=head1 NAME
+X<character class>
perlrecharclass - Perl Regular Expression Character Classes
is found in L<perlre>.
This manual page discusses the syntax and use of character
-classes in Perl Regular Expressions.
+classes in Perl regular expressions.
-A character class is a way of denoting a set of characters,
+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
+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, backslashed sequences, and the bracketed form.
+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.
=head2 The dot
The dot (or period), C<.> 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 with the I<single line> modifier: either
-for the entire regular expression using the C</s> modifier, or
-locally using C<(?s)>.
+add matching the newline by using the I<single line> modifier: either
+for the entire regular expression with the C</s> modifier, or
+locally with C<(?s)>. (The experimental C<\N> backslash sequence, described
+below, matches any character except newline without regard to the
+I<single line> modifier.)
Here are some examples:
"\n" =~ /(?s:.)/ # Match (local 'single line' modifier)
"ab" =~ /^.$/ # No match (dot matches one character)
+=head2 Backslash sequences
+X<\w> X<\W> X<\s> X<\S> X<\d> X<\D> X<\p> X<\P>
+X<\N> X<\v> X<\V> X<\h> X<\H>
+X<word> X<whitespace>
-=head2 Backslashed 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.
-Perl regular expressions contain many backslashed sequences that
-constitute a character class. That is, they will match a single
-character, if that character belongs to a specific set of characters
-(defined by the sequence). A backslashed sequence is a sequence of
-characters starting with a backslash. Not all backslashed sequences
-are character class; for a full list, see L<perlrebackslash>.
+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 L<perlrebackslash>.)
-Here's a list of the backslashed sequences, which are discussed in
-more detail below.
-
- \d Match a digit character.
- \D Match a non-digit character.
+ \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 white space character.
- \S Match a non-white space character.
- \h Match a horizontal white space character.
- \H Match a character that isn't horizontal white space.
- \v Match a vertical white space character.
- \V Match a character that isn't vertical white space.
- \pP, \p{Prop} Match a character matching a Unicode property.
- \PP, \P{Prop} Match a character that doesn't match a Unicode property.
+ \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
=head3 Digits
-C<\d> matches a single character that is considered to be a I<digit>.
-What is considered a digit depends on the internal encoding of
-the source string. If the source string is in UTF-8 format, C<\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 digits. Without
-a locale, C<\d> matches the digits '0' to '9'.
-See L</Locale, Unicode and UTF-8>.
+C<\d> matches a single character that is considered to be a decimal I<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, C<\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, C<\d> matches just the digits '0' to '9'.
+See L</Locale, EBCDIC, Unicode and UTF-8>.
+
+Unicode digits may cause some confusion, and some security issues. In UTF-8
+strings, C<\d> matches the same characters matched by
+C<\p{General_Category=Decimal_Number}>, or synonymously,
+C<\p{General_Category=Digit}>. Starting with Unicode version 4.1, this is the
+same set of characters matched by C<\p{Numeric_Type=Decimal}>.
+
+But Unicode also has a different property with a similar name,
+C<\p{Numeric_Type=Digit}>, which matches a completely different set of
+characters. These characters are things such as subscripts.
+
+The design intent is for C<\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 L<http://www.unicode.org/notes/tn21>.)
+
+Some of the non-European digits that C<\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 L<Unicode::UCD/charscript()>.
Any character that isn't matched by C<\d> will be matched by C<\D>.
=head3 Word characters
-C<\w> matches a single I<word> character: an alphanumeric character
-(that is, an alphabetic character, or a digit), or the underscore (C<_>).
-What is considered a word character depends on the internal encoding
-of the string. If it's in UTF-8 format, C<\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, C<\w> matches those characters
-that are considered word characters by the current locale. Without
-a locale in effect, C<\w> matches the ASCII letters, digits and the
-underscore.
+A C<\w> matches a single alphanumeric character (an alphabetic character, or a
+decimal digit) or an underscore (C<_>), not a whole word. To match a whole
+word, use C<\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, C<\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, C<\w> matches those characters that are considered word characters by
+the current locale or EBCDIC code page. Without a locale or EBCDIC code page,
+C<\w> matches the ASCII letters, digits and the underscore.
+See L</Locale, EBCDIC, Unicode and UTF-8>.
+
+There are a number of security issues with the full Unicode list of word
+characters. See L<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 L<http://unicode.org/reports/tr31>.
Any character that isn't matched by C<\w> will be matched by C<\W>.
