MalformedPolicyDocument error while creating an IAM Policy - json

Question

I'm trying to create a managed policy by AWS CLI:
POLICY='
{
"Version":"2012-10-17",
"Statement":
[{
"Effect":"Allow",
"Action":
[
"cloudformation:*"
],
"Resource":"*"
},
{
"Effect":"Deny",
"Action":
[
"cloudformation:UpdateStack",
"cloudformation:DeleteStack"
],
"Resource": "'${arn}'"
}]
}'
# Create policy if not already created
[ $(aws iam list-policies | grep -ce CloudFormation-policy-${StackName}) -eq 0 ] && (aws iam create-policy --policy-name CloudFormation-policy-${StackName} --policy-document "'${POLICY}'")
When I run the script I get this error:
An error occurred (MalformedPolicyDocument) when calling the CreatePolicy operation: Syntax errors in policy.
I can't figure out where the error is.
Any idea?

Answer 1

Each operating systems has its own way of treating single quote vs double quote escaping and as per AWS CLI documentation:
When passing in large blocks of data, you might find it easier to save
the JSON to a file and reference it from the command line. JSON data
in a file is easier to read, edit, and share with others.
Quoting Strings approach might not be best choice while passing Json data, instead use Loading parameters from file approach.