git-edit-commit

#!/usr/bin/env bash
#
# Run a rebase to `edit` or `reword` a specific commit:
#
# ```bash
# # Open the 3th commit back from HEAD, in rebase "edit" mode.
# # A subsequent `rebase --continue` will rebase the remaining 3 commits on top of it.
# git edit-commit HEAD~3
#
# # "Dry run" of the above:
# git edit-commit -n HEAD~3
# # Would run git rebase -i d6aae97^:
# # edit d6aae97 rm orphaned(?) `commit-filename{,s}` aliases
# # pick ed9447b `cmba="commit-body -a"`, `cnb="commit-body --amend"`
# # pick df33af4 `git-diff-json.py` fixes
# # pick 3c166c3 `dtl`/`details`: commit details
#
# # Same as above, but preserve the "committer dates" of `HEAD^` and `HEAD`:
# git edit-commit -p -m "new message" HEAD^
#
# # As an example, this should be a no-op (same HEAD SHA before and after).
# # `gby = git body = git log -1 --format=%B`, so this rewrites the parent commit with its existing
# # message, and preserves committer dates of both HEAD^ and HEAD.
# git edit-commit -p -m "`gby HEAD^`" HEAD^
# ```

dry_run=()
execs=()
msg=
msg_file=
cmd=edit
while getopts "m:nprx:" opt; do
  case "$opt" in
    m) msg="$OPTARG"; msg_file="$(mktemp)"; cmd=pick ;;
    n) dry_run=(-n) ;;
    p) execs+=("git reset-committer-date-rebase-head") ;;
    r) cmd=reword ;;
    x) execs+=("$OPTARG") ;;
    *) exit 1 ;;
  esac
done
shift $((OPTIND-1))

err() {
  echo "$*" >&2
}
if [ $# -ne 1 ]; then
  err "Usage: $0 [-m <message>] [-n] [-p] [-x <cmd>] <commit>"
  err "  -m: update commit message (non-interactively)"
  err "  -n: dry run"
  err "  -p: preserve committer dates"
  err "  -r: reword commit (interactively)"
  err "  -x: execute command after each commit"
  exit 1
fi

ref="$1"; shift
ref="$(git log -1 --format=%h "$ref")"
sbj="$(git log -1 --format=%s "$ref")"

exec_lines() {
  for exec in "${execs[@]}"; do
    echo "exec $exec"
  done
}

plan_file="$(mktemp)"
(
  echo "$cmd $ref $sbj"
  if [ -n "$msg" ]; then
    echo "$msg" > "$msg_file"
    echo "exec git commit --amend -F$msg_file"
  fi
  exec_lines
  git log --reverse "--format=%h %s" "$ref..HEAD" | \
  while IFS= read -r line; do
    echo "pick $line"
    exec_lines
  done
) > "$plan_file"

git rebase-noninteractive "${dry_run[@]}" -f "$plan_file" "$ref^"

cleanup() {
  rm -f "$plan_file"
  if [ -n "$msg_file" ]; then
    rm -f "$msg_file"
  fi
}
trap cleanup EXIT