From: "Jesús Gabriel y Galán" <jgabrielygalan@...>
Date: 2010-08-10T06:58:00+09:00
Subject: Re: Overriding ENV[]

On Mon, Aug 9, 2010 at 11:01 PM, Jos Backus <jos@catnook.com> wrote:
> $ cat x
> #!/usr/bin/env ruby
> class << ENV
>  define_method(:[], lambda { |v| v.upcase })
> end
> p ENV['FOO']
> $ FOO=foo ./x
>  "FOO"
> $
>
> But what if I want to call the original ENV[] inside the new method?

You can use alias_method like this:

irb(main):001:0> a = [1,2,3]
=> [1, 2, 3]
irb(main):005:0> class << a
irb(main):006:1> alias_method :old, :[]
irb(main):007:1> end
=> #<Class:#<Array:0x2932038>>
irb(main):008:0> a.old(0)
=> 1
irb(main):009:0> class << a
irb(main):010:1> def [](val)
irb(main):011:2> old(val).to_s.upcase
irb(main):012:2> end
irb(main):013:1> end
=> nil
irb(main):014:0> a[0]
=> "1"

I tested with an array, but ENV should work too.