git-backtag

#!/usr/bin/env bash
#
# A custom git command that implements backdating tags as described in
# https://git-scm.com/docs/git-tag#_on_backdating_tags .
#
# Author: Lucas Magasweran <lucas.magasweran@ieee.org>
#
set -o errexit

usage() {
	echo "usage: git backtag [-h|-a|-s|-u <key-id>] [-f] [-m <msg>|-F <file>] <tagname> <commit>"
	echo -e "    commit    date of commit will be used to backdate tag"
}

opts=`getopt --options hasfu:m:F: --long annotate,sign,force,local-user:,message:,file: -- "$@"`
if [ $? != 0 ] ; then echo "Failed parsing options." >&2 ; exit 1 ; fi
eval set -- "$opts"

while [[ $# != 0 ]]; do
	case "$1" in
	-h)
		usage
		exit
		;;
	-a|--annotate) ;&
	-s|--sign) ;&
	-f|--force)
		shift
		;;
	-u|--local-user) ;&
	-m|--message) ;&
	-F|--file)
		shift 2
		;;
	--)
		shift
		break
		;;
	esac
done

if [[ -z ${1} ]] || [[ -z ${2} ]]; then
	usage
	exit 1
fi

tagname=$1
commit=$2
branch=$(git symbolic-ref --short -q HEAD)

remove_commit() {
   echo "${@:1:$#-1}"
}

opts2=`remove_commit ${opts}`

git checkout --quiet $commit

GIT_COMMITTER_DATE="$(git show --format=%aD | head -1)" eval git tag ${opts2}

git checkout --quiet $branch