PERLRECHARCLASS(1) Perl Programmers Reference Guide PERLRECHARCLASS(1)
NAME
perlrecharclass - Perl Regular Expression Character Classes
DESCRIPTION
The top level documentation about Perl regular expressions is found in
perlre.
This manual page discusses the syntax and use of character classes in
Perl regular expressions.
A character class is a way of denoting a set of characters in such a
way that one character of the set is matched. It's important to
remember that: matching a character class consumes exactly one
character in the source string. (The source string is the string the
regular expression is matched against.)
There are three types of character classes in Perl regular expressions:
the dot, backslash sequences, and the form enclosed in square brackets.
Keep in mind, though, that often the term "character class" is used to
mean just the bracketed form. Certainly, most Perl documentation does
that.
The dot
The dot (or period), "." is probably the most used, and certainly the
most well-known character class. By default, a dot matches any
character, except for the newline. That default can be changed to add
matching the newline by using the single line modifier: either for the
entire regular expression with the "/s" modifier, or locally with
"(?s)". (The experimental "\N" backslash sequence, described below,
matches any character except newline without regard to the single line
modifier.)
Here are some examples:
"a" =~ /./ # Match
"." =~ /./ # Match
"" =~ /./ # No match (dot has to match a character)
"\n" =~ /./ # No match (dot does not match a newline)
"\n" =~ /./s # Match (global 'single line' modifier)
"\n" =~ /(?s:.)/ # Match (local 'single line' modifier)
"ab" =~ /^.$/ # No match (dot matches one character)
Backslash sequences
A backslash sequence is a sequence of characters, the first one of
which is a backslash. Perl ascribes special meaning to many such
sequences, and some of these are character classes. That is, they
match a single character each, provided that the character belongs to
the specific set of characters defined by the sequence.
Here's a list of the backslash sequences that are character classes.
They are discussed in more detail below. (For the backslash sequences
that aren't character classes, see perlrebackslash.)
\d Match a decimal digit character.
\D Match a non-decimal-digit character.
\w Match a "word" character.
\W Match a non-"word" character.
\s Match a whitespace character.
\S Match a non-whitespace character.
\h Match a horizontal whitespace character.
\H Match a character that isn't horizontal whitespace.
\v Match a vertical whitespace character.
\V Match a character that isn't vertical whitespace.
\N Match a character that isn't a newline. Experimental.
\pP, \p{Prop} Match a character that has the given Unicode property.
\PP, \P{Prop} Match a character that doesn't have the Unicode property
\N
"\N" is new in 5.12, and is experimental. It, like the dot, matches
any character that is not a newline. The difference is that "\N" is not
influenced by the single line regular expression modifier (see "The
dot" above). Note that the form "\N{...}" may mean something
completely different. When the "{...}" is a quantifier, it means to
match a non-newline character that many times. For example, "\N{3}"
means to match 3 non-newlines; "\N{5,}" means to match 5 or more non-
newlines. But if "{...}" is not a legal quantifier, it is presumed to
be a named character. See charnames for those. For example, none of
"\N{COLON}", "\N{4F}", and "\N{F4}" contain legal quantifiers, so Perl
will try to find characters whose names are respectively "COLON", "4F",
and "F4".
Digits
"\d" matches a single character considered to be a decimal digit. If
the "/a" regular expression modifier is in effect, it matches [0-9].
Otherwise, it matches anything that is matched by "\p{Digit}", which
includes [0-9]. (An unlikely possible exception is that under locale
matching rules, the current locale might not have [0-9] matched by
"\d", and/or might match other characters whose code point is less than
256. Such a locale definition would be in violation of the C language
standard, but Perl doesn't currently assume anything in regard to
this.)
What this means is that unless the "/a" modifier is in effect "\d" not
only matches the digits '0' - '9', but also Arabic, Devanagari, and
digits from other languages. This may cause some confusion, and some
security issues.
Some digits that "\d" matches look like some of the [0-9] ones, but
have different values. For example, BENGALI DIGIT FOUR (U+09EA) looks
very much like an ASCII DIGIT EIGHT (U+0038). An application that is
expecting only the ASCII digits might be misled, or if the match is
"\d+", the matched string might contain a mixture of digits from
different writing systems that look like they signify a number
different than they actually do. "num()" in Unicode::UCD can be used
to safely calculate the value, returning "undef" if the input string
contains such a mixture.
