A quick hack:

opendir(INCLUDES, $includesdir) or die $!;
@includefiles = grep (/exclusives\d+\.tmpl$/, readdir(INCLUDES));
closedir INCLUDES;

$num_of_files = scalar @includefiles;

# ...

$num = $num == 1 ? $num_of_files : 1;
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This implies that the number in the filenames and the actual count of files go together. (E.g. you don't delete a file in the middle of the row.)