=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 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, which 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 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.
- \N Match a character that isn't newline.
- \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 \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 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>.
-
-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>.
+If the C</a> regular expression modifier in effect, it matches [0-9].
+Otherwise, it
+matches anything that is matched by C<\p{Digit}>, which includes [0-9].
+(An unlikely possible exception is that under locale matching rules, the
+current locale might not have [0-9] matched by C<\d>, and/or might match
+other characters whose code point is less than 256. Such a locale
+definition would be in violation of the C language standard, but Perl
+doesn't currently assume anything in regard to this.)
+
+What this means is that unless the C</a> modifier is in effect C<\d> not
+only matches the digits '0' - '9', but also Arabic, Devanagari, and
+digits from other languages. This may cause some confusion, and some
+security issues.
+
+Some digits that C<\d> matches look like some of the [0-9] ones, but
+have different values. For example, BENGALI DIGIT FOUR (U+09EA) looks
+very much like an ASCII DIGIT EIGHT (U+0038). An application that
+is expecting only the ASCII digits might be misled, or if the match is
+C<\d+>, the matched string might contain a mixture of digits from
+different writing systems that look like they signify a number different
+than they actually do. L<Unicode::UCDE<sol>num()|Unicode::UCD/num> can
+be used to safely
+calculate the value, returning C<undef> if the input string contains
+such a mixture.
+
+What C<\p{Digit}> means (and hence C<\d> except under the C</a>
+modifier) is 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 C<CIRCLED DIGIT ONE>
+or subscripts, or are from writing systems that lack all ten digits.
+
+The design intent is for C<\d> to exactly match the set of characters
+that can safely be used with "normal" big-endian positional decimal
+syntax, where, for example 123 means one 'hundred', plus two 'tens',
+plus three 'ones'. This positional notation does not necessarily apply
+to characters that match the other type of "digit",
+C<\p{Numeric_Type=Digit}>, and so C<\d> doesn't match them.
+
+The Tamil digits (U+0BE6 - U+0BEF) can also legally be
+used in old-style Tamil numbers in which they would appear no more than
+one in a row, separated by characters that mean "times 10", "times 100",
+etc. (See L<http://www.unicode.org/notes/tn21>.)
+
+Any character not matched by C<\d> is 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.
-
-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 considered 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.
-
-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<\N>, 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, since C<\N{}> is also used for
-named characters, 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. 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}> is not a legal quantifier, and will cause
-perl to look for a character named C<4F> (and won't find it unless custom names
-have been defined.)
-
-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.
+A C<\w> matches a single alphanumeric character (an alphabetic character, or a
+decimal digit) or a connecting punctuation character, such as an
+underscore ("_"). It does not match a whole word. To match a whole
+word, use 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.
+
+=over
+
+=item If the C</a> modifier is in effect ...
+
+C<\w> matches the 63 characters [a-zA-Z0-9_].
+
+=item otherwise ...
+
+=over
+
+=item For code points above 255 ...
+
+C<\w> matches the same as C<\p{Word}> matches in this range. That is,
+it matches Thai letters, Greek letters, etc. This includes connector
+punctuation (like the underscore) which connect two words together, or
+diacritics, such as a C<COMBINING TILDE> and the modifier letters, which
+are generally used to add auxiliary markings to letters.
+
+=item For code points below 256 ...
+
+=over
+
+=item if locale rules are in effect ...
+
+C<\w> matches the platform's native underscore character plus whatever
+the locale considers to be alphanumeric.
+
+=item if Unicode rules are in effect or if on an EBCDIC platform ...
+
+C<\w> matches exactly what C<\p{Word}> matches.
+
+=item otherwise ...
+
+C<\w> matches [a-zA-Z0-9_].
+
+=back
+
+=back
+
+=back
+
+Which rules apply are determined as described in L<perlre/Which character set modifier is in effect?>.
+
+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 L</Unicode Properties>, C<\p{ID_Start}>,
+C<\p{ID_Continue}>, C<\p{XID_Start}>, and C<\p{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 considered whitespace.
+
+=over
+
+=item If the C</a> modifier is in effect ...
+
+C<\s> matches the 5 characters [\t\n\f\r ]; that is, the horizontal tab,
+the newline, the form feed, the carriage return, and the space. (Note
+that it doesn't match the vertical tab, C<\cK> on ASCII platforms.)