What "\p{Digit}" means (and hence "\d" except under the "/a" modifier)
is "\p{General_Category=Decimal_Number}", or synonymously,
"\p{General_Category=Digit}". Starting with Unicode version 4.1, this
is the same set of characters matched by "\p{Numeric_Type=Decimal}".
But Unicode also has a different property with a similar name,
"\p{Numeric_Type=Digit}", which matches a completely different set of
characters. These characters are things such as "CIRCLED DIGIT ONE" or
subscripts, or are from writing systems that lack all ten digits.
The design intent is for "\d" to exactly match the set of characters
that can safely be used with "normal" big-endian positional decimal
syntax, where, for example 123 means one 'hundred', plus two 'tens',
plus three 'ones'. This positional notation does not necessarily apply
to characters that match the other type of "digit",
"\p{Numeric_Type=Digit}", and so "\d" doesn't match them.
The Tamil digits (U+0BE6 - U+0BEF) can also legally be used in old-
style Tamil numbers in which they would appear no more than one in a
row, separated by characters that mean "times 10", "times 100", etc.
(See <http://www.unicode.org/notes/tn21>;.)
Any character not matched by "\d" is matched by "\D".
Word characters
A "\w" matches a single alphanumeric character (an alphabetic
character, or a decimal digit) or a connecting punctuation character,
such as an underscore ("_"). It does not match a whole word. To match
a whole word, use "\w+". This isn't the same thing as matching an
English word, but in the ASCII range it is the same as a string of
Perl-identifier characters.
If the "/a" modifier is in effect ...
"\w" matches the 63 characters [a-zA-Z0-9_].
otherwise ...
For code points above 255 ...
"\w" matches the same as "\p{Word}" matches in this range.
That is, it matches Thai letters, Greek letters, etc. This
includes connector punctuation (like the underscore) which
connect two words together, or diacritics, such as a "COMBINING
TILDE" and the modifier letters, which are generally used to
add auxiliary markings to letters.
For code points below 256 ...
if locale rules are in effect ...
"\w" matches the platform's native underscore character
plus whatever the locale considers to be alphanumeric.
if Unicode rules are in effect or if on an EBCDIC platform ...
"\w" matches exactly what "\p{Word}" matches.
otherwise ...
"\w" matches [a-zA-Z0-9_].
Which rules apply are determined as described in "Which character set
modifier is in effect?" in perlre.
There are a number of security issues with the full Unicode list of
word characters. See <http://unicode.org/reports/tr36>;.
Also, for a somewhat finer-grained set of characters that are in
programming language identifiers beyond the ASCII range, you may wish
to instead use the more customized "Unicode Properties",
"\p{ID_Start}", "\p{ID_Continue}", "\p{XID_Start}", and
"\p{XID_Continue}". See <http://unicode.org/reports/tr31>;.
Any character not matched by "\w" is matched by "\W".
Whitespace
"\s" matches any single character considered whitespace.
If the "/a" modifier is in effect ...
"\s" matches the 5 characters [\t\n\f\r ]; that is, the horizontal
tab, the newline, the form feed, the carriage return, and the
space. (Note that it doesn't match the vertical tab, "\cK" on
ASCII platforms.)
otherwise ...
For code points above 255 ...
"\s" matches exactly the code points above 255 shown with an
"s" column in the table below.
For code points below 256 ...
if locale rules are in effect ...
"\s" matches whatever the locale considers to be
whitespace. Note that this is likely to include the
vertical space, unlike non-locale "\s" matching.
if Unicode rules are in effect or if on an EBCDIC platform ...
"\s" matches exactly the characters shown with an "s"
column in the table below.
otherwise ...
"\s" matches [\t\n\f\r ]. Note that this list doesn't
include the non-breaking space.
Which rules apply are determined as described in "Which character set
modifier is in effect?" in perlre.
Any character not matched by "\s" is matched by "\S".
"\h" matches any character considered horizontal whitespace; this
includes the platform's space and tab characters and several others
listed in the table below. "\H" matches any character not considered
horizontal whitespace. They use the platform's native character set,
and do not consider any locale that may otherwise be in use.
"\v" matches any character considered vertical whitespace; this
includes the platform's carriage return and line feed characters
(newline) plus several other characters, all listed in the table below.
"\V" matches any character not considered vertical whitespace. They
use the platform's native character set, and do not consider any locale
that may otherwise be in use.
