Editing Ed (software) (section)

== Features ==
Features of ed include:
* available on essentially all Unix systems (and mandatory on systems conforming to the [[Single Unix Specification]]).
* support for [[regular expression]]s
* powerful automation can be achieved by feeding commands from [[standard streams|standard input]]

Known for its terseness, ed, compatible with [[teletype]] terminals like [[Teletype Model 33]], gives almost no visual feedback,<ref name="norman" /> 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 (text editor)|TECO]].{{r|penguin}} 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.<ref name="norman">{{cite journal |title=The truth about UNIX |author=Donald A. Norman |year=1981 |journal=[[Datamation]] |url=http://www.ceri.memphis.edu/people/smalley/ESCI7205_misc_files/The_truth_about_Unix_cleaned.pdf|archive-url=https://web.archive.org/web/20140416205707/http://www.ceri.memphis.edu/people/smalley/ESCI7205_misc_files/The_truth_about_Unix_cleaned.pdf |archive-date=2014-04-16 }}</ref> This terseness was appropriate in the early versions of Unix, when consoles were [[teleprinter|teletypes]], [[modem]]s were slow, and [[Random access memory|memory]] was precious. As computer technology improved and these constraints were loosened, editors with more visual feedback became the norm.
[[File:Ed first lines of man page.png|thumb|The [[man page]] for ed]]
In current practice, ed is rarely used interactively, but does find use in some [[shell script]]s. For interactive use, ed was subsumed by the [[sam (text editor)|sam]], [[Vi (text editor)|vi]] and [[Emacs]] editors in the 1980s. ed can be found on virtually every version of Unix and [[Linux]] available, and as such is useful for people who have to work with multiple versions of Unix. On Unix-based operating systems, some utilities like [[SQL*Plus]] run ed as the editor if the EDITOR and VISUAL environment variables are not defined.<ref>[https://docs.oracle.com/cd/E11882_01/server.112/e10839/admn_sqlpls.htm#UNXAR166 Administering SQL*Plus]. Accessed 7/23/2016.</ref> If something goes wrong, ed is sometimes the only editor available. This is often the only time when it is used interactively.

The version of ed provided by [[GNU]] has a few switches to enhance the feedback. Using {{PreCode|ed -v -p:}} provides a simple prompt and enables more useful feedback messages.<ref>{{man|1|ed|ManKier}}</ref> The {{PreCode|-p}} switch is defined in POSIX since [[X/Open|XPG2]] (1987).<ref name=sus/>

The ed commands are often imitated in other line-based editors. For example, [[edlin|EDLIN]] in early [[MS-DOS]] versions and [[32-bit]] versions of [[Windows NT]] has a somewhat similar syntax, and text editors in many [[Multi-user dungeon|MUD]]s ([[LPMud]] and descendants, for example) use ed-like syntax. These editors, however, are typically more limited in function.