cmd line options parser

option_parser.sh

#!/bin/bash

# for optional arguments: short - there can't be any spaces between the option and the argument
#                         long  - the argument can only be passed by "="

# parse options
OPTIONS=$(getopt -o o::r:n -l optional::,required:,none -n "$0" -- "$@")

# check result
[ $? -ne 0 ] && exit 1

# set parsed options
eval set -- "$OPTIONS"

optional=""
required=""
none=0

# process
while true; do
    case "$1" in
        -o|--optional)
            case "$2" in
                "") optional='default'
                    shift 2 ;;
                *)  optional=$2
                    shift 2 ;;
            esac ;;
        -r|--required)
            required=$2
            shift 2 ;;
        -n|--none)
            none=1
            shift ;;
        --) shift
            break ;;
        *) echo "error!"
           exit 1 ;;
    esac
done

echo "none = $none"
echo "required = $required"
echo "optional = $optional"
echo "left = $@"

http://www.bahmanm.com/blogs/command-line-options-how-to-parse-in-bash-using-getopt

https://stackoverflow.com/a/29754866/797539