In C one of the most common errors to make is an off-by-one error. If you use explicit for loops in Perl, you will make the same error just as often. This is a good reason to use foreach loops whenever possible.

I mention this because your second observation has an off-by-one in it. The odds of an off-by-one can be reduced, though, by: 

foreach my $i (0..$#filenames) {
  # ...
}

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since that removes an inequality that people may miswrite. An even cleaner solution is offered by tye at mapcar -- map for more than one list.

In reply to Observation 2 illustrates a danger by tilly
in thread compilation errors??? by maddfisherman

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