I have just installed ruby 1.9.1-p429 with macports. Every time I use it, it displays this error message:
$ ruby1.9 -e "puts 'hi.'"
Error loading gem paths on load path in gem_prelude
can't modify frozen string
<internal:gem_prelude>:69:in `force_encoding'
<internal:gem_prelude>:69:in `set_home'
<internal:gem_prelude>:38:in `dir'
<internal:gem_prelude>:76:in `set_paths'
<internal:gem_prelude>:47:in `path'
<internal:gem_prelude>:286:in `push_all_highest_version_gems_on_load_path'
<internal:gem_prelude>:355:in `<compiled>'
hi.
It’s a bug: see bug report here
I don’t know if either is available from MacPorts, but Ruby 1.9.1-p378 and 1.9.2-rc1 are both free of the problem.
If you haven’t already tried it, I highly recommend rvm for multiple Ruby interpreters.