perlrecharclass - Perl Regular Expression Character Classes
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 (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. The 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)
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
\d
matches a single character considered to be a decimal digit.
If the /a
modifier 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.
In Unicode 5.2, 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
.
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.
/a
modifier is in effect ...
\w
matches the 63 characters [a-zA-Z0-9_].
\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.
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, "ID_Start", ID_Continue", "XID_Start", and "XID_Continue". See http://unicode.org/reports/tr31.
Any character not matched by \w
is matched by \W
.
\s matches any single character considered whitespace.
/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.)
\s matches exactly the code points above 255 shown with an "s" column
in the table below.
\s matches whatever the locale considers to be whitespace. Note that
this is likely to include the vertical space, unlike non-locale \s
matching.
\s matches exactly the characters shown with an "s" column in the
table below.
\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 space and tab characters and several others
listed in the table below. \H
matches any character
not considered horizontal whitespace.
\v
matches any character considered vertical whitespace;
this includes the 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.
\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).
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 whether the
source string is in UTF-8 format.
One might think that \s is equivalent to [\h\v]
. This is not true.
For example, 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 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).
- 0x00009 CHARACTER TABULATION h s
- 0x0000a LINE FEED (LF) vs
- 0x0000b LINE TABULATION v
- 0x0000c FORM FEED (FF) vs
- 0x0000d CARRIAGE RETURN (CR) vs
- 0x00020 SPACE h s
- 0x00085 NEXT LINE (NEL) vs [1]
- 0x000a0 NO-BREAK SPACE h s [1]
- 0x01680 OGHAM SPACE MARK h s
- 0x0180e MONGOLIAN VOWEL SEPARATOR h s
- 0x02000 EN QUAD h s
- 0x02001 EM QUAD h s
- 0x02002 EN SPACE h s
- 0x02003 EM SPACE h s
- 0x02004 THREE-PER-EM SPACE h s
- 0x02005 FOUR-PER-EM SPACE h s
- 0x02006 SIX-PER-EM SPACE h s
- 0x02007 FIGURE SPACE h s
- 0x02008 PUNCTUATION SPACE h s
- 0x02009 THIN SPACE h s
- 0x0200a HAIR SPACE h s
- 0x02028 LINE SEPARATOR vs
- 0x02029 PARAGRAPH SEPARATOR vs
- 0x0202f NARROW NO-BREAK SPACE h s
- 0x0205f MEDIUM MATHEMATICAL SPACE h s
- 0x03000 IDEOGRAPHIC SPACE h s
NEXT LINE and NO-BREAK SPACE may or may not match \s depending
on the rules in effect. See
the beginning of this section.
\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
.
\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 as 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 matching 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.
- "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.
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 only a
single character. When the class is to match caselessely 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
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 ].
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 old 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).
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 almost a hundred thousand
Unicode letters. 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 not list it first.
In inverted bracketed character classes, Perl ignores the Unicode rules
that normally say that a given character matches a sequence of multiple
characters under caseless /i matching, which otherwise could be
highly confusing:
- "ss" =~ /^[^\xDF]+$/ui;
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?
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.
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 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.
The column labelled "backslash sequence" is a (short) synonym for
the Full-range Unicode form.
(Each of the counterparts has various synonyms as well.
Properties accessible through \p{} and \P{} in perluniprops lists all
synonyms, plus all characters matched by each ASCII-range property.
For example, \p{AHex}
is a synonym for \p{ASCII_Hex_Digit}
,
and any \p
property name can be prefixed with "Is" such as \p{IsAlpha}
.)
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:
/a
modifier, is in effect ...
Each of the POSIX classes matches exactly the same as their ASCII-range counterparts.
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@perl.org
.
- [[:...:]] 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}
\p{Blank}
and \p{HorizSpace}
are synonyms.
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.
Any character that is graphical, that is, visible. This class consists of all alphanumeric characters and all punctuation characters.
All printable characters, which is the set of all graphical characters plus those whitespace characters which are not also controls.
\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 [$+<=>^`|~]
.
This is because Unicode splits what POSIX considers to be punctuation into two
categories, Punctuation and Symbols.
\p{XPosixPunct}
and (in Unicode mode) [[: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.
\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 for these besides
\p{HorizSpace}
and \\p{XPosixBlank}
. For example,
\p{PosixAlpha}
can be written as \p{Alpha}
. All are listed
in Properties accessible through \p{} and \P{} in perluniprops.
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.
Perl recognizes the POSIX character classes [=class=]
and
[.class.], but does not (yet?) support them. Any attempt to use
either construct raises an exception.
- /[[: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'.