Quoteing ptkwt / aracnet.com, on Fri, Mar 26, 2004 at 09:54:28AM +0900:
> How do you get the up arrow to give prior commands in irb on OSX?
> 
> When I try to use the up arrow I just get garbage characters...

There's a way you can do without recompiling (for 10.2, anyhow).

See:

  http://www.rubygarden.org/ruby?RubyOnMacintosh

Look for "OS X Ruby with readline".

Cheers,
Sam