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      • Git Undo

      In the process of using Git, you will inevitably encounter situations where you need to undo operations. This chapter details various undo and restore operations to help you safely handle "regret" scenarios.

      Basic Concepts of Undo

      Git's Three Areas

      Before understanding undo operations, you need to be clear about Git's three main areas:

      Working Directory
    ↓ git add
Staging Area
    ↓ git commit
Repository

      Undo methods and scopes differ across these areas.

      Safety of Undo Operations

      • 🟢 Safe: No data loss, recoverable.
      • 🟡 Caution: May lose uncommitted changes.
      • 🔴 Dangerous: Will permanently lose data, proceed with extreme caution.

      Undo in Working Directory

      Undo File Changes

      # Undo changes to a single file 🟢
git checkout -- filename.txt

# Undo changes to multiple files 🟢
git checkout -- file1.txt file2.txt

# Undo changes to all files 🟡
git checkout -- .

# Using new syntax (Git 2.23+) 🟢
git restore filename.txt
git restore .

      Demo: Undo File Changes

      # Create demo environment
mkdir git-undo-demo
cd git-undo-demo
git init

# Create initial file
echo "Original content" > file.txt
git add file.txt
git commit -m "Initial commit"

# Modify file
echo "Modified content" > file.txt
echo "New content" >> file.txt

# Check changes
git diff

# Undo changes
git checkout -- file.txt

# Verify result
cat file.txt  # Should show "Original content"

      Delete Untracked Files

      # Check untracked files
git clean -n

# Delete untracked files 🟡
git clean -f

# Delete untracked files and directories 🟡
git clean -fd

# Interactive delete 🟢
git clean -i

# Delete ignored files 🟡
git clean -fX

# Delete all untracked files (including ignored) 🔴
git clean -fx

      Undo in Staging Area

      Unstage Files

      # Unstage single file 🟢
git reset HEAD filename.txt

# Unstage all files 🟢
git reset HEAD

# Using new syntax (Git 2.23+) 🟢
git restore --staged filename.txt
git restore --staged .

      Demo: Unstage

      # Modify file and add to staging
echo "New modification" >> file.txt
git add file.txt

# Check status
git status

# Unstage
git reset HEAD file.txt

# Check status (File modified but not staged)
git status

      Partial Unstage

      # Interactive partial unstage
git reset -p

# Or use restore
git restore --staged -p filename.txt

      Undo Commits

      Modify Last Commit

      # Modify last commit message 🟢
git commit --amend

# Modify message without opening editor 🟢
git commit --amend -m "New commit message"

# Add file to last commit 🟢
git add forgotten_file.txt
git commit --amend --no-edit

      Demo: Modify Commit

      # Create commit
echo "Feature A" > feature_a.txt
git add feature_a.txt
git commit -m "Add Feature A"

# Realized missed file
echo "Feature A Config" > feature_a_config.txt
git add feature_a_config.txt

# Modify last commit
git commit --amend -m "Add Feature A and Config"

# Check history
git log --oneline

      Undo Commit but Keep Changes

      # Undo last commit, keep changes in Working Directory 🟢
git reset --soft HEAD~1

# Undo last commit, keep changes in Staging Area 🟢
git reset --mixed HEAD~1
# Or simply
git reset HEAD~1

# Undo last commit, discard all changes 🔴
git reset --hard HEAD~1

      Undo Multiple Commits

      # Undo last 3 commits 🟡
git reset --soft HEAD~3

# Undo to specific commit 🟡
git reset --soft commit_hash

# View revocable commits
git log --oneline -10