git-advanced

What this skill does

# Git Advanced Operations Skill

This skill provides comprehensive guidance on advanced git operations, sophisticated rebase strategies, commit surgery techniques, and complex history manipulation for experienced git users.

## When to Use

Activate this skill when:
- Performing complex interactive rebases
- Rewriting commit history
- Splitting or combining commits
- Advanced merge strategies
- Cherry-picking across branches
- Commit message editing in history
- Author information changes
- Complex conflict resolution

## Interactive Rebase Strategies

### Basic Interactive Rebase

```bash
# Rebase last 5 commits
git rebase -i HEAD~5

# Rebase from specific commit
git rebase -i abc123^

# Rebase entire branch
git rebase -i main
```

### Rebase Commands

```bash
# Interactive rebase editor commands:
# p, pick = use commit
# r, reword = use commit, but edit commit message
# e, edit = use commit, but stop for amending
# s, squash = use commit, but meld into previous commit
# f, fixup = like squash, but discard commit message
# x, exec = run command (the rest of the line) using shell
# d, drop = remove commit
```

### Squashing Commits

```bash
# Example: Squash last 3 commits
git rebase -i HEAD~3

# In editor:
pick abc123 feat: add user authentication
squash def456 fix: resolve login bug
squash ghi789 style: format code

# Squash all commits in feature branch
git rebase -i main
# Mark all except first as 'squash'
```

### Fixup Workflow

```bash
# Create fixup commit automatically
git commit --fixup=abc123

# Autosquash during rebase
git rebase -i --autosquash main

# Set autosquash as default
git config --global rebase.autosquash true

# Example workflow:
git log --oneline -5
# abc123 feat: add authentication
# def456 feat: add authorization
git commit --fixup=abc123
git rebase -i --autosquash HEAD~3
```

### Reordering Commits

```bash
# Interactive rebase
git rebase -i HEAD~5

# In editor, change order:
pick def456 feat: add database migration
pick abc123 feat: add user model
pick ghi789 feat: add API endpoints

# Reorder by moving lines:
pick abc123 feat: add user model
pick def456 feat: add database migration
pick ghi789 feat: add API endpoints
```

### Splitting Commits

```bash
# Start interactive rebase
git rebase -i HEAD~3

# Mark commit to split with 'edit'
edit abc123 feat: add user and role features

# When rebase stops:
git reset HEAD^

# Stage and commit parts separately
git add user.go
git commit -m "feat: add user management"

git add role.go
git commit -m "feat: add role management"

# Continue rebase
git rebase --continue
```

### Editing Old Commits

```bash
# Start interactive rebase
git rebase -i HEAD~5

# Mark commit with 'edit'
edit abc123 feat: add authentication

# When rebase stops, make changes
git add modified-file.go
git commit --amend --no-edit

# Or change commit message
git commit --amend

# Continue rebase
git rebase --continue
```

## Commit Surgery

### Amending Commits

```bash
# Amend last commit (add changes)
git add forgotten-file.go
git commit --amend --no-edit

# Amend commit message
git commit --amend -m "fix: correct typo in feature"

# Amend author information
git commit --amend --author="John Doe <[email protected]>"

# Amend date
git commit --amend --date="2024-03-15 10:30:00"
```

### Changing Commit Messages

```bash
# Change last commit message
git commit --amend

# Change older commit messages
git rebase -i HEAD~5
# Mark commits with 'reword'

# Change commit message without opening editor
git commit --amend -m "new message" --no-edit
```

### Changing Multiple Authors

```bash
# Filter-branch (legacy method, use filter-repo instead)
git filter-branch --env-filter '
if [ "$GIT_COMMITTER_EMAIL" = "[email protected]" ]; then
    export GIT_COMMITTER_NAME="New Name"
    export GIT_COMMITTER_EMAIL="[email protected]"
fi
if [ "$GIT_AUTHOR_EMAIL" = "[email protected]" ]; then
    export GIT_AUTHOR_NAME="New Name"
    export GIT_AUTHOR_EMAIL="[email protected]"
fi
' --tag-name-filter cat -- --branches --tags

# Modern method with git-filter-repo
git filter-repo --email-callback '
    return email.replace(b"[email protected]", b"[email protected]")
'
```

