cherry-pick.sh

#!/bin/bash

# Usage: ./usr/local/bin/cherry-pick <second_branch> [author-or-username] [--commit] [--commit-separate]
# Examples:
#   ./usr/local/bin/cherry-pick feature-branch
#   ./usr/local/bin/cherry-pick feature-branch "[email protected]" --commit
#   ./usr/local/bin/cherry-pick feature-branch --commit-separate
# Description:
#   Find commits in <second_branch> newer than the last commit on the current
#   branch by the same author (or provided author/username). By default the script
#   stages the combined changes without creating commits. Use --commit to create
#   a single combined commit, or --commit-separate to replay each found commit
#   as an individual commit preserving original author and message.

set -euo pipefail

if [ -z "${1-}" ]; then
  echo "Usage: $0 <second_branch> [author-or-username] [--commit] [--commit-separate]"
  exit 1
fi

SECOND_BRANCH="$1"
ARG2="${2-}"
COMMIT_FLAG=false
COMMIT_SEPARATE=false

# parse remaining args
for arg in "${@:2}"; do
  case "$arg" in
    --commit) COMMIT_FLAG=true ;;
    --commit-separate) COMMIT_SEPARATE=true ;;
    *) AUTHOR_ARG="$arg" ;;
  esac
done

# ensure repo
if ! git rev-parse --git-dir >/dev/null 2>&1; then
  echo "Error: not a git repository"
  exit 2
fi

CURRENT_BRANCH=$(git rev-parse --abbrev-ref HEAD)
LAST_COMMIT_DATE=$(git log -1 --format="%ct" "$CURRENT_BRANCH" 2>/dev/null || echo 0)

# Determine author identifier (prefer provided arg). Use username (email local-part) from last commit when not provided.
if [ -n "${AUTHOR_ARG-}" ]; then
  AUTHOR_IDENTIFIER="$AUTHOR_ARG"
else
  LAST_AUTHOR_EMAIL=$(git log -1 --format="%ae" "$CURRENT_BRANCH" 2>/dev/null || echo "")
  if [ -n "$LAST_AUTHOR_EMAIL" ]; then
    AUTHOR_IDENTIFIER="${LAST_AUTHOR_EMAIL%%@*}"   # username (local-part)
  else
    AUTHOR_IDENTIFIER=$(git log -1 --format="%an" "$CURRENT_BRANCH" 2>/dev/null || echo "")
  fi
fi

echo "Current branch: $CURRENT_BRANCH"
echo "Second branch: $SECOND_BRANCH"
echo "Author identifier (username/email/regex): $AUTHOR_IDENTIFIER"
echo "Last commit date (epoch): $LAST_COMMIT_DATE"
echo "Create combined commit: $COMMIT_FLAG"
echo "Replay as separate commits: $COMMIT_SEPARATE"

# check branch exists
if ! git show-ref --verify --quiet "refs/heads/$SECOND_BRANCH" && ! git rev-parse --verify --quiet "$SECOND_BRANCH" >/dev/null 2>&1; then
  echo "Error: branch '$SECOND_BRANCH' not found"
  exit 3
fi

# collect qualifying commits (oldest->newest)
mapfile -t NEW_COMMITS < <(git log --reverse "$SECOND_BRANCH" --author="$AUTHOR_IDENTIFIER" --format="%H %ct" | awk -v ref="$LAST_COMMIT_DATE" '$2 > ref {print $1}')

if [ "${#NEW_COMMITS[@]}" -eq 0 ]; then
  echo "No newer commits matching '$AUTHOR_IDENTIFIER' found in '$SECOND_BRANCH'."
  exit 0
fi

echo "Found ${#NEW_COMMITS[@]} commit(s) to apply."

ORIG_HEAD=$(git rev-parse --verify HEAD 2>/dev/null || echo "none")

# Helper: list unmerged files
unmerged_files() {
  git diff --name-only --diff-filter=U || true
}

# Iterate commits
for COMMIT in "${NEW_COMMITS[@]}"; do
  echo "Processing commit: $COMMIT"

  PREV_HEAD=$(git rev-parse --verify HEAD 2>/dev/null || echo "none")

  if [ "$COMMIT_SEPARATE" = true ]; then
    # Replay as individual commit: do normal cherry-pick (creates commit unless conflicts)
    if git cherry-pick --allow-empty "$COMMIT"; then
      echo "Cherry-picked $COMMIT as a separate commit without conflicts."
      continue
    fi

    echo "Conflict detected while cherry-picking $COMMIT; accepting theirs for conflicts."
    # Resolve conflicts by taking theirs, stage and continue
    while IFS= read -r file; do
      [ -z "$file" ] && continue
      echo "Resolving conflict by taking theirs for: $file"
      git checkout --theirs -- "$file" || true
      git add -- "$file"
    done < <(unmerged_files)

