Write Author Name/Email in git's commit history.

git-rewrite-author.sh

#!/bin/sh
# git-rewrite-author.sh
#
# Rewrite git-commit author's Name/EmailAddress.
#
# Based on previous versions of this tool  This version runs in POSIX compliant
# shell and .. IMHO .. cleans up a large portion of the filter logic and the
# core syntax such that is is readable and not full of back-slash escape hell.
#
# Other versions:
#  - https://gist.github.com/Hackl0us/490f56dbc135b2fae47d8e2b97c9d8b3
#  - https://gist.github.com/octocat/0831f3fbd83ac4d46451
#  - https://gist.github.com/frz-dev/adf8c2c7275da1369e0cc340feda0ba0
#  - https://gist.github.com/octocat/0831f3fbd83ac4d46451#gistcomment-2178506

error() { echo "error: $*"; }
die() { echo "error: $*"; exit 1; }
usage() {
	if test "$#" -gt '0'; then
		error "error: $*"
		echo "try '${0} --help'" >&2
		exit 1
	fi

	sed -e 's/^	//' << END_OF_USAGE
	usage: ${0} [<options>] [--] [<git filter options>]

	Options:
	  -n, --cur-name "First Last"		Match commits with this name
	  -N, --new-name "First Last"		New name to write to commits
	  -e, --cur-email EMAIL			Match commits with this email address
	  -E, --new-email EMAIL			New email address write to commits
	  -c, --current				Use current git configured user/email when updating commits
	  --dry-run				Do not actually make any changes
	  -x, --trace				Enable execution tracing
	  -h, --help				Display this help

	Notes:
	  - For all matches, both author/committer name and email will be
	    replaced (if both are provided)
	  - You can pass the git-filter option --force to foricbly overwrite
	    backups if you need to run the command multiple times.
	  - To push the changes use the following command:
	    git push --force --tags origin 'refs/heads/*'"
END_OF_USAGE

	# requests for help are not an error
	exit 0
}

## gen_filter
# $1: cur_name
# $2: cur_email
# $3: new_name
# $4: new_email
gen_filter() {
cat<<END_OF_FILTER
if [ "\${GIT_AUTHOR_NAME}" = "${1}" ] || [ "\${GIT_AUTHOR_EMAIL}" = "${2}" ]; then
	test -z "${3}" || export GIT_AUTHOR_NAME="${3}"
	test -z "${4}" || export GIT_AUTHOR_EMAIL="${4}"
fi
END_OF_FILTER
}


##
# parse args
current='false'
dry_run='false'
while test "$#" -gt '0'; do
	case "$1" in
	(-h|-help|--help)
		usage;;
	(-n|--cur-name)
		cur_name="$2"
		shift;;
	(-N|--new-name)
		new_name="$2"
		shift;;
	(-e|--cur-email)
		cur_email="$2"
		shift;;
	(-E|--new-email)
		new_email="$2"
		shift;;
	(-c|--current)
		current='true';;
	(--dry-run)
		dry_run='true';;
	(-x|--trace)
		set -x;;

	# POSIX CLI handling
	(--)	shift; break;;
	(-*)	usage "unknown option '$1'";;
	(*)	break;;
	esac
	shift
done


##
# Validate our inputs
if ${current}; then
	new_email="$(git config user.email)"
	new_name="$(git config user.name)"
fi

if test -z "${cur_name}" && test -z "${cur_email}"; then
	usage 'must specify a current name or email address to match'
fi

if test -z "${new_name}" && test -z "${new_email}"; then
	usage 'must specify a new name or email address to write'
fi

##
# Just do it
if "${dry_run}"; then
	echo git filter-branch \
		--env-filter "$(gen_filter "${cur_name}" "${cur_email}" "${new_name}" "${new_email}")" \
		"$@" --tag-name-filter cat -- --branches --tags
else
	exec git filter-branch \
		--env-filter "$(gen_filter "${cur_name}" "${cur_email}" "${new_name}" "${new_email}")" \
		"$@" --tag-name-filter cat -- --branches --tags
fi