The undef is not necessary, as per split's documentation:

When assigning to a list, if LIMIT is omitted, Perl supplies a LIMIT one larger than the number of variables in the list, to avoid unnecessary work.

Essentially, this means that all the extra text you're worried about gets assigned to that nonexistent fourth variable in the list on the left hand side.

Good thinking, but Perl beat you to it.

hdp.