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 by using the I<single line> modifier: either
+character, except for the newline. That default can be changed to
+add matching the newline by using the I<single line> modifier:
for the entire regular expression with the C</s> modifier, or
-locally with C<(?s)>. (The experimental C<\N> backslash sequence, described
+locally with C<(?s)> (and even globally within the scope of
+L<C<use re '/s'>|re/'E<sol>flags' mode>). (The C<L</\N>> backslash
+sequence, described
below, matches any character except newline without regard to the
I<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<\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>
\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.
+ \N Match a character that isn't a newline.
\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
+=head3 \N
+
+C<\N>, available starting in v5.12, 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>.
-C<\d> matches a single character that is 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 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'.
-
-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}>.
+=head3 Digits
+C<\d> matches a single character considered to be a decimal I<digit>.
+If the C</a> regular expression modifier is 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 C<[0-9]> matched by C<\d>, and/or might match
+other characters whose code point is less than 256. The only such locale
+definitions that are legal would be to match C<[0-9]> plus another set of
+10 consecutive digit characters; anything else 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::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 subscripts.
+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 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>.)
+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.
-Some of the 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()>.
+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 that isn't matched by C<\d> will be matched by C<\D>.
+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. 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 several factors, detailed below in L</Locale,
-EBCDIC, Unicode and UTF-8>. If those factors indicate a Unicode
-interpretation, C<\w> matches the 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 a Unicode interpretation
-is not indicated, 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.
+decimal digit); or a connecting punctuation character, such as an
+underscore ("_"); or a "mark" character (like some sort of accent) that
+attaches to one of those. 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 instead, Unicode rules are in effect ...
+
+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 Unicode properties, "ID_Start", ID_Continue", "XID_Start", and
-"XID_Continue". See L<http://unicode.org/reports/tr31>.
+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 that isn't matched by C<\w> will be matched by C<\W>.
+Any character not matched by C<\w> is matched by C<\W>.
=head3 Whitespace
-C<\s> matches any single character that is 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 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 a Unicode
-interpretation is indicated, or the locale or EBCDIC code page that is
-in effect has that character.
-
-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 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 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<\s> matches any single character considered whitespace.
+
+=over
+
+=item If the C</a> modifier is in effect ...
+
+In all Perl versions, 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.
+Starting in Perl v5.18, it also matches the vertical tab, C<\cK>.
+See note C<[1]> below for a discussion of this.
+
+=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.
+
+=item if instead, Unicode rules are in effect ...
+
+C<\s> matches exactly the characters shown with an "s" column in the
+table below.
+
+=item otherwise ...
+
+C<\s> matches [\t\n\f\r ] and, starting in Perl
+v5.18, the vertical tab, C<\cK>.
+(See note C<[1]> below for a discussion of this.)
+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 platform's space and tab characters and several others
+listed in the table below. C<\H> matches any character
+not considered horizontal whitespace. They use the platform's native
+character set, and do not consider any locale that may otherwise be in
+use.
+
+C<\v> matches any character considered vertical whitespace;
+this includes the platform's 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.
+They use the platform's native character set, and do not consider any
+locale that may otherwise be in use.
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; use C<\v> instead (vertical whitespace).
+rules. It can match a multi-character sequence. It cannot be used inside
+a bracketed character class; use C<\v> instead (vertical whitespace).
+It uses the platform's
+native character set, and does not consider any locale that may
+otherwise be in use.
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, without regard to other factors, such as if the
-source string is in UTF-8 format or not.
+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 the active
+locale or 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 (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>.
+One might think that C<\s> is equivalent to C<[\h\v]>. This is indeed true
+starting in Perl v5.18, but prior to that, the sole difference was that the
+vertical tab (C<"\cK">) was not 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.
+C<\s>, C<\h> and C<\v> as of Unicode 6.3.
-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 (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
- 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 is in
+effect that changes the C<\s> matching).
