Meta-characters

The power of regular expressions comes from the ability to include alternatives and repetitions in the pattern. These are encoded in the pattern by the use of meta-characters, which do not stand for themselves but instead are interpreted in some special way.

There are two different sets of meta-characters: those that are recognized anywhere in the pattern except within square brackets, and those that are recognized in square brackets. Outside square brackets, the meta-characters are as follows:

Meta-characters outside square brackets

Meta-character	Description
\	general escape character with several uses
^	assert start of subject (or line, in multiline mode)
$	assert end of subject or before a terminating newline (or end of line, in multiline mode)
.	match any character except newline (by default)
[	start character class definition
]	end character class definition
|	start of alternative branch
(	start subpattern
)	end subpattern
?	Introduces a special construct, such as a non-capturing group, a named subpattern, an assertion or an option setting, if used as the first character after (. If used as a quantifier it is the optional quantifier (equivalent to {0,1}). It also transforms greedy quantifiers into lazy quantifiers (see repetition).
*	0 or more quantifier
+	1 or more quantifier
{	start min/max quantifier
}	end min/max quantifier

Part of a pattern that is in square brackets is called a character class. In a character class the only meta-characters are:

Meta-characters inside square brackets (character classes)

Meta-character	Description
\	general escape character
^	negate the class, but only if the first character
-	indicates character range

The following sections describe the use of each of the meta-characters.