git-rebase

Git Rebase — Craft a Clean History

Core Mental Model

Before rebase (merge commits clutter history):
A───M───A'───M'───A''     (M = merge commits)

After rebase (linear, readable):
A───A'───A''───A'''       (no merge commits, one clean line)

Golden rule: Never rebase commits that have been pushed to a shared branch.

Interactive Rebase (git rebase -i)

How it works

# Rebase last N commits interactively
git rebase -i HEAD~3

# Opens editor with:
pick abc1234 Add user authentication
pick def5678 Fix typo in auth
pick ghi9012 Add password validation

# Editor commands (change "pick" to these):
pick   → keep commit as-is
reword → keep commit, change message
edit   → stop here, amend/rebase manually
squash → combine with previous commit
fixup  → like squash, discard this commit's message
drop   → remove commit
reorder→ move lines up/down

Example: Clean up a messy branch before PR

git rebase -i HEAD~5

pick  a1b2c3d WIP: started auth
pick  e4f5g6h WIP: auth working
pick  i7j8k9l Fixed bug in auth (oops, went in wrong commit)
pick  m1n2o3p Add password validation
pick  q4r5s6t Final polish

# Change to:
pick  a1b2c3d WIP: started auth
f     i7j8k9l Fix bug in auth (squash into previous)
f     e4f5g6h WIP: auth working (squash into first)
pick  m1n2o3p Add password validation
r     q4r5s6t Final polish: add complete auth flow

Result: 3 clean commits instead of 5 messy ones.

Common Operations

1. Squash consecutive commits

# Squash last 3 commits into one
git rebase -i HEAD~3
# Mark 2nd and 3rd as "squash" or "fixup"

2. Split a commit into multiple

git rebase -i HEAD~1
# Mark the commit as "edit"

# When rebase stops at that commit:
git reset HEAD~1
# Now commit pieces separately:
git add src/auth.go && git commit -m "Add auth package"
git add src/auth_test.go && git commit -m "Add auth tests"
git add src/middleware.go && git commit -m "Add auth middleware"

# Continue rebase:
git rebase --continue