gitkatas

Bad Commit

One of the commits on master introduced a bad file. Find the commit and revert it using bisect.

Setup:

1. Run source setup.sh (or .\setup.ps1 in PowerShell)

The task

Use git bisect to find the "bad" commit and then use git revert to revert it. When running git bisect, you indicate if the "state" is "good" or "bad" until it finds the commit that introduced the change.

For this exercise, the version is bad if badfile exists.

1. Start git bisect.
2. Usually the HEAD is "bad", as it is in this exercise. Use git bisect bad to indicate it.
3. Usually some old version will be good. In this exercise, the start version is. Use git bisect good <commit-ish> to indicate it.
4. git bisect will then checkout various commits to find the bad commit. Continue indicating the state until it tells you the first bad commit. Keep track of this commit.
5. Run git bisect reset so we can work on the repository.
6. Use git diff to make sure that the bad commit only introduced badfile.
7. Use git revert to it.

If you have a script that can tell if the current source code is good or bad, you can bisect by issuing git bisect run.

Useful commands

• git bisect start
• git bisect bad
• git bisect good <commit-ish>
• git bisect good
• git bisect reset
• git diff <commit-ish-1> <commit-ish-2>
• git revert <commit-ish>
• git bisect run <cmd>
• test ! -f badfile (or gci . badfile in PowerShell) to test the existence of a file
• test ! -f badfile;echo $? to output the result of the test to the console