+
+ 0x0009 CHARACTER TABULATION h s
+ 0x000a LINE FEED (LF) vs
+ 0x000b LINE TABULATION vs [1]
+ 0x000c FORM FEED (FF) vs
+ 0x000d CARRIAGE RETURN (CR) vs
+ 0x0020 SPACE h s
+ 0x0085 NEXT LINE (NEL) vs [2]
+ 0x00a0 NO-BREAK SPACE h s [2]
+ 0x1680 OGHAM SPACE MARK 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, or the locale or EBCDIC code page that is in effect includes them.
+Prior to Perl v5.18, C<\s> did not match the vertical tab.
+C<[^\S\cK]> (obscurely) matches what C<\s> traditionally did.
-=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+>.
+=item [2]
-=head3 \N
+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>.
-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>.
+=back
=head3 Unicode Properties
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
+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 locale rules are not in effect, the use of
+a Unicode property will force the regular expression into using Unicode
+rules, if it isn't already.
+
+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>.
+Unicode properties are defined (surprise!) only on Unicode code points.
+Starting in v5.20, when matching against C<\p> and C<\P>, Perl treats
+non-Unicode code points (those above the legal Unicode maximum of
+0x10FFFF) as if they were typical unassigned Unicode code points.
+
+Prior to v5.20, Perl raised a warning and made all matches fail on
+non-Unicode code points. This could be somewhat surprising:
+
+ chr(0x110000) =~ \p{ASCII_Hex_Digit=True} # Fails on Perls < v5.20.
+ chr(0x110000) =~ \p{ASCII_Hex_Digit=False} # Also fails on Perls
+ # < v5.20
+
+Even though these two matches might be thought of as complements, until
+v5.20 they were so only on Unicode code points.
=head4 Examples
# Thai Unicode class.
"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
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 L<quantifier|perlre/Quantifiers>. For
-instance, C<[aeiou]+> matches a string of one or more lowercase English vowels.
+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 are two exceptions to a bracketed character class matching a
+single character only. Each requires special handling by Perl to make
+things work:
+
+=over
+
+=item *
+
+When the class is to match caselessly under C</i> matching rules, and a
+character that is explicitly mentioned inside the class matches a
+multiple-character sequence caselessly under Unicode rules, the class
+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
+
+For this to happen, the class must not be inverted (see L</Negation>)
+and the character must be explicitly specified, and not be part of a
+multi-character range (not even as one of its endpoints). (L</Character
+Ranges> will be explained shortly.) Therefore,
+
+ 'ss' =~ /\A[\0-\x{ff}]\z/ui # Doesn't match
+ 'ss' =~ /\A[\0-\N{LATIN SMALL LETTER SHARP S}]\z/ui # No match
+ 'ss' =~ /\A[\xDF-\xDF]\z/ui # Matches on ASCII platforms, since
+ # \xDF is LATIN SMALL LETTER SHARP S,
+ # and the range is just a single
+ # element
+
+Note that it isn't a good idea to specify these types of ranges anyway.
+
+=item *
+
+Some names known to C<\N{...}> refer to a sequence of multiple characters,
+instead of the usual single character. When one of these is included in
+the class, the entire sequence is matched. For example,
+
+ "\N{TAMIL LETTER KA}\N{TAMIL VOWEL SIGN AU}"
+ =~ / ^ [\N{TAMIL SYLLABLE KAU}] $ /x;
+
+matches, because C<\N{TAMIL SYLLABLE KAU}> is a named sequence
+consisting of the two characters matched against. Like the other
+instance where a bracketed class can match multiple characters, and for
+similar reasons, the class must not be inverted, and the named sequence
+may not appear in a range, even one where it is both endpoints. If
+these happen, it is a fatal error if the character class is within the
+scope of L<C<use re 'strict>|re/'strict' mode>, or within an extended
+L<C<(?[...])>|/Extended Bracketed Character Classes> class; otherwise
+only the first code point is used (with a C<regexp>-type warning
+raised).
