in reply to opening a file destroys nulling entries in a list?!?!
and now for something entirely different..
just as an aside, using map in a void context (i.e. not returning anything), is generally considered a BadThing(TM). If you are simply looking for a way to do simple single line loops, you can always use for().. ala
print "before: $_\n" for @instances;
screwed "$_" for @instances;
print "after: $_\n" for @instances;
You might already know this, you might not, but I figured I would toss it out there. The reason it't not so good, is Perl can go through a lot of trouble to build a list of things to return from the map block, and if you don't use them its simply a waste of processor time and memory that could be better spent doing other things.