Common Operators
****************

  You compose regular expressions from operators.  In the following
sections, we describe the regular expression operators specified by
POSIX; GNU also uses these.  Most operators have more than one
representation as characters.  See Regular Expression Syntax, for
what characters represent what operators under what circumstances.

  For most operators that can be represented in two ways, one
representation is a single character and the other is that character
preceded by `\'.  For example, either `(' or `\(' represents the
open-group operator.  Which one does depends on the setting of a syntax
bit, in this case `RE_NO_BK_PARENS'.  Why is this so?  Historical
reasons dictate some of the varying representations, while POSIX
dictates others.

  Finally, almost all characters lose any special meaning inside a list
(see List Operators.).

Menu

Match-self Operator

Ordinary characters.

Match-any-character Operator

.

Concatenation Operator

Juxtaposition.

Repetition Operators

* + ? {}

Alternation Operator

|

List Operators

[...] [^...]

Grouping Operators

(...)

Back-reference Operator

\digit

Anchoring Operators

^ $