From: Adam Skobi <dxm997@...>
Date: 2008-10-17T07:39:09+09:00
Subject: Damn you cmd.exe!

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Hi,

As an exercise in metaprogramming I decided to write a DSL shell. One of the
requirements was that it should be working on both - win32 and unix
platforms. I quickly encountered some problems with cmd.exe.

My first understanding was that I open a stream to cmd.exe and write/read it
synchronously. In linux it would look like this

IO.popen( "/bin/bash", "r+" ) do |cmd|
  cmd.puts 'pwd'
  puts cmd.gets
end

Everything's dandy. It works like a charm. When I try to create an
equivalent in win32:

IO.popen( "cmd.exe", "r+" ) do |cmd|
  cmd.puts 'cd'
  puts cmd.gets
end

This thing fails miserably. I can't really pinpoint what is the root cause
of it. I have found here on comp.lang.ruby two solutions. First one:

IO.popen( "cmd.exe", "r+" ) do |cmd|
  Thread.new(cmd) do |io|
    while line = io.gets
      puts line
    end
  end

  cmd.puts "dir"
  cmd.puts "cd \\"
  cmd.puts "dir"

  sleep 3
end

It works but is sucks badly on many levels as you can see. Other one:

IO.popen("cmd.exe /c #{single_command}") do | pipe |
      pipe.each_line { |line| puts line }
end

This thing is not so bad but there is a small problem. I want my DSL user to
be able to write such simple commands as

cd C:\
dir

The problem is although the both command will run correctly, the change of
current directory will be lost between the commands. I can think of some
crazy workarounds but I was wondering if there is a way for the cmd.exe to
behave normally. Any help would be appreciated.

-- 
Adam Skobi

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