"\R" matches anything that can be considered a newline under Unicode
rules. It's not a character class, as it can match a multi-character
sequence. Therefore, it cannot be used inside a bracketed character
class; use "\v" instead (vertical whitespace). It uses the platform's
native character set, and does not consider any locale that may
otherwise be in use. Details are discussed in perlrebackslash.
Note that unlike "\s" (and "\d" and "\w"), "\h" and "\v" always match
the same characters, without regard to other factors, such as the
active locale or whether the source string is in UTF-8 format.
One might think that "\s" is equivalent to "[\h\v]". This is not true.
The difference is that the vertical tab ("\x0b") is not matched by
"\s"; it is however considered vertical whitespace.
The following table is a complete listing of characters matched by
"\s", "\h" and "\v" as of Unicode 6.0.
The first column gives the Unicode code point of the character (in hex
format), the second column gives the (Unicode) name. The third column
indicates by which class(es) the character is matched (assuming no
locale or EBCDIC code page is in effect that changes the "\s"
matching).
0x0009 CHARACTER TABULATION h s
0x000a LINE FEED (LF) vs
0x000b LINE TABULATION v
0x000c FORM FEED (FF) vs
0x000d CARRIAGE RETURN (CR) vs
0x0020 SPACE h s
0x0085 NEXT LINE (NEL) vs [1]
0x00a0 NO-BREAK SPACE h s [1]
0x1680 OGHAM SPACE MARK h s
0x180e MONGOLIAN VOWEL SEPARATOR h s
0x2000 EN QUAD h s
0x2001 EM QUAD h s
0x2002 EN SPACE h s
0x2003 EM SPACE h s
0x2004 THREE-PER-EM SPACE h s
0x2005 FOUR-PER-EM SPACE h s
0x2006 SIX-PER-EM SPACE h s
0x2007 FIGURE SPACE h s
0x2008 PUNCTUATION SPACE h s
0x2009 THIN SPACE h s
0x200a HAIR SPACE h s
0x2028 LINE SEPARATOR vs
0x2029 PARAGRAPH SEPARATOR vs
0x202f NARROW NO-BREAK SPACE h s
0x205f MEDIUM MATHEMATICAL SPACE h s
0x3000 IDEOGRAPHIC SPACE h s
[1] NEXT LINE and NO-BREAK SPACE may or may not match "\s" depending on
the rules in effect. See the beginning of this section.
Unicode Properties
"\pP" and "\p{Prop}" are character classes to match characters that fit
given Unicode properties. One letter property names can be used in the
"\pP" form, with the property name following the "\p", otherwise,
braces are required. When using braces, there is a single form, which
is just the property name enclosed in the braces, and a compound form
which looks like "\p{name=value}", which means to match if the property
"name" for the character has that particular "value". For instance, a
match for a number can be written as "/\pN/" or as "/\p{Number}/", or
as "/\p{Number=True}/". Lowercase letters are matched by the property
Lowercase_Letter which has the short form Ll. They need the braces, so
are written as "/\p{Ll}/" or "/\p{Lowercase_Letter}/", or
"/\p{General_Category=Lowercase_Letter}/" (the underscores are
optional). "/\pLl/" is valid, but means something different. It
matches a two character string: a letter (Unicode property "\pL"),
followed by a lowercase "l".
If neither the "/a" modifier nor locale rules are in effect, the use of
a Unicode property will force the regular expression into using Unicode
rules.
Note that almost all properties are immune to case-insensitive
matching. That is, adding a "/i" regular expression modifier does not
change what they match. There are two sets that are affected. The
first set is "Uppercase_Letter", "Lowercase_Letter", and
"Titlecase_Letter", all of which match "Cased_Letter" under "/i"
matching. The second set is "Uppercase", "Lowercase", and "Titlecase",
all of which match "Cased" under "/i" matching. (The difference
between these sets is that some things, such as Roman numerals, come in
both upper and lower case, so they are "Cased", but aren't considered
to be letters, so they aren't "Cased_Letter"s. They're actually
"Letter_Number"s.) This set also includes its subsets "PosixUpper" and
"PosixLower", both of which under "/i" match "PosixAlpha".
For more details on Unicode properties, see "Unicode Character
Properties" in perlunicode; for a complete list of possible properties,
see "Properties accessible through \p{} and \P{}" in perluniprops,
which notes all forms that have "/i" differences. It is also possible
to define your own properties. This is discussed in "User-Defined
Character Properties" in perlunicode.
