What is the correct way to detect if ruby is running on Windows?

It turns out, there's this way:

Gem.win_platform?

ruby windows operating-system

Preferred Option (Updated based on @John's recommendations):

require 'rbconfig'is_windows = (RbConfig::CONFIG['host_os'] =~ /mswin|mingw|cygwin/)

This could also work, but is less reliable (it won't work with much older versions, and the environment variable can be modified)

is_windows = (ENV['OS'] == 'Windows_NT')

(I can't easily test either on all of the rubies listed, or anything but Windows 7, but I know that both will work for 1.9.x, IronRuby, and JRuby).

ruby windows operating-system

(File::ALT_SEPARATOR || File::SEPARATOR) == '\\'

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