Subject: ps -ef | grep "test" in eshell gives a beep

From: Sum Proxy <[email-masked]>
Date: Wed, 16 Sep 2015 16:42:17 +0300

It also hangs with some of the output.
Emacs version:
GNU Emacs 24.4.1 (x86_64-apple-darwin13.4.0, NS apple-appkit-1265.21) of 2014-10-21 on builder10-9.porkrind.org
eshell version 2.4.2

Please let me know why this happens and how to fix it. 
Thanks.