opt_test.sh

#!/bin/bash

usage() {
  echo 'usage: ./opt_test.sh --alpha [ALPHA] --bravo [BRAVO] [--charlie [CHARLIE]]'
}

while [[ ${#} -gt 0 ]]; do
  opt="${1}"
  shift
  value="${1}"
  if [[ "${value}" =~ ^-{1,2}.* ]]; then
    echo "Error: Argument is blank."
    exit 1
  fi
  case "${opt}" in
    "-a"|"--alpha" )
      alpha="${1}"
      shift
    ;;
    "-b"|"--bravo" )
      bravo="${1}"
      shift
    ;;
    "-c"|"--charlie" )
      charlie="${1}"
      shift
    ;;
    * )
      echo "ERROR: Invalid option: \""${opt}"\"" >&2
      exit 1
    ;;
  esac
done

if [[ -z "${alpha}" || -z "${bravo}" ]]; then
  usage
  exit 1
fi