I'm still trying to figure this out. It seems it runs contrary to some of the culture of perl. For about the same reason why there are no "private" methods (well, unless you do something really silly), or any way to prevent someone from subclassing your package, the ability to go and install new modules is generally a good thing. In fact, in my setup script, I only expand CPAN modules that haven't been superseded by whatever is on the system already - allowing for a newer module is probably a good thing.

That said, you may be more interested in the only module. It may get you what you want without all the hackery of @INC. (Well, it will do its own hackery, rather than relying on your own hackery :-))

Well, this has nothing to do with subclassing. The application, specially this particular distribution, is intented to use only required CPAN modules disributed with it.The only module is close to what I need, but then I have to track the version of all modules to make sure the expected targets are the ones get loaded.

Out of all, it may really sound silly, but I really hope I only do this once.

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Open source softwares? Share and enjoy. Make profit from them if you can. Yet, share and enjoy!

I take it that you have not yet stumbled-upon use lib ...?

Anyway, when you do, this is probably going to be what you want. I would have one directory for application-specific modules, another for CPAN-overrides, and in the main-programs of your application simply list them both in a use lib declaration.

Perl will search the libraries declared here, in order, before it walks down the @INC list... (I've got several deployed apps where I'm having to override CPAN-modules that are seriously-broken, and the owners of those modules continue to “upgrade” them without fixing the bugs. I will not name them here.)

I didn't use use lib because it only prepends dir parameters to @INC, while my need is to override @INC completely by setting it manually. But yes, I should have mentioned this in the first place.

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Open source softwares? Share and enjoy. Make profit from them if you can. Yet, share and enjoy!

Given those caveats, if you can get your code to be more reliable rather than less reliable by doctoring your lib paths and you don't intend to mess with the defaults for other programs, then I think every option is open to you.

I'll give you a bit of free advice about common wisdom that not enough people seem to grasp. There are conventions, best practices, and recommendations enough that work well enough for most people in most situations. Usually, it's a good idea to follow the collective wisdom of a well-experienced, thoughtful group. When all the cards are down, so to speak, your chips depend on having the best hand at the table and not a pretty good one on average. If you're finding that you have an odd requirement that falls outside of the common wisdom, then perhaps you're right to have an odd solution. You'd just better be right about it, or someone's going to call you a fool when your system falls down and you have to explain why you stepped outside the norm. If you can make your system ten times as reliable by breaking convention, then do it and document the decision process. If you're making it 100% harder for another Perl programmer to take over the project later for a 5% increase in reliability under someone who knows the whole custom installation and configuration process, you'll be canned and for good reason.

Long before this distro showers, I always knew that the "standard" Perl module directory started with /usr/lib/perl5. Whenever I installed Perl myself, I never felt the need to reconfigure @INC or other stuff, except once or twice for debugging and thread options. Why? Because I always intented to replace Perl (including non-core modeuls, if any) came with the distro. Before I leave this old history, just in case it rang a bell, I just want to emphasize that "I always wonder why Linux distros...." is not a real question. I can understand the reason behind distros decision, I just don't like the result.

You don't really ever know where the "standard" Perl module directory is, do you?

If you really asked me refering to the Perl installation shipped with a random distro, my answer was: I would never be sure until I did some test or lookup.

So, put the long story short, eventually, only this application in this particular distribution that sets @INC in such way. I believe this @INC hackery (borrowed from Tanktalus) won't affect other systems I don't need or don't have any interest to control.

I know it's against common practices, it's against my standard practices as well. I think the hard part with my OP is that it tries to force a frame, unusual frame of thinking. Now I can see it fails :-) That's why I said earlier that "Let's put aside for a while the debate around....". I kinda expected typical reactions I got so far, which I'm grateful for because it lets me know my sanity level (or, is it my insanity level?)

If you can make your system ten times as reliable by breaking convention, then do it and document the decision process

I will, and thanks for reminding me. My OP is absolutely part of the docs :) The lengty was mostly to accommodate my intention to share what I went through during the process of the decision making. The part I apologized because I realized it might end up useless to anybody else.

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Open source softwares? Share and enjoy. Make profit from them if you can. Yet, share and enjoy!

It is kind of a pain to install a second perl alongside the distro's perl installation to keep from breaking things, but I've found it worthwhile for the polish and reliability I get with the management tools for my distro.

I don't think your original post fails at all. I'm a big believer that common wisdom should be used in common situations, but that sometimes it falls down. You just need to be careful about when and how you break the rules and make sure there's actual benefit from it. I can't speak to your case very directly, because I'm not as familiar with your situation as you are. From what you've said, though, you may have one of those situations in which it's worthwhile to write an exception in your local copy of the rules. Just be sure you write it legibly, and, well, cover your behind.

If you want to be sure certain modules are loaded from your application library, you can set @INC to include only the application library (or libraries as the case may be) rather than prepending the application library. In this way, if the module isn't in the application library it isn't loaded. For example:

#!/usr/bin/perl
#
use strict;
use warnings;

BEGIN {
    local @INC = ( "/opt/app/lib" );
    eval "use Application::Module";
}
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If the modules in your application library use modules from the standard library and assume a default @INC, then you can't change @INC when you use them but you can check %INC after they are loaded to ensure they are loaded form the correct location.

For example, if you wanted to load a patched version of File::Find from your application directory and fail if it was accidentally omitted from there you could do something like the following:

#!/usr/bin/perl
#
use strict;
use warnings;

use constant APPLIB => "/opt/app/lib";
use lib APPLIB;
use File::Find;
substr($INC{'File/Find.pm'},0,length(APPLIB)) eq APPLIB
    or die "File::Find incorrectly loaded from " . $INC{'File/Find.pm'
+};
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