show_help() { 
	echo "Usage: ..."
	exit 0
}

[ -z $1 ] && show_help

input="$1"

OPTIND=1
output_file="default.txt"
while getopts "h?vo:" opt; do
	case "$opt" in
		h|\?) show_help ;;
		o) output_file=$OPTARG ;;
	esac
done
shift $((OPTIND-1))