$ ruby --version
ruby 1.8.6 (2007-06-07 patchlevel 36) [universal-darwin9.0]
$ curl ftp://ftp.ruby-lang.org/pub/ruby/1.8/ruby-1.8.7-p71.tar.gz | tar xz
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100 4692k  100 4692k    0     0  47090      0  0:01:42  0:01:42 --:--:-- 32309
$ cd ruby-1.8.7-p71/
$ ./configure
[...]
creating config.h
configure: creating ./config.status
config.status: creating Makefile
$ make test
[...]
test succeeded
ruby-1.8.7-p71 $ sudo make install
Password:
./miniruby -I./lib -I.ext/common -I./- -r./ext/purelib.rb  ./instruby.rb --make="make" --dest-dir="" --extout=".ext" --mflags="" --make-flags="" --data-mode=0644 --prog-mode=0755 --installed-list .installed.list --mantype="doc"
installing binary commands
installing command scripts
installing library scripts
installing headers
installing manpages
installing extension objects
installing extension scripts
$ ruby --version
ruby 1.8.6 (2007-06-07 patchlevel 36) [universal-darwin9.0]
$ ./ruby --version
ruby 1.8.7 (2008-08-08 patchlevel 71) [i686-darwin9.0.0]
$ mate Makefile
$ /usr/local/bin/ruby --version
ruby 1.8.7 (2008-08-08 patchlevel 71) [i686-darwin9.0.0]
$ sudo rm
$ sudo rm `which ruby`
$ which ruby
/usr/local/bin/ruby
$ ruby --version
ruby 1.8.7 (2008-08-08 patchlevel 71) [i686-darwin9.0.0]