#!/usr/bin/env bash -f

SCRIPT_NAME=`basename $0`

read -rd '' HELP << HELP
$SCRIPT_NAME - what the script does

Usage:

$SCRIPT_NAME
  [-a|--option-a A]             - the first option
                                  (default: some sensible default)
  [-b|--option-b B]             - another option
                                  Falls back on \$SOME_SYSTEM_VARIABLE
  positional-args ...           - A longer description
                                  spanning several lines


Examples:
* $SCRIPT_NAME -a an -b example           # With a description
HELP

[[ $# -lt 1 ]] && echo "$HELP" && exit 1;

option_a=
option_b="$SOME_SYSTEM_VARIABLE"

while [ "${1+defined}" ]; do
  case $1 in
    -h|--help) echo "$HELP" && exit 0;;
    -a|--option-a) option_a=$2; shift;;
    -b|--option-b) option_b=$2; shift;;
    *) echo "Unknown option $1" >&2 && exit 1;;
  esac
  shift
done