From: Sam Stephenson <sstephenson@...>
Date: 2005-11-07T08:33:35+09:00
Subject: Lazy fun: Make unary minus silence stderr for backticks

I was reading about mentalguy's lazy.rb and thought it'd be fun to use
lazy evaluation as a vehicle for adding new syntactic sugar to Ruby. 
Here's one such example, which lets you prefix backticks with a unary
minus to silence stderr:

| % irb -r lazy_backtick
| irb(main):001:0> `hello`
| /opt/local/lib/ruby/1.8/irb/workspace.rb:81: command not found: hello
| => ""
| irb(main):002:0> -`hello`
| => ""

lazy_backtick.rb:

| class LazyBacktick < String
|   instance_methods.each {|m| undef_method(m) unless m =~ /^__/}
|
|   def initialize(command)
|     @command, @silence_stderr = command, false
|   end
|
|   def -@
|     @swallow_stderr = true
|     value
|   end
|
|   def method_missing(method, *arguments, &block)
|     value.send(method, *arguments, &block)
|   end
|
| private
|   def value
|     @value ||= evaluate
|   end
|
|   def evaluate
|     real_backtick "#@command#{' 2>/dev/null' if @silence_stderr}"
|   end
| end
|
| module Kernel
|   alias_method :real_backtick, :'`'
|
|   def `(command)
|     LazyBacktick.new(command)
|   end
| end

Note that I'm using the same approach as BlankSlate to remove
LazyBacktick's methods, but inheriting from String instead -- this is
so "String === `foo`" doesn't break. (It would be nice to have a mixin
alternative to BlankSlate.)

The way I'm silencing stderr is a bit, um, agile.  Can it be made to
work in Ruby on Windows without loading an external library (since
open3 doesn't work there)?

Sam