From: Joel VanderWerf <vjoel@...>
Date: 2008-07-07T06:11:01+09:00
Subject: Re: Accessing variables when loading a file to irb

Ib Lis wrote:
> Hi
> I'm new to Ruby. Coming from Perl I really do enjoy the syntax and...
> irb.
> 
> When I load a file, classes are loaded but not the variables set in the
> file.

Normally(*) in ruby you can't get at the local vars in a file:

$ cat x.rb
x = 4
$ ruby -e 'eval File.read("x.rb"); p x'
-e:1: undefined local variable or method `x' for main:Object (NameError)

However, irb is a little different from ruby:

$ irb
irb(main):001:0> eval File.read("x.rb"); x
NameError: undefined local variable or method `x' for main:Object
         from (irb):1
irb(main):002:0> x
=> 4

Note that x is undefined if you use it in the same line that defines it, 
but x is defined thereafter. This is because irb parses the whole line 
at a time before executing it. After the eval, x is defined in irb's 
scope. That's special to irb--doing the same eval in a separate file 
doesn't work:

$ cat y.rb
eval File.read("x.rb")
p x
$ ruby y.rb
y.rb:2: undefined local variable or method `x' for main:Object (NameError)

-------------------------
(*) However:

$ cat x2.rb
x = 4
$scope = proc{}

$ ruby -e 'eval File.read("x2.rb"); p eval("x", $scope)'
4

The global is just one way to break out of the scope of the file. You 
could also use a constant.

The global might be best if you are just doing this interactively. If 
you need to load files from a program, and keep their instance (not 
local) variables, constants, and methods in separate scopes, you might 
be interested in these:

http://raa.ruby-lang.org/project/script/
http://raa.ruby-lang.org/project/dynaload/

-- 
       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407