Supporting Multiple Versions of Ruby on OSX 10.6.7

I wanted a clean way of upgrading the default ruby 1.8.7 installation on my new Mac OSX 10.6.7 host, and couldn’t locate a decent explanation. As a result I’ve spent surprisingly little time unpicking the dependencies and getting my shiny new ruby 1.9.x installation sorted. Here’s how I achieved that. (Please note you need to have XCode installed if you plan to build the ruby installation from source.)

Firstly it’s important to understand the landscape when considering this upgrade. Firstly, the existing 1.8.x ruby installation exists in the /System/Library/Frameworks/Ruby.framework location. Beneath that root folder is a Versions folder. Versions contained another folder called 1.8 (referring to the version of ruby contained therein) and a symlink by the name of Current, which pointed to that 1.8 folder.

Decision 1: Seemed like a good idea to place all my future versions of ruby in version-aware subfolders in this …/Ruby.framework/Versions folder.

Next thing to understand is that all of the key commands relating to using the ruby framework (e.g. ruby, gem, irb, erb, …) live in the /usr/bin folder. Each of these commands are symlinks to executable files within the current ruby framework subtree. The convention here can be seen in this example:

/usr/bin/ruby -> /System/Library/Frameworks/Ruby.framework/Versions/Current/usr/bin/ruby

Next thing to understand is that all of the key commands relating to using the ruby framework (e.g. ruby, gem, irb, erb, …) live in the /usr/bin folder. Each of these commands are symlinks to executable files within the

Decision 2: If I correctly install all my subsequent versions of ruby into this same location then it should be possible for me to simply modify the Current symlink in the …/Ruby.framework/Versions folder to set the active ruby version I wish to use. All /usr/bin dependencies can simply resolve to the correct subfolder beneath the frameworks root.

Next I downloaded the latest source distribution from somewhere, in my case I used the 1.9.2 source from here (http://www.ruby-lang.org/en/news/2010/12/25/ruby-1-9-2-p136-is-released/). After downloading and unpacking into a temporary folder, I then executed the following commands from the root of the ruby source folder structure:

1. sudo mkdir /System/Frameworks/Library/Ruby.framework/Versions/1.9.2/usr to create the new version subtree root.
2. ./configure –prefix=/System/Frameworks/Library/Ruby.framework/Versions/1.9.2/usr to instruct the make utility to use my new installation folder for the deployment of the newly compiled binaries.
3. sudo make && make install to create my new subtree and binaries beneath my newly created target.

When all that is done, assuming it goes OK, you will have all the necessary ruby executables in the subfolders beneath …/1.9.2/usr location but your system will still be set to use the ‘Current’ version which in my case was the pre-installed 1.8.7 version.

Final thing to do is to re-link the …/Ruby.framework/Versions/Current link to the 1.9.2 folder. I simply executed the following from the …/Ruby.framework/Versions folder:

1. sudo unlink Current
2. sudo ln -s 1.9.2 Current

When I now run my ruby commands – they report the correct version of 1.9.2. When and if I decide to revert to another version I can simply modify this Current link, and that can be made even easier with some alias’s and other bash helpers.

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