From: ptkwt@...2.teleport.com (Phil Tomson)
Date: 2001-01-23T08:10:01+09:00
Subject: [ruby-talk:9739] Workaround for Windows backquote problem


First a little background:

If you're running Ruby on Windows the following will not work:
version = `ver`
#or:
dircontents = `dir` #of course there are better ways to do this anyway
You get some error about the command not being found.
[BTW: This isn't an issue on Perl, anybody know why? seems like we could
get the same behaviour in Ruby.]

The problem has to do with certain commands being built into the Windows
command shell (command.com on '95 & '93, cmd.exe on NT & Win2K).
In order to get it to work you need to prefix with either command.com or
cmd.exe depending on which kind of Windows you're running.  So the
following will work:
version = `command.com /c ver` #on Win(95|98)
version = `cmd.exe /c ver` #on Win(NT|2k)

This is obviously annoying since you might have a mix of various
Windows(95|98|NT|2K|ME) machines around that you need to run your script
on.  So I came up with the following workaround that's working for me and
I post it here hoping that others will find it useful and improve on it:

#backtick.rb
require 'rbconfig'
include Config
#platform neutral backquotes - works on Win(95|98|NT|2K) and on Linux
      alias oldBackquote ` #`#just to make all the colorization workout

      def `(cmd)
         command_shell = "" 
         puts "In redefined backquote!" if $DEBUG
         if CONFIG["arch"] =~ /win/
            if ENV.has_key?("OS") && ENV["OS"] =~ /nt/i
               puts "It's either NT or 2K, use 'cmd.exe /c '" if $DEBUG
               #it's either NT or Win2K
               command_shell = "cmd.exe /c " 
            else
               #it's Win(95|98)
               puts "It's Win(95|98), use 'command.com /c '" if $DEBUG
               command_shell = "command.com /c " 
            end
         else
               puts "It's a 'nix, do nothing" if $DEBUG
         end
         cmd = command_shell + cmd
         oldBackquote(cmd)
      end

#now test it:

version = `ver`
puts "version is:\n #{version}"
#THE END

It's based on the fact that there is an OS entry in the environment
variables section on NT and 2K, so I check for it's existence and then
check to see if it's defined to be NT (as it is in NT and 2K).  I'm not
sure if this will work under ME, I don't have any ME machines to try it
on.

Another improvement would be to make it so it doesn't have to check the OS
env variable everytime backquotes are encountered - I suppose some kind of
closure would allow us to keep a state variable or something similer.  Any
ideas?

Phil