Netcat -e on Mac OS X
After doing some research, it appears that the netcat distributed in MacOS is a rather old (imported at 2005-10-07) version of netcat-openbsd clone. Here is the header file from the netcat.c hosted at opensource.apple.com.

/* $OpenBSD: netcat.c,v 1.82 2005/07/24 09:33:56 marius Exp $ */

There are three popular versions of netcat in the wild:


gnu-netcat or netcat ver. 0.71
netcat 1.10 or nc110 (also known as netcat-traditional in debian) 
and the openbsd version (netcat-openbsd, the netcat metapackage points to it) which is in active development.


Currently only the gnu and 1.10 versions support -e option and it's considered insecure. In the 1.10 version you should compile with -DGAPING_SECURITY_HOLE define to enable the -e switch.

The easiest way to install this version would be to use homebrew or other ports system (homebrew uses netcat 0.71 source).