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 form enclosed in square
+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. This is true in other Perl documentation.
+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 Backslashed sequences
+=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>
-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 classes; for a full list, see L<perlrebackslash>.
+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 backslashed sequences that are character classes. They
-are discussed in more detail below.
+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>.)
- \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 whitespace character.
\S Match a non-whitespace character.
\h Match a horizontal whitespace character.
\H Match a character that isn't horizontal whitespace.
- \N Match a character that isn't newline. Experimental.
\v Match a vertical whitespace character.
\V Match a character that isn't vertical whitespace.
- \pP, \p{Prop} Match a character matching a Unicode property.
- \PP, \P{Prop} Match a character that doesn't match a Unicode property.
+ \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 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 digits. Without a locale, C<\d>
-matches the digits '0' to '9'. See L</Locale, EBCDIC, Unicode and UTF-8>.
-
-Any character that isn't matched by C<\d> will be matched by C<\D>.
+C<\d> matches a single character considered to be a decimal I<digit>.
+What is considered a decimal digit depends on several factors, detailed
+below in L</Locale, EBCDIC, Unicode and UTF-8>. If those factors
+indicate a Unicode interpretation, C<\d> not only matches the digits
+'0' - '9', but also Arabic, Devanagari, and digits from other languages.
+Otherwise, if a locale is in effect, it matches whatever characters that
+locale considers decimal digits. Only when neither a Unicode interpretation
+nor locale prevails does C<\d> match only the digits '0' to '9' alone.
+
+Unicode digits may cause some confusion, and some security issues. In UTF-8
+strings, unless the C<"a"> regular expression modifier is specified,
+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 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 non-European digits that C<\d> matches look like European ones, but
+have different values. For example, BENGALI DIGIT FOUR (U+09EA) 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 not matched by C<\d> is matched by C<\D>.
=head3 Word characters
A C<\w> matches a single alphanumeric character (an alphabetic character, or a
-decimal digit) or an underscore (C<_>), not a whole word. Use C<\w+> to match
-a string of Perl-identifier characters (which isn't the same as matching an
-English word). 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
+decimal digit) or a connecting punctuation character, such as an
+underscore ("_"). It does not match a whole word. To match a whole
+word, use C<\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. What is considered a
+word character depends on several factors, detailed below in L</Locale,
+EBCDIC, Unicode and UTF-8>. If those factors indicate a Unicode
+interpretation, C<\w> matches the characters 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>.
+but also Thai letters, Greek letters, etc. This includes connector
+punctuation (like the underscore) which connect two words together, or
+diacritics, such as a C<COMBINING TILDE> and the modifier letters, which
+are generally used to add auxiliary markings to letters. If a Unicode
+interpretation is not indicated, C<\w> matches those characters considered
+word characters by the current locale or EBCDIC code page. Without a
+locale or EBCDIC code page, C<\w> matches the underscore and ASCII letters
+and digits.
+
+There are a number of security issues with the full Unicode list of word
+characters. See L<http://unicode.org/reports/tr36>.
-Any character that isn't matched by C<\w> will be matched by C<\W>.
+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 not matched by C<\w> is matched by C<\W>.
=head3 Whitespace
-C<\s> matches any single character that is considered whitespace. 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 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 five
-characters mentioned in the beginning of this paragraph. 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 whitespace;
-this includes the space and the tab characters and 17 other characters that are
-listed in the table below. C<\H> will match any character
-that is not considered horizontal whitespace.
-
-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> will not be
-influenced by the single line C</s> regular expression modifier. (Note that,
-there is a second meaning of C<\N> when of the form C<\N{...}>. This form is
-for named characters. See L<charnames> for those. If C<\N> is followed by an
-opening brace and something that is not a quantifier, perl will assume that a
-character name is coming, and not this meaning of C<\N>. For example, C<\N{3}>
-means to match 3 non-newlines; C<\N{5,}> means to match 5 or more non-newlines,
-but C<\N{4F}> and C<\N{F4}> are not legal quantifiers, and will cause perl to
-look for characters named C<4F> or C<F4>, respectively (and won't find them,
-thus raising an error, unless they have been defined using custom names).
-
-C<\v> will match any character that is considered vertical whitespace;
-this includes the carriage return and line feed characters (newline) plus 5
-other characters listed in the table below.
-C<\V> will match any character that is not considered vertical whitespace.
