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Rewriting your git history
Sep 6, 2016
3 minutes read

Editing the latest commit:

Important The following tip is about changing previous commits. If these commits are pushed to the remote, I would strongly advise to not mess with your history as it could break stuff

Pretty easy to do so as stated on the git scm book#Changing the last commit. But a quick overview shows the simplicity:

$ git commit --amend "Your new message"

Editing a commit earlier in your commit history

That is great for the last commit message you just created, but what about a message type of reword that is after your latest commit message.

I have an alias set up in my git config, ci = commit -m. This allows me to do the following:

$ git ci "Just done something"

This comes with it’s problems though, sometimes I commit stuff like this:

$ git ci "Add `someMethod` to add some business value"

Run a git lg and you would see the following:

$ git lg
* n18e676d - (HEAD, master) Add  to add some business value (5 seconds ago)

There is a part missing from the commit message that is important for the context of the commit and allows an overview without having to look further into it, the someMethod part. The issue (incase you didn’t spot it; I didn’t escape the backtick (`)). Easy enough to change as it was the last commit, so git commit --amend and show the log again:

$ git lg
* 62h8sy22 - (HEAD, master) Add `someMethod` to add some business value (3 seconds ago)

Notice that the commit hash has changed from the n18e676d to 62h8sy22. Remember, this should only be done before pushing your changes to the remote repository.

Now, imagine I committed this a few commits ago:

$ git lg
* ch379a63 - (HEAD, your-branch) Fix #3: Popup displayed off center (7 minutes ago)
* j82s56gh - Add new popup styling (10 minutes ago)
* 18sg7dbp - Reduce body marging (1 hour ago)
* n18e676d - Add  to add some business value (1 hour ago)
* 71gv177w - Fix #28: Correct log timestamp (4 hours ago)

Now, I have not pushed my local changes to the remote repository so I can amend that commit, but this time I will require rebase to help me.

I need to perform an interactive rebase, but this should be done by passing the commit hash previous to the one I wish to edit. In this case it will be the hash 71gv177w:

You will only be able to do this with a branch that has a remote that it can rebase from

$ git rebase -i 71gv177w

This will take you to your $EDITOR where you can start to modify your commit message. You will be presented with a series of steps.

Step one, select the commit you want to amend and use reword:

1 pick ch379a63 Fix #3: Popup displayed off center
2 pick j82s56gh Add new popup styling
3 pick 18sg7dbp Reduce body marging
4 reword n18e676d Add  to add some business value
5 pick 71gv177w Fix #28: Correct log timestamp

Step two, modify the content of your commit, save and exit your editor.

Add `someMethod` to add some business value

Run git lg and you will see the new modified git message:

$ git lg
* ch379a63 - (HEAD, your-branch) Fix #3: Popup displayed off center (7 minutes ago)
* j82s56gh - Add new popup styling (10 minutes ago)
* 18sg7dbp - Reduce body marging (1 hour ago)
* n18e676d - Add `someMethod` to add some business value (5 seconds ago)
* 71gv177w - Fix #28: Correct log timestamp (4 hours ago)

Summary

This is a great way to modify commit messages where you find a typo or a badly structured comment in your history that you have not pushed to the remote repository.


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