### Removing Files from History

```bash
# Remove file from all history
git filter-branch --tree-filter 'rm -f passwords.txt' HEAD

# Better performance with index-filter
git filter-branch --index-filter 'git rm --cached --ignore-unmatch passwords.txt' HEAD

# Modern method with git-filter-repo (recommended)
git filter-repo --path passwords.txt --invert-paths

# Remove large files
git filter-repo --strip-blobs-bigger-than 10M
```

### BFG Repo-Cleaner

```bash
# Install BFG
# brew install bfg (macOS)
# apt-get install bfg (Ubuntu)

# Remove files by name
bfg --delete-files passwords.txt

# Remove large files
bfg --strip-blobs-bigger-than 50M

# Replace passwords in history
bfg --replace-text passwords.txt

# After BFG cleanup
git reflog expire --expire=now --all
git gc --prune=now --aggressive
```

## Advanced Cherry-Picking

### Basic Cherry-Pick

```bash
# Cherry-pick single commit
git cherry-pick abc123

# Cherry-pick multiple commits
git cherry-pick abc123 def456 ghi789

# Cherry-pick range of commits
git cherry-pick abc123..ghi789

# Cherry-pick without committing (stage only)
git cherry-pick -n abc123
```

### Cherry-Pick with Conflicts

```bash
# When conflicts occur
git cherry-pick abc123
# CONFLICT: resolve conflicts

# After resolving conflicts
git add resolved-file.go
git cherry-pick --continue

# Or abort cherry-pick
git cherry-pick --abort

# Skip current commit
git cherry-pick --skip
```

### Cherry-Pick Options

```bash
# Edit commit message during cherry-pick
git cherry-pick -e abc123

# Sign-off cherry-picked commit
git cherry-pick -s abc123

# Keep original author date
git cherry-pick --ff abc123

# Apply changes without commit attribution
git cherry-pick -n abc123
git commit --author="New Author <[email protected]>"
```

### Mainline Selection for Merge Commits

```bash
# Cherry-pick merge commit (specify parent)
git cherry-pick -m 1 abc123

# -m 1 = use first parent (main branch)
# -m 2 = use second parent (merged branch)

# Example workflow:
git log --graph --oneline
#   *   abc123 Merge pull request #123
#   |\
#   | * def456 feat: feature commit
#   * | ghi789 fix: main branch commit

# To cherry-pick the merge keeping main branch changes:
git cherry-pick -m 1 abc123
```

## Advanced Merging

### Merge Strategies

```bash
# Recursive merge (default)
git merge -s recursive branch-name

# Ours (keep our changes on conflict)
git merge -s ours branch-name

# Theirs (keep their changes on conflict)
git merge -s theirs branch-name

# Octopus (merge 3+ branches)
git merge -s octopus branch1 branch2 branch3

# Subtree merge
git merge -s subtree branch-name
```

### Merge Strategy Options

```bash
# Ours (resolve conflicts with our version)
git merge -X ours branch-name

# Theirs (resolve conflicts with their version)
git merge -X theirs branch-name

# Ignore whitespace
git merge -X ignore-space-change branch-name
git merge -X ignore-all-space branch-name

# Patience algorithm (better conflict detection)
git merge -X patience branch-name

# Renormalize line endings
git merge -X renormalize branch-name
```

### Three-Way Merge

```bash
# Standard three-way merge
git merge feature-branch

# With custom merge message
git merge feature-branch -m "Merge feature: add authentication"

# No fast-forward (always create merge commit)
git merge --no-ff feature-branch

# Fast-forward only (fail if merge commit needed)
git merge --ff-only feature-branch

# Squash merge (combine all commits)
git merge --squash feature-branch
git commit -m "feat: add complete authentication system"
```

## Advanced Conflict Resolution

### Understanding Conflict Markers

```
<<<<<<< HEAD (Current Change)
int result = add(a, b);
=======
int sum = calculate(a, b);
>>>>>>> feature-branch (Incoming Change)
```

### Conflict Resolution Tools

```bash
# Use mergetool
git mergetool

# Specify merg