Using Magento Api to create shell scripts seems to be easy, but there are too many things to take into account to get the most of it. In this case, I want to explain how to pass an argument from the command line when executing a magento shell script.
You have to call the script passing the argument title and argument value:
php shellscript.php --argument_title argument_value
Then, on the script code, you can retrieve this value using from your class using: