features:listUrl writes its output to the console using session.getConsole().println() instead of System.out.println(). The GrepAction.java wraps System.in in a BufferedLineReader() in order to grab the output of the preceding command. Because features:listurl doesn't write anything to the System, grep has nothing to filter. The fix for this is to change all instances of session.getConsole().println() in ListUrlcommand.java with System.out.println(). I will be submitting a patch for this shortly.