$ENV{} modifies the environment.  Deleting from an array tied to a DBM
file deletes the entry from the DBM file.  (But deleting from a 
tie()
d
hash doesn't necessarily return anything.)
The following deletes all the values of an associative array:
(But it would be faster to use the undef() command.) Note that the EXPR can be arbitrarily complicated as long as the final operation is a hash key lookup: