# Line editor

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{{Short description|Computer text editor}}
{{More sources needed|date=September 2024}}

In computing, a '''line editor''' is a [text editor](/source/text_editor) in which each editing command applies to one or more complete lines of text designated by the user. Line editors predate screen-based text editors and originated in an era when a computer operator typically interacted with a [teleprinter](/source/teleprinter) (essentially a [printer](/source/computer_printer) with a [keyboard](/source/Computer_keyboard)), with no video display, and no ability to move a cursor interactively within a document.<ref>{{Cite web |title=line editor |url=https://www.computer-dictionary-online.org/definitions-l/line-editor |access-date=2024-09-11 |website=Computer Dictionary of Information Technology |language=en}}</ref>

Line editors are limited to typewriter keyboard text-oriented input and output methods. Most edits are a line-at-a-time. Typing, editing, and document display do not occur simultaneously.  Typically, typing does not enter text directly into the document.  Instead, users modify the document text by entering these commands on a text-only terminal.  Commands and text, and corresponding output from the editor, will scroll up from the bottom of the screen in the order that they are entered or printed to the screen. Although the commands typically indicate the line(s) they modify, displaying the edited text within the context of larger portions of the document requires a separate command.

Line editors keep a reference to the "current line" to which the entered commands usually are applied. In contrast, modern screen based editors allow the user to interactively and directly navigate, select, and modify portions of the document. Generally line numbers or a search based context (especially when making changes within lines) are used to specify which part of the document is to be edited or displayed.

Early line editors included [Expensive Typewriter](/source/Expensive_Typewriter) and [QED](/source/QED_(text_editor)). Both pre-dated the advent of [Unix](/source/Unix); the former two ran on [DEC](/source/Digital_Equipment_Corporation) [PDP-1](/source/PDP-1)'s, while the latter was a [Unisys](/source/Unisys) product. Unix systems offer both [ed](/source/ed_(text_editor)) and [ex](/source/ex_(text_editor)), the latter typically as a specialized mode of a full-screen editor. For the first 10 years of the [IBM PC](/source/IBM_PC), the only editor provided in [MS-DOS](/source/MS-DOS) / [IBM PC DOS](/source/IBM_PC_DOS) was the [Edlin](/source/Edlin) line editor.

Line editors are still used non-interactively in [shell script](/source/shell_script)s and when dealing with failing operating systems. Update systems such as [patch](/source/patch_(Unix)) traditionally used [diff](/source/diff) data converted into a script of [ed](/source/ed_(text_editor)) commands. They are also used in many [MUD](/source/Multi-user_dungeon) systems, though many people edit text on their own computer using MUD's download and upload features.

==References==
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Category:Line editor

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Adapted from the Wikipedia article [Line editor](https://en.wikipedia.org/wiki/Line_editor) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Line_editor?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.