Unix in a Nutshell, 4th Edition

ex Basics

The ex line editor serves as the foundation for the screen editor vi. Commands in ex work on the current line or on a range of lines in a file. Most often, you use ex from within vi. In vi, ex commands are preceded by a colon and entered by pressing ENTER.

You can also invoke ex on its own—from the command line—just as you would invoke vi. (You could execute an ex script this way.) Or you can use the vi command Q to quit the vi editor and enter ex.