Syntax to Map Virtual-Server's Character with Data-Group which Contains Pool Name

The biggest problem here is that the pool command is expecting the name of a pool only, but your [class match -element ] command is returning the key (virtual server name) and value (pool name) of the data group search as a list.

So if you're data group looks like this:

apuat.leni2.com-vs-http := pool_apuat_leni2.com_http
apbuild.leni2.com-vs-http := pool_apbuild.leni2.com_http
apctdev.leni2.com-vs-http := pool_apctdev.leni2.com_http

** Notice that the virtual server names are all completely lower case since your class match is doing the same.

Then your class match should more appropriately look like this:

[class match [string tolower [virtual]] equals dg_parveez_dynamic_pools]

This will return the corresponding pool name to be fed into the pool command.