Gotcha: rvm and No binary rubies available for: ubuntu/12.04/x86_64/ruby-1.8.7

I'm working with a legacy rails system. We're still stuck on Rails 2.3.2 (yes really) and ruby 1.8.7 (it's better than 1.8.6 which we were on only a few months back).

I've just been given a new computer at work (finally) and it has ubuntu 12.04 - and I was trying to set it up with a rails stack. For which I can strongly recommend Ryan Bigg's howto article: Ubuntu, Ruby, RVM, Rails, and You

I got through the tutorial ok, happily installed ruby 1.9.3... but when I tried to install 1.8.7, I hit a snag.

    triton:[~]% rvm install 1.8.7
    Searching for binary rubies, this might take some time.
    No binary rubies available for: ubuntu/12.04/x86_64/ruby-1.8.7-p374.
    Continuing with compilation. Please read 'rvm help mount' to get more information on binary rubies.
    You requested building with 'gcc-4.4' but it is not in your path.

According to rvm, you can list the set of available rubies using rvm remote which gave me:

    # Rubies available for 'ubuntu/12.04/x86_64':
    
       ruby-1.9.3-p194
       ruby-1.9.3-p286
       ruby-1.9.3-p327
       ruby-1.9.3-p362
       ruby-1.9.3-p374
       ruby-1.9.3-p392
       ruby-1.9.3-p429
       ruby-1.9.3-p448
       ruby-2.0.0-p0
       ruby-2.0.0-p195
       ruby-2.0.0-p247

Ruh-roh!

Now, I know 1.8.7 is ancient news, but I didn't think they'd drop support for it so entirely.

I went wandering about looking for a way to specify an older repository - perhaps the 10.04 repo would still have 1.8.7 in a useable format...

Turns out I'd just made a simple mistake, easily rectified.

The important clue was in the last line of the result for rvm install:

You requested building with 'gcc-4.4' but it is not in your path.

I'd copied a whole bunch of things across to the new 'puter, including my .zshrc file - which is what was specifying the gcc version (can't remember why). And on the new 'puter I had gcc version 4.6 but my .zshrc (copied from my previous computer) was pointing at this older version.

Because of this small mistake, rvm thought I didn't have a c-compiler. Which means that rvm wasn't able to install any rubies from source - only pre-compiled rubies - which means it was restricted to only those already pre-compiled for my platform (ie 64-bit ubuntu 12.04).

oops.

When I fixed the gcc line in my .zshrc - rvm was able to figure out how to install+compile source-code rubies - including v1.8.7