+
+=item otherwise ...
+
+=over
+
+=item For code points above 255 ...
+
+C<\s> matches exactly the code points above 255 shown with an "s" column
+in the table below.
+
+=item For code points below 256 ...
+
+=over
+
+=item if locale rules are in effect ...
+
+C<\s> matches whatever the locale considers to be whitespace. Note that
+this is likely to include the vertical space, unlike non-locale C<\s>
+matching.
+
+=item if Unicode rules are in effect or if on an EBCDIC platform ...
+
+C<\s> matches exactly the characters shown with an "s" column in the
+table below.
+
+=item otherwise ...
+
+C<\s> matches [\t\n\f\r ].
+Note that this list doesn't include the non-breaking space.
+
+=back
+
+=back
+
+=back
+
+Which rules apply are determined as described in L<perlre/Which character set modifier is in effect?>.
+
+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
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.
+Note that unlike C<\s> (and C<\d> and C<\w>), C<\h> and C<\v> always match
+the same characters, without regard to other factors, such as whether the
+source string is in UTF-8 format.
-One might think that 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.
+For example, the vertical tab (C<"\x0b">) is not matched by C<\s>, it is
+however considered vertical whitespace.
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 6.0.
-The first column gives the code point of the character (in hex format),
+The first column gives the Unicode code point of the character (in hex format),
the second column gives the (Unicode) name. The third column indicates
-by which class(es) the character is matched.
-
- 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
+by which class(es) the character is matched (assuming no locale or EBCDIC code
+page is in effect that changes the C<\s> matching).
+
+ 0x0009 CHARACTER TABULATION h s
+ 0x000a LINE FEED (LF) vs
+ 0x000b LINE TABULATION v
+ 0x000c FORM FEED (FF) vs
+ 0x000d CARRIAGE RETURN (CR) vs
+ 0x0020 SPACE h s
+ 0x0085 NEXT LINE (NEL) vs [1]
+ 0x00a0 NO-BREAK SPACE h s [1]
+ 0x1680 OGHAM SPACE MARK h s
+ 0x180e MONGOLIAN VOWEL SEPARATOR h s
+ 0x2000 EN QUAD h s
+ 0x2001 EM QUAD h s
+ 0x2002 EN SPACE h s
+ 0x2003 EM SPACE h s
+ 0x2004 THREE-PER-EM SPACE h s
+ 0x2005 FOUR-PER-EM SPACE h s
+ 0x2006 SIX-PER-EM SPACE h s
+ 0x2007 FIGURE SPACE h s
+ 0x2008 PUNCTUATION SPACE h s
+ 0x2009 THIN SPACE h s
+ 0x200a HAIR SPACE h s
+ 0x2028 LINE SEPARATOR vs
+ 0x2029 PARAGRAPH SEPARATOR vs
+ 0x202f NARROW NO-BREAK SPACE h s
+ 0x205f MEDIUM MATHEMATICAL SPACE h s
+ 0x3000 IDEOGRAPHIC SPACE h s
=over 4
=item [1]
-NEXT LINE and NO-BREAK SPACE only match C<\s> if the source string is in
-UTF-8 format.
+NEXT LINE and NO-BREAK SPACE may or may not match C<\s> depending
+on the rules in effect. See
+L<the beginning of this section|/Whitespace>.
=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),
-use C<\d+>; to match a word, use C<\w+>.
-
-
=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 C<name> for the character has the particular C<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
-has as short form I<Ll>. They need the braces, so are written as C</\p{Ll}/> or
+has the 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 more details, see L<perlunicode/Unicode Character Properties>; for a
+If neither the C</a> modifier nor locale rules are in effect, the use of
+a Unicode property will force the regular expression into using Unicode
+rules.
+
+Note that almost all properties are immune to case-insensitive matching.
+That is, adding a C</i> regular expression modifier does not change what
+they match. There are two sets that are 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> 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.
"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.
+It is worth emphasizing that C<\d>, C<\w>, etc, match single characters, not
+complete numbers or words. To match a number (that consists of digits),
+use C<\d+>; to match a word, use C<\w+>. But be aware of the security
+considerations in doing so, as mentioned above.
=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
-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.
+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 is matched.* To match
+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 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.
