I guess I need to get into the habit of using chomp to take care of the white spaces.

chomp won't save you here because the whitespace is in the middle of $subject and you probably do actually want to retain the spaces anyway.

My work environment is so strict and chances are that we don't have the modules installed.

Which OS? Many of them have packages for perl modules.

What is the command to check if a module is installed?

TIMTOWTDI but a simple test to see if (eg.) DBI is installed could be

perl -MDBI -e 1

which will just return you to the prompt if it is loaded or throw an error otherwise.