Learning the vi Editor, Sixth Edition

8.4. Extended Regular Expressions

The metacharacters available in vi's search and substitution regular expressions are described in Section 6.3.1 in Chapter 6. Each of the clones provides some form of extended regular expressions, either as an option or always available. Typically these are the same (or almost the same) as what's provided by egrep. Unfortunately, each one's extended flavor is slightly different from the others'.

To give you a feel for what extended regular expressions can do, we present them in the context of nvi. Each clone's chapter then describes that editor's extended syntax, without repeating the examples.

nvi extended regular expressions are the Extended Regular Expressions (EREs) as defined by the POSIX standard. In order to enable this feature, use set extended from either your .nexrc file or from the ex colon prompt.

Besides the standard metacharacters described in Chapter 6, and the POSIX bracket expressions mentioned in Section 6.3.2 in the same chapter, the following metacharacters are available:

|

Indicates alternation. For example, a|b matches either a or b. However, this construct is not limited to single characters: house|home matches either of the strings house or home.

(...)

Used for grouping, to allow the application of additional regular expression operators. For example, house|home can be shortened (if not simplified) to ho(use|me). The * operator can be applied to text in parentheses: (house|home)* matches home, homehouse, househomehousehouse ...