As others have said, you cannot prevent a Perl script from being disclosed to the sysadmins ... nor to anyone else who has read-access to the directory in which the script has been stored.
You can, however, use ordinary directory-access rules on the server to ensure that no web user ever has the ability to “purloin” any source-code from the machine.
Incidentally... you do need to pay close attention to the directory permissions that you establish on your stuff if you've deployed to a shared hosting environment! You’d be rather amazed (and shocked) by what is available to even a casually-curious fellow subscriber to whatever web-hosting service you happen to be using . . . :-O