[Melbourne-pm] CPAN module

Scott Penrose scottp at dd.com.au
Wed Mar 15 01:48:51 PST 2006

On 15/03/2006, at 20:29, Rick Measham wrote:

> Scott Penrose wrote:
>> CPAN & Debian are virtually identical, as is all Package  
>> Management systems.
> I'd disagree here, but am happy to be wrong.
> With apt you can have many repository sources, they are all  
> searched for the highest-version number when you ask to install a  
> given package.

You are agreeing with me :-)

> With CPAN.pm you give it a list of repositories, but that's only  
> for high-availability. The module gets an up-to-date module list  
> from the first repository that is willing to give it. Recently the  
> repository I've been using here in .au stopped updating and so I  
> had no new sources since December 18th. CPAN.pm gave me a warning,  
> but didn't bother checking any other mirror for a more up-to-date  
> list.

Yes sort of. But APT is not a package management system, I wrote that  
wrong, that is dpkg - APT is a repository management system really -  
all about multiple repositories. (this is an oversimplification and  
they run together).

This discussion has been confusing because everyone is mixing their  

CPAN - is a single repository - like Debian.org - not Debian the  
system, not debians package management system DPKG, not the APT  
system for getting multiple repositories downloaded etc etc.

CPAN.pm - is a system for accessing that repository - and it is like  
the old DPKG download system dselect - which was used before APT - it  
was not very flexible.

> When I ask to install a module that list is considered canonical.  
> CPAN.pm does not check any other repository for any other version.  
> You cannot set up a new CPAN repository with a single module and  
> put that at the top of your urllist, and have all other modules  
> installed from the second preference.
> Many apologies if I'm wrong :)

Sort of. CPAN itself is for accessing CPAN. And CPAN is not a System  
like APT, which is designed to have multiple repositories. CPAN IS  
the repository. It is like having a repository (in debian anyway)  
called "debian-unofficial" - that is the name of the repository. The  
name of the CPAN repository is CPAN.

Package management systems are usually broken up into three things.

1) The repository - of which you can have many
2) The collection system (not sure of the right name for this thing)  
- of which you can have many
	eg: apt is one for Debian which works with others in concurrency
3) The package management/install system - there must be only one of  

In Debian these are:

1) (simplified) debian.org, debian-unofficial.org, cdrom, etc
2) apt, dselect, (there used to be heaps others but apt is so good we  
just use that now)
3) dpkg

In Perl these are usually:

1) CPAN & Manually installed
2) CPAN (only really works with CPAN, but see previous post for  
alternatives) & Manual
3) Perl Modules (it is self managed and can even have multiple  
versions installed at once)

But of course this is an over simplification - what about APT &  
Debian - they too can install Perl Modules.

So to answer Mathew's original question - he can use APT or GenToo or  
RPM or MakeUpYourOwnModule or the CPAN modules I mentioned to manage  
his repository.

But... that is not CPAN.

So Rick - yes you are right CPAN is really the repository and it  
comes with a free tool to get stuff - but people have extended it to  
be both part 1 and part 2 - but what matters is part 3 - and you can  
have multiple concurrent paths to part 3.

CPAN - Comprehensive Perl Archive Network - NOT a package management  
system - a repository.

* - *  http://www.osdc.com.au - Open Source Developers Conference * - *
Scott Penrose
VP in charge of Pancakes
scottp at dd.com.au

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