2020 twenty four merry days of Perl Feed


CPAN::Mini - 2020-12-11

2020 has been time consuming - a global pandemic, giant fires, horrific floods and political unrest - which has left us little time for side projects. This year we're looking back to happier times into the 20+ year archive with the Best of the Perl Advent Calendar.

As you can probably guess, I like CPAN. I've come to rely on the fact that I have thousands of modules at my fingertips that enable me to do a wide range of stuff using other people tools. Which is a bit of a problem when I'm working offline. There's nothing more frustrating when you're coding Perl than hacking on a quick script and thinking something like "It'd be nice to use DBD::SQLite to store this data" then discovering it's not installed, and you're offline so you can't download it.

What I actually want is a copy of CPAN on my laptop so that I can always install modules whenever I want. Of course, CPAN is big - several gigabytes - and I don't really have the patience to download the whole thing using rsync. Rather than the whole thing, I just need the latest version of each module - on the odd occasion I want an older version of a module I can wait till I'm back online.

Enter the minicpan script, part of CPAN::Mini. This script creates (and update) a small - but perfectly usable - local copy of CPAN. I'm never going to be stuck up the proverbial creek without a Perl module to paddle with again.

Creating a mirror of CPAN couldn't be easier. First you need to install CPAN::Mini with the cpan shell (or use cpanplus if you prefer)

  travis:~ mark$ sudo cpan
  cpan shell -- CPAN exploration and modules installation (v1.76)
  ReadLine support enabled

  cpan> install CPAN::Mini

Then you need to work out which CPAN you're going to mirror from and where you're going to store it locally. The former is easy - you can either go to the list of mirrors on cpan.org, or you can just set it to be whatever you set the cpan shell to use:

  bash$ sudo cpan
  cpan shell -- CPAN exploration and modules installation (v1.76)
  ReadLine support enabled</pre>

  cpan> o conf urllist

Where you put your local mirror isn't really important - anywhere that's got half a gigabyte of free space will do. I put mine in my webserver's document root (/Library/WebServer/Documents/CPAN) so it can be accessed from a webbrowser if I need to.

All that's left for us to do now is run the minicpan command passing the remote server with -r and the local location with -l.

  bash$ minicpan -r ftp://ftp.demon.co.uk/pub/CPAN/ \
                 -l /Library/WebServer/Documents/CPAN

This'll then chug away for a fair old time downloading the CPAN indexes and every file pointed to in the indices (with the exception of new versions of Perl or Ponie). A few days later when you want to update your mirror you just need to run the same command again:

  bash$ minicpan -r ftp://ftp.demon.co.uk/pub/CPAN/ \
                 -l /Library/WebServer/Documents/CPAN</pre>

And it'll redownload these indices, download any new files and delete any files that it's previously downloaded that aren't needed anymore. It'll be much much quicker this time as probably only a few modules will have been released for the first time or updated in that time period.

Using Your New Mirror

If you want to quickly configure the cpan shell to use the mirror (if for example you're offline at the time) then you can tell it to use your mirror for the rest of the session

  bash$ sudo cpan
  cpan shell -- CPAN exploration and modules installation (v1.76)
  ReadLine support enabled</pre>

  cpan> o conf urllist unshift file:///Library/WebServer/Documents/CPAN/

If you want to always use your mirror (which will be much much quicker but you'll have to remember to keep it up to date) you can then save that new configuration:

  cpan> o conf commit

And that's it! You now have a fast copy of CPAN that you can use wherever you are.

Gravatar Image This article contributed by: Mark Fowler <mark@twoshortplanks.com>