WYNTK: UNIX System Admininistrator

If TERM is not set, programs may not run.

If your TERM environment variable is not defined, then programs have no way to know how to move the cursor or output text at the top of a screen. If you try running Emacs without TERM defined, you’ll see something like this:

% emacs
Please set the environment variable TERM; see tset(1).

Emacs won’t run at all without TERM defined.

vi, on the other hand, will run, but you sort of wish it hadn’t.

% vi
Visual needs addressable cursor or upline capability
:

vi cannot run without knowing how to move the cursor. So its response is to put you in its underlying editor, ex. Most people don’t know ex, or don’t know that they know it; vi users may recognize it as the “colon prompt” at the bottom of a vi window and realize that they can exit by typing q and Return.

Programs can’t tell you if your terminal type is wrong

UNIX can bring out the worst in people. It can make them paranoid. It can make them rant. Sometimes with good reason. When Rebecca started working here, she hated the editing program, vi. She would get almost rabid when she talked about it. The old UNIX hands in the office would figuratively pat her on the head and tell her that it wasn’t so bad. Finally, someone sat down with her. It turned out that she had been using the wrong terminal definition. The reason that vi was so terrible for her was that it wasn’t working correctly, not that she couldn’t grasp how to use a screen editor. She knew that something had been wrong, but had been talked ...