Lesson 12: Undoing Changes

What You'll Learn

In this lesson, you'll learn how to undo changes in Git. Whether you made a mistake, want to discard changes, or need to revert a commit, Git has tools to help you fix things safely.

Types of Undo Operations

Part 1: Undoing Unstaged Changes

Discard Changes in a File

If you modified a file but haven't staged it yet:

git restore index.html

Warning: This permanently discards your changes! The file returns to how it looked in the last commit.

Discard All Unstaged Changes

git restore .

Old Command (Still Works)

git checkout -- index.html

Part 2: Unstaging Files

Remove File from Staging Area

If you staged a file but want to unstage it:

git restore --staged index.html

The changes stay in the file, but it's removed from the staging area.

Unstage All Files

git restore --staged .

Old Command (Still Works)

git reset HEAD index.html

Part 3: Amending the Last Commit

Fix the Last Commit Message

git commit --amend -m "New commit message"

Add Forgotten Files to Last Commit

# Oh no! Forgot to add a file
git add forgotten-file.txt
git commit --amend --no-edit

The --no-edit flag keeps the same commit message.

# Made commit
git commit -m "Add login feature"

# Oops! Forgot style.css
git add style.css
git commit --amend --no-edit

# Now the commit includes style.css!

Warning: Only amend commits that haven't been pushed! Amending changes the commit hash.

Part 4: git reset

What is git reset?

Moves the branch pointer to a different commit, potentially changing your staging area and working directory.

Three Types of Reset

Undo Last Commit (Keep Changes)

git reset --soft HEAD~1

Commits are undone, but changes stay staged.

Undo Last Commit (Unstage Changes)

git reset HEAD~1

Commits are undone, changes are unstaged but still in files.

Completely Undo Last Commit

git reset --hard HEAD~1

⚠️ DANGER: This permanently deletes your changes!

Reset to Specific Commit

git reset --hard abc1234

Part 5: git revert

What is git revert?

Creates a new commit that undoes a previous commit. Unlike reset, it's safe to use on public branches.

When to Use Revert

• After pushing: Already pushed the bad commit
• Team collaboration: Others may have pulled your changes
• Keep history: Want to preserve the record of the mistake

Revert the Last Commit

git revert HEAD

Git opens an editor with a commit message like:

Revert "Add broken feature"

This reverts commit abc1234.

Revert Specific Commit

git revert abc1234

Revert Without Opening Editor

git revert HEAD --no-edit

Part 6: Reset vs Revert

Part 7: Recovering Lost Commits

git reflog

If you accidentally reset too far, reflog can save you!

git reflog

Output:

abc1234 HEAD@{0}: reset: moving to HEAD~1
def5678 HEAD@{1}: commit: Add feature
ghi9012 HEAD@{2}: commit: Fix bug

To recover a lost commit:

git reset --hard def5678

The reflog is a lifesaver! It tracks every HEAD movement for 90 days.

Part 8: Other Useful Undo Commands

Temporarily Save Changes (Stash)

# Save current changes
git stash

# Do something else...

# Restore changes
git stash pop

Clean Untracked Files

# See what would be removed
git clean -n

# Actually remove untracked files
git clean -f

# Also remove untracked directories
git clean -fd

Practice Exercise

1. Make a change to a file and discard it:

   echo "Test" >> test.txt
   git restore test.txt

2. Stage a file, then unstage it:

   echo "Test" >> test.txt
   git add test.txt
   git restore --staged test.txt

3. Make a commit with a typo, then fix it:

   git commit -m "Add feture"  # Oops, typo!
   git commit --amend -m "Add feature"

4. View your reflog:

   git reflog

Summary

Remember: Be careful with --hard flags - they permanently delete changes!

What's Next?

In the next lesson, you'll learn how to collaborate with others - forking repositories, contributing to open source, and working effectively in teams.