+C<\s> matches any single character considered whitespace. The exact
+set of characters matched by C<\s> depends on several factors, detailed
+below in L</Locale, EBCDIC, Unicode and UTF-8>. If those factors
+indicate a Unicode interpretation, C<\s> matches what is considered
+whitespace in the Unicode database; the complete list is in the table
+below. Otherwise, if a locale or EBCDIC code page is 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 B<only> if a Unicode
+interpretation is indicated, or the locale or EBCDIC code page that is
+in effect happens to have that character.
+
+Any character not matched by C<\s> is matched by C<\S>.
+
+C<\h> matches any character considered horizontal whitespace;
+this includes the space and tab characters and several others
+listed in the table below. C<\H> matches any character
+not considered horizontal whitespace.
+
+C<\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.
+C<\V> matches any character 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
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 or EBCDIC code page.
+the same characters, without regard to other factors, such as whether the
+source string is in UTF-8 format.
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 (C<"\x85">) and the no-break space (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>.
+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 C<"a"> modifier is not in effect and 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> as of Unicode 5.2.
=item [1]
NEXT LINE and NO-BREAK SPACE only match C<\s> if the source string is in
-UTF-8 format, or the locale or EBCDIC code page that is in effect includes them.
+UTF-8 format and the C<"a"> modifier is not in effect, or if the locale
+or EBCDIC code page in effect includes them.
=back
It is worth noting that C<\d>, C<\w>, etc, match single characters, not
-complete numbers or words. To match a number (that consists of integers),
+complete numbers or words. To match a number (that consists of digits),
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, matches 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, braces are required.
-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".
+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 that 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
It matches a two character string: a letter (Unicode property C<\pL>),
followed by a lowercase C<l>.
-For more details, see L<perlunicode/Unicode Character Properties>; for a
+Note that almost all properties are immune to case-insensitive matching.
+That is, adding a C</i> regular expression modifier does not change what
+they match. There are two sets affected. The first set is
+C<Uppercase_Letter>,
+C<Lowercase_Letter>,
+and C<Titlecase_Letter>,
+all of which match C<Cased_Letter> under C</i> matching.
+The second set is
+C<Uppercase>,
+C<Lowercase>,
+and C<Titlecase>,
+all of which match C<Cased> under C</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 C<Cased>, but
+aren't considered to be letters, so they aren't C<Cased_Letter>s. They're
+actually C<Letter_Number>s.)
+This set also includes its subsets C<PosixUpper> and C<PosixLower>, both
+of which under C</i> matching match C<PosixAlpha>.
+
+For more details on Unicode properties, see L<perlunicode/Unicode
+Character Properties>; for a
complete list of possible properties, see
-L<perluniprops/Properties accessible through \p{} and \P{}>.
+L<perluniprops/Properties accessible through \p{} and \P{}>,
+which notes all forms that have C</i> differences.
It is also possible to define your own properties. This is discussed in
L<perlunicode/User-Defined Character Properties>.
-
=head4 Examples
"a" =~ /\w/ # Match, "a" is a 'word' 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]>.
+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
+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,
-C<[aeiou]+> matches a string of one or more lowercase ASCII vowels.
+class, follow the character class with a L<quantifier|perlre/Quantifiers>. For
+instance, C<[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.
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.
C<\f>,
C<\n>,
C<\N{I<NAME>}>,
-C<\N{U+I<wide hex char>}>,
+C<\N{U+I<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.
+are also special and have the same meanings as they do outside a
+bracketed character class. (However, inside a bracketed character
+class, if C<\N{I<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 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 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.
-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.
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
=head3 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 (C<->).
+of listing all characters in the range, one may use the hyphen (C<->).
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
+by a hyphen, it's treated as if all characters between the two were in
the class. For instance, C<[0-9]> matches any ASCII digit, and C<[a-m]>
-matches any lowercase letter from the first half of the ASCII alphabet.
+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
-necessary both letters or both digits. Any character is possible,
+necessarily both letters or both digits. Any character is possible,
although not advisable. C<['-?]> contains a range of characters, but
-most people will not know which characters that will be. Furthermore,
+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 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 could be considered part
-of a range.
+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'.
+ [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'.
It is also possible to instead list the characters you do not want to
match. You can do so by using a caret (C<^>) as the first character in the
-character class. For instance, C<[^a-z]> matches a character that is not a
-lowercase ASCII letter.