-=head3 White space
-
-C<\s> matches any single character that is consider white space. In the
-ASCII range, C<\s> matches the horizontal tab (C<\t>), the new line
-(C<\n>), the form feed (C<\f>), the carriage return (C<\r>), and the
-space (the vertical tab, C<\cK> is not matched by C<\s>). The exact set
-of characters matched by C<\s> depends on whether the source string is
-in UTF-8 format. If it is, C<\s> matches what is considered white space
-in the Unicode database. Otherwise, if there is a locale in effect, C<\s>
-matches whatever is considered white space by the current locale. Without
-a locale, C<\s> matches the five characters mentioned in the beginning
-of this paragraph. Perhaps the most notable difference is that C<\s>
-matches a non-breaking space only if the non-breaking space is in a
-UTF-8 encoded string.
+=head3 Whitespace
+
+C<\s> matches any single character that is considered whitespace. The exact
+set of characters matched by C<\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, C<\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, C<\s> matches whatever is considered
+whitespace by the current locale or EBCDIC code page. Without a locale or
+EBCDIC code page, C<\s> matches the horizontal tab (C<\t>), the newline
+(C<\n>), the form feed (C<\f>), the carriage return (C<\r>), and the space.
+(Note that it doesn't match the vertical tab, C<\cK>.) Perhaps the most notable
+possible surprise is that C<\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 L</Locale, EBCDIC, Unicode and UTF-8>.
Any character that isn't matched by C<\s> will be matched by C<\S>.
-C<\h> will match any character that is considered horizontal white space;
-this includes the space and the tab characters. C<\H> will match any character
-that is not considered horizontal white space.
+C<\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. C<\H> will match any character
+that is not considered horizontal whitespace.
-C<\v> will match any character that is considered vertical white space;
-this includes the carriage return and line feed characters (newline).
-C<\V> will match any character that is not considered vertical white space.
+C<\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.
+C<\V> will match any character that is not considered vertical whitespace.
C<\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. Details are discussed in L<perlrebackslash>.
-
-C<\h>, C<\H>, C<\v>, C<\V>, and C<\R> are new in perl 5.10.0.
+class; use C<\v> instead (vertical whitespace).
+Details are discussed in L<perlrebackslash>.
Note that unlike C<\s>, C<\d> and C<\w>, C<\h> and C<\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.
+by locale nor EBCDIC code page.
-One might think that C<\s> is equivalent with C<[\h\v]>. This is not true.
-The vertical tab (C<"\x0b">) is not matched by C<\s>, it is however
-considered vertical white space. Furthermore, if the source string is
-not in UTF-8 format, the next line (C<"\x85">) and the no-break space
-(C<"\xA0">) are not matched by C<\s>, but are by C<\v> and C<\h> respectively.
-If the source string is in UTF-8 format, both the next line and the
-no-break space are matched by C<\s>.
+One might think that C<\s> is equivalent to C<[\h\v]>. This is not true. The
+vertical tab (C<"\x0b">) is not matched by C<\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 C<"\x85">) and the no-break space (ASCII-platform
+C<"\xA0">) characters are not matched by C<\s>, but are by C<\v> and C<\h>
+respectively. If the source string is in UTF-8 format, both the next line and
+the no-break space are matched by C<\s>.
The following table is a complete listing of characters matched by
-C<\s>, C<\h> and C<\v>.
+C<\s>, C<\h> and C<\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.
+by which class(es) the character is matched (assuming no locale or EBCDIC code
+page is in effect that changes the C<\s> matching).
0x00009 CHARACTER TABULATION h s
0x0000a LINE FEED (LF) vs
=item [1]
NEXT LINE and NO-BREAK SPACE only match C<\s> if the source string is in
-UTF-8 format.
+UTF-8 format, or the locale or EBCDIC code page that is in effect includes them.
=back
complete numbers or words. To match a number (that consists of integers),
use C<\d+>; to match a word, use C<\w+>.
+=head3 \N
+
+C<\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 C<\N> is not influenced
+by the I<single line> regular expression modifier (see L</The dot> above). Note
+that the form C<\N{...}> may mean something completely different. When the
+C<{...}> is a L<quantifier|perlre/Quantifiers>, it means to match a non-newline
+character that many times. For example, C<\N{3}> means to match 3
+non-newlines; C<\N{5,}> means to match 5 or more non-newlines. But if C<{...}>
+is not a legal quantifier, it is presumed to be a named character. See
+L<charnames> for those. For example, none of C<\N{COLON}>, C<\N{4F}>, and
+C<\N{F4}> contain legal quantifiers, so Perl will try to find characters whose
+names are, respectively, C<COLON>, C<4F>, and C<F4>.
