Squashes git history before a specified hash in a new branch and cherry picks all newer history

squash-git-history-before-hash.sh

#!/bin/bash

# Specify the name of the branch you want to squash the history for
BRANCH_NAME=$1

# Specify the name of the new branch
NEW_BRANCH_NAME=$2

# Specify cutoff hash
CUTOFF_HASH=$3

# Find the initial commit hash
INITIAL_COMMIT_HASH=$(git log --reverse --pretty=format:"%H" | head -n 1)

# Confirm the operation
echo "This will create a new orphan branch '$NEW_BRANCH_NAME' with git history older than $CUTOFF_HASH squashed into a single commit."
read -p "Are you sure? (y/n): " CONFIRMATION
if [[ $CONFIRMATION != "y" ]]; then
  echo "❌ Operation canceled."
  exit 0
fi

# Checkout the branch we want to reduce the history for
git checkout $BRANCH_NAME

# Get all the commit hashes for original branch
commit_hashes=$(git log --pretty=format:"%h" --first-parent --reverse $CUTOFF_HASH..HEAD)

# Checkout the cutoff hash
git checkout $CUTOFF_HASH

# Reset git to initial commit soft 
git reset --soft $INITIAL_COMMIT_HASH

# Create new orphan branch
git checkout --orphan $NEW_BRANCH_NAME

# Commit all the changes from initial commit to cutoff date as a single new commit
git commit -m "Squashed history older than $CUTOFF_HASH"

# Iterate over the commit hashes and apply them on the new branch
for commit_hash in $commit_hashes; do
  # Perform actions with each commit hash
  echo "🍒 Cherry picking commit: $commit_hash"
  git cherry-pick "$commit_hash" -m 1
  echo ""
  echo ""
done

# Check diff to verify that the new branch matches the original branch
if git diff $BRANCH_NAME $NEW_BRANCH_NAME --quiet; then
  echo "🎉 New branch matches original branch."
else
  echo "🟠 New branch does not match original branch."
  git --no-pager diff $BRANCH_NAME $NEW_BRANCH_NAME --stat
fi

# Show stats
echo "📈 Number of commits in original branch: $(git rev-list --count $BRANCH_NAME)"
echo "📉 Number of commits in new branch: $(git rev-list --count $NEW_BRANCH_NAME)"
echo "✅ Done - New branch '$NEW_BRANCH_NAME' created with git history older than $CUTOFF_HASH squashed."