Unicode properties are defined (surprise!) only on Unicode code points.
A warning is raised and all matches fail on non-Unicode code points
(those above the legal Unicode maximum of 0x10FFFF). This can be
somewhat surprising,
chr(0x110000) =~ \p{ASCII_Hex_Digit=True} # Fails.
chr(0x110000) =~ \p{ASCII_Hex_Digit=False} # Also fails!
Even though these two matches might be thought of as complements, they
are so only on Unicode code points.
Examples
"a" =~ /\w/ # Match, "a" is a 'word' character.
"7" =~ /\w/ # Match, "7" is a 'word' character as well.
"a" =~ /\d/ # No match, "a" isn't a digit.
"7" =~ /\d/ # Match, "7" is a digit.
" " =~ /\s/ # Match, a space is whitespace.
"a" =~ /\D/ # Match, "a" is a non-digit.
"7" =~ /\D/ # No match, "7" is not a non-digit.
" " =~ /\S/ # No match, a space is not non-whitespace.
" " =~ /\h/ # Match, space is horizontal whitespace.
" " =~ /\v/ # No match, space is not vertical whitespace.
"\r" =~ /\v/ # Match, a return is vertical whitespace.
"a" =~ /\pL/ # Match, "a" is a letter.
"a" =~ /\p{Lu}/ # No match, /\p{Lu}/ matches upper case letters.
"\x{0e0b}" =~ /\p{Thai}/ # Match, \x{0e0b} is the character
# 'THAI CHARACTER SO SO', and that's in
# Thai Unicode class.
"a" =~ /\P{Lao}/ # Match, as "a" is not a Laotian character.
It is worth emphasizing that "\d", "\w", etc, match single characters,
not complete numbers or words. To match a number (that consists of
digits), use "\d+"; to match a word, use "\w+". But be aware of the
security considerations in doing so, as mentioned above.
Bracketed Character Classes
The third form of character class you can use in Perl regular
expressions is the bracketed character class. In its simplest form, it
lists the characters that may be matched, surrounded by square
brackets, like this: "[aeiou]". This matches one of "a", "e", "i", "o"
or "u". Like the other character classes, exactly one character is
matched.* To match a longer string consisting of characters mentioned
in the character class, follow the character class with a quantifier.
For instance, "[aeiou]+" matches one or more lowercase English vowels.
Repeating a character in a character class has no effect; it's
considered to be in the set only once.
Examples:
"e" =~ /[aeiou]/ # Match, as "e" is listed in the class.
"p" =~ /[aeiou]/ # No match, "p" is not listed in the class.
"ae" =~ /^[aeiou]$/ # No match, a character class only matches
# a single character.
"ae" =~ /^[aeiou]+$/ # Match, due to the quantifier.
-------
* There is an exception to a bracketed character class matching a
single character only. When the class is to match caselessly under
"/i" matching rules, and a character inside the class matches a
multiple-character sequence caselessly under Unicode rules, the class
(when not inverted) will also match that sequence. For example,
Unicode says that the letter "LATIN SMALL LETTER SHARP S" should match
the sequence "ss" under "/i" rules. Thus,
'ss' =~ /\A\N{LATIN SMALL LETTER SHARP S}\z/i # Matches
'ss' =~ /\A[aeioust\N{LATIN SMALL LETTER SHARP S}]\z/i # Matches
Special Characters Inside a Bracketed Character Class
Most characters that are meta characters in regular expressions (that
is, characters that carry a special meaning like ".", "*", or "(") lose
their special meaning and can be used inside a character class without
the need to escape them. For instance, "[()]" matches either an opening
parenthesis, or a closing parenthesis, and the parens inside the
character class don't group or capture.
Characters that may carry a special meaning inside a character class
are: "\", "^", "-", "[" and "]", and are discussed below. They can be
escaped with a backslash, although this is sometimes not needed, in
which case the backslash may be omitted.
The sequence "\b" is special inside a bracketed character class. While
outside the character class, "\b" is an assertion indicating a point
that does not have either two word characters or two non-word
characters on either side, inside a bracketed character class, "\b"
matches a backspace character.
The sequences "\a", "\c", "\e", "\f", "\n", "\N{NAME}", "\N{U+hex
char}", "\r", "\t", and "\x" are also special and have the same
meanings as they do outside a bracketed character class. (However,
inside a bracketed character class, if "\N{NAME}" expands to a sequence
of characters, only the first one in the sequence is used, with a
warning.)
Also, a backslash followed by two or three octal digits is considered
an octal number.
A "[" is not special inside a character class, unless it's the start of
a POSIX character class (see "POSIX Character Classes" below). It
normally does not need escaping.
A "]" is normally either the end of a POSIX character class (see "POSIX
Character Classes" below), or it signals the end of the bracketed
character class. If you want to include a "]" in the set of
characters, you must generally escape it.
However, if the "]" is the first (or the second if the first character
is a caret) character of a bracketed character class, it does not
denote the end of the class (as you cannot have an empty class) and is
considered part of the set of characters that can be matched without
escaping.
Examples:
"+" =~ /[+?*]/ # Match, "+" in a character class is not special.
"\cH" =~ /[\b]/ # Match, \b inside in a character class
# is equivalent to a backspace.
"]" =~ /[][]/ # Match, as the character class contains.
# both [ and ].
"[]" =~ /[[]]/ # Match, the pattern contains a character class
# containing just ], and the character class is
# followed by a ].
Character Ranges
It is not uncommon to want to match a range of characters. Luckily,
instead of listing all characters in the range, one may use the hyphen
("-"). If inside a bracketed character class you have two characters
separated by a hyphen, it's treated as if all characters between the
two were in the class. For instance, "[0-9]" matches any ASCII digit,
and "[a-m]" matches any lowercase letter from the first half of the
ASCII alphabet.
Note that the two characters on either side of the hyphen are not
necessarily both letters or both digits. Any character is possible,
although not advisable. "['-?]" contains a range of characters, but
most people will not know which characters that means. Furthermore,
such ranges may lead to portability problems if the code has to run on
a platform that uses a different character set, such as EBCDIC.
If a hyphen in a character class cannot syntactically be part of a
range, for instance because it is the first or the last character of
the character class, or if it immediately follows a range, the hyphen
isn't special, and so is considered a character to be matched
literally. If you want a hyphen in your set of characters to be
matched and its position in the class is such that it could be
considered part of a range, you must escape that hyphen with a
backslash.
Examples:
[a-z] # Matches a character that is a lower case ASCII letter.
[a-fz] # Matches any letter between 'a' and 'f' (inclusive) or
# the letter 'z'.
[-z] # Matches either a hyphen ('-') or the letter 'z'.
[a-f-m] # Matches any letter between 'a' and 'f' (inclusive), the
# hyphen ('-'), or the letter 'm'.
['-?] # Matches any of the characters '()*+,-./0123456789:;<=>?
# (But not on an EBCDIC platform).
Negation
It is also possible to instead list the characters you do not want to
match. You can do so by using a caret ("^") as the first character in
the character class. For instance, "[^a-z]" matches any character that
is not a lowercase ASCII letter, which therefore includes more than a
million Unicode code points. The class is said to be "negated" or
"inverted".
This syntax make the caret a special character inside a bracketed
character class, but only if it is the first character of the class. So
if you want the caret as one of the characters to match, either escape
the caret or else don't list it first.
In inverted bracketed character classes, Perl ignores the Unicode rules
that normally say that certain characters should match a sequence of
multiple characters under caseless "/i" matching. Following those
rules could lead to highly confusing situations:
"ss" =~ /^[^\xDF]+$/ui; # Matches!
This should match any sequences of characters that aren't "\xDF" nor
what "\xDF" matches under "/i". "s" isn't "\xDF", but Unicode says
that "ss" is what "\xDF" matches under "/i". So which one "wins"? Do
you fail the match because the string has "ss" or accept it because it
has an "s" followed by another "s"? Perl has chosen the latter.
Examples:
"e" =~ /[^aeiou]/ # No match, the 'e' is listed.
"x" =~ /[^aeiou]/ # Match, as 'x' isn't a lowercase vowel.
"^" =~ /[^^]/ # No match, matches anything that isn't a caret.
"^" =~ /[x^]/ # Match, caret is not special here.
Backslash Sequences
You can put any backslash sequence character class (with the exception
of "\N" and "\R") inside a bracketed character class, and it will act
just as if you had put all characters matched by the backslash sequence
inside the character class. For instance, "[a-f\d]" matches any decimal
digit, or any of the lowercase letters between 'a' and 'f' inclusive.
"\N" within a bracketed character class must be of the forms "\N{name}"
or "\N{U+hex char}", and NOT be the form that matches non-newlines, for
the same reason that a dot "." inside a bracketed character class loses
its special meaning: it matches nearly anything, which generally isn't
what you want to happen.
