| REGEXP(7) | REGEXP(7)

NAME

| regexp – Plan 9 regular expression notation

DESCRIPTION

This manual page describes the regular expression syntax used by the Plan 9 regular expression library regexp(3). It is the form used by egrep(1) before egrep got complicated.

A regular expression specifies a set of strings of characters. A member of this set of strings is said to be matched by the regular expression. In many applications a delimiter character, commonly `/`, bounds a regular expression. In the following specification for regular expressions the word ‘character’ means any character (rune) but newline.

The syntax for a regular expression `e0` is

`e3: literal | charclass | '.' | '^' | '$' | '(' e0 ')'
e2: e3

| | e2 REP

REP: '*' | '+' | '?'
e1: e2

| | e1 e2

e0: e1

| e0 '|' e1

`

A `literal` is any non-metacharacter, or a metacharacter (one of `.*+?[]()|\^$`), or the delimiter preceded by `\`.

A `charclass` is a nonempty string s bracketed `[`s`]` (or `[^`s`]`); it matches any character in (or not in) s. A negated character class never matches newline. A substring a`−`b, with a and b in ascending order, stands for the inclusive range of characters between a and b. In s, the metacharacters `−`, `]`, an initial `^`, and the regular expression delimiter must be preceded by a `\`; other metacharacters have no special meaning and may appear unescaped.

A `.` matches any character.

A `^` matches the beginning of a line; `$` matches the end of the line.

The `REP` operators match zero or more (`*`), one or more (`+`), zero or one (`?`), instances respectively of the preceding regular expression `e2`.

A concatenated regular expression, `e1e2`, matches a match to `e1` followed by a match to `e2`.

An alternative regular expression, `e0|e1`, matches either a match to `e0` or a match to `e1`.

A match to any part of a regular expression extends as far as possible without preventing a match to the remainder of the regular expression.

SEE ALSO

| regexp(3)