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:

\

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:

\

general escape character

^

negate the class, but only if the first character

-

indicates character range

]

terminates the character class

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