Correct git author name and email for a branch by rewriting its history.

git-fix-author

#!/bin/bash
# shellcheck disable=SC2016

# Rewrite git history.

readonly VERSION='2.0.5'

# Exit immediately if a command exits with a non-zero status.
set -e

exit_with_help_text() {
  printf '
usage:
    git fix-author (--set-name=<name> | --set-email=<email>) [<args>]

args:
    -v, --version        Print version number.
    -h, --help           Print this help text.
    -n, --set-name       Rewrite commits to have this author name.
    -e, --set-email      Rewrite commits to have this author email.
    -N, --filter-name    Only rewrite commits originally by this author name.
    -E, --filter-email   Only rewrite commits originally by this author email.

description:
    This command corrects git author name and email for a branch by by rewriting
    its history. By default it will update all commits; use the optional filter
    flags to update commits from a specific author.

example:
    git fix-author -e bob@example.com -E alice@example.com
'
  exit 0
}

exit_with_version_text() {
  printf '%s\n' "$VERSION"
  exit 0
}

exit_with_unknown_param_error() {
  printf 'Error: Unknown parameter %s.\n' "$1"
  exit 1
}

clean_up() {
  unset filter replace_email replace_name search_email search_name
}

get_params() {
  for _; do
    case "$1" in
      # Version param.
      -v|--version)
        exit_with_version_text
      ;;
      # Help param.
      -h|--help)
        exit_with_help_text
      ;;
      # Replacement email.
      -e|--set-email)
        shift
        replace_email=$1
      ;;
      --set-email=*)
        replace_email="${1#*=}"
      ;;
      # Replacement name.
      -n|--set-name)
        shift
        replace_name=$1
      ;;
      --set-name=*)
        replace_name="${1#*=}"
      ;;
      # Search email.
      --filter-email)
        shift
        search_email=$1
      ;;
      --filter-email=*)
        search_email="${1#*=}"
      ;;
      # Search name.
      --filter-name)
        shift
        search_name=$1
      ;;
      --filter-name=*)
        search_name="${1#*=}"
      ;;
      # Unknown params.
      *)
        exit_with_unknown_param_error "$1"
      ;;
    esac
    shift
  done

  # Exit with help text if neither replace_name nor replace_email has been set.
  if [[ -z "$replace_name" ]] && [[ -z "$replace_email" ]]; then
    exit_with_help_text
  fi
}

create_commit_filter() {
  # We use double quoted strings to build our filter and these variables need
  # to be passed verbatim to git filter-branch. It's convenient to store these
  # as variables to avoid escaping later.
  local git_author_email='"$GIT_AUTHOR_EMAIL"'
  local git_author_name='"$GIT_AUTHOR_NAME"'
  local default_filter='git commit-tree "$@"'

  # Starting point for the commit filter.
  filter="$default_filter;"

  # If specified, add name replacing to filter command.
  if [[ -n "$replace_name" ]]; then
    filter="
      GIT_COMMITTER_NAME='$replace_name';
      GIT_AUTHOR_NAME='$replace_name';
      $filter
    "
  fi

  # If specified, add email replacing to filter command.
  if [[ -n "$replace_email" ]]; then
    filter="
      GIT_COMMITTER_EMAIL='$replace_email';
      GIT_AUTHOR_EMAIL='$replace_email';
      $filter
    "
  fi

  # If specified, add name search to filter command.
  if [[ -n "$search_name" ]]; then
    filter="
    if [[ $git_author_name = '$search_name' ]]; then
      $filter
    else
      $default_filter;
    fi
    "
  fi

  # If specified, add email search to filter command.
  if [[ -n "$search_email" ]]; then
    filter="
    if [[ $git_author_email = '$search_email' ]]; then
      $filter
    else
      $default_filter;
    fi
    "
  fi
}

execute_commit_filter() {
  git filter-branch --commit-filter "$filter" --force HEAD
}

main() {
  get_params "$@"
  create_commit_filter
  execute_commit_filter
}

main "$@"