=head3 Unicode Properties
-C<\pP> and C<\p{Prop}> are character classes to match characters that
-fit given Unicode classes. One letter classes can be used in the C<\pP>
-form, with the class name following the C<\p>, otherwise, the property
-name is enclosed in braces, and follows the C<\p>. For instance, a
-match for a number can be written as C</\pN/> or as C</\p{Number}/>.
-Lowercase letters are matched by the property I<LowercaseLetter> which
-has as short form I<Ll>. They have to be written as C</\p{Ll}/> or
-C</\p{LowercaseLetter}/>. C</\pLl/> is valid, but means something different.
+C<\pP> and C<\p{Prop}> are character classes to match characters that fit given
+Unicode properties. One letter property names can be used in the C<\pP> form,
+with the property name following the C<\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 C<\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 C</\pN/> or as
+C</\p{Number}/>, or as C</\p{Number=True}/>.
+Lowercase letters are matched by the property I<Lowercase_Letter> which
+has as short form I<Ll>. They need the braces, so are written as C</\p{Ll}/> or
+C</\p{Lowercase_Letter}/>, or C</\p{General_Category=Lowercase_Letter}/>
+(the underscores are optional).
+C</\pLl/> is valid, but means something different.
It matches a two character string: a letter (Unicode property C<\pL>),
followed by a lowercase C<l>.
-For a list of possible properties, see
-L<perlunicode/Unicode Character Properties>. It is also possible to
-defined your own properties. This is discussed in
+For more details, see L<perlunicode/Unicode Character Properties>; for a
+complete list of possible properties, see
+L<perluniprops/Properties accessible through \p{} and \P{}>.
+It is also possible to define your own properties. This is discussed in
L<perlunicode/User-Defined Character Properties>.
"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 white space.
+ " " =~ /\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-white space.
+ " " =~ /\S/ # No match, a space is not non-whitespace.
- " " =~ /\h/ # Match, space is horizontal white space.
- " " =~ /\v/ # No match, space is not vertical white space.
- "\r" =~ /\v/ # Match, a return is vertical white space.
+ " " =~ /\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 Laoian character.
+ "a" =~ /\P{Lao}/ # Match, as "a" is not a Laotian character.
=head2 Bracketed Character Classes
The third form of character class you can use in Perl regular expressions
-is the bracketed form. In its simplest form, it lists the characters
-that may be matched inside square brackets, like this: C<[aeiou]>.
-This matches one of C<a>, C<e>, C<i>, C<o> or C<u>. Just as the other
+is the bracketed character class. In its simplest form, it lists the characters
+that may be matched, surrounded by square brackets, like this: C<[aeiou]>.
+This matches one of C<a>, C<e>, C<i>, C<o> or C<u>. Like the other
character classes, exactly one character will be matched. To match
-a longer string consisting of characters mentioned in the characters
-class, follow the character class with a quantifier. For instance,
-C<[aeiou]+> matches a string of one or more lowercase ASCII vowels.
+a longer string consisting of characters mentioned in the character
+class, follow the character class with a L<quantifier|perlre/Quantifiers>. For
+instance, C<[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.
=head3 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 C<*> or C<(>) lose
+is, characters that carry a special meaning like C<.>, C<*>, or C<(>) lose
their special meaning and can be used inside a character class without
the need to escape them. For instance, C<[()]> matches either an opening
parenthesis, or a closing parenthesis, and the parens inside the character
case the backslash may be omitted.
The sequence C<\b> is special inside a bracketed character class. While
-outside the character class C<\b> is an assertion indicating a point
+outside the character class, C<\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, C<\b> matches a
backspace character.
-A C<[> is not special inside a character class, unless it's the start
-of a POSIX character class (see below). It normally does not need escaping.
-
-A C<]> is either the end of a POSIX character class (see below), or it
-signals the end of the bracketed character class. Normally it needs
-escaping if you want to include a C<]> in the set of characters.
+The sequences
+C<\a>,
+C<\c>,
+C<\e>,
+C<\f>,
+C<\n>,
+C<\N{I<NAME>}>,
+C<\N{U+I<wide hex char>}>,
+C<\r>,
+C<\t>,
+and
+C<\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 C<[> is not special inside a character class, unless it's the start of a
+POSIX character class (see L</POSIX Character Classes> below). It normally does
+not need escaping.
+
+A C<]> is normally either the end of a POSIX character class (see
+L</POSIX Character Classes> below), or it signals the end of the bracketed
+character class. If you want to include a C<]> in the set of characters, you
+must generally escape it.
