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Meta-characters


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.



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