It's hard to believe that all three scripts and servers are identical, when one of them is giving a warning, and the other two do not. Therefore I strongly believe that the script on the dev-server uses `perl -w`, while the others do not :) Perl doesn't warn you just because it likes to do so, so much, but rather to inform you that your code isn't what it should be. To make it go away? Make sure $HASH{key} contains a value (or don't use it), or delete the "-w" from the hashbang ;)

Update: besides the hashbang, the warnings can be turned on using use warnings; and maybe your sysadmin created an alias for perl (alias perl='perl -w'). Who knows? Would make sense on a dev. machine.