However, if the C<]> is the I<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)
"+" =~ /[+?*]/ # Match, "+" in a character class is not special.
"\cH" =~ /[\b]/ # Match, \b inside in a character class
- # is equivalent with a backspace.
+ # is equivalent to a backspace.
"]" =~ /[][]/ # Match, as the character class contains.
# both [ and ].
"[]" =~ /[[]]/ # Match, the pattern contains a character class
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 be part of a range, for instance
-because it is the first or the last character of the character class,
+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 may be matched. 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 can be considered
-part of a range.
+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'.
+ [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'.
=head3 Backslash Sequences
-You can put a backslash sequence character class 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,
-C<[a-f\d]> will match any digit, or any of the lowercase letters between
-'a' and 'f' inclusive.
+You can put any backslash sequence character class (with the exception of
+C<\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, C<[a-f\d]> will match any decimal digit, or any
+of the lowercase letters between 'a' and 'f' inclusive.
+
+C<\N> within a bracketed character class must be of the forms C<\N{I<name>}>
+or C<\N{U+I<wide hex char>}>, and NOT be the form that matches non-newlines,
+for the same reason that a dot C<.> inside a bracketed character class loses
+its special meaning: it matches nearly anything, which generally isn't what you
+want to happen.
+
Examples:
# character, nor a parenthesis.
Backslash sequence character classes cannot form one of the endpoints
-of a range.
+of a range. Thus, you can't say:
+
+ /[\p{Thai}-\d]/ # Wrong!
-=head3 Posix Character Classes
+=head3 POSIX Character Classes
+X<character class> X<\p> X<\p{}>
+X<alpha> X<alnum> X<ascii> X<blank> X<cntrl> X<digit> X<graph>
+X<lower> X<print> X<punct> X<space> X<upper> X<word> X<xdigit>
-Posix character classes have the form C<[:class:]>, where I<class> is
-name, and the C<[:> and C<:]> delimiters. Posix character classes appear
+POSIX character classes have the form C<[:class:]>, where I<class> is
+name, and the C<[:> and C<:]> delimiters. POSIX character classes only appear
I<inside> bracketed character classes, and are a convenient and descriptive
-way of listing a group of characters. Be careful about the syntax,
+way of listing a group of characters, though they currently suffer from
+portability issues (see below and L<Locale, EBCDIC, Unicode and UTF-8>).
+
+Be careful about the syntax,
# Correct:
$string =~ /[[:alpha:]]/
The latter pattern would be a character class consisting of a colon,
and the letters C<a>, C<l>, C<p> and C<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.
- alnum Any alphanumerical character.
- ascii Any ASCII character.
- blank A GNU extension, equal to a space or a horizontal tab (C<\t>).
- cntrl Any control character.
- digit Any digit, equivalent to C<\d>.
- graph Any printable character, excluding a space.
- lower Any lowercase character.
- print Any printable character, including a space.
- punct Any punctuation character.
- space Any white space character. C<\s> plus the vertical tab (C<\cK>).
- upper Any uppercase character.
- word Any "word" character, equivalent to C<\w>.
- xdigit Any hexadecimal digit, '0' - '9', 'a' - 'f', 'A' - 'F'.
-
-The exact set of characters matched depends on whether the source string
-is internally in UTF-8 format or not. See L</Locale, Unicode and UTF-8>.
-
-Most POSIX character classes have C<\p> counterparts. The difference
-is that the C<\p> classes will always match according to the Unicode
-properties, regardless whether the string is in UTF-8 format or not.
-
-The following table shows the relation between POSIX character classes
-and the Unicode properties:
-
- [[:...:]] \p{...} backslash
-
- alpha IsAlpha
- alnum IsAlnum
- ascii IsASCII
- blank
- cntrl IsCntrl
- digit IsDigit \d
- graph IsGraph
- lower IsLower
- print IsPrint
- punct IsPunct
- space IsSpace
- IsSpacePerl \s
- upper IsUpper
- word IsWord
- xdigit IsXDigit
-
-Some character classes may have a non-obvious name:
+ 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 C<\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,
+C<\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.
+L<perluniprops/Properties accessible through \p{} and \P{}> lists all the
+synonyms, plus all the characters matched by each of the ASCII-range
+properties. For example C<\p{AHex}> is a synonym for C<\p{ASCII_Hex_Digit}>,
+and any C<\p> property name can be prefixed with "Is" such as C<\p{IsAlpha}>.)
