A way to change environment variables in Windows and notify processes about change.

persisting_windows_environment_variables.rb

# Not my idea. Don't remember where I've picked it up.
# Just stored here for future reference.

require 'win32/registry.rb'
require 'Win32API'  

Win32::Registry::HKEY_CURRENT_USER.open('Environment', Win32::Registry::KEY_WRITE) do |reg|
  reg['my_value'] = '123'
end

SendMessageTimeout = Win32API.new('user32', 'SendMessageTimeout', 'LLLPLLP', 'L') 
HWND_BROADCAST = 0xffff
WM_SETTINGCHANGE = 0x001A
SMTO_ABORTIFHUNG = 2
result = 0
SendMessageTimeout.call(HWND_BROADCAST, WM_SETTINGCHANGE, 0, 'Environment', SMTO_ABORTIFHUNG, 5000, result)