+character class. For instance, C<[^a-z]> matches any character that is not a
+lowercase ASCII letter, which therefore includes almost a hundred thousand
+Unicode letters.
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.
+the caret as one of the characters to match, either escape the caret or
+else not list it first.
Examples:
=head3 Backslash Sequences
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 digit, or any of the
-lowercase letters between 'a' and 'f' inclusive.
+C<\N> and C<\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, C<[a-f\d]> matches 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<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.
-C<\N> within a bracketed character class must be of the forms C<\N{I<name>}> or
-C<\N{U+I<wide hex char>}> 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:
-=head3 Posix Character Classes
+ /[\p{Thai}-\d]/ # Wrong!
+
+=head3 POSIX Character Classes
X<character class> X<\p> X<\p{}>
-fix
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 only 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 can 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>.
-These character classes can be part of a larger bracketed character class. For
-example,
+POSIX character classes can be part of a larger bracketed character class.
+For example,
[01[:alpha:]%]
Perl recognizes the following POSIX character classes:
alpha Any alphabetical character ("[A-Za-z]").
- alnum Any alphanumerical character. ("[A-Za-z0-9]")
+ 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.
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. See Note [5]
+ 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".
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 range. (On EBCDIC platforms,
-they match those characters which have ASCII equivalents.)
+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,
-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.
+C<\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.
-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}>,
+L<perluniprops/Properties accessible through \p{} and \P{}> lists all
+synonyms, plus all characters matched by each ASCII-range property.
+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
+Both the C<\p> forms are unaffected by any locale 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]) 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.
+In contrast, the POSIX character classes are affected, unless the
+regular expression is compiled with the C<"a"> modifier. If the C<"a">
+modifier is not in effect, and the source string is in UTF-8 format, the
+POSIX classes behave like their "Full-range" Unicode counterparts. If
+C<"a"> modifier is in effect; or 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
+the UTF-8-ness 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>.
+
wish to comment on this proposal, send email to C<perl5-porters@perl.org>.
- [[:...:]] ASCII-range Full-range backslash Note
- Unicode Unicode sequence
+ [[:...:]] ASCII-range Full-range backslash Note
+ Unicode Unicode sequence
-----------------------------------------------------
- alpha \p{PosixAlpha} \p{Alpha}
- alnum \p{PosixAlnum} \p{Alnum}
+ alpha \p{PosixAlpha} \p{XPosixAlpha}
+ alnum \p{PosixAlnum} \p{XPosixAlnum}
ascii \p{ASCII}
- blank \p{PosixBlank} \p{Blank} =
- \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}
+ 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{ASCII_Hex_Digit} \p{XPosixXDigit}
=over 4
=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.
+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.
-On EBCDIC platforms, it is likely that the code page will define this character
-class to be the counterparts to the ASCII controls, plus the controls that in
-Unicode have ordinals from 128 through 139.
+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 [3]
Any character that is I<graphical>, that is, visible. This class consists
-of all the alphanumerical characters and all punctuation characters.
+of all alphanumeric characters and all punctuation characters.
=item [4]
-All printable characters, which is the set of all the graphical characters
-plus whitespace characters that are not also controls.
+All printable characters, which is the set of all graphical characters
+plus those whitespace characters which are not also controls.
=item [5]
-C<\p{PosixPunct}> and C<[[:punct:]]> in the ASCII range match all the
+C<\p{PosixPunct}> and C<[[:punct:]]> in the ASCII range match all
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:]]>).
-When the matching string is in UTF-8 format, C<[[:punct:]]> matches the above
-set, plus whatever C<\p{Punct}> matches beyond the ASCII range. It matches
-more than what C<\p{Punct}> matches in the ASCII range, because the POSIX
-definition of "Punct" includes more than what Unicode calls "Punct"; namely, it
-includes what Unicode calls "Symbol". In other words, the Posix C<[[:punct:]]>
-lumps the Unicode "Punct" and "Symbol" together.
+The similarly named property, 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.
-This character class does not match any characters of Unicode type "Symbol"
-outside the ASCII range when the matching string is in UTF-8 format.
+C<\p{XPosixPunct}> and (in Unicode mode) C<[[:punct:]]>, match what
+C<\p{PosixPunct}> 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 characters that Unicode
+considers punctuation, plus all ASCII-range characters that Unicode
+considers symbols.
