Delete tags from a git repository that reference commits that aren't part of the named branch.

git-delete-tags-not-part-of-branch.sh

#!/bin/bash -eu
#
# Delete tags from a git repository that reference commits that aren't part of the named branch
#
# This is useful if you've split a branch out of a repository and want to remove all of the commits
# that referenced activity in other branches.

usage() {
	echo "usage: $0 [-d] [-p <remote>] <branch>" >&1
	echo "  -d dry run" >&1
	echo "  -p push tag deletes to the remote" >&1
}

dryrun=0
push=

while getopts ":dp:" opt; do
	case $opt in
		d)
			dryrun=1
			;;
		p)
			push="$OPTARG"
			;;
		\?)
			echo "Invalid option: -$OPTARG" >&2
			exit 1
			;;
	esac
done

shift $((OPTIND-1))

branch="${1:-}"

if [ -z "$branch" ]; then
	usage
	exit 1
fi

tags=$(git tag --list)

for tag in $tags ; do
	tagref=$(git rev-list -n 1 "$tag")
	if [ -z "$tagref" ]; then
		echo "Failed to find ref for tag: $tag" >&1
		exit 1
	fi

	set +e
	git rev-list "$branch" | grep -q "$tagref"
	if [ $? == 1 ]; then
		if [ $dryrun == 1 ]; then
			echo "Would delete $tag"
		else
			git tag --delete "$tag"
			if [ -n $push ]; then
				git push $push :refs/tags/"$tag"
			fi
		fi
	fi
	set -e
done