QED (text editor)

QED was an early line-oriented text editor developed in the late 1960s at the University of California, Berkeley. It is notable as a predecessor to the more widely known text editor ed, and consequently influenced the development of vi and other Unix text editors.

QED operated by allowing users to manipulate text files through a series of commands entered on a terminal. These commands allowed for actions such as inserting, deleting, and substituting text. While lacking a graphical user interface, QED's command-line interface provided a powerful means for editing text files, particularly in resource-constrained environments common at the time.

Unlike modern text editors with real-time display updates, QED typically displayed only the current line or a limited portion of the file being edited. Changes were made based on command input, and the user could then verify the changes before saving the file.

QED was developed primarily for the SDS 940 timesharing system, and versions were subsequently adapted to other systems. Its syntax and functionality provided a foundation for subsequent text editors, shaping the landscape of text editing tools in the early days of computing. Its influence can be seen in the design principles of ed, which in turn was used as the standard editor in early versions of Unix. While QED itself is not widely used today, its legacy as a pioneering text editor remains significant.