Examples:
/[\p{Thai}\d]/ # Matches a character that is either a Thai
# character, or a digit.
/[^\p{Arabic}()]/ # Matches a character that is neither an Arabic
# character, nor a parenthesis.
Backslash sequence character classes cannot form one of the endpoints
of a range. Thus, you can't say:
/[\p{Thai}-\d]/ # Wrong!
POSIX Character Classes
POSIX character classes have the form "[:class:]", where class is name,
and the "[:" and ":]" delimiters. POSIX character classes only appear
inside bracketed character classes, and are a convenient and
descriptive way of listing a group of characters.
Be careful about the syntax,
# Correct:
$string =~ /[[:alpha:]]/
# Incorrect (will warn):
$string =~ /[:alpha:]/
The latter pattern would be a character class consisting of a colon,
and the letters "a", "l", "p" and "h". POSIX character classes can be
part of a larger bracketed character class. For example,
[01[:alpha:]%]
is valid and matches '0', '1', any alphabetic character, and the
percent sign.
Perl recognizes the following POSIX character classes:
alpha Any alphabetical character ("[A-Za-z]").
alnum Any alphanumeric character. ("[A-Za-z0-9]")
ascii Any character in the ASCII character set.
blank A GNU extension, equal to a space or a horizontal tab ("\t").
cntrl Any control character. See Note [2] below.
digit Any decimal digit ("[0-9]"), equivalent to "\d".
graph Any printable character, excluding a space. See Note [3] below.
lower Any lowercase character ("[a-z]").
print Any printable character, including a space. See Note [4] below.
punct Any graphical character excluding "word" characters. Note [5].
space Any whitespace character. "\s" plus the vertical tab ("\cK").
upper Any uppercase character ("[A-Z]").
word A Perl extension ("[A-Za-z0-9_]"), equivalent to "\w".
xdigit Any hexadecimal digit ("[0-9a-fA-F]").
Most POSIX character classes have two Unicode-style "\p" property
counterparts. (They are not official Unicode properties, but Perl
extensions derived from official Unicode properties.) The table below
shows the relation between POSIX character classes and these
counterparts.
One counterpart, in the column labelled "ASCII-range Unicode" in the
table, matches only characters in the ASCII character set.
The other counterpart, in the column labelled "Full-range Unicode",
matches any appropriate characters in the full Unicode character set.
For example, "\p{Alpha}" matches not just the ASCII alphabetic
characters, but any character in the entire Unicode character set
considered alphabetic. An entry in the column labelled "backslash
sequence" is a (short) equivalent.
[[:...:]] ASCII-range Full-range backslash Note
Unicode Unicode sequence
-----------------------------------------------------
alpha \p{PosixAlpha} \p{XPosixAlpha}
alnum \p{PosixAlnum} \p{XPosixAlnum}
ascii \p{ASCII}
blank \p{PosixBlank} \p{XPosixBlank} \h [1]
or \p{HorizSpace} [1]
cntrl \p{PosixCntrl} \p{XPosixCntrl} [2]
digit \p{PosixDigit} \p{XPosixDigit} \d
graph \p{PosixGraph} \p{XPosixGraph} [3]
lower \p{PosixLower} \p{XPosixLower}
print \p{PosixPrint} \p{XPosixPrint} [4]
punct \p{PosixPunct} \p{XPosixPunct} [5]
\p{PerlSpace} \p{XPerlSpace} \s [6]
space \p{PosixSpace} \p{XPosixSpace} [6]
upper \p{PosixUpper} \p{XPosixUpper}
word \p{PosixWord} \p{XPosixWord} \w
xdigit \p{PosixXDigit} \p{XPosixXDigit}
[1] "\p{Blank}" and "\p{HorizSpace}" are synonyms.
[2] Control characters don't produce output as such, but instead
usually control the terminal somehow: for example, newline and
backspace are control characters. In the ASCII range, characters
whose code points are between 0 and 31 inclusive, plus 127 ("DEL")
are control characters.
On EBCDIC platforms, it is likely that the code page will define
"[[:cntrl:]]" to be the EBCDIC equivalents of the ASCII controls,
plus the controls that in Unicode have code pointss from 128
through 159.
[3] Any character that is graphical, that is, visible. This class
consists of all alphanumeric characters and all punctuation
characters.
