The document provides an overview of undoing changes in Git, including commands for discarding local changes, fixing the last commit using 'commit --amend', and reverting commits with 'git revert'. It explains the implications of using 'git reset' to go back to previous commits and warns against amending commits that have already been pushed to remote repositories. Additionally, it mentions functionality in desktop applications for Git, such as the ability to reset and revert commits through user interfaces.

1. Learn Version Control with Git
Undoing Things in Git

2. Undoing Local Changes
$ git checkout -- file.ext
!
$ git reset --hard HEAD
discards all local changes in a
file since it was last committed
discards all local changes in your working
copy - resetting your project completely
to the last committed state
Discarding uncommitted local changes cannot be undone!

3. Fixing the Last Commit
$ git commit -m “Fix bug #300”
!
$ git add forgotten-change.txt
!
$ git commit --amend -m “Fix bug #299”
D’oh! Wrong bug number
and forgot to add a change…
simply add the change(s)
as usual…
…and commit using the
“--amend” option with
the correct message
“--amend” lets you fix (only) the very last commit very easily.
Since this rewrites history, never amend commits that have
already been pushed to a remote repository!

4. Reverting Commits
C1
$ git revert 8c1f20a
C3 C4
Modifies “index.html” in the “opposite” way:
(old) <div>About</div>
(new) <div>About This Project</div>
C2
Modified “index.html”:
(old) <div>About This Project</div>
(new) <div>About</div>
Reverting Commit
“git revert” creates a new commit (C4) that
reverts the effects of a specified commit (C2).

5. Resetting / Rolling Back
to a Commit
C1 C2 C3 C4 master HEAD
C1 C2 master HEAD
Before reset
After reset
$ git reset --hard 8c1f20a
“git reset” sets your HEAD pointer (and thereby also
your working copy) to an older revision. Commits
that came after this revision appear to be undone.

6. Revert & Reset in a Desktop App
in a desktop app like
Tower right-click on
a commit to access
“Reset” & “Revert”

7. Learn Git with our free online book on
www.git-tower.com/learn