'sudo gem install' or 'gem install' and gem locations
Contrary to all the other posts I suggest NOT using sudo when installing gems.
Instead I recommend you install RVM and start a happy life with portable gem homes and different version of Ruby all living under one roof.
For the uninitiated, from the documentation:
RVM is a command line tool which allows us to easily install, manage and work with multiple ruby environments and sets of gems.
The reason why installing gems with sudo is worse than just gem install is because it installs the gems for ALL USERS as root. This might be fine if you're the only person using the machine, but if you're not it can cause weirdness.
If you decide you want to blow away all your gems and start again it's much easier, and safer, to do so as a non-root user.
If you decide you want to use RVM then using sudo will cause all kinds of weirdness because each Ruby version you install through RVM has its own GEM_HOME.
Also, it's nice if you can make your development environment as close to your production environment as possible, and in production you'll most likely install gems as a non-root user.
You can also install gems in your local environment (without sudo) with
gem install --user-install <gemname>I recommend that so you don't mess with your system-level configuration even if it's a single-user computer.
You can check where the gems go by looking at gempaths with gem environment. In my case it's "~/.gem/ruby/1.8".
If you need some binaries from local installs added to your path, you can add something to your bashrc like:
if which ruby >/dev/null && which gem >/dev/null; then PATH="$(ruby -r rubygems -e 'puts Gem.user_dir')/bin:$PATH"fi
Better yet, put --user-install in your ~/.gemrc file so you don't have to type it every time
gem: --user-install