This is a little old but it was helpful the first time I installed ruby 
on OS X:
http://richkilmer.blogs.com/ether/2003/10/building_ruby_1.html

It has been a while since I compiled and installed readline on my 
system - I am using 4.3, looks like 5.0 is available now:
http://directory.fsf.org/GNU/readline.html
Compiling that from source... installing... works fine.

So I am using Ruby 1.8.2pre2 with readline 5.0 all installed under 
/usr/local.  irb works as expected.
Are you compiling everything from source?
-Charlie

On Sep 28, 2004, at 8:24 AM, James Edward Gray II wrote:

> On Sep 28, 2004, at 10:00 AM, why the lucky stiff wrote:
>
>> In case, you're still strugglin...
>>
>> Chris has a few distribution links:
>> <http://rubyforge.org/pipermail/poignant-stiffs/2004-July/000086.html>
>
> Thanks.  This link explains the Mac OS X problem.  Unfortunately, it's 
> a little dated (focusing on OS X.2).  I'll fiddle around a bit, now 
> that I know what I'm looking for though.
>
> If anybody has managed to get readline working with Ruby 1.8.2pre2 on 
> Mac OS X though, please chime in with the steps...
>
> James Edward Gray II
>
>