A small function that uses enhanced getopt(1) to define parameters

parseopt.bash

parseopt() {
    [[ -n $1 ]] || return 1

    # Use "--options +" to prevent arguments from being rearranged.
    local -r opts=$(getopt --name "$0" --options + --longoptions "$1" -- "${@:2}")
    case $((10#$?)) in
        1)
            # getopt(1) will print an error first.
            echo >&2 "Try \`$0 --help' for more information."
            return 2
            ;;
        [!0]*)
            errmesg 'Internal error while parsing options'
            return 4
            ;;
    esac

    local -a validopts
    IFS=, read -ar validopts <<<"$1"
    readonly validopts=("${validopts[@]/#/--}")

    eval set -- "$opts"

    local opt validopt
    # getopt(1) ensures that the options are always terminated with "--".
    while [[ $1 != -- ]]; do
        opt=$1
        shift
        # XXX Do NOT touch anything below unless you know exactly what
        # you're doing (http://mywiki.wooledge.org/BashFAQ/006#eval).
        for validopt in "${validopts[@]}"; do
            if [[ $validopt == "${opt}:" || $validopt == "${opt}::" ]]; then
                opt=${opt#--}
                # $1 is null for omitted optional arguments.
                eval 'option_'"${opt//-/_}"'=$1'
                shift
                continue 2
            fi
            if [[ $validopt == "$opt" ]]; then
                opt=${opt#--}
                eval '(( ++option_'"${opt//-/_}"' ))'
                continue 2
            fi
        done
        # Unreachable unless there is a bug in this function or in getopt(1).
        errmsg 'Internal error while parsing options'
        return 4
    done
    remaining_args=("${@:2}")
}

# Process options.
declare -a remaining_args
parseopt archive-site:,help,port:,prefix:,svn:,svn_revision:,svn_url:,staging-dir:,variants:,workdir: "$@" || exit $?
set -- "${remaining_args[@]}"