+
+=back
+
=head3 Special Characters Inside a Bracketed Character Class
Most characters that are meta characters in regular expressions (that
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
-class don't group or capture.
+class don't group or capture. Be aware that, unless the pattern is
+evaluated in single-quotish context, variable interpolation will take
+place before the bracketed class is parsed:
+
+ $, = "\t| ";
+ $a =~ m'[$,]'; # single-quotish: matches '$' or ','
+ $a =~ q{[$,]}' # same
+ $a =~ m/[$,]/; # double-quotish: matches "\t", "|", or " "
Characters that may carry a special meaning inside a character class are:
C<\>, C<^>, C<->, C<[> and C<]>, and are discussed below. They can be
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. (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.)
+bracketed character class.
Also, a backslash followed by two or three octal digits is considered an octal
number.
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 to a backspace.
- "]" =~ /[][]/ # Match, as the character class contains.
+ "]" =~ /[][]/ # Match, as the character class contains
# both [ and ].
"[]" =~ /[[]]/ # Match, the pattern contains a character class
- # containing just ], and the character class is
+ # containing just [, and the character class is
# followed by a ].
+=head3 Bracketed Character Classes and the C</xx> pattern modifier
+
+Normally SPACE and TAB characters have no special meaning inside a
+bracketed character class; they are just added to the list of characters
+matched by the class. But if the L<C</xx>|perlre/E<sol>x and E<sol>xx>
+pattern modifier is in effect, they are generally ignored and can be
+added to improve readability. They can't be added in the middle of a
+single construct:
+
+ / [ \x{10 FFFF} ] /xx # WRONG!
+
+The SPACE in the middle of the hex constant is illegal.
+
+To specify a literal SPACE character, you can escape it with a
+backslash, like:
+
+ /[ a e i o u \ ]/xx
+
+This matches the English vowels plus the SPACE character.
+
+For clarity, you should already have been using C<\t> to specify a
+literal tab, and C<\t> is unaffected by C</xx>.
+
=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 syntactically be part of a range, for
instance because it is the first or the last character of the character class,
-or if it immediately follows a range, the hyphen isn't special, and will be
-considered a character that is to be matched literally. You have to escape the
-hyphen with a backslash if you want to have a hyphen in your set of characters
-to be matched, and its position in the class is such that it could be
-considered part of a range.
+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:
# hyphen ('-'), or the letter 'm'.
['-?] # Matches any of the characters '()*+,-./0123456789:;<=>?
# (But not on an EBCDIC platform).
-
+ [\N{APOSTROPHE}-\N{QUESTION MARK}]
+ # Matches any of the characters '()*+,-./0123456789:;<=>?
+ # even on an EBCDIC platform.
+ [\N{U+27}-\N{U+3F}] # Same. (U+27 is "'", and U+3F is "?")
+
+As the final two examples above show, you can achieve portablity to
+non-ASCII platforms by using the C<\N{...}> form for the range
+endpoints. These indicate that the specified range is to be interpreted
+using Unicode values, so C<[\N{U+27}-\N{U+3F}]> means to match
+C<\N{U+27}>, C<\N{U+28}>, C<\N{U+29}>, ..., C<\N{U+3D}>, C<\N{U+3E}>,
+and C<\N{U+3F}>, whatever the native code point versions for those are.
+These are called "Unicode" ranges. If either end is of the C<\N{...}>
+form, the range is considered Unicode. A C<regexp> warning is raised
+under C<S<"use re 'strict'">> if the other endpoint is specified
+non-portably:
+
+ [\N{U+00}-\x09] # Warning under re 'strict'; \x09 is non-portable
+ [\N{U+00}-\t] # No warning;
+
+Both of the above match the characters C<\N{U+00}> C<\N{U+01}>, ...
+C<\N{U+08}>, C<\N{U+09}>, but the C<\x09> looks like it could be a
+mistake so the warning is raised (under C<re 'strict'>) for it.
