Things every Perl programmer should know...

How to manipulate the variable types, take and use references to them, and probably by extension how they are stored in the symbol table. What the performance benefits are between them, and how to determine if the speed increase from using say an array over a hash is really worth it, if they spend extra cycles attempting to determine which index to get the data back out of. Also the difference between passing around an array vs passing around a reference to an array

slices, map, and grep should be tossed out there as well I suppose ;).. Most notably slices, it's amazing how a loop can be inlined via map/grep and an array/hash slice.

Update:everybody's favorite friend Data::Dumper should probably be tossed out there too ;)

MMMMM... Chocolaty Perl Goodness.....