dateProc = IO.popen("date", 'w+')
dateProc.puts "\n"
dateProc.close_write
s2 = dateProc.gets
puts s2

Execution Result:
D:\ruby\jruby-1.7.18\bin\jruby.exe --1.9 -e $stdout.sync=true;$stderr.sync=true;load($0=ARGV.shift) D:/ruby/projects/test1/test/test1.rb
IOError: Cannot run program "date" (in directory "D:\ruby\projects\test1\test"): CreateProcess error=2, ?????????
popen at org/jruby/RubyIO.java:4345
(root) at D:/ruby/projects/test1/test/test1.rb:1
load at org/jruby/RubyKernel.java:1087
(root) at -e:1