The narf executable is quite useful.  It can parse .narf files:

    <? puts "hello world" ?>

Also, it will print syntax errors to the screen.  To compile, run this from the project root (./narf):

    ruby build.rb compile

The compiled binary will be in

    ./narf/bin/narf

Copy this file where ever you like, make it executable, and tell apache to run it with a shebang:

    #!/usr/local/bin/narf

Mac OS X Note: If you get this message with compiling:

    ld: Undefined symbols:

You may need to re-compile ruby with --enable-shared:

    http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/47248
