A simple hook to prevent commits adding Ruby string interpolations in single quotes, that will fail

pre-commit

#!/bin/sh
#
# A simple hook to prevent commits adding Ruby string interpolations
# in single quotes, that will fail.

if git rev-parse --verify HEAD >/dev/null 2>&1
then
	against=HEAD
else
	# Initial commit: diff against an empty tree object
	against=4b825dc642cb6eb9a060e54bf8d69288fbee4904
fi

# Redirect output to stderr.
exec 1>&2

if [ $(git diff --cached -z $against |
	  grep -c "^\+.*'.*#{.*") != 0 ]
then
	echo "ERROR: Attempt to commit a single quoted interpolation."
	echo
	echo "This won't work, as interpolations don't get expanded in"
	echo "single quotes. Use double quotes instead:"
	echo
	echo "  puts '#{object.message} won\\'t work'"
	echo
	echo "should become:"
	# echo
	echo "  puts \"#{object.message} will work\""
	echo
	echo "You can"
	# echo
	echo "  git commit --no-verify"
	# echo
	echo "to avoid this check and get your commit done anyway"
	# echo
	echo
	echo "Offending lines are:"
	echo
	git diff --cached -z $against | grep "^\+.*'.*#{.*"
	exit 1
fi