git pre-push hook preventing a push to master when a line with NEXT_STABLE has been added

pre-push

#!/bin/sh

# A hook script to prevent pushing changes to master branch where a line
# with NEXT_STABLE has been added.
#
# Called by "git push" after it has checked the remote status, but before
# anything has been pushed.  If this script exits with a non-zero status
# nothing will be pushed.
#
# This hook is called with the following parameters:
#
# $1 -- Name of the remote to which the push is being done
# $2 -- URL to which the push is being done
#
# If pushing without using a named remote those arguments will be equal.
#
# Information about the commits which are being pushed is supplied as lines to
# the standard input in the form:
#
#   <local ref> <local sha1> <remote ref> <remote sha1>
#

remote="$1"
url="$2"
branch=`git symbolic-ref HEAD | sed -e 's,.*/\(.*\),\1,'`

z40=0000000000000000000000000000000000000000

# echo "remote == $remote"
# echo "url    == $url"
# echo "branch == $branch"

if [ "$branch" != "master" ]
then
	# only check on master branch
	exit 0
fi

while read local_ref local_sha remote_ref remote_sha
do
	if [ "$local_sha" = $z40 ]
	then
		# Handle delete
		:
	else
		if [ "$remote_sha" = $z40 ]
		then
			# New branch, examine all commits
			range="$local_sha"
		else
			# Update to existing branch, examine new commits
			range="$remote_sha..$local_sha"
		fi

		# Check for WIP commit

		commit=`git rev-list -n 1 "$range"`
		if [ -n "$commit" ]
		then
			next_stable=`git diff $commit^ $commit | grep '^+.*NEXT_STABLE'`
			if [ -n "$next_stable" ]
			then
				echo >&2 "Found NEXT_STABLE commit in $local_ref, not pushing"
				exit 1
			fi
		fi
	fi
done

exit 0