+
+Perl also guarantees that the ranges C<A-Z>, C<a-z>, C<0-9>, and any
+subranges of these match what an English-only speaker would expect them
+to match on any platform. That is, C<[A-Z]> matches the 26 ASCII
+uppercase letters;
+C<[a-z]> matches the 26 lowercase letters; and C<[0-9]> matches the 10
+digits. Subranges, like C<[h-k]>, match correspondingly, in this case
+just the four letters C<"h">, C<"i">, C<"j">, and C<"k">. This is the
+natural behavior on ASCII platforms where the code points (ordinal
+values) for C<"h"> through C<"k"> are consecutive integers (0x68 through
+0x6B). But special handling to achieve this may be needed on platforms
+with a non-ASCII native character set. For example, on EBCDIC
+platforms, the code point for C<"h"> is 0x88, C<"i"> is 0x89, C<"j"> is
+0x91, and C<"k"> is 0x92. Perl specially treats C<[h-k]> to exclude the
+seven code points in the gap: 0x8A through 0x90. This special handling is
+only invoked when the range is a subrange of one of the ASCII uppercase,
+lowercase, and digit ranges, AND each end of the range is expressed
+either as a literal, like C<"A">, or as a named character (C<\N{...}>,
+including the C<\N{U+...> form).
+
+EBCDIC Examples:
+
+ [i-j] # Matches either "i" or "j"
+ [i-\N{LATIN SMALL LETTER J}] # Same
+ [i-\N{U+6A}] # Same
+ [\N{U+69}-\N{U+6A}] # Same
+ [\x{89}-\x{91}] # Matches 0x89 ("i"), 0x8A .. 0x90, 0x91 ("j")
+ [i-\x{91}] # Same
+ [\x{89}-j] # Same
+ [i-J] # Matches, 0x89 ("i") .. 0xC1 ("J"); special
+ # handling doesn't apply because range is mixed
+ # case
=head3 Negation
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 named sequence, and certain characters should
+match a sequence of multiple characters use under caseless C</i>
+matching. Following those rules could 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. (See note in L</Bracketed Character Classes> above.)
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 decimal digit, or any
+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<wide hex char>}>, and NOT be the form that matches non-newlines,
+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.
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
+POSIX character classes have the form C<[:class:]>, where I<class> is the
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, though they currently suffer from
-portability issues (see below and L<Locale, EBCDIC, Unicode and UTF-8>).
+way of listing a group of characters.
Be careful about the syntax,
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,
+
+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.
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").
+ space Any whitespace character. "\s" including 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]").
+Like the L<Unicode properties|/Unicode Properties>, most of the POSIX
+properties match the same regardless of whether case-insensitive (C</i>)
+matching is in effect or not. The two exceptions are C<[:upper:]> and
+C<[:lower:]>. Under C</i>, they each match the union of C<[:upper:]> and
+C<[:lower:]>.
+
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 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.
-
-(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
+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)
+equivalent.
+
+ [[:...:]] 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}
+ 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 [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.
-
-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.
+the terminal somehow: for example, newline and backspace are control characters.
+On ASCII platforms, in the ASCII range, characters whose code points are
+between 0 and 31 inclusive, plus 127 (C<DEL>) are control characters; on
+EBCDIC platforms, their counterparts are control characters.
=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] (punct)
+=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:]]>).
-C<\p{Punct}> matches a somewhat different set in the ASCII range, namely
-C<[-!"#%&'()*,./:;?@[\\\]_{}]>. That is, it is missing C<[$+E<lt>=E<gt>^`|~]>.
+The similarly named property, C<\p{Punct}>, matches a somewhat different
+set in the ASCII range, namely
+C<[-!"#%&'()*,./:;?@[\\\]_{}]>. That is, it is missing the nine
+characters 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.
+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.
=item [6]
-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.
