Code example using getopts in bash with short options and a subcommand with it's own short options

getopts-ba.sh

#!/bin/bash

###
# This is a code example showing how to use getops to parse short options and a
# subcommand with short options of it's own. Based on Kevin Sookocheff's post:
# https://sookocheff.com/post/bash/parsing-bash-script-arguments-with-shopts/
# 
# Please feel free to use it and modify it as you see fit. Any questions and/or
# recommendations are more than welcome.
###

# get the scripts name for the usage message
_filename=$0

# verbose mode deactivated
verbose=false

# argument variables
a=""
f=""

# Display usage message function
usage(){
    echo "Usage:"
    echo -e "\t$_filename -h                          Display usage message"
    echo -e "\t$_filename [-v] pow -a <arg> -f <arg>  Options with required arg"
}

if [ ! 0 == $# ] # If options provided then 
then
    while getopts ":hv" opt; do # Go through the options
        case $opt in
            h ) # Help
                usage
                exit 0 # Exit correctly
            ;;
            v ) # Debug
                echo "Read verbose flag"
                verbose=true
            ;;
            ? ) # Invalid option
                echo "[ERROR]: Invalid option: -${OPTARG}"
                usage
                exit 1 # Exit with erro
            ;;
        esac
    done
    shift $((OPTIND-1))
    subcommand=$1; shift # Get subcommand and shift to next option
    case "$subcommand" in
        pow ) # pow chicka pow pow
            unset OPTIND # in order to make -v pow -a <arg> -f <arg> work -> https://stackoverflow.com/questions/2189281/how-to-call-getopts-in-bash-multiple-times
            if [ $verbose == true ]; then echo "Read pow subcommand"; fi
            if [ ! 0 == $# ] # if options provided
            then
                if [ $verbose == true ]; then echo "Remaining args are: <${@}>"; fi
                while getopts ":a:f:" opt; do
                    case $opt in
                        a ) # option -a with required argument
                            echo "Read option -a with argument ${OPTARG}"
                            a=$OPTARG
                        ;;
                        f ) # option -f with required argument
                            echo "Read option -f with argument ${OPTARG}"
                            f=$OPTARG
                        ;;
                        : ) # catch no argument provided
                            echo "[ERROR]: option -${OPTARG} requires an argument"
                            usage
                            exit 1
                        ;;
                        ? ) # Invalid option
                            echo "[ERROR]: Invalid option: -${OPTARG}"
                            usage
                            exit 1 # Exit with erro
                        ;;
                    esac
                done
                if [ -z $a ] || [ -z $f ] # if a or f aren't set
                then
                    echo "[ERROR]: Both -a & -f are required" # throw error
                    usage
                    exit 1
                fi
                shift $((OPTIND-1))
            else
                usage
                exit 1
            fi
        ;;
        * ) # Invalid subcommand
            if [ ! -z $subcommand ]; then  # Don't show if no subcommand provided
                echo "Invalid subcommand: $subcommand"
            fi
            usage
            exit 1 # Exit with error
        ;;
    esac
else # else if no options provided throw error
    usage
    exit 1
fi