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. 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)
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
Digits
"\d" matches a single character that is considered to be a decimal
digit. What is considered a decimal digit depends on the internal
encoding of the source string and the locale that is in effect. If the
source string is in UTF-8 format, "\d" not only matches the digits '0'
- '9', but also Arabic, Devanagari and digits from other languages.
Otherwise, if there is a locale in effect, it will match whatever
characters the locale considers decimal digits. Without a locale, "\d"
matches just the digits '0' to '9'. See "Locale, EBCDIC, Unicode and
UTF-8".
Unicode digits may cause some confusion, and some security issues. In
UTF-8 strings, "\d" matches the same characters matched by
"\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 subscripts.
The design intent is for "\d" to match all the digits (and no other
characters) that can be used with "normal" big-endian positional
decimal syntax, whereby a sequence of such digits {N0, N1, N2, ...Nn}
has the numeric value (...(N0 * 10 + N1) * 10 + N2) * 10 ... + Nn). 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>.)
Some of the non-European digits that "\d" matches look like European
ones, but have different values. For example, BENGALI DIGIT FOUR
(U+09A) looks very much like an ASCII DIGIT EIGHT (U+0038).
It may be useful for security purposes for an application to require
that all digits in a row be from the same script. See "charscript()"
in Unicode::UCD.
Any character that isn't matched by "\d" will be matched by "\D".
Word characters
A "\w" matches a single alphanumeric character (an alphabetic
character, or a decimal digit) or an underscore ("_"), not a whole
word. To match a whole word, use "\w+". This isn't the same thing as
matching an English word, but is the same as a string of Perl-
identifier characters. What is considered a word character depends on
the internal encoding of the string and the locale or EBCDIC code page
that is in effect. If it's in UTF-8 format, "\w" matches those
characters that are considered word characters in the Unicode database.
That is, it not only matches ASCII letters, but also Thai letters,
Greek letters, etc. If the source string isn't in UTF-8 format, "\w"
matches those characters that are considered word characters by the
current locale or EBCDIC code page. Without a locale or EBCDIC code
page, "\w" matches the ASCII letters, digits and the underscore. See
"Locale, EBCDIC, Unicode and UTF-8".
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 that isn't matched by "\w" will be matched by "\W".
Whitespace
"\s" matches any single character that is considered whitespace. The
exact set of characters matched by "\s" depends on whether the source
string is in UTF-8 format and the locale or EBCDIC code page that is in
effect. If it's in UTF-8 format, "\s" matches what is considered
whitespace in the Unicode database; the complete list is in the table
below. Otherwise, if there is a locale or EBCDIC code page in effect,
"\s" matches whatever is considered whitespace by the current locale or
EBCDIC code page. Without a locale or EBCDIC code page, "\s" matches
the horizontal tab ("\t"), the newline ("\n"), the form feed ("\f"),
the carriage return ("\r"), and the space. (Note that it doesn't match
the vertical tab, "\cK".) Perhaps the most notable possible surprise
is that "\s" matches a non-breaking space only if the non-breaking
space is in a UTF-8 encoded string or the locale or EBCDIC code page
that is in effect has that character. See "Locale, EBCDIC, Unicode and
UTF-8".
Any character that isn't matched by "\s" will be matched by "\S".
"\h" will match any character that is considered horizontal whitespace;
this includes the space and the tab characters and a number other
characters, all of which are listed in the table below. "\H" will
match any character that is not considered horizontal whitespace.
"\v" will match any character that is considered vertical whitespace;
this includes the carriage return and line feed characters (newline)
plus several other characters, all listed in the table below. "\V"
will match any character that is 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", "\d" and "\w", "\h" and "\v" always match the
same characters, regardless whether the source string is in UTF-8
format or not. The set of characters they match is also not influenced
by locale nor EBCDIC code page.
One might think that "\s" is equivalent to "[\h\v]". This is not true.
The vertical tab ("\x0b") is not matched by "\s", it is however
considered vertical whitespace. Furthermore, if the source string is
not in UTF-8 format, and any locale or EBCDIC code page that is in
effect doesn't include them, the next line (ASCII-platform "\x85") and
the no-break space (ASCII-platform "\xA0") characters are not matched
by "\s", but are by "\v" and "\h" respectively. If the source string
is in UTF-8 format, both the next line and the no-break space are
matched by "\s".
The following table is a complete listing of characters matched by
"\s", "\h" and "\v" as of Unicode 5.2.
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
[1] NEXT LINE and NO-BREAK SPACE only match "\s" if the source string
is in UTF-8 format, or the locale or EBCDIC code page that is in
effect includes them.
It is worth noting that "\d", "\w", etc, match single characters, not
complete numbers or words. To match a number (that consists of
integers), use "\d+"; to match a word, use "\w+".
\N
"\N" is new in 5.12, and is experimental. It, like the dot, will match
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".
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 the 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".
For more details, see "Unicode Character Properties" in perlunicode;
for a complete list of possible properties, see "Properties accessible
through \p{} and \P{}" in perluniprops. It is also possible to define
your own properties. This is discussed in "User-Defined Character
Properties" in perlunicode.
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.
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 will
be 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 a string of 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.
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+wide hex
char}", "\r", "\t", and "\x" are also special and have the same
meanings as they do outside a bracketed character class.
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 the 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 the characters
between the two are 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
necessary 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 will be. 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 will be considered a character that is to be matched
literally. You have to escape the hyphen with a backslash if you want
to have 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.
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 a character that is
not a lowercase ASCII letter.
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 to have the caret as one of the characters you want to
match, you either have to escape the caret, or not list it first.
