#!/bin/bash

while getopts a:b:cd param;
do
    case $param in
        a) echo "parameter 'a' with argument: $OPTARG"
            ;;
        b) echo "parameter 'b' selected with argument: $OPTARG"
            ;;
        c) echo "parameter 'c' selected (no colon, no argument)"
            ;;
        d) echo "parameter 'd' selected"
            ;;
    esac
done