git-set-author

#!/usr/bin/env bash
#
# Update the author of the last commit.
#
# Usage:
#
#     # 0 args ⟹ read author name and email from Git config
#     git set-author [-p|--preserve-committer-date]
#
#     # If 1 arg is provided:
#     # - If it contains a space, treat it as a name
#     # - If it matches an existing "ref" (branch/tag/SHA), copy author info from the corresponding commit
#     # - Otherwise, treat it as an email address
#     git set-author [-p|--preserve-committer-date] <name|email|ref>
#
#     # 2 args ⟹ name, email
#     git set-author [-p|--preserve-committer-date] <name> <email>

committer=
preserve_committer_date=
while getopts "cp" opt; do
  case "$opt" in
    c) committer=1 ;;
    p) preserve_committer_date=1 ;;
    \?) echo "Unknown option: -$opt" >&2
      exit 1
  esac
done
shift $((OPTIND - 1))

if [ $# -eq 0 ]; then
  name="$(git config user.name)"
  email="$(git config user.email)"
  author="$name <$email>"
  echo "Setting author: $author" >&2
elif [ $# -eq 1 ]; then
  if [[ "$1" == *' '* ]]; then
    # If the argument has more than one word, assume it's the author's name.
    name="$1"; shift
    email="$(git log -1 --format=%ae)"
    author="$name <$email>"
    echo "Updating author name: $author" >&2
  elif git cat-file -t "$1" &>/dev/null; then
    # Otherwise, check whether it's a Git "ref", and copy that author name/email if so
    ref="$1"; shift
    name="$(git show -s --format='%an' "$ref")"
    email="$(git show -s --format='<%ae>' "$ref")"
    author="$name <$email>"
    echo "Updating author from commit $ref: $author" >&2
  else
    # Otherwise, assume we're updating the author's email address
    email="$1"; shift
    name="$(git log -1 --format=%an)"
    author="$name <$email>"
    echo "Updating author email: $author" >&2
  fi
elif [ $# -eq 2 ]; then
  name="$1"; shift
  email="$1"; shift
  author="$name <$email>"
  echo "Setting author: $author" >&2
else
  echo "Usage: git set-author [-p|--preserve-committer-date] [name <email>]" >&2
  echo "Usage: git set-author [-p|--preserve-committer-date] <name> <email>" >&2
  exit 1
fi

if [ "$preserve_committer_date" ]; then
  GIT_COMMITTER_DATE="$(git log -1 --format=%cd)"
  export GIT_COMMITTER_DATE
  echo "Preserving committer date: $GIT_COMMITTER_DATE" >&2
fi

if [ -z "$committer" ]; then
  committer_flags=()
else
  committer_flags=(-c user.name="$name" -c user.email="$email")
fi
cmd=(git "${committer_flags[@]}" commit --amend --no-edit --allow-empty --author "$author")
echo "Running: ${cmd[*]}" >&2
"${cmd[@]}"