If you start from the modules directory on CPAN, you’ll see that the modules are categorized into three subdirectories:
by-authors Modules by author's registered CPAN name by-category Modules by subject matter (see below) by-module Modules by namespace (i.e., MIME)
If you know what module you want, you can go directly to it by clicking on the by-module entry. If you are looking for a module in a particular category, you can find it in the by-category subdirectory. If you know the author, click on by-author. However, if you aren’t familiar with the categories and want to find a module that performs a certain task, you might want to get the file 00modlist.long.html, also in the modules directory. This file is the “Perl 5 Modules List.” It contains a list of all the modules, by category, with a brief description of the purpose of each module and a link to the author’s CPAN directory for downloading.
Here is a list of the Perl Module categories, plus two for modules that don’t fit anywhere else:
02_Perl_Core_Modules 03_Development_Support 04_Operating_System_Interfaces 05_Networking_Devices_IPC 06_Data_Type_Utilities 07_Database_Interface 08_User_Interfaces 09_Language_Interfaces 10_File_Names_Systems_Locking 11_String_Lang_Text_Proc 12_Opt_Arg_Param_Proc 13_Internationalization_Locale 14_Security_and_Encryption 15_World_Wide_Web_HTML_HTTP_CGI 16_Server_and_Daemon_Utilities 17_Archiving_and_Compression 18_Images_Pixmaps_Bitmaps 19_Mail_and_Usenet_News 20_Control_Flow_Utilities 21_File_Handle_Input_Output 22_Microsoft_Windows_Modules 23_Miscellaneous_Modules 24_Commercial_Software_Interfaces 99_Not_In_Modulelist 99_Not_Yet_In_Modulelist
If you are in the by-categories subdirectory and have selected an area from which you’d like to download a module, you’ll find a list of the files in the directory. tar files have a .tar.gz extension, and README files have a .readme extension. You’ll generally find a README file for each module; take a look at it before you decide to download the file.
Here’s a sample directory listing from category 14, under the MD5 directory:
Digest-MD5-2.09.readme Digest-MD5-2.09.tar.gz GAAS GARY MD5-1.5.3.readme MD5-1.5.3.tar.gz MD5-1.6.readme MD5-1.6.tar.gz MD5-1.7.readme MD5-1.7.tar.gz NWINT
You’ll notice that multiple versions are sometimes listed—for example, the MD5 module has Versions 1.5.3 through 1.7 available. Generally, this is to facilitate the transition to a new version of the module.
Select the .readme file of the most current archive and review its contents carefully. README files often give special instructions about building the module; they warn you about other modules needed for proper functioning and if the module can’t be built under certain versions of Perl. If you’re satisfied with what you read, download the file.