Deleting a git commit
When working with Git you will find that sometimes commits need to be removed as they have introduced a bug or need to be reworked.
If it is the last commit this is very straight forward. Simply run:
git reset HEAD
This will pop off the latest commit but leave all of your changes to the files intact.
If you need to delete more than just the last commit there are two methods you can use. The first is using rebase this will allow you to remove one or more consecutive commits the other is cherry-pick which allows you to remove non consecutive commits.
Example git log
|1||2c6a45b||(HEAD) Adding public method to access protected method||Tom|
|2||ae45fab||Updates to database interface||Contractor 1|
|3||77b9b82||Improving database interface||Contractor 2|
|4||3c9093c||Merged develop branch into master||Tom|
|5||b3d92c5||Adding new Event CMS Module||Paul|
|6||7feddbb||Adding CMS class and files||Tom|
|7||a809379||Adding project to Git||Tom|
Using the git log above we want to remove the following commits; 2 & 3 (ae45fab & 77b9b82). As they are consecutive commits we can use rebase.
git rebase --onto <branch name>~<first commit number to remove> <branch name>~<first commit to be kept> <branch name>
e.g to remove commits 2 & 3 above
git rebase --onto repair~3 repair~1 repair
Using Cherry Pick
Step 1: Find the commit before the commit you want to remove
Step 2: Checkout that commit
git checkout <commit hash>
Step 3: Make a new branch using your current checkout commit
git checkout -b <new branch>
Step 4: Now you need to add the commit after the removed commit
git cherry-pick <commit hash>
Step 5: Now repeat Step 4 for all other commits you want to keep.
Step 6: Once all commits have been added to your new branch and have been commited. Check that everything is in the correct state and working as intended. Double check everything has been commited:
Step 7: Switch to your broken branch
git checkout <broken branch>
Step 8: Now perform a hard reset on the broken branch to the commit prior to the one your want to remove
git reset --hard <commit hash>
Step 9: Merge your fixed branch into this branch
git merge <branch name>
Step 10: Push the merged changes back to origin.
WARNING: This will overwrite the remote repo!
git push --force origin <branch name>
You can do the process without creating a new branch by replacing Step 2 & 3 with Step 8 then not carry out Step 7 & 9.
Say we want to remove commits 2 & 4 from the repo.
git checkout b3d92c5Checkout the last usable commit.
git checkout -b repairCreate a new branch to work on.
git cherry-pick 77b9b82Run through commit 3.
git cherry-pick 2c6a45bRun through commit 1.
git checkout masterCheckout master.
git reset --hard b3d92c5Reset master to last usable commit.
git merge repairMerge our new branch onto master.
git push --hard origin masterPush master to the remote repo.
Git rebase & cherrypick are dangerous but powerful solutions that should only be used as a last option and only be undertaken by someone who knows what they are doing. Beware that both solutions could have adverse effects on other users who are working on the same repository / branch.
Finally remember to be careful and good luck!