Rake which method

rake_which

def which(cmd)
    exts = ENV['PATHEXT'] ? ENV['PATHEXT'].split(';') : ['']
    ENV['PATH'].split(File::PATH_SEPARATOR).each do |path|
    exts.each { |ext|
        sep = File::ALT_SEPARATOR || File::SEPARATOR
        exe = "#{path}#{sep}#{cmd}#{ext}"
        return exe if File.executable? exe
    }
    end
    return nil
end