+
+Both the C<\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 C<[[: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 C<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}
=over 4
-=item cntrl
+=item [1]
+
+C<\p{Blank}> and C<\p{HorizSpace}> are synonyms.
+
+=item [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 (C<DEL>) are control characters.
-Any control character. Usually, control characters don't produce output
-as such, but instead control the terminal somehow: for example newline
-and backspace are control characters. All characters with C<ord()> less
-than 32 are usually classified as control characters (in ASCII, the ISO
-Latin character sets, and Unicode), as is the character C<ord()> value
-of 127 (C<DEL>).
+On EBCDIC platforms, it is likely that the code page will define C<[[:cntrl:]]>
+to be the EBCDIC equivalents of the ASCII controls, plus the controls
+that in Unicode have ordinals from 128 through 159.
-=item graph
+=item [3]
Any character that is I<graphical>, that is, visible. This class consists
of all the alphanumerical characters and all punctuation characters.
-=item print
+=item [4]
All printable characters, which is the set of all the graphical characters
-plus the space.
+plus whitespace characters that are not also controls.
+
+=item [5] (punct)
+
+C<\p{PosixPunct}> and C<[[:punct:]]> in the ASCII range match all the
+non-controls, non-alphanumeric, non-space characters:
+C<[-!"#$%&'()*+,./:;<=E<gt>?@[\\\]^_`{|}~]> (although if a locale is in effect,
+it could alter the behavior of C<[[:punct:]]>).
+
+C<\p{Punct}> matches a somewhat different set in the ASCII range, namely
+C<[-!"#%&'()*,./:;?@[\\\]_{}]>. That is, it is missing C<[$+E<lt>=E<gt>^`|~]>.
+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, C<[[:punct:]]> matches what it
+matches in the ASCII range, plus what C<\p{Punct}> matches. This is different
+than strictly matching according to C<\p{Punct}>. Another way to say it is that
+for a UTF-8 string, C<[[:punct:]]> matches all the characters that Unicode
+considers to be punctuation, plus all the ASCII-range characters that Unicode
+considers to be symbols.
-=item punct
+=item [6]
-Any punctuation (special) character.
+C<\p{SpacePerl}> and C<\p{Space}> differ only in that C<\p{Space}> additionally
+matches the vertical tab, C<\cK>. Same for the two ASCII-only range forms.
=back
=head4 Negation
+X<character class, 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 (C<^>).
Some examples:
- POSIX Unicode Backslash
- [[:^digit:]] \P{IsDigit} \D
- [[:^space:]] \P{IsSpace} \S
- [[:^word:]] \P{IsWord} \W
+ 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
=head4 [= =] and [. .]
Perl will recognize the POSIX character classes C<[=class=]>, and
-C<[.class.]>, but does not (yet?) support this construct. Use of
+C<[.class.]>, but does not (yet?) support them. Use of
such a construct will lead to an error.
/[[: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,
- # but the letters 'a' to 'f' in either case.
- # This is because the character class contains
- # all digits, and anything that isn't a
- # hex digit, resulting in a class containing
- # all characters, but the letters 'a' to 'f'
- # and 'A' to 'F'.
+ /[[: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'.
-=head2 Locale, Unicode and UTF-8
+=head2 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.
+in effect, and if the program is running on an EBCDIC platform.
C<\w>, C<\d>, C<\s> and the POSIX character classes (and their negations,
-including C<\W>, C<\D>, C<\S>) suffer from this behaviour.
+including C<\W>, C<\D>, C<\S>) suffer from this behaviour. (Since the backslash
+sequences C<\b> and C<\B> are defined in terms of C<\w> and C<\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 is
-in effect. If there is no locale, they match the ASCII defaults
-(52 letters, 10 digits and underscore for C<\w>, 0 to 9 for C<\d>, etc).
+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 C<\d>; 52 letters, 10 digits and underscore for C<\w>;
+etc.).
This usually means that if you are matching against characters whose C<ord()>
values are between 128 and 255 inclusive, your character class may match
-or not depending on the current locale, and whether the source string is
-in UTF-8 format. The string will be in UTF-8 format if it contains
-characters whose C<ord()> value exceeds 255. But a string may be in UTF-8
-format without it having such characters.
+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 C<ord()> value exceeds 255. But a string may be in
+UTF-8 format without it having such characters. See L<perlunicode/The
+"Unicode Bug">.
For portability reasons, it may be better to not use C<\w>, C<\d>, C<\s>
or the POSIX character classes, and use the Unicode properties instead.
https://perl5.git.perl.org / perl5.git / blobdiff