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<h2 class="title">Character classes</h2>
<p class="para">
An opening square bracket introduces a character class,
terminated by a closing square bracket. A closing square
bracket on its own is not special. If a closing square
bracket is required as a member of the class, it should be
the first data character in the class (after an initial
circumflex, if present) or escaped with a backslash.
</p>
<p class="para">
A character class matches a single character in the subject;
the character must be in the set of characters defined by
the class, unless the first character in the class is a
circumflex, in which case the subject character must not be in
the set defined by the class. If a circumflex is actually
required as a member of the class, ensure it is not the
first character, or escape it with a backslash.
</p>
<p class="para">
For example, the character class [aeiou] matches any lower
case vowel, while [^aeiou] matches any character that is not
a lower case vowel. Note that a circumflex is just a
convenient notation for specifying the characters which are in
the class by enumerating those that are not. It is not an
assertion: it still consumes a character from the subject
string, and fails if the current pointer is at the end of
the string.
</p>
<p class="para">
When case-insensitive (caseless) matching is set, any letters
in a class represent both their upper case and lower case
versions, so for example, an insensitive [aeiou] matches "A"
as well as "a", and an insensitive [^aeiou] does not match
"A", whereas a sensitive (caseful) version would.
</p>
<p class="para">
The newline character is never treated in any special way in
character classes, whatever the setting of the <a href="reference.pcre.pattern.modifiers.html" class="link">PCRE_DOTALL</a>
or <a href="reference.pcre.pattern.modifiers.html" class="link">PCRE_MULTILINE</a>
options is. A class such as [^a] will always match a newline.
</p>
<p class="para">
The minus (hyphen) character can be used to specify a range
of characters in a character class. For example, [d-m]
matches any letter between d and m, inclusive. If a minus
character is required in a class, it must be escaped with a
backslash or appear in a position where it cannot be
interpreted as indicating a range, typically as the first or last
character in the class.
</p>
<p class="para">
It is not possible to have the literal character "]" as the
end character of a range. A pattern such as [W-]46] is
interpreted as a class of two characters ("W" and "-")
followed by a literal string "46]", so it would match "W46]" or
"-46]". However, if the "]" is escaped with a backslash it
is interpreted as the end of range, so [W-\]46] is
interpreted as a single class containing a range followed by two
separate characters. The octal or hexadecimal representation
of "]" can also be used to end a range.
</p>
<p class="para">
Ranges operate in ASCII collating sequence. They can also be
used for characters specified numerically, for example
[\000-\037]. If a range that includes letters is used when
case-insensitive (caseless) matching is set, it matches the
letters in either case. For example, [W-c] is equivalent to
[][\^_`wxyzabc], matched case-insensitively, and if character
tables for the "fr" locale are in use, [\xc8-\xcb] matches
accented E characters in both cases.
</p>
<p class="para">
The character types \d, \D, \s, \S, \w, and \W may also
appear in a character class, and add the characters that
they match to the class. For example, [\dABCDEF] matches any
hexadecimal digit. A circumflex can conveniently be used
with the upper case character types to specify a more
restricted set of characters than the matching lower case type.
For example, the class [^\W_] matches any letter or digit,
but not underscore.
</p>
<p class="para">
All non-alphanumeric characters other than \, -, ^ (at the
start) and the terminating ] are non-special in character
classes, but it does no harm if they are escaped. The pattern
terminator is always special and must be escaped when used
within an expression.
</p>
<p class="para">
Perl supports the POSIX notation for character classes. This uses names
enclosed by <em>[:</em> and <em>:]</em> within the enclosing square brackets. PCRE also
supports this notation. For example, <em>[01[:alpha:]%]</em>
matches "0", "1", any alphabetic character, or "%". The supported class
names are:
<table class="doctable table">
<caption><strong>Character classes</strong></caption>
<tbody class="tbody">
<tr><td><em>alnum</em></td><td>letters and digits</td></tr>
<tr><td><em>alpha</em></td><td>letters</td></tr>
<tr><td><em>ascii</em></td><td>character codes 0 - 127</td></tr>
<tr><td><em>blank</em></td><td>space or tab only</td></tr>
<tr><td><em>cntrl</em></td><td>control characters</td></tr>
<tr><td><em>digit</em></td><td>decimal digits (same as \d)</td></tr>
<tr><td><em>graph</em></td><td>printing characters, excluding space</td></tr>
<tr><td><em>lower</em></td><td>lower case letters</td></tr>
<tr><td><em>print</em></td><td>printing characters, including space</td></tr>
<tr><td><em>punct</em></td><td>printing characters, excluding letters and digits</td></tr>
<tr><td><em>space</em></td><td>white space (not quite the same as \s)</td></tr>
<tr><td><em>upper</em></td><td>upper case letters</td></tr>
<tr><td><em>word</em></td><td>"word" characters (same as \w)</td></tr>
<tr><td><em>xdigit</em></td><td>hexadecimal digits</td></tr>
</tbody>
</table>
The <em>space</em> characters are HT (9), LF (10), VT (11), FF (12), CR (13),
and space (32). Notice that this list includes the VT character (code
11). This makes "space" different to <em>\s</em>, which does not include VT (for
Perl compatibility).
</p>
<p class="para">
The name <em>word</em> is a Perl extension, and <em>blank</em> is a GNU extension
from Perl 5.8. Another Perl extension is negation, which is indicated
by a <em>^</em> character after the colon. For example,
<em>[12[:^digit:]]</em> matches "1", "2", or any non-digit.
</p>
<p class="para">
In UTF-8 mode, characters with values greater than 128 do not match any
of the POSIX character classes.
As of PHP 5.3.0 and libpcre 8.10 some character classes are changed to use
Unicode character properties, in which case the mentioned restriction does
not apply. Refer to the <a href="http://www.pcre.org/pcre.txt" class="link external">» PCRE(3) manual</a>
for details.
</p>
<p class="para">
Unicode character properties can appear inside a character class. They can
not be part of a range. The minus (hyphen) character after a Unicode
character class will match literally. Trying to end a range with a Unicode
character property will result in a warning.
</p>
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