# a single character.
"ae" =~ /^[aeiou]+$/ # Match, due to the quantifier.
+ -------
+
+* There is an exception to a bracketed character class matching only a
+single character. When the class is to match caselessely under C</i>
+matching rules, and a character inside the class matches a
+multiple-character sequence caselessly under Unicode rules, the class
+(when not L<inverted|/Negation>) will also match that sequence. For
+example, Unicode says that the letter C<LATIN SMALL LETTER SHARP S>
+should match the sequence C<ss> under C</i> rules. Thus,
+
+ 'ss' =~ /\A\N{LATIN SMALL LETTER SHARP S}\z/i # Matches
+ 'ss' =~ /\A[aeioust\N{LATIN SMALL LETTER SHARP S}]\z/i # Matches
+
=head3 Special Characters Inside a Bracketed Character Class
Most characters that are meta characters in regular expressions (that
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<\e>,
C<\f>,
C<\n>,
-C<\N{NAME}>,
+C<\N{I<NAME>}>,
+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.
-Also, a backslash followed by 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 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 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.
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 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.
+If a hyphen in a character class cannot syntactically be part of a range, for
+instance because it is the first or the last character of the character class,
+or if it immediately follows a range, the hyphen isn't special, and so is
+considered a character to be matched literally. If you want a hyphen in
+your set of characters to be matched and its position in the class is such
+that it could be considered part of a range, you must escape that hyphen
+with a backslash.
Examples:
[a-z] # Matches a character that is a lower case ASCII letter.
- [a-fz] # Matches any letter between 'a' and 'f' (inclusive) or the
- # letter 'z'.
+ [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 more than a million
+Unicode code points. The class is said to be "negated" or "inverted".
This syntax make the caret a special character inside a bracketed character
class, but only if it is the first character of the class. So if you want
-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 don't list it first.
+
+In inverted bracketed character classes, Perl ignores the Unicode rules
+that normally say that certain characters match a sequence of multiple
+characters under caseless C</i> matching. Following those rules
+can lead to highly confusing situations:
+
+ "ss" =~ /^[^\xDF]+$/ui; # Matches!
+
+This should match any sequences of characters that aren't C<\xDF> nor
+what C<\xDF> matches under C</i>. C<"s"> isn't C<\xDF>, but Unicode
+says that C<"ss"> is what C<\xDF> matches under C</i>. So which one
+"wins"? Do you fail the match because the string has C<ss> or accept it
+because it has an C<s> followed by another C<s>? Perl has chosen the
+latter.
Examples:
=head3 Backslash Sequences
-You can put any backslash sequence character class (with one exception listed
-in the next paragraph) 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> 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 form C<\N{NAME}> 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
+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.
+
Examples:
/[\p{Thai}\d]/ # Matches a character that is either a Thai
# 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.
+
+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.
+ alpha Any alphabetical character ("[A-Za-z]").
+ alnum Any alphanumeric character. ("[A-Za-z0-9]")
+ ascii Any character in the ASCII character set.
blank A GNU extension, equal to a space or a horizontal tab ("\t").
- cntrl Any control character.
- digit Any digit, equivalent to "\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. "\s" plus the vertical tab ("\cK").
- upper Any uppercase character.
- word Any "word" character, equivalent to "\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 of these names may not be obvious:
+ 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, 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}> matches not just the ASCII alphabetic characters, but any
+character in the entire Unicode character set considered alphabetic.
+An entry in the column labelled "backslash sequence" is a (short)
+synonym for the Full-range Unicode form.
+
+ [[:...:]] ASCII-range Full-range backslash Note
+ Unicode Unicode sequence
+ -----------------------------------------------------
+ alpha \p{PosixAlpha} \p{XPosixAlpha}
+ alnum \p{PosixAlnum} \p{XPosixAlnum}
+ ascii \p{ASCII}
+ blank \p{PosixBlank} \p{XPosixBlank} \h [1]
+ or \p{HorizSpace} [1]
+ cntrl \p{PosixCntrl} \p{XPosixCntrl} [2]
+ digit \p{PosixDigit} \p{XPosixDigit} \d
+ graph \p{PosixGraph} \p{XPosixGraph} [3]
+ lower \p{PosixLower} \p{XPosixLower}
+ print \p{PosixPrint} \p{XPosixPrint} [4]
+ punct \p{PosixPunct} \p{XPosixPunct} [5]
+ \p{PerlSpace} \p{XPerlSpace} \s [6]
+ space \p{PosixSpace} \p{XPosixSpace} [6]
+ upper \p{PosixUpper} \p{XPosixUpper}
+ word \p{PosixWord} \p{XPosixWord} \w
+ xdigit \p{PosixXDigit} \p{XPosixXDigit}
=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 code points 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 code pointss 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.
