What does TERM=dumb in eshell mean?

Question

In eshell, if I echo $TERM, the result is dumb. What does this mean? Is this an emacs specific thing, or a tty thing?

Answer 1

First, it's an Emacs thing. It tells the used shell, that the buffer for input/output has only limited capabilities. See the following comment and code in lisp/startup.el:

;; Subprocesses of Emacs do not have direct access to the terminal, so
;; unless told otherwise they should only assume a dumb terminal.
;; We are careful to do it late (after term-setup-hook), although the
;; new multi-tty code does not use $TERM any more there anyway.
(setenv "TERM" "dumb")

It is also an OS specific setting, see http://en.wikipedia.org/wiki/Computer_terminal#Dumb_terminals