Install Ruby

The next step is to install Ruby. It’s possible that your system already has it; try running

to see the version number. Rails 3 requires Ruby 1.8.7 or later and works best with Ruby 1.9.x. This tutorial assumes that most readers are using Ruby 1.9.2 or 1.9.3, but Ruby 1.8.7 should work as well (although there is one syntax difference, covered in Chapter 4, and assorted minor differences in output).

       As part of installing Ruby, if you are using OS X or Linux, I strongly recommend using Ruby Version Manager (RVM), which allows you to install and manage multiple versions of Ruby on the same machine. (The Pik project accomplishes a similar feat on Windows.) This is particularly important if you want to run different versions of Ruby or Rails on the same machine. If you run into any problems with RVM, you can often find its creator, Wayne E. Seguin, on the RVM IRC channel (#rvm on freenode.net).10 If you are running Linux, I particularly recommend the installation tutorial for Linux Ubuntu and Linux Mint by Mircea Goia.

      After installing RVM, you can install Ruby as follows:11

 Here the first command updates and reloads RVM itself, which is a good practice since RVM gets updated frequently. The second installs the 1.9.3 version of Ruby; depending on your system, it might take a while to download and compile, so don’t worry if it seems to be taking forever.

        Some Linux users report having to include the path to a library called OpenSSL:

On some older OS X systems, you might have to include the path to the readline library:

(Like I said, lots of things can go wrong. The only solution is web searches and determination.)

   After installing Ruby, you should configure your system for the other software needed to run Rails applications. This typically involves installing gems, which are self-contained packages of Ruby code. Since gems with different version numbers sometimes conflict, it is often convenient to create separate gemsets, which are selfcontained bundles of gems. For the purposes of this tutorial, I suggest creating a gemset called rails3tutorial2ndEd:

This command creates (--create) the gemset rails3tutorial2ndEd associated with Ruby 1.9.3 while arranging to start using it immediately (use) and setting it as the default (--default) gemset, so that any time we open a new terminal window the 1.9.3@rails3tutorial2ndEd Ruby/gemset combination is automatically selected. RVM supports a large variety of commands for manipulating gemsets; see the documentation at http://rvm.beginrescueend.com/gemsets. If you ever get stuck with RVM, running commands like these should help you get your bearings: