I want get document_root path from "Command to run before making changes to a domain" of virtualmin

I find "public_html_path" in /etc/webmin/virtual-server/domains/$DOM but I can't get it in my shell script

I'v tried use $public_html_path , $VIRTUALSERVER_public_html_path , $VIRTUALSERVER_PUBLIC_HTML_PATH and $PUBLIC_HTML_PATH as variable name, but they all don't work.

I searched google and website of virtualmin.com and find nothing usable.

Is there anyone knows that? thank you very much!

Below is the document from virtualmin:

If you want to perform some action before altering a domain (creation, alteration, or deletion) you may specify a command to run here. If multiple actions are to be performed the command to run can be a script. The command has access to special environment variables specific to the domain, such as VIRTUALSERVER_DOM, VIRTUALSERVER_IP, VIRTUALSERVER_USER, VIRTUALSERVER_HOME, VIRTUALSERVER_PASS, and more. Any variable found in the /etc/webmin/virtual-server/domains/$DOM file will be available as an environment variable.