SunshinePHP Developer Conference 2015

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-characterDescription
\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-characterDescription
\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.

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