+C<\p{XPerlSpace}> and C<\p{Space}> match identically starting with Perl
+v5.18. In earlier versions, these differ only in that in non-locale
+matching, C<\p{XPerlSpace}> did not match 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{XPosixAlpha}> can be written as
+C<\p{Alpha}>. All are listed in
+L<perluniprops/Properties accessible through \p{} and \P{}>.
+
+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:
+
+=over
+
+=item If the C</a> modifier, is in effect ...
+
+Each of the POSIX classes matches exactly the same as their ASCII-range
+counterparts.
+
+=item otherwise ...
+
+=over
+
+=item For code points above 255 ...
+
+The POSIX class matches the same as its Full-range counterpart.
+
+=item For code points below 256 ...
+
+=over
+
+=item if locale rules are in effect ...
+
+The POSIX class matches according to the locale, except:
+
+=over
+
+=item C<word>
+
+also includes the platform's native underscore character, no matter what
+the locale is.
+
+=item C<ascii>
+
+on platforms that don't have the POSIX C<ascii> extension, this matches
+just the platform's native ASCII-range characters.
+
+=item C<blank>
+
+on platforms that don't have the POSIX C<blank> extension, this matches
+just the platform's native tab and space characters.
+
+=back
+
+=item if instead, Unicode rules are in effect ...
+
+The POSIX class matches the same as the Full-range counterpart.
+
+=item otherwise ...
+
+The POSIX class matches the same as the ASCII range counterpart.
+
+=back
+
+=back
+
+=back
+
+Which rules apply are determined as described in
+L<perlre/Which character set modifier is in effect?>.
+
+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, 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
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
+ [[:^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 as described in L<perlre/Which character set modifier is in effect?>.
-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
/[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'.
-
-
-=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, if the regular expression
-is marked as having Unicode semantics, 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>) 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.)
-
-The rule is that if the source string is in UTF-8 format or the regular
-expression is marked as indicating Unicode semantics (see the next
-paragraph), the character classes match according to the Unicode
-properties. Otherwise, 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.).
-
-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.
-
-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, 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 just characters in
-the ASCII character set, or any Unicode characters.
-C<S<use feature "unicode_strings">> will allow seamless Unicode behavior
-no matter what the internal encodings are, but won't allow restricting
-to just the ASCII characters.
+ # except the letters 'a' to 'f' and '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 OR adds the digits, leaving only the
+ # letters 'a' to 'f' and 'A' to 'F' excluded.
+
+=head3 Extended Bracketed Character Classes
+X<character class>
+X<set operations>
-=head4 Examples
+This is a fancy bracketed character class that can be used for more
+readable and less error-prone classes, and to perform set operations,
+such as intersection. An example is
+
+ /(?[ \p{Thai} & \p{Digit} ])/
+
+This will match all the digit characters that are in the Thai script.
+
+This is an experimental feature available starting in 5.18, and is
+subject to change as we gain field experience with it. Any attempt to
+use it will raise a warning, unless disabled via
+
+ no warnings "experimental::regex_sets";
+
+Comments on this feature are welcome; send email to
+C<perl5-porters@perl.org>.
+
+The rules used by L<C<use re 'strict>|re/'strict' mode> apply to this
+construct.
+
+We can extend the example above:
+
+ /(?[ ( \p{Thai} + \p{Lao} ) & \p{Digit} ])/
+
+This matches digits that are in either the Thai or Laotian scripts.
+
+Notice the white space in these examples. This construct always has
+the C<E<sol>xx> modifier turned on within it.
+
+The available binary operators are:
+
+ & intersection
+ + union
+ | another name for '+', hence means union
+ - subtraction (the result matches the set consisting of those
+ code points matched by the first operand, excluding any that
+ are also matched by the second operand)
+ ^ symmetric difference (the union minus the intersection). This
+ is like an exclusive or, in that the result is the set of code
+ points that are matched by either, but not both, of the
+ operands.
+
+There is one unary operator:
+
+ ! complement
+
+All the binary operators left associate; C<"&"> is higher precedence
+than the others, which all have equal precedence. The unary operator
+right associates, and has highest precedence. Thus this follows the
+normal Perl precedence rules for logical operators. Use parentheses to
+override the default precedence and associativity.
