If you can make sure the script runs under taint mode (it isn't just for CGIs!), then you've taken a significant step towards making your script secure. Taint mode (-T on the command or '#!' line) isn't a magic bullet, though. It can stop you from making some subtle mistakes, like using unexamined user input in eval or system (not just system) calls. See perldoc perlsec for more.

Philosophy can be made out of anything. Or less -- Jerry A. Fodor