=item [6]
=back
+There are various other synonyms that can be used for these besides
+C<\p{HorizSpace}> and \C<\p{XPosixBlank}>. For example,
+C<\p{PosixAlpha}> can be written as C<\p{Alpha}>. All are listed
+in L<perluniprops/Properties accessible through \p{} and \P{}>.
+
=head4 Negation
X<character class, negation>
POSIX ASCII-range Full-range backslash
Unicode Unicode sequence
-----------------------------------------------------
- [[:^digit:]] \P{PosixDigit} \P{Digit} \D
- [[:^space:]] \P{PosixSpace} \P{Space}
- [[:^word:]] \P{PerlWord} \P{Word} \W
+ [[:^digit:]] \P{PosixDigit} \P{XPosixDigit} \D
+ [[:^space:]] \P{PosixSpace} \P{XPosixSpace}
+ \P{PerlSpace} \P{XPerlSpace} \S
+ [[:^word:]] \P{PerlWord} \P{XPosixWord} \W
-=head4 [= =] and [. .]
+The backslash sequence can mean either ASCII- or Full-range Unicode,
+depending on various factors. See L</Locale, EBCDIC, Unicode and UTF-8>
+below.
-Perl will recognize the POSIX character classes C<[=class=]>, and
-C<[.class.]>, but does not (yet?) support them. Use of
-such a construct will lead to an error.
+=head4 [= =] and [. .]
+Perl recognizes the POSIX character classes C<[=class=]> and
+C<[.class.]>, but does not (yet?) support them. Any attempt to use
+either construct raises an exception.
=head4 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,
- # 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, 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.
-
-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. (This also affects
-the backslash sequences C<\b> and C<\B>.)
-
-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 (52 letters, 10 digits and underscore for C<\w>; 0 to 9 for C<\d>;
-L</Whitespace> above gives the list for C<\s>).
-
-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 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<perluniprops/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.
+Some of the character classes have a somewhat different behaviour
+depending on the internal encoding of the source string, whether the regular
+expression is marked as having Unicode semantics, whatever locale is in
+effect, and whether 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>) have 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.)
+
+Starting in Perl 5.14, if the regular expression is compiled with the
+C<"a"> modifier, the behavior doesn't differ regardless of any other
+factors. C<\d> matches the 10 digits 0-9; C<\D> any character but those
+10; C<\s>, exactly the five characters "[ \f\n\r\t]"; C<\w> only the 63
+characters "[A-Za-z0-9_]"; and the C<"[[:posix:]]"> classes only the
+appropriate ASCII characters, the same characters as are matched by the
+corresponding C<\p{}> property given in the "ASCII-range Unicode" column
+in the table above. (The behavior of all of their complements follows
+the same paradigm.)
+
+Otherwise, a regular expression is marked for Unicode semantics if it is
+encoded in utf8 (usually as a result of including a literal character
+whose code point is above 255), or if it contains a C<\N{U+...}> or
+C<\N{I<name>}> construct, or (starting in Perl 5.14) if it was compiled
+in the scope of a C<S<use feature "unicode_strings">> pragma and not in
+the scope of a C<S<use locale>> pragma, or has the C<"u"> regular
+expression modifier.
+
+Note that one can specify C<"use re '/l'"> for example, for any regular
+expression modifier, and this has precedence over either of the
+C<S<use feature "unicode_strings">> or C<S<use locale>> pragmas.
+
+The differences in behavior between locale and non-locale semantics
+can affect any character whose code point is 255 or less. The
+differences in behavior between Unicode and non-Unicode semantics
+affects only ASCII platforms, and only when matching against characters
+whose code points are between 128 and 255 inclusive. See
+L<perlunicode/The "Unicode Bug">.
+
+For portability reasons, unless the C<"a"> modifier is specified,
+it may be better to not use C<\w>, C<\d>, C<\s> or the POSIX character
+classes and use the Unicode properties instead.
+
+That way you can control whether you want matching of characters in
+the ASCII character set alone, or whether to match Unicode characters.
+C<S<use feature "unicode_strings">> allows seamless Unicode behavior
+no matter the internal encodings, but won't allow restricting
+to ASCII characters only.
=head4 Examples
https://perl5.git.perl.org / perl5.git / blobdiff