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Fri, 3 Sep 2010

Travelling in time: the CP2000AN

My mad experiment in CPAN mirrors has grown a couple of new tentacles. Previously it could be a perl-X.Y.Z-specific mirror, such as the CP5.6.2AN, or an OS-specific mirror such as the cpMSWin32an. Now it can combine the two such as in the CP5.8.8-irixAN and all of those can optionally be combined with a date/time to only include stuff that was already on the CPAN as at that time, such as at the CP2000AN.

Why do this? Let's assume that you have a large complex application which uses lots of stuff from the CPAN, and depends on Elk version 1.009 and ListOfDogs version 5.1, and will break with any later version of Elk (or of ListOfDogs). You get a feature request from a user, and think "ah-ha, there's a module for that", and so you go to install Some::Module. Unfortunately, the latest version of Some::Module depends on Some::Other::Module which in turn needs Another::Module which needs Elk 1.234, so your CPAN client merrily upgrades Elk, breaking everything. Doom and Disaster. Having a CPAN "mirror" nailed to the date of the last release of Elk and ListOfDogs that works for you will save you from pain, suffering, and the Dark Side. Either you'll get older versions that Just Work, or you'll get nothing, and nothing is far better than breaking everything!

Posted at 00:46 by David Cantrell
keywords: geeky | perl
Permalink | 1 Comment

Dave, this is just *awesome*

I used some of your code when sussing out my own solution for being able to reproduce a client's production systems running some ancient CentOS and perl and it looks like you've since taken it to the next level!

Something I've built that might be useful (though I have yet to finish it) is BackPAN::Version::Discover Which attempts to figure out exactly which versions of which dists you've installed and are using on an existing system, based on the modules it finds.

Posted by Hercynium on Fri, 3 Sep 2010 at 18:17:52


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