Because vi is built on top of the ex line editor, you get all the power of a line editor as well. Any experienced vi user issues ex commands all the time — but usually one by one, at the colon (:) prompt.
The one exception is the .exrc file (Section 17.5), which is, at bottom, a list of commands for ex to run on startup — in short, an editor script.
What many beginners don't know is that you can save a sequence of ex commands in any file and execute it with the :so command (Section 20.4). For example, Bruce Barnett uses this trick to set himself up specially for editing FORTRAN programs (Section 18.10).
In general, sed (
Section 34.1) is better for
general-purpose batch editing — such as making a set of global substitutions
over and over again on multiple files — therefore, :so is most often used for reading in setup commands. Keep in
mind, though, any time you find yourself issuing the same commands over and over
again, think script!
— TOR