shelling out with mkdir -p with ubuntu Ruby 1.8.7

#tried this with ` Kernel.system IO.popen and open3:popen3
p "mkdir -p tmp/demo/{first/{app,views},second}"  #works on command line tmp/demo/first/app /views   tmp/demp/second
`mkdir -p tmp/demo/{first/{app,views},second}` #doesnt - literally creates tmp/demo/{first/{app,views},second}/ 


#sh -c "/bin/mkdir -p tmp/demo/{first/{app,views},second}" on command line also creates the same error, if that helps
`bash -c "mkdir -p tmp/demo/{first/{app,views},second}"`  DOES WORK