[4] All printable characters, which is the set of all graphical
characters plus those whitespace characters which are not also
controls.
[5] "\p{PosixPunct}" and "[[:punct:]]" in the ASCII range match all
non-controls, non-alphanumeric, non-space characters:
"[-!"#$%&'()*+,./:;<=>?@[\\\]^_`{|}~]" (although if a locale is in
effect, it could alter the behavior of "[[:punct:]]").
The similarly named property, "\p{Punct}", matches a somewhat
different set in the ASCII range, namely
"[-!"#%&'()*,./:;?@[\\\]_{}]". That is, it is missing the nine
characters "[$+<=>^`|~]". This is because Unicode splits what
POSIX considers to be punctuation into two categories, Punctuation
and Symbols.
"\p{XPosixPunct}" and (under Unicode rules) "[[:punct:]]", match
what "\p{PosixPunct}" matches in the ASCII range, plus what
"\p{Punct}" matches. This is different than strictly matching
according to "\p{Punct}". Another way to say it is that if Unicode
rules are in effect, "[[:punct:]]" matches all characters that
Unicode considers punctuation, plus all ASCII-range characters that
Unicode considers symbols.
[6] "\p{SpacePerl}" and "\p{Space}" differ only in that in non-locale
matching, "\p{Space}" additionally matches the vertical tab, "\cK".
Same for the two ASCII-only range forms.
There are various other synonyms that can be used besides the names
listed in the table. For example, "\p{PosixAlpha}" can be written as
"\p{Alpha}". All are listed in "Properties accessible through \p{} and
\P{}" in perluniprops, plus all characters matched by each ASCII-range
property.
Both the "\p" counterparts always assume Unicode rules are in effect.
On ASCII platforms, this means they assume that the code points from
128 to 255 are Latin-1, and that means that using them under locale
rules is unwise unless the locale is guaranteed to be Latin-1 or UTF-8.
In contrast, the POSIX character classes are useful under locale rules.
They are affected by the actual rules in effect, as follows:
If the "/a" modifier, is in effect ...
Each of the POSIX classes matches exactly the same as their ASCII-
range counterparts.
otherwise ...
For code points above 255 ...
The POSIX class matches the same as its Full-range counterpart.
For code points below 256 ...
if locale rules are in effect ...
The POSIX class matches according to the locale, except
that "word" uses the platform's native underscore
character, no matter what the locale is.
if Unicode rules are in effect or if on an EBCDIC platform ...
The POSIX class matches the same as the Full-range
counterpart.
otherwise ...
The POSIX class matches the same as the ASCII range
counterpart.
Which rules apply are determined as described in "Which character set
modifier is in effect?" in perlre.
It is proposed to change this behavior in a future release of Perl so
that whether or not Unicode rules are in effect would not change the
behavior: Outside of locale or an EBCDIC code page, the POSIX classes
would behave like their ASCII-range counterparts. If you wish to
comment on this proposal, send email to "perl5-porters AT perl.org".
Negation of POSIX character classes
A Perl extension to the POSIX character class is the ability to negate
it. This is done by prefixing the class name with a caret ("^"). Some
examples:
POSIX ASCII-range Full-range backslash
Unicode Unicode sequence
-----------------------------------------------------
[[:^digit:]] \P{PosixDigit} \P{XPosixDigit} \D
[[:^space:]] \P{PosixSpace} \P{XPosixSpace}
\P{PerlSpace} \P{XPerlSpace} \S
[[:^word:]] \P{PerlWord} \P{XPosixWord} \W
The backslash sequence can mean either ASCII- or Full-range Unicode,
depending on various factors as described in "Which character set
modifier is in effect?" in perlre.
[= =] and [. .]
Perl recognizes the POSIX character classes "[=class=]" and
"[.class.]", but does not (yet?) support them. Any attempt to use
either construct raises an exception.
Examples
/[[:digit:]]/ # Matches a character that is a digit.
/[01[:lower:]]/ # Matches a character that is either a
# lowercase letter, or '0' or '1'.
/[[:digit:][:^xdigit:]]/ # Matches a character that can be anything
# except the letters 'a' to 'f'. This is
# because the main character class is composed
# of two POSIX character classes that are ORed
# together, one that matches any digit, and
# the other that matches anything that isn't a
# hex digit. The result matches all
# characters except the letters 'a' to 'f' and
# 'A' to 'F'.
perl v5.16.3 2013-03-04 PERLRECHARCLASS(1)
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