ex, (short for extended),[1][2][better source needed] is a line editor for Unix systems originally written by Bill Joy[3] in 1976, beginning with an earlier program written by Charles Haley.
[5] The original Unix editor ed was distributed with the Bell Labs versions of the operating system in the 1970s.
George Coulouris of Queen Mary College, London, which had installed Unix in 1973, developed an improved version called em in 1975 that could take advantage of video terminals.
ex was eventually given a full-screen visual interface (adding to its command line oriented operation), thereby becoming the vi text editor.
The core ex commands which relate to search and replace are essential to vi.