As IlyaM points out, you should always check the return codes from functions. opendir will return 1 on success and 0 on failure. I would code it slightly differently:

opendir(DIR, $some_dir) || die "Could not open $some_dir - $!\n";
for my $fileFound(readdir(DIR)) {
   my $fullPath = $some_dir . "/" . $fileFound;
   next if (-d $fullPath);
   # do stuff with each file in $some_dir
}
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-- vek --