1st Step Get a list of all security groups.

aws ec2 describe-security-groups --query 'SecurityGroups[*].GroupId' --output text |tr '\t' '\n'

2nd Step

Then get all security groups tied to an instance, then piped to sort & uniq them.

aws ec2 describe-instances --query 'Reservations[].Instances[].SecurityGroups[*].GroupId' --output text |tr '\t' '\n' | sort | uniq

3rd Step

Then put it together and compare the 2 lists and see what’s not being used from the master list.

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