From: Robert Klemme <shortcutter@...>
Date: 2008-02-13T01:11:27+09:00
Subject: Re: Ruby equivalent to source command

2008/2/12, Brett Williams <brettandbecky@gmail.com>:
> I am trying to make a "source" command for Ruby (a la sh or tcl), but I
> think lexical scoping is tripping me up.  I've done a lot of reading
> about bindings, and it seems I just can't do what I'm trying to do.
>
> def source(filename, bind = TOPLEVEL_BINDING)
>   code = nil
>   File.open(filename) { |f| code = f.read }
>   eval(code, bind)
> end
>
> This works as I would like, with the exception of local variables
> present in the sourced file.  For example, if I had something like this
> in the sourced file:
>
> x = "value set in sourced file"
>
> then I get an error :  undefined local variable or method 'x'

Can you show more code?  For me it works:

17:05:12 ~
$ echo "x=123; puts x" | ruby -e 'eval(ARGF.read, TOPLEVEL_BINDING)'
123
17:05:18 ~
$ echo "x=123; puts x" | ruby -e 'eval(ARGF.read, binding)'
123
17:05:25 ~
$

Or are you seeing this:

17:05:25 ~
$ echo "x=123" | ruby -e 'eval(ARGF.read, binding); puts x'
-e:1: undefined local variable or method `x' for main:Object (NameError)
17:06:31 ~
$

> unless I extend the scope of x by setting it before sourcing the file.

Like

17:06:31 ~
$ echo "x=123" | ruby -e 'x=1; eval(ARGF.read, binding); puts x'
123
17:07:32 ~
$

This is because local variables are detected at compile time.  That's
why Ruby thinks "x" in my bit above is a method because there is no
assignment.

> Is there any way to accomplish what I want?  I could work around this by
> sticking to instance variables or *gulp* global variables for this
> application, but before I throw in the towel I wanted to throw this out
> to people here.

A global is probably much more appropriate here.  If the code you
source somehow generates configuration settings then maybe you can set
a global Hash that will receive values.  It depends on the larger
context of what you want to achieve.

> P.S.:  Things have changed since I was a pretty regular poster back in
> 2002-2003... ;)

Does this have to do with your email address? ;-)  If yes, congrats
and greetings to Becky!

Cheers

robert


-- 
use.inject do |as, often| as.you_can - without end