git purge merge commit from history

list-merges.sh

#!/usr/bin/env bash

N=${1:-5}

if ! git rev-parse --is-inside-work-tree > /dev/null 2>&1; then
    echo "Error: Not inside a Git repository."
    exit 1
fi

git log --merges -n "$N" \
  --pretty=format:$'%C(yellow)%H%C(reset)\t%C(cyan)%ad%C(reset)\t%s' \
  --date=short --color=always \
| sed "s/\tMerge branch '\([^']*\)' into .*$/\t\1/"

echo
exit 0

purge-merge.sh

#!/usr/bin/env bash

MERGE_SHA=$1

if [ -z "${MERGE_SHA}" ]; then
  echo "Error: Please provide the merge commit SHA."
  exit 1
fi

if ! git rev-parse --is-inside-work-tree >/dev/null 2>&1; then
  echo "Error: Not inside a Git repository."
  exit 1
fi

if ! git diff-index --quiet HEAD --; then
  echo "Error: Working directory is not clean."
  echo "Please commit, stash, or reset your changes before running this command."
  exit 1
fi

BRANCH_NAME=$(git rev-parse --abbrev-ref HEAD)

FIRST_PARENT=$(git rev-parse "${MERGE_SHA}^1")

cat <<EOF
Starting to purge merge from history (local only, no force pushing)
Target Branch: ${BRANCH_NAME}
Merge to Undo: ${MERGE_SHA}
New Base (First Parent): ${FIRST_PARENT}
EOF

if git rebase --onto "${FIRST_PARENT}" "${MERGE_SHA}" HEAD; then
  git branch -f "${BRANCH_NAME}" HEAD
  git checkout "${BRANCH_NAME}"
  cat <<EOF_SUCCESS
Merge Undo Successful
History rewritten. The merge commit is gone.
Local branch is now at the new tip.

WARNING: To update the remote branch, run:
    git push --force-with-lease origin ${BRANCH_NAME}
EOF_SUCCESS
  exit 0
else
  cat <<'EOF_FAILURE'
Rebase Failed ---
The rebase stopped due to conflicts or an error. Resolve conflicts, then run:
    git rebase --continue
If you want to abort, run:
    git rebase --abort
EOF_FAILURE
  exit 1
fi