command.sh

#!/bin/bash

# Global variables
package=
command=

# Some have default values
parsing_succeeded=true

# Parses the install specific arguments
# Needed parameter: $@
function parse_install_args(){
	for (( i=1; i<=$#; i++ ))
	do
		arg=${@:$i:1}   # Gets the string i
		val=${@:$i+1:1} # Gets the string i+1

		case $arg in
		-h|--help)
			echo "Show help text for the install command here"
			exit 0
			;;
		-p)
			package=$val
			# The parse the next argument and not this value
			((i++))
			;;
		--package=*)
			# split at = char and remove the shortest match from beginning
			package=${arg#*=}
			;;
		*)
			echo "Unknown argument number $i: '$arg'"
			parsing_succeeded=false
			;;
		esac
	done
}

# Parses the list specific arguments
# Needed parameter: $@
function parse_list_args(){
	for (( i=1; i<=$#; i++ ))
	do
		arg=${@:$i:1}   # Gets the string i
		val=${@:$i+1:1} # Gets the string i+1

		case $arg in
		-h|--help)
			echo "Show help text for the list command here"
			exit 0
			;;
		*)
			echo "Unknown argument number $i: '$arg'"
			parsing_succeeded=false
			;;
		esac
	done
}

arg=${@:1:1}
# To parse the next argument and not the command again
shift

# First we accept a command or the help-flag
case $arg in
-h|--help)
	echo "Show help text here"
	exit 0
	;;
install)
	command=install
	parse_install_args $@
	;;
list)
	command=list
	parse_list_args $@
	;;
*)
	echo "Unknown command '$arg'."
	exit 1
	;;
esac

# Only if parsing succeeded, execute the actual application logic
# (This might not always be wanted, but change it as you like)
if [ "$parsing_succeeded" == "true" ]
then
	case $command in
	install)
		echo "Install package '$package'"
		# Call install-routine
		;;
	list)
		echo "List all packages:"
		# Call list-routine here
		;;
	"")
		echo "Missing command"
		exit 1
		;;
	*)
		echo "Unknown command"
		exit 1
		;;
	esac
else
	echo "Error during parsing. Exit application."
	exit 1
fi