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") inside a bracketed character class, and it will act just as if
you put all the characters matched by the backslash sequence inside the
character class. For instance, "[a-f\d]" will match 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+wide 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, though they currently
suffer from portability issues (see below and "Locale, EBCDIC, Unicode
and UTF-8").
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 alphanumerical 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, will only match 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}" will match not just the ASCII alphabetic
characters, but any character in the entire Unicode character set that
is considered to be alphabetic.
(Each of the counterparts has various synonyms as well. "Properties
accessible through \p{} and \P{}" in perluniprops lists all the
synonyms, plus all the characters matched by each of the ASCII-range
properties. 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" forms are unaffected by any locale that is in effect, or
whether the string is in UTF-8 format or not, or whether the platform
is EBCDIC or not. In contrast, the POSIX character classes are
affected. If the source string is in UTF-8 format, the POSIX classes
(with the exception of "[[:punct:]]", see Note [5] below) behave like
their "Full-range" Unicode counterparts. If the source string is not
in UTF-8 format, and no locale is in effect, and the platform is not
EBCDIC, all the POSIX classes behave like their ASCII-range
counterparts. Otherwise, they behave based on the rules of the locale
or EBCDIC code page.
It is proposed to change this behavior in a future release of Perl so
that the the UTF8ness of the source string will be irrelevant to the
behavior of the POSIX character classes. This means they will always
behave in strict accordance with the official POSIX standard. That is,
if either locale or EBCDIC code page is present, they will behave in
accordance with those; if absent, the classes will match only their
ASCII-range counterparts. If you disagree with this proposal, send
email to "perl5-porters@perl.org".
[[:...:]] ASCII-range Full-range backslash Note
Unicode Unicode sequence
-----------------------------------------------------
alpha \p{PosixAlpha} \p{Alpha}
alnum \p{PosixAlnum} \p{Alnum}
ascii \p{ASCII}
blank \p{PosixBlank} \p{Blank} = [1]
\p{HorizSpace} \h [1]
cntrl \p{PosixCntrl} \p{Cntrl} [2]
digit \p{PosixDigit} \p{Digit} \d
graph \p{PosixGraph} \p{Graph} [3]
lower \p{PosixLower} \p{Lower}
print \p{PosixPrint} \p{Print} [4]
punct \p{PosixPunct} \p{Punct} [5]
\p{PerlSpace} \p{SpacePerl} \s [6]
space \p{PosixSpace} \p{Space} [6]
upper \p{PosixUpper} \p{Upper}
word \p{PerlWord} \p{Word} \w
xdigit \p{ASCII_Hex_Digit} \p{XDigit}
[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 ordinals 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 ordinals from 128 through
159.
[3] Any character that is graphical, that is, visible. This class
consists of all the alphanumerical characters and all punctuation
characters.
[4] All printable characters, which is the set of all the graphical
characters plus whitespace characters that are not also controls.
[5] (punct)
"\p{PosixPunct}" and "[[:punct:]]" in the ASCII range match all the
non-controls, non-alphanumeric, non-space characters:
"[-!"#$%&'()*+,./:;<=>?@[\\\]^_`{|}~]" (although if a locale is in
effect, it could alter the behavior of "[[:punct:]]").
"\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.
When the matching string is in UTF-8 format, "[[:punct:]]" matches
what it 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 for a UTF-8 string, "[[:punct:]]"
matches all the characters that Unicode considers to be
punctuation, plus all the ASCII-range characters that Unicode
considers to be symbols.
[6] "\p{SpacePerl}" and "\p{Space}" differ only in that "\p{Space}"
additionally matches the vertical tab, "\cK". Same for the two
ASCII-only range forms.
Negation
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{Digit} \D
[[:^space:]] \P{PosixSpace} \P{Space}
\P{PerlSpace} \P{SpacePerl} \S
[[:^word:]] \P{PerlWord} \P{Word} \W
[= =] and [. .]
Perl will recognize the POSIX character classes "[=class=]", and
"[.class.]", but does not (yet?) support them. Use of such a construct
will lead to an error.
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'.
Locale, EBCDIC, Unicode and UTF-8
Some of the character classes have a somewhat different behaviour
depending on the internal encoding of the source string, and the locale
that is in effect, and if the program is running on an EBCDIC platform.
"\w", "\d", "\s" and the POSIX character classes (and their negations,
including "\W", "\D", "\S") suffer from this behaviour. (Since the
backslash sequences "\b" and "\B" are defined in terms of "\w" and
"\W", they also are affected.)
The rule is that if the source string is in UTF-8 format, the character
classes match according to the Unicode properties. If the source string
isn't, then the character classes match according to whatever locale or
EBCDIC code page is in effect. If there is no locale nor EBCDIC, they
match the ASCII defaults (0 to 9 for "\d"; 52 letters, 10 digits and
underscore for "\w"; etc.).
This usually means that if you are matching against characters whose
"ord()" values are between 128 and 255 inclusive, your character class
may match or not depending on the current locale or EBCDIC code page,
and whether the source string is in UTF-8 format. The string will be in
UTF-8 format if it contains characters whose "ord()" value exceeds 255.
But a string may be in UTF-8 format without it having such characters.
See "The "Unicode Bug"" in perlunicode.
For portability reasons, it may be better to not use "\w", "\d", "\s"
or the POSIX character classes, and use the Unicode properties instead.
Examples
$str = "\xDF"; # $str is not in UTF-8 format.
$str =~ /^\w/; # No match, as $str isn't in UTF-8 format.
$str .= "\x{0e0b}"; # Now $str is in UTF-8 format.
$str =~ /^\w/; # Match! $str is now in UTF-8 format.
chop $str;
$str =~ /^\w/; # Still a match! $str remains in UTF-8 format.
perl v5.12.5 2012-11-03 PERLRECHARCLASS(1)
