695> sudo gem install -r oniguruma
Bulk updating Gem source index for: http://gems.rubyforge.org
Select which gem to install for your platform (i686-darwin8.9.1)
1. oniguruma 1.1.0 (ruby)
2. oniguruma 1.1.0 (mswin32)
3. oniguruma 1.0.1 (ruby)
4. oniguruma 1.0.1 (mswin32)
5. Skip this gem
6. Cancel installation
 > 1
Building native extensions.  This could take a while...
ERROR:  While executing gem ... (Gem::Installer::ExtensionBuildError)
     ERROR: Failed to build gem native extension.

ruby extconf.rb install -r oniguruma
checking for main() in -lonig... no
creating Makefile

make
gcc -I. -I. -I/usr/local/lib/ruby/1.8/i686-darwin8.9.1 -I.  -fno- 
common -Wall  -c oregexp.c
oregexp.c:2:23: error: oniguruma.h: No such file or directory
oregexp.c:9: error: parse error before 'regex_t'
oregexp.c:9: warning: no semicolon at end of struct or union
oregexp.c:10: warning: type defaults to 'int' in declaration of  
'ORegexp'
oregexp.c:10: warning: data definition has no type or storage class
oregexp.c:15: error: parse error before '*' token

... and so on ...