From: Brian Candler <b.candler@...>
Date: 2009-03-31T18:13:33+09:00
Subject: Re: REG: How can we debug a ruby script

Something in your environment is making ruby do -rubygems (require 
'rubygems')
Perhaps the RUBYOPT environment variable is set, because I can replicate 
your problem like this:

$ export RUBYOPT=-rubygems
$ ruby -rdebug fact.rb
Debug.rb
Emacs support available.

/usr/local/lib/site_ruby/1.8/ubygems.rb:10:require 'rubygems'
(rdb:1)

So if this is the case, solution 1 is simply to unset the RUBYOPT 
variable.

Solution 2 is to set a breakpoint at the start of your program.

$ ruby -rdebug fact.rb
Debug.rb
Emacs support available.

/usr/local/lib/site_ruby/1.8/ubygems.rb:10:require 'rubygems'
(rdb:1) b fact.rb:1
Set breakpoint 1 at fact.rb:1
(rdb:1) cont
Breakpoint 1, toplevel at fact.rb:1
fact.rb:1:def fact(n)
(rdb:1) n
fact.rb:9:print fact(2), "\n"
(rdb:1) n
2
$

Solution 3 is to require rubygems *before* requiring debug, because when 
it has been required once, it won't be required again:

$ ruby -rubygems -rdebug fact.rb
Debug.rb
Emacs support available.

fact.rb:1:def fact(n)
(rdb:1)

This third one probably involves the least work.
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