Often you type the same long phrases over and over in a file. vi and ex have a number of different ways of saving long sequences of commands, both in command mode and in insert mode. When you call up one of these saved sequences to execute it, all you do is type a few characters (or even only one), and the entire sequence is executed as if you had entered the whole sequence of commands one by one.
You can define abbreviations that vi will automatically expand into the full text whenever you type the abbreviation in insert mode. To define an abbreviation, use the ex command:
:ab abbr phrase
abbr is an abbreviation for the specified phrase. The sequence of characters that make up the abbreviation will be expanded in insert mode only if you type it as a full word; abbr will not be expanded within a word.
Suppose in the file practice you want to enter text that contains a frequently recurring phrase such as a difficult product or company name. The command:
:ab imrc International Materials Research Centerabbreviates International Materials Research Center to the initials imrc. Now whenever you type imrc in insert mode, imrc expands to the full text.
Abbreviations expand as soon as you press a non-alphanumeric character (e.g., punctuation), a space, a carriage return, or ESC (returning to command mode). ...