Category: Ruby on Rails

If you are running RVM and have the MySQL Community edition database on your Mac, you will need the MySQL2 gem to access it from Rails. If you install the Gem (gem install mysql2), and then try to start WEBrick, you get this scary error:
[bash]
/Users/cosjef/.rvm/gems/ruby-1.9.2-p290/gems/mysql2-0.3.7/lib/mysql2.rb:9:in `require’: dlopen(/Users/cosjef/.rvm/gems/ruby-1.9.2-p290/gems/mysql2-0.3.7/lib/mysql2/mysql2.bundle, 9): Library not loaded: libmysqlclient.18.dylib (LoadError)[/bash]
To fix this error, run the following command, ensuring that the ~/.rvm path to the MySQL 0.3.7 bundle file listed below is accurate for your system:
[bash]sudo install_name_tool -change libmysqlclient.18.dylib /usr/local/mysql/lib/libmysqlclient.18.dylib ~/.rvm/gems/ruby-1.9.2-p290/gems/mysql2-0.3.7/lib/mysql2/mysql2.bundle[/bash]
Note that this command must be run with the “sudo” prefix (which will require a password) in order to write to the required files. You should then be able to start WEBrick successfully.

I was working through Exercise 35 of  Zed Shaw’s excellent tutorial Learn Ruby the Hard Way when I hit question three in the Extra Credit section.  There he instructs you to “Write comments for the functions you do not understand. Remember RDoc comments?”  And when I Googled for how to use RDoc, nothing really jumped out. Here’s how difficult it is:

In the directory containing your Ruby file, type:

"rdoc <name_of_ruby_file"

That’s it.

That command kicks off a small set of actions, including a scan of your code. Note that it found only a single class, and lists many items as “undocumented.”

The command also creates a “doc” directory containing HTLM, CSS, and Javascript files for presenting documentation of your code.

Opening the index.html file you find in that directory will reveal your documented code:

RDoc has cleanly listed out the objects it found in your file, as well as the methods it discovered. Clicking on any of the method names drills down into more detail, including showing the method code itself:

All this was generated with one simple command.  To truly unlock the power of RDoc, you need to add a few more detailed comments to your code. Such comments allow RDoc to provide much greater detail on the code itself, and remove the “undocumented” response when you build your RDoc documentation.

It will also help anyone in the future who wants to implement your code-which is the whole point of RDoc.

CentOS 6 ships with updated version of Ruby (version 1.8.7), but does not include the flexibility provided by the Ruby Version Manager (RVM). You will definitely want to use RVM, as it lets you easily manage the roll-forward and roll-back of Ruby and associated Gemsets. Assuming you begin with a Minimal installation of CentOS 6, here is how you install RVM:

1) Install the base packages Ruby needs (all 115 of them)

yum groupinstall "Development Tools"

2) Install NTP and force a time update.

yum install ntp
ntpdate tick.gatech.edu

3) Install zlib and sqlite3

yum install zlib zlib-devel sqlite-devel

4) Download and install RVM

bash < <(curl -s https://rvm.beginrescueend.com/install/rvm)

UPDATE:
bash -s stable < <(curl -s https://raw.github.com/wayneeseguin/rvm/master/binscripts/rvm-installer)

Once installed, log out of your SSH session, then log back in.
5) Verify your RVM installation. You should see “RVM is a function” echoed back.

type rvm | head -1

6) Install Ruby version 1.9.2

rvm install 1.9.2

7) Set version 1.9.2 to be the default Ruby version.

rvm use 1.9.2 --default

8) Verify your version of Ruby is 1.9.2

ruby -v

9) Install Rake gem

gem install rake

10) Install Rails gem

gem install rails

11) Verify Rails install

rails -v

12) Install SQLite gem

gem install sqlite3

You should now have a fully functioning Ruby development environment for your CentOS Linux server.