How can I tell if I have these modules already?
In many cases you can type perl -M<module> (e.g, perl -MDigest::MD5) and perl will either pause waiting for input (if you have the module installed) or it will issue an error message (if you don't have it installed). That won't work for libnet or libwww-perl but should work for the other modules you mention.

Also I believe most modules will warn you about existing versions of the same module when you build them.

In reply to Re: How to install Date::Calc on a Mac by jdalbec
in thread How to install Date::Calc on a Mac by cpiety

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