A pre-commit git hook that will make sure CloudFormation templates have had their JSON cleaned up. Really helps with merging and diffing of CloudFormation templates.

pre-commit.sh

#!/bin/bash
#
# git pre-commit hook to make sure you are commiting properly formatted CloudFormation code
# This should go in .git/hooks/pre-commit in a repo with CFN templates.

if git-rev-parse --verify HEAD >/dev/null 2>&1; then
    against=HEAD
else
    against=4b825dc642cb6eb9a060e54bf8d69288fbee4904
fi
 
# This assumes your CloudFormation templates end in .template
for filename in `git diff-index --name-status $against -- | cut -c3-` ; do
    if [[ $filename =~ .*\.template ]]
  then
	
	# Make a temporary file with properly formatted JSON.
	tempfile=`mktemp /tmp/json-validator.XXXXX`
	python -mjson.tool $filename > $tempfile
	
	# Are the files different?
	diff $filename $tempfile > /dev/null 2>&1
	if [ $? -eq 0 ]
	then
	    # If no, just remove the temp file and move on.
	    rm $tempfile
	else
	    # Files are different. You can't commit.
	   rm $tempfile
	   echo "You may not commit."
	   echo "The JSON in file $filename is not formatted properly."
	   echo "Use python -mjson.tool to fix this before committing."
	   exit 1
	fi
    fi
done
exit 0