Port of em to modern OS 
(http://www.eecs.qmul.ac.uk/~gc/history/)

From  http://en.wikipedia.org/wiki/Vi

"Coulouris considered the cryptic commands of ed to be only suitable
for "immortals", and thus in February, 1976, he enhanced ed (using Ken
Thompson's ed source as a starting point) to make em (the "editor for
mortals") while acting as a lecturer at Queen Mary College.

The em editor was designed for display terminals and was a
single-line-at-a-time visual editor. It was one of the first programs
on Unix to make heavy use of "raw terminal input mode", in which the
running program, rather than the terminal device driver, handled all
keystrokes. When Coulouris visited UC Berkeley in the summer of 1976,
he brought a DECtape containing em, and showed the editor to various
people. Some people considered this new kind of editor to be a
potential resource hog, but others, including Bill Joy were impressed"

Inspired by em, and by their own tweaks to ed, Bill Joy and Chuck
Haley, both graduate students at UC Berkeley, took code from em to
make en, and then "extended" en to create ex version 0.1.

I used the unix v6 manpage conveniently available from:
* http://man.cat-v.org/unix-6th/
to figure out what the old function did.

Also useful was the v6 C reference manual:
http://wwwlehre.dhbw-stuttgart.de/~helbig/os/v6/doc/index.html