poison tooth wrote:
> Grab a text editor and type in the following:
> 
> puts "Hello World"
> 
> Save the file as hello.rb and run it by typing
> ruby hello.rb"

If you just want to make sure that you can run that book example, here 
is a quick low-level solution. In a terminal, run:

  echo 'puts "Hello World"' > hello.rb
  ruby hello.rb

Alternatively, you can run:

  ruby -e 'puts "Hello World"'

As for your program editing troubles, I suggest having a look at the 
Ruby garden (skip down to the "Ruby development environments" section):

  http://wiki.rubygarden.org/Ruby/page/show/RubyOnMacintosh

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