    # If CHERRY_PICK_HEAD exists, continue; otherwise abort and restore
    GIT_DIR=$(git rev-parse --git-dir)
    if [ -e "$GIT_DIR/CHERRY_PICK_HEAD" ]; then
      if git cherry-pick --continue; then
        echo "cherry-pick --continue succeeded for $COMMIT."
        continue
      else
        echo "Error: failed to continue cherry-pick for $COMMIT. Aborting and restoring."
        git cherry-pick --abort || true
        if [ "$PREV_HEAD" != "none" ]; then git reset --hard "$PREV_HEAD" || true; fi
        exit 4
      fi
    else
      echo "Warning: no cherry-pick in progress after resolving conflicts for $COMMIT."
      git add -A || true
      if git diff --name-only --diff-filter=U | read -r _; then
        echo "Remaining unmerged paths found. Restoring previous HEAD ($PREV_HEAD)."
        git reset --hard "$PREV_HEAD" || true
        exit 5
      fi
      # create a commit using original commit metadata
      AUTHOR_LINE=$(git show -s --format='%an <%ae>' "$COMMIT")
      COMMIT_MSG=$(git show -s --format='%B' "$COMMIT")
      COMMIT_DATE=$(git show -s --format='%aI' "$COMMIT")
      GIT_COMMITTER_DATE="$COMMIT_DATE" git commit --author="$AUTHOR_LINE" -m "$COMMIT_MSG"
      echo "Committed resolved result for $COMMIT preserving original metadata."
    fi
  else
    # Default behavior: apply with --no-commit to stage changes (single combined commit later)
    if git cherry-pick --no-commit --allow-empty "$COMMIT"; then
      echo "Applied $COMMIT without conflicts (changes staged)."
      continue
    fi

    echo "Conflict detected while applying $COMMIT. Accepting incoming changes (theirs) for all conflicts."

    while IFS= read -r file; do
      [ -z "$file" ] && continue
      echo "Resolving conflict by taking theirs for: $file"
      git checkout --theirs -- "$file" || true
      git add -- "$file"
    done < <(unmerged_files)

    GIT_DIR=$(git rev-parse --git-dir)
    if [ -e "$GIT_DIR/CHERRY_PICK_HEAD" ]; then
      if git cherry-pick --continue; then
        # cherry-pick --continue created a commit; we reset soft to PREV_HEAD to leave changes staged as intended
        if [ "$PREV_HEAD" = "none" ]; then
          git reset --soft HEAD^ || true
        else
          git reset --soft "$PREV_HEAD" || true
        fi
        echo "Uncommitted the cherry-picked changes and left them staged."
      else
        echo "Error: failed to continue cherry-pick after resolving conflicts for $COMMIT."
        git cherry-pick --abort || true
        if [ "$PREV_HEAD" != "none" ]; then git reset --hard "$PREV_HEAD" || true; fi
        exit 4
      fi
    else
      echo "Warning: no cherry-pick in progress after resolving conflicts for $COMMIT."
      git add -A || true
      if git diff --name-only --diff-filter=U | read -r _; then
        echo "Remaining unmerged paths found. Aborting and restoring previous HEAD ($PREV_HEAD)."
        git reset --hard "$PREV_HEAD" || true
        exit 5
      fi
    fi
  fi
done

# After applying all commits:
if [ "$COMMIT_SEPARATE" = true ]; then
  echo "All commits replayed as separate commits. Review the log to see new commits."
  exit 0
fi

if [ "$COMMIT_FLAG" = true ]; then
  if git diff --staged --quiet; then
    echo "No staged changes to commit."
  else
    git commit -m "Cherry-picked ${#NEW_COMMITS[@]} commit(s) from $SECOND_BRANCH by $AUTHOR_IDENTIFIER"
    echo "Created combined commit."
  fi
else
  echo "All cherry-picks applied and changes staged. No commit has been made."
  echo "To see these changes in your branch log, create a commit."
  echo "Inspect staged changes with: git diff --staged"
  echo 'Create a single commit with: git commit -m "<your combined message>"'
  echo "Or replay commits as separate commits by re-running with --commit-separate."
fi