How to check if AWS CLI SSO is logged in

You can check for the sts caller identity call

Returns details about the IAM user or role whose credentials are used to call the operation.

https://docs.aws.amazon.com/cli/latest/reference/sts/get-caller-identity.html

#!/bin/bash

SSO_ACCOUNT=$(aws sts get-caller-identity --query "Account" --profile sso)
#you can add a better check, but this is just an idea for quick check
if [ ${#SSO_ACCOUNT} -eq 14 ];  then 
echo "session still valid" ;
else 
echo "Seems like session expired"
# performed login here
fi

If the session is still valid, it will return

{
    "UserId": "AIDASAMPLEUSERID",
    "Account": "123456789012",
    "Arn": "arn:aws:iam::123456789012:user/DevAdmin"
}

If the session is not valid, it will return

The SSO session associated with this profile has expired or is otherwise invalid. To refresh this SSO session run aws sso login with the corresponding profile.

Or you can use this utility which is designed for this purpose

https://github.com/benkehoe/aws-sso-util