When things go wrong: how to amend a git commit?

While working on a data science project did you ever git commit a bunch of .R files only to realize a few seconds later that you forget to include something? I certainly did. Today alone 3 times.

What can you do? The obvious solution is to make a second commit. But that’s a bad one. Instead do the following:

git add <forgotten.file>
git commit --amend --no-edit

Replace <forgotten.file> with the actual file name, e.g. analysis.R. This will add the file to your previous commit while keeping the commit message. If you want to change the commit message remove the --no-edit argument. When you do so a text editor will pop up where you can change the commit message.

Another scenario: you committed all files but forgot to make a change in one file. In that case simply edit the respective file and run the exact same two commands as above. Make sure to replace <forgotten.file> with the name of the file you just edited.

Finally to push the commit to GitHub run

git push -f origin <your branch>

where <your branch> is the branch you are currently working in, e.g. master.

A note to RStudio users: you need to run the git commands from the terminal instead of using the git GUI.