5. Skipping Commits:

If a commit is not relevant to the bug, you can skip it during the bisect process:

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git bisect skip

This command tells Git to skip the current commit and move on to the next one.

6. Resetting Bisect State:

To exit the bisect process and return to the original state, use:

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git bisect reset

This is helpful when you've identified and fixed the bug or need to abort the bisect process.

7. Visualizing Bisect Process:

To visualize the bisect process, you can use:

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git log --oneline --graph --all

This displays a compact log with a graphical representation of all commits, making it easier to understand the bisect process.

8. Running a Specific Command on Each Bisect Step:

You can use git bisect run with a custom script or command to perform an action at each step:

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git bisect start <good-commit> <bad-commit>
git bisect run make test

This example runs the make test command at each step, automating the testing process.

9. Using Bisect with Grep:

To search for a specific keyword in commit messages during bisect:

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git bisect start <good-commit> <bad-commit>
git bisect run git log --oneline --grep=<keyword>

This narrows down the search to commits containing the specified keyword.

10. Customizing the Test Script:

When using git bisect run, create a custom script that returns different exit codes based on the test result:

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#!/bin/bash

# Your test logic here

if  $? -eq 0 ; then
  exit 0 # Good commit
else
  exit 1 # Bad commit
fi

11. Bisecting Only Specific Paths:

If the bug is specific to certain files or directories, you can bisect only changes within those paths:

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git bisect start <good-commit> <bad-commit> -- path/to/files

This focuses the bisect process on the specified paths.

12. Debugging with Bisect:

To debug or inspect the state of the repository at each bisect step, you can use:

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git bisect visualize

This opens a visual representation of the repository state at each step, aiding in debugging.