An editor is a program that allows you to edit files. Editing is the process of changing the contents of a file character by character. It is distinct from word processing. Word processing inserts formatting and layout information into a text whereas editing does not. Editors can however have features word processors do not have. They can do indentation, automatic insertion of line breaks for program source code. They can be freely programmed to do a multitude of tasks, emacs even goes as far as offering e mail, news and file manager facilities.
We will look at three common UNIX editors all of which are available for MS-DOS and Windows as well.
Ed is a very basic line editor and available on almost all systems including the most basic. Vi is the classic UNIX full screen editor, it is available on most systems, except the very basic. EMACS is a very more powerful editor that even allows programs to be written with its internal LISP language. A knowledge of these three editors should enable you to do editing on all UNIX systems.