remove-commit.md

Remove a file from git history

Note: you will need a clean working directory to do this.

We will be rewriting history! This will entirely remove the commit from history

You should probably only do this if you really need to remove a file entirely from history. For example if the file you added is too large and GitHub won't accept it. If you are just trying to undo what a commit has done, there are better ways to do it without modifying history, check out git revert.

We are assuming that the problematic file was added in one commit and not modified since.

Explicit steps and explanation

1. find the sha of the commit that introduced the bad file

   # will display the hash of the commit where the file was introduced
   git log --pretty='%H' problematic-file.jpg | tail -n 1

   replace problematic-file.jpg with the file that you want to remove from history.

   copy down that hash

2. get rid of that commit

   git rebase --onto <hash>^ <hash> HEAD

   Replacing <hash> with the commit you coppied in the previous step

   Note that we will paste the hash twice, the first time with a ^ after it

3. create a new branch based off of where we are and switch to it

   The previous command will leave us in a detached HEAD state, so we'll need to create a branch based off of our current state.

   git branch branch-without-problematic-file
   git checkout branch-without-problematic-file

4. do a git log to verify that the problematic file is not longer in your commit history

   git log
   

5. delete the old master branch as it still contains the problematic file

   Note: replace master with the branch you are working from if it's different than master

   at this point we should be in our branch-without-problematic-file branch

   git branch -D master
   

6. rename our branch to master

   git branch -m master
   

Now we will have removed the problem file from our commit history!

Shortcut

# from 'my-branch' remove 'problem.file' from 'my-branch's history entirely
for commit in $(git log --pretty='%H' problem.file); do git rebase --onto $commit^ $commit my-branch; done