Instead of forcing the users of a shell script to manipulate/adjust the content of one of your shell scripts for his/her own needs you can separate this concerns into a Java-like property file.
There are two scripts.
'properties.sh' is the essential one.
It provides the functionality to read the prop file and getting a value by key.
The second one, 'propertiesCheck.sh', is intended for checking the integrity of your prop file.
Using this script is optional.
In the 'application' directory you will find a demo to demonstrate the functionality.
It wraps the 'tar' command parametrised by the prop file.
(Background : The whole thing was created to establish a backup strategy for a multiple project Eclipse/Osgi application to archive some of sub projects for a later reuse by other persons. Outside any git repository.)
Best regards, Uli