Line editor
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A line editor is a text editor computer program that is oriented around lines. Now considered extremely old-fashioned, they stem from the days when a computer operator would be sitting in front of a teletype (essentially a printer with a keyboard), so there was no screen and no way to move a cursor around a document.
Line editors are limited to the most primitive text-oriented input and output methods. Typing, editing, and document display do not occur simultaneously. Typically, typing does not enter text directly into the document. Instead, users add new text or edit existing text by typing terse 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 commands typically display the line(s) they modify, displaying the edited text within the context of larger portions of the document requires a separate command. Instead of a cursor to move around and use to select portions of the document being worked on or otherwise indicate where changes should be made, line editors have only the concept of the 'current line' being edited. Generally line numbers or, especially when making changes within lines, a search based context are used to specify which part of the document is to be edited or displayed. Naturally most edits are a line-at-a-time.
The UNIX editor ed is a classic example of a line editor, and is still in use; DOS users would be familiar with Edlin.
Line editors are still used non-interactively in shell scripts. They are also frequently seen in many MUD systems, though many people prefer to edit text on their own computer and then use their MUD client's upload feature to paste the text directly in the line editor.
See also:
Contrast visual editor