Accessing the default path for the user keychain folder via terminal

Ruby "Gems" are not generally applications, most often they are libraries. From the Ruby Gems website

1.1 Really Quick Start Question: I’ve installed RubyGems and I want to install Rails (for example). How do I do that?

Answer:

gem install rails

1.2 What is a Gem?

A gem is a packaged Ruby application or library. It has a name (e.g. rake) and a version (e.g. 0.4.16).

(emphasis mine)

Also, see this information on how to inspect a gem:

2.5 Looking at an installed gem When you run

gem specification  progressbar
# shortcut: gem spec progressbar

you will see all the details of the ’’progressbar’’ gem.

You should consult the documentation which came with the gem, or, post more details so we can assist you more.

Even administrator users should use sudo -s or sudo chmod /Library/Webserver since the default group structure on OS X is to protect system resources from modification without the logging the privilege escalation. You will need to be an administrator of the mac to use sudo, so you can always su to an existing admin account first before using sudo.