perl log.pl
Can't use an undefined value as a symbol reference at log.pl line 30, <$_[...]>
        line 532 (#1)
    (F) A value used as either a hard reference or a symbolic reference must
    be a defined value.  This helps to delurk some insidious errors.

Uncaught exception from user code:
        Can't use an undefined value as a symbol reference at log.pl line 30, <$_[...]> line 532.
 at log.pl line 30