Advanced Git: Internals and Advanced Commands

# View a commit object
git cat-file -p HEAD
 
# View a tree object
git cat-file -p HEAD^{tree}
 
# View a blob object (a specific file)
git cat-file -p HEAD:src/app.ts
 
# Check the object type
git cat-file -t abc1234

# Check HEAD
cat .git/HEAD
# ref: refs/heads/main
 
# Check the commit a branch points to
cat .git/refs/heads/main
# a1b2c3d4e5f6...

main:    A ─── B ─── C ──────── M (merge commit)
                      \        /
feature:               D ─── E

main:    A ─── B ─── C
                      \
feature:               D' ─── E' (new commit hashes)

git rebase -i HEAD~5

pick   abc1234 feat: add user model
squash def5678 fix: typo in user model      # merge into the previous commit
pick   ghi9012 feat: add user repository
reword jkl3456 feat: add user service        # edit the message only
drop   mno7890 WIP: debugging                # delete the commit

# Cherry-pick a single commit
git cherry-pick abc1234
 
# Cherry-pick several commits
git cherry-pick abc1234 def5678
 
# Cherry-pick a range (abc1234 excluded, def5678 included)
git cherry-pick abc1234..def5678
 
# Stage the changes without committing
git cherry-pick --no-commit abc1234

# Start bisect
git bisect start
 
# Mark the current version as buggy
git bisect bad
 
# Mark a known good version
git bisect good v1.0.0
 
# Git automatically checks out a midpoint commit
# Test, then report the result
git bisect good   # this commit is fine
# or
git bisect bad    # this commit has the bug
 
# Git checks out another midpoint...
# Repeating pinpoints the offending commit in O(log n)
 
# Finish bisect
git bisect reset

# Automated bisect driven by a test script
# Script exit code: 0 = good, 1 = bad
git bisect start HEAD v1.0.0
git bisect run ./test-for-bug.sh

# Shelve the current changes
git stash
 
# Save with a message
git stash save "WIP: payment integration"
 
# Include untracked files
git stash -u
 
# List stashes
git stash list
# stash@{0}: On feature/auth: WIP: payment integration
# stash@{1}: On main: debugging session
 
# Apply the most recent stash (keeping it)
git stash apply
 
# Apply the most recent stash and drop it
git stash pop
 
# Apply a specific stash
git stash apply stash@{2}
 
# Apply a stash onto a new branch
git stash branch new-branch-name
 
# Inspect a stash
git stash show -p stash@{0}
 
# Drop a specific stash
git stash drop stash@{0}
 
# Drop all stashes
git stash clear

# Inspect HEAD movement history
git reflog
# a1b2c3d HEAD@{0}: commit: feat: add payment
# d4e5f6g HEAD@{1}: checkout: moving from main to feature
# h7i8j9k HEAD@{2}: reset: moving to HEAD~3
# l0m1n2o HEAD@{3}: commit: feat: add user model
 
# Reflog for a specific branch
git reflog show feature/auth
 
# Recover a deleted commit
git checkout HEAD@{3}
# or
git branch recovered-branch HEAD@{3}
 
# Undo a bad reset
git reset --hard HEAD@{2}

# Create a worktree for an existing branch
git worktree add ../project-hotfix hotfix/payment-bug
 
# Create a worktree with a new branch
git worktree add -b feature/new-api ../project-new-api
 
# List worktrees
git worktree list
# /Users/jk/project          abc1234 [main]
# /Users/jk/project-hotfix   def5678 [hotfix/payment-bug]
# /Users/jk/project-new-api  ghi9012 [feature/new-api]
 
# Remove a worktree
git worktree remove ../project-hotfix
 
# Prune stale worktrees
git worktree prune

# Install and initialize Git LFS
git lfs install
 
# Track large-file patterns
git lfs track "*.psd"
git lfs track "*.zip"
git lfs track "data/**"
 
# The patterns are recorded in .gitattributes
cat .gitattributes
# *.psd filter=lfs diff=lfs merge=lfs -text
# *.zip filter=lfs diff=lfs merge=lfs -text
 
# Commit .gitattributes
git add .gitattributes
git commit -m "chore: configure Git LFS"
 
# From then on, normal add/commit/push is handled by LFS automatically
git add design.psd
git commit -m "feat: add design asset"
git push

# Delete a file from all of history (a secret key committed by mistake, for example)
git filter-repo --path secrets.env --invert-paths
 
# Keep only one directory and delete the rest (splitting a monorepo)
git filter-repo --path src/auth-service/ --path-rename src/auth-service/:
 
# Rewrite email addresses in bulk
git filter-repo --email-callback '
    return email.replace(b"old@company.com", b"new@company.com")
'
 
# Identify large files
git filter-repo --analyze

Loose objects (initially)
.git/objects/
├── a1/b2c3d4...  (blob)
├── d4/e5f6g7...  (blob)
└── ...
 
Packfile (after compression)
.git/objects/pack/
├── pack-abc123.pack  (object data)
└── pack-abc123.idx   (index -- fast lookup)

# Create packfiles manually
git gc
 
# Check repository size
git count-objects -vH
 
# Packfile statistics
git verify-pack -v .git/objects/pack/pack-*.idx | head -20

# Clone only the latest commit (when history is not needed)
git clone --depth 1 https://github.com/org/monorepo.git
 
# Fetch the rest of the history when needed
git fetch --unshallow

# Initialize sparse-checkout
git sparse-checkout init --cone
 
# Check out only the directories you need
git sparse-checkout set services/auth-service shared/common
 
# Add another
git sparse-checkout add services/payment-service
 
# Show the current configuration
git sparse-checkout list

# Clone without blobs (downloaded on demand)
git clone --filter=blob:none https://github.com/org/monorepo.git
 
# Exclude trees as well for a minimal clone
git clone --filter=tree:0 https://github.com/org/monorepo.git

# Best combination: partial clone + sparse checkout
git clone --filter=blob:none --sparse https://github.com/org/monorepo.git
cd monorepo
git sparse-checkout set services/my-service shared/utils