+of all alphanumeric characters and all punctuation characters.
+
+=item [4]
+
+All printable characters, which is the set of all graphical characters
+plus those whitespace characters which are not also controls.
+
+=item [5]
-=item print
+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:]]>).
-All printable characters, which is the set of all the graphical characters
-plus the space.
+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.
-=item punct
+C<\p{XPosixPunct}> and (under Unicode rules) 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
+if Unicode rules are in effect, C<[[:punct:]]> matches all characters
+that Unicode considers punctuation, plus all ASCII-range characters that
+Unicode considers symbols.
-Any punctuation (special) character.
+=item [6]
+
+C<\p{SpacePerl}> and C<\p{Space}> differ only in that in non-locale
+matching, C<\p{Space}> additionally
+matches the vertical tab, C<\cK>. Same for the two ASCII-only range forms.
=back
-=head4 Negation
+There are various other synonyms that can be used besides the names
+listed in the table. For example, C<\p{PosixAlpha}> can be written as
+C<\p{Alpha}>. All are listed in
+L<perluniprops/Properties accessible through \p{} and \P{}>,
+plus all characters matched by each ASCII-range property.
-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:
+Both the C<\p> counterparts always assume Unicode rules are in effect.
+On ASCII platforms, this means they assume that the code points from 128
+to 255 are Latin-1, and that means that using them under locale rules is
+unwise unless the locale is guaranteed to be Latin-1 or UTF-8. In contrast, the
+POSIX character classes are useful under locale rules. They are
+affected by the actual rules in effect, as follows:
- POSIX Unicode Backslash
- [[:^digit:]] \P{IsDigit} \D
- [[:^space:]] \P{IsSpace} \S
- [[:^word:]] \P{IsWord} \W
+=over
-=head4 [= =] and [. .]
+=item If the C</a> modifier, is in effect ...
-Perl will recognize the POSIX character classes C<[=class=]>, and
-C<[.class.]>, but does not (yet?) support this construct. Use of
-such a construct will lead to an error.
+Each of the POSIX classes matches exactly the same as their ASCII-range
+counterparts.
+=item otherwise ...
-=head4 Examples
+=over
- /[[: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'.
+=item For code points above 255 ...
+The POSIX class matches the same as its Full-range counterpart.
-=head2 Locale, Unicode and UTF-8
+=item For code points below 256 ...
-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.
+=over
-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.
+=item if locale rules are in effect ...
-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).
+The POSIX class matches according to the locale.
-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.
+=item if Unicode rules are in effect or if on an EBCDIC platform ...
-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.
+The POSIX class matches the same as the Full-range counterpart.
-=head4 Examples
+=item otherwise ...
+
+The POSIX class matches the same as the ASCII range counterpart.
+
+=back
- $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.
+=back
+
+=back
+
+Which rules apply are determined as described in
+L<perlre/Which character set modifier is in effect?>.
-=cut
+It is proposed to change this behavior in a future release of Perl so that
+whether or not Unicode rules are in effect would not change the
+behavior: Outside of locale or an EBCDIC code page, the POSIX classes
+would behave like their ASCII-range counterparts. If you wish to
+comment on this proposal, send email to C<perl5-porters@perl.org>.
+
+=head4 Negation of POSIX character classes
+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 ASCII-range Full-range backslash
+ Unicode Unicode sequence
+ -----------------------------------------------------
+ [[:^digit:]] \P{PosixDigit} \P{XPosixDigit} \D
+ [[:^space:]] \P{PosixSpace} \P{XPosixSpace}
+ \P{PerlSpace} \P{XPerlSpace} \S
+ [[:^word:]] \P{PerlWord} \P{XPosixWord} \W
+
+The backslash sequence can mean either ASCII- or Full-range Unicode,
+depending on various factors as described in L<perlre/Which character set modifier is in effect?>.
+
+=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
+ # 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'.
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