simple.sh

#!/bin/bash

# Global variables
package=
command=

# Some have default values
parsing_succeeded=true

for (( i=1; i<=$#; i++ ))
do
	arg=${@:$i:1}   # Gets the string i
	val=${@:$i+1:1} # Gets the string i+1

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

echo "Arguments:"
echo "  package: $package"
echo "  command: $command"
echo ""

if [ "$parsing_succeeded" == "true" ]
then
	if [ ! -z $command ]
	then
		echo "Start command: '$command'"
		# Check and start the corresponding routine here
	else
		echo "Missing command"
		exit 1
	fi
else
	echo "Error during parsing. Exit application."
	exit 1
fi