Final answer:
To undo an unwanted change in Git after committing, use the command 'git reset HEAD~1' to uncommit changes while keeping them in the working directory, or 'git revert HEAD' to create a new commit that undoes the previous changes. The choice depends on whether you want to keep or discard changes.
Step-by-step explanation:
If you've made an unwanted change in Git and committed it with git commit -m "whoops", you can undo this commit using either git reset or git revert. The choice between the two depends on whether you want to keep the changes made in the working directory or discard them entirely.
To remove the last commit and keep the changes in the working directory you can use:
git reset HEAD~1
Git reset moves the current branch backward by one commit but leaves the changes in your working directory.
However if you want to create a new commit that undoes the changes introduced in the last commit you can use:
git revert HEAD
Git revert will create a new commit on top of the current one which undoes the changes of the commit made in error.
The command git undo is not a valid Git command, and git checkout -- is used to discard changes in the working directory, not to undo a commit that has already been made.