usage() { echo "Usage: $0 [-s <45|90>] [-p <string>]" 1>&2; exit 1; }
while getopts ":s:p:" o; do
    case "${o}" in
        s)  s=${OPTARG}
            ((s == 45 || s == 90)) || usage
            ;;
        p)  p=${OPTARG}
            ;;
        *)  usage
            ;;
    esac
done
shift $((OPTIND-1))
if [ -z "${s}" ] || [ -z "${p}" ]; then
    usage
fi
echo "s = ${s} and p = ${p}"
$# = total number of arguments / $1 is the first argument / $0 is the script itself.
!# = last argument