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em - the editor for mortals - is a variant of the standard Unix text
editor - ed. It includes all of ed, so the documentation for ed is
fully applicable to em. Em also has a number of new commands and
facilities designed to improve its interaction and increase its
usefulness.
Em differs from ed in that it normally prefixes command lines with a
'>'. For those who prefer silence, if the editor is invoked by any
name not having 'm' as its second character, no prompts will appear.
Other ways of controlling prompts are described below.
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.
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.
This version was translated from V6 Unix C (mid-70s era) to the
present day by Pierre Gaston.
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