Perl ecosystem or when updating modules inside your Perl ecosystem you do most likely use CPAN or CPANM. CPAN stands for Comprehensive Perl Archive Network and is the default location where a large set of additional modules for the Perl programming language do reside and which you can download. CPAN provides an interactive CLI interface which you can use to install new modules. In essence CPAN is much more then just a tool and a download location, CPAN is a thriving ecosystem where people add new software and modules to the extending CPAN archive on a daily basis. The below image shows how the CPAN ecosystem looks like from a high level perspective;
The warning messages you get when using CPAN might look like the ones below;
"YAML' not installed, falling back to Data::Dumper and Storable to read prefs '/root/.cpan/prefs"
"Warning (usually harmless): 'YAML' not installed, will not store persistent state"
The way to resolve this is very simple, first ensure you have the YAML module installed. If this is the case ensure you inform CPAN that you would like to use YAML, this can be done by excuting the 2 commands below and this should resolve the issue of the repeating warnings when using CPAN.
o conf yaml_module YAML
o conf commit