Git: how to add a file to a commit

Suppose you have just committed your beautiful changes in a clean commit, but suddenly you realize that there is a missing file, say missing.py containing changes that should have been included before. What to do?

First of all add the file to the stage area, with the well-known git add <your-file>. So for example, if you want to add missing.py, just do git add missing.py.

Now that the file is staged, git commit --amend comes to the rescue. The --amend flag is basically a way to fix up the most recent commit. Invoke it and the text editor will pop up: you may also change the commit message if needed.

Save the message and missing.py will be properly included in your last commit. If you want to skip the message editing part, add the --no-edit flag like that: git commit --amend --no-edit. Sweet!