How do I tell CPAN.pm to use an application-specific mini-cpan?

Question

Is there a way to use app-specific mini-CPANs (to ensure specific module versions for different apps and make an install work without net access). The 'standard' mini-cpan way of things relies on setting 'o conf urllist' with a file url in your CPAN/Config.pm

That's fine with one single mini-cpan. However, I need to automate having a CPAN install from a different directory for each app (local to the app), as each app has different version requirements.

The following almost works, but then has only a partially working shell, and still fetches from the web instead of using the mini-cpan from $file_url location:

use CPAN;
use FindBin qw($Bin);

my $file_url="file:///$Bin/../cpan";
CPAN::Shell->o(qw( conf urllist ),$file_url);

CPAN::shell();

Answer 1

You load a different configuration file for each application. The latest cpan command has a -j switch to do just that:

$ cpan -j some/app/Config.pm -i Foo::Bar

This latest feature isn't included in the CPAN.pm distribution yet since it's experimental. I've been using it for several months, however, as part of my DPAN work.

If you don't like any of that, you just have to provide your application-specific CPAN::Config module somewhere Perl will find it before it finds your personal or site-wide version. Copy your current CPAN/Config.pm into your application modules directory and ensure that the directory is first in @INC (perhaps using the PERL5LIB environment variable). CPAN.pm should find that one first and use it. It only uses the first one it finds. This is handy when the configuration is fixed, although it's a bit flexible since you can run code in the module. It's configuration as Perl code.

If that is not good enough for you, you can override CPAN::HandleConfig() in your application so CPAN.pm doesn't load any files. You then set the values yourself. This is especially handy when you have a lot of application logic to resolve to figure out some of the configurations values. The CPAN.pm configuration is just the %CPAN::Config hash, so you just have to set the right values for the appropriate keys.

In any case, you probably want to set the "connect_to_internet_ok" configuration to a false value and clean out your "urllist" to have only the local minicpans.