Git Interactive Rebase: Rewrite History Without Losing Your Job

# io.thecodeforge — DevOps tutorial

# Simulate an ugly local history
git init ugly-history
cd ugly-history
echo "initial" > file.txt
git add file.txt && git commit -m "initial"
echo "feature start" >> file.txt
git commit -am "WIP: started feature"
echo "fix typo" >> file.txt
git commit -am "fix typo"
echo "actually working" >> file.txt
git commit -am "actually fix it"
echo "tests" >> file.txt
git commit -am "add tests"

# View the mess
git log --oneline
# Output:
# 4a3b2c1 add tests
# 9f8e7d6 actually fix it
# 1a2b3c4 fix typo
# 5e6f7a8 WIP: started feature
# 0d1e2f3 initial

# io.thecodeforge — DevOps tutorial

# Continuing from the ugly-history example
cd ugly-history

# Rebase the last 4 commits (excluding 'initial')
git rebase -i HEAD~4

# In the editor, change the second 'pick' to 'squash' and third to 'squash':
# pick 5e6f7a8 WIP: started feature
# squash 1a2b3c4 fix typo
# squash 9f8e7d6 actually fix it
# pick 4a3b2c1 add tests

# Save and close. Git will prompt for a combined commit message.
# Enter: "Implement payment validation"

# Result: clean history
git log --oneline
# Output:
# b7c8d9e add tests
# a1b2c3d Implement payment validation
# 0d1e2f3 initial

# io.thecodeforge — DevOps tutorial

cd ugly-history

# Rebase last 4 commits
git rebase -i HEAD~4

# To squash all into the first, reorder and use fixup:
# pick 5e6f7a8 WIP: started feature
# fixup 1a2b3c4 fix typo
# fixup 9f8e7d6 actually fix it
# pick 4a3b2c1 add tests

# fixup is like squash but discards the commit message.
# Save and close. Git will only prompt for the first commit's message.

# Result:
git log --oneline
# Output:
# d4e5f6g add tests
# h1i2j3k WIP: started feature (now contains all changes)
# 0d1e2f3 initial

# io.thecodeforge — DevOps tutorial

git log --oneline -3
# Output:
# d4e5f6g add tests
# h1i2j3k WIP: started feature
# 0d1e2f3 initial

# Reword the middle commit
git rebase -i HEAD~2

# Change 'pick' to 'reword' on the line for h1i2j3k:
# reword h1i2j3k WIP: started feature
# pick d4e5f6g add tests

# Save and close. Git opens editor for new message.
# Enter: "Implement payment validation with edge cases"

# Result:
git log --oneline -3
# Output:
# d4e5f6g add tests
# i9j8k7l Implement payment validation with edge cases
# 0d1e2f3 initial

# io.thecodeforge — DevOps tutorial

# Assume we have a commit that added both login and db refactor
git log --oneline -1
# Output:
# a1b2c3d Add login and refactor database

# Start rebase to edit that commit
git rebase -i HEAD~1
# Change 'pick' to 'edit' on that line, save and close.

# Git stops at that commit. Now split it:
git reset HEAD^  # Unstage all files, keep changes working

# Stage and commit login part
git add login/
git commit -m "Add login functionality"

# Stage and commit db refactor
git add db/
git commit -m "Refactor database layer"

# Continue rebase
git rebase --continue

# Result: two commits instead of one
git log --oneline -3
# Output:
# b2c3d4e Refactor database layer
# c3d4e5f Add login functionality
# 0d1e2f3 initial

# io.thecodeforge — DevOps tutorial

# Simulate a commit that added a debug log with secrets
echo "console.log('API_KEY: ' + process.env.API_KEY)" >> debug.js
git add debug.js && git commit -m "Add debug logging"

# Later commits that don't touch debug.js
echo "feature" >> app.js
git add app.js && git commit -m "Add feature"

# Now drop the debug commit
git rebase -i HEAD~2
# Change 'pick' to 'drop' on the debug commit line, save and close.

# Git replays the feature commit on top of the parent of the dropped commit.
# No conflicts because feature commit doesn't depend on debug.js.

git log --oneline
# Output:
# d4e5f6g Add feature
# 0d1e2f3 initial

# io.thecodeforge — DevOps tutorial

# Current order: tests first, then implementation
git log --oneline -3
# Output:
# a1b2c3d Add tests for payment
# b2c3d4e Implement payment logic
# 0d1e2f3 initial

# Reorder so implementation comes first
git rebase -i HEAD~2

# In editor, swap the lines:
# pick b2c3d4e Implement payment logic
# pick a1b2c3d Add tests for payment

# Save and close. Git replays in new order.
# No conflicts because tests don't depend on implementation (ideally).

git log --oneline -3
# Output:
# c3d4e5f Add tests for payment
# d4e5f6g Implement payment logic
# 0d1e2f3 initial

# io.thecodeforge — DevOps tutorial

# Simulate a conflict during reorder
git init conflict-demo
cd conflict-demo
echo "line1" > file.txt
git add file.txt && git commit -m "initial"
echo "line2" >> file.txt
git commit -am "add line2"
echo "line3" >> file.txt
git commit -am "add line3"

# Reorder commits (swap)
git rebase -i HEAD~2
# Swap lines, save. Git will try to apply 'add line3' before 'add line2'.
# Conflict: both add line2 and line3 to the same file.

# Git says: CONFLICT (content) in file.txt
# Open file.txt:
# <<<<<<< HEAD
# line1
# line3
# =======
# line1
# line2
# >>>>>>> add line2

# Fix: keep both lines in order:
# line1
# line2
# line3

nano file.txt  # edit to resolve
git add file.txt
git rebase --continue

# Git applies the next commit (now 'add line2') on top of the fixed state.
# No further conflicts.

git log --oneline
# Output:
# e5f6g7h add line2
# f6g7h8i add line3
# 0d1e2f3 initial

# io.thecodeforge — DevOps tutorial

# Start feature branch
git checkout -b feature/payment-validation

# Work and commit freely
echo "validate card" > payment.js
git add payment.js && git commit -m "WIP: card validation"
echo "handle decline" >> payment.js
git commit -am "WIP: handle decline"
echo "refund logic" >> payment.js
git commit -am "WIP: refund"

# Before pushing, clean up history
git rebase -i $(git merge-base HEAD master)
# Squash all WIP into one commit, reword to "Add payment validation"

# Push
git push -u origin feature/payment-validation

# Later, master has new commits. Rebase instead of merge:
git pull --rebase origin master
# If conflicts, resolve them, then git rebase --continue

# Force-push (since you rebased, history changed)
git push --force-with-lease

# Open PR. Clean linear history.

# io.thecodeforge — DevOps tutorial

# After a bad rebase, check reflog
git reflog
# Output:
# a1b2c3d HEAD@{0}: rebase finished: returning to refs/heads/feature
# b2c3d4e HEAD@{1}: rebase: add tests
# c3d4e5f HEAD@{2}: rebase: implement payment
# d4e5f6g HEAD@{3}: commit: add tests
# e5f6g7h HEAD@{4}: commit: implement payment
# 0d1e2f3 HEAD@{5}: checkout: moving from master to feature

# The commit before rebase is e5f6g7h (HEAD@{4})
git reset --hard e5f6g7h
# Now you're back to the state before the rebase.

# Verify
git log --oneline -3
# Output:
# e5f6g7h implement payment
# d4e5f6g add tests
# 0d1e2f3 initial