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Sunday, 20 October by David Farrell
CPAN mirrors are online repositories which host or "mirror" the Perl module distributions on CPAN. There are hundreds of CPAN mirrors dispersed throughout the World. When the CPAN program is run for the first time on a machine, it will configure the CPAN mirror list to use for checking for new versions of modules and downloading Perl distributions. All CPAN mirrors are not created equally though: the distribution list's age, speed and the geographic location vary from mirror to mirror and so you may want to re-configure your local CPAN mirror list to suit your needs. This article describes how to find CPAN mirrors and edit the local CPAN mirror configuration.
An online list of public CPAN mirrors can be found here. The list is frequently updated and lists mirrors by location, the scheme used (ftp, http), the age of the module list and some test results. Viewing this list you can see that some mirrors do not refresh their module list for days at a time - if you are using these mirrors you could be missing out on the latest version of your favourite module! A JSON formatted CPAN mirror list can be found here.
Once you have identified the URLs of the CPAN mirrors you want to use, fire up the terminal and load the cpan shell:
cpan cpan shell -- CPAN exploration and modules installation (v2.00) Enter 'h' for help. cpan>
The CPAN mirror list is stored in the "urllist" variable. To view the list of mirrors, type "o conf urllist" in the CPAN shell:
cpan>o conf urllist urllist 0 [http://httpupdate3.cpanel.net/CPAN/] 1 [http://httpupdate23.cpanel.net/CPAN/] 2 [http://mirrors.servercentral.net/CPAN/] 3 [ftp://cpan.cse.msu.edu/]
To add a CPAN mirror use the "unshift" or "push" functions to add the mirror's url to the front or end of the mirror list. Make sure that the URL for the mirror includes the scheme (http, ftp).
cpan> o conf urllist push http://mirror.waia.asn.au/pub/cpan/
To remove a CPAN mirror use the "shift" or "pop" functions to remove the mirror URL from the front or end of the mirror list:
cpan> o conf urllist pop
To overwrite the existing mirror list with a new one, just provide the URLs to the new mirrors as a space separated list:
cpan> o conf urllist http://mirror.waia.asn.au/pub/cpan/ ftp://mirrors.coopvgg.com.ar/CPAN/
Once you have updated the CPAN mirror list, make sure you commit the changes to file so they are saved beyond the current session:
cpan> o conf commit commit: wrote '/home/sillymoose/.cpan/CPAN/MyConfig.pm'
You can also edit the CPAN config file directly. For local user Perl installations this is */CPAN/MyConfig.pm and system Perl installations */CPAN/Config.pm (the parent directory will depend on the platform). When editing the file, urllist is a hash key for an array reference of mirror urls. Note the urls are quoted using Perl's quoting operator ("q"). Simply edit and save the file.
'urllist' => [ q[http://httpupdate3.cpanel.net/CPAN/], q[http://httpupdate23.cpanel.net/CPAN/], q[http://mirrors.servercentral.net/CPAN/], q[ftp://cpan.cse.msu.edu/] ],
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