One program should be one file, unless the "parts" are truly going to be reused by other programs (which they usually are not)

I hope you're not recommending 14,000 lines of main program in a single file! On the contrary, I recommend keeping the main program file short, with most of the work done in (highly cohesive, loosely coupled) modules -- with documentation and a test suite around each module.

You can find many examples of this approach on the CPAN. For example, in Perl::Tidy and Perl::Critic, the perltidy and perlcritic main programs are not much more than one-liners, essentially just:

use Perl::Tidy;
Perl::Tidy::perltidy();
[download]

use Perl::Critic::Command qw< run >;
run();
[download]

I hope you're not recommending 14,000 lines of main program in a single file!

I prefer writing, and hacking on, single file programs. It's much easier than remembering which module contains what code that's performing some action from a distance. I like to keep as much code as possible in the main program file. That being said, I also use plenty of modules, impose sane order on the source to ease navigation, and document everything.