Git Undo

I will start with simple cheat sheet before diving into reset/revert/checkout

• Undo changes git checkout changed_file
• Undo git add
git checkout HEAD added_file # changes to the file is lost
  or git reset (HEAD) added_file # changes persist, HEAD is default
• Undo git commit
git reset --soft HEAD~
• Undo git push
git revert --no-edt 2f5451f
  followed by git push

There are 3 working trees: the Working Dictory, git add to the Staging Index, and git commit to the Commit Tree (HEAD)

1 Checkout

Checkout a branch is the most common usage and what happens behind the scence is moving HEAD to a specific commit

Here is the example of git checkout hotfix followed by git checkout HEAD~2

2 Reset

A reset is an operation that takes a specified commit and resets the “three trees” to match the state of the repository at that specified commit.
git checkout hotfix followed by git reset HEAD~2 will leave orphaned commits

3 Revert

Reverting undoes a commit by creating a new commit. This is a safe way to undo changes, as it has no chance of re-writing the commit history.

4 Comparison

Work level	Reset	Revert	Checkout
Commit	Discard commits in a private branch	Undo commits in a public branch	Switch between branches (or inspect old snapshots)
File	unstage a file	N/A	Discard changes in the working directory

5 Reset vs Check a FILE

git reset (HEAD) file_name
The –soft, –mixed, and –hard flags do not have any effect on the file-level version of git reset, as the staged snapshot is always updated, and the working directory is never updated. Thus changes persist

git checkout HEAD file_name
Checking out a file is similar to using git reset with a file path, except it updates the working directory instead of the stage, so you lost the changes. Unlike the commit-level version of this command, this does not move the HEAD reference, which means that you won’t switch branches.

This is like git reset HEAD --hard but on one file

6 Reset Options

--mixed is the default option for git reset commit_hash and it undo git add options but not resetting working directory, so changes persist

--hard would reset working directory so changes are lost

--soft is resetting HEAD only.