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Basic Perl Configuration

In essence, this section is nothing more than a quick and dirty explanation of how to install modules in Perl. I may well include a more detailed section on perl at a later date, given that it will also be the basis of the sample application on the cluster, but module installation is not something that is explicitly addressed as often as it should be, and if you're not familiar with perl it is likely something that will hold you up.


There are two primary ways to install modules in perl: the cpan module and downloading the desired module, compiling it, and installing it. (Actually, there is a third method that can be used if you've installed the perl distribution packaged by ActiveState Corporation, and there may be other analogous methods with the versions of perl that are maintained by other corporations, but the two I'm going to describe should probably be considered the basic ones, especially in the linux world.)


The CPAN module is part of the basic perl distribution, and if your computer has a direct internet connection it is the easiest way to install modules, providing a command-line interface to module installation from the Comprehensive Perl Archive Network (CPAN), but may not always work. To use this installation method simply issue the command "perl -MCPAN -e shell". When you first start the utility on any given machine you will launch into a configuration script that sets your preferences for the manner in which the module should work on your machine. For the most part you can let the defaults ride, but when you are asked how the module should handle prerequisite modules (modules required for the functioning of the module you are trying to install) I would suggest that you respond with either "follow" or "ask". "Follow" will automatically install any requisite modules will "ask" will prompt you to confirm their installation. When I first started using this method of module installation I routinely specified "ask", but as the list of required modules can on occasion prove lengthy I've recently started setting this to "follow" to allow the process to proceed automatically, and to this point there have been no problems that I've experienced as a result of the change. The only setting you absolutely must specify is the location(s) of the cpan mirror(s) from which the modules should be retrieved. You can choose from a large number of alternative sites, and can readily choose all of them if you wish to go to that trouble. Generally, however, you should choose more than one, and it is suggested that you choose sites near you. Most sites are academic, so my personal strategy has been to select two nearby academic sites and a commercial site in Mexico. This has proved to be effective. The business day in Mexico is oriented somewhat later than the business day in the U.S., so when the academic mirrors in the U.S. do not have available connections I've generally been able to get a connection from the Mexican site. Once the module is configured, installation is as simple as typing "install whatever". Note that the module is case-sensitive and not tolerant of variations in module specification. For example, there is a new version of the CPAN module available, and when you start the shell it will urge you to install the new one, Bundle::CPAN. Trying "install bundle::cpan" or "install Bundle:CPAN" will not work, it has to be "install Bundle::CPAN". That is just the way it is.


If this automatic module installation fails, or if you are downloading the modules manually and don't wish to deal with the network overhead associated with routine updates of the module lists, etc., you can simply download the gzipped tarball of the module source from CPAN and extract it on your machine. Once you've done that, go into the created directory and take a look at the README and INSTALL files. It is a very good idea to actually do that. I would say that in 20-30% of module installations, the information contained therein will save you anywhere from 5 minutes to half of a day and you may not be able to install at all until you do what it says. For the most part, however, all you have to do is make sure you're logged in as root, from the source directory type "perl Makefile.PL" ... spelled just like that ... then type "make", "make test", and "make install". These are the same scripts that are called by the cpan module, here you're running them independently. Most of the time this is all you need to do .... most of the time. (evil grin)