ed (pronounced as distinct letters, /ˌiːˈdiː/)[1] is a line editor for Unix and Unix-like operating systems.

[2] It remains part of the POSIX and Open Group standards for Unix-based operating systems,[3] alongside the more sophisticated full-screen editor vi.

[2] Many features of ed came from the qed text editor developed at Thompson's alma mater University of California, Berkeley.

[6][failed verification][7] Features of ed include: Known for its terseness, ed, compatible with teletype terminals like Teletype Model 33, gives almost no visual feedback,[8] and has been called (by Peter H. Salus) "the most user-hostile editor ever created", even when compared to the contemporary (and notoriously complex) TECO.

[2] For example, the message that ed will produce in case of error, and when it wants to make sure the user wishes to quit without saving, is "?".

It does not report the current filename or line number, or even display the results of a change to the text, unless requested.

Older versions (c. 1981) did not even ask for confirmation when a quit command was issued without the user saving changes.

[8] This terseness was appropriate in the early versions of Unix, when consoles were teletypes, modems were slow, and memory was precious.

As computer technology improved and these constraints were loosened, editors with more visual feedback became the norm.

For clarity, commands and text typed by the user are in normal face, and output from ed is emphasized.