## 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
? | extends the meaning of (, also 0 or 1 quantifier, also makes greedy quantifiers lazy (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.