+
+The main restriction is that everything is a metacharacter. Thus,
+you cannot refer to single characters by doing something like this:
+
+ /(?[ a + b ])/ # Syntax error!
+
+The easiest way to specify an individual typable character is to enclose
+it in brackets:
+
+ /(?[ [a] + [b] ])/
+
+(This is the same thing as C<[ab]>.) You could also have said the
+equivalent:
+
+ /(?[[ a b ]])/
+
+(You can, of course, specify single characters by using, C<\x{...}>,
+C<\N{...}>, etc.)
+
+This last example shows the use of this construct to specify an ordinary
+bracketed character class without additional set operations. Note the
+white space within it. This is allowed because C<E<sol>xx> is
+automatically turned on within this construct.
+
+All the other escapes accepted by normal bracketed character classes are
+accepted here as well.
+
+Because this construct compiles under
+L<C<use re 'strict>|re/'strict' mode>, unrecognized escapes that
+generate warnings in normal classes are fatal errors here, as well as
+all other warnings from these class elements, as well as some
+practices that don't currently warn outside C<re 'strict'>. For example
+you cannot say
+
+ /(?[ [ \xF ] ])/ # Syntax error!
+
+You have to have two hex digits after a braceless C<\x> (use a leading
+zero to make two). These restrictions are to lower the incidence of
+typos causing the class to not match what you thought it would.
+
+If a regular bracketed character class contains a C<\p{}> or C<\P{}> and
+is matched against a non-Unicode code point, a warning may be
+raised, as the result is not Unicode-defined. No such warning will come
+when using this extended form.
+
+The final difference between regular bracketed character classes and
+these, is that it is not possible to get these to match a
+multi-character fold. Thus,
+
+ /(?[ [\xDF] ])/iu
+
+does not match the string C<ss>.
+
+You don't have to enclose POSIX class names inside double brackets,
+hence both of the following work:
+
+ /(?[ [:word:] - [:lower:] ])/
+ /(?[ [[:word:]] - [[:lower:]] ])/
+
+Any contained POSIX character classes, including things like C<\w> and C<\D>
+respect the C<E<sol>a> (and C<E<sol>aa>) modifiers.
+
+C<< (?[ ]) >> is a regex-compile-time construct. Any attempt to use
+something which isn't knowable at the time the containing regular
+expression is compiled is a fatal error. In practice, this means
+just three limitations:
+
+=over 4
+
+=item 1
+
+When compiled within the scope of C<use locale> (or the C<E<sol>l> regex
+modifier), this construct assumes that the execution-time locale will be
+a UTF-8 one, and the generated pattern always uses Unicode rules. What
+gets matched or not thus isn't dependent on the actual runtime locale, so
+tainting is not enabled. But a C<locale> category warning is raised
+if the runtime locale turns out to not be UTF-8.
+
+=item 2
+
+Any
+L<user-defined property|perlunicode/"User-Defined Character Properties">
+used must be already defined by the time the regular expression is
+compiled (but note that this construct can be used instead of such
+properties).
+
+=item 3
+
+A regular expression that otherwise would compile
+using C<E<sol>d> rules, and which uses this construct will instead
+use C<E<sol>u>. Thus this construct tells Perl that you don't want
+C<E<sol>d> rules for the entire regular expression containing it.
+
+=back
+
+Note that skipping white space applies only to the interior of this
+construct. There must not be any space between any of the characters
+that form the initial C<(?[>. Nor may there be space between the
+closing C<])> characters.
+
+Just as in all regular expressions, the pattern can be built up by
+including variables that are interpolated at regex compilation time.
+Care must be taken to ensure that you are getting what you expect. For
+example:
+
+ my $thai_or_lao = '\p{Thai} + \p{Lao}';
+ ...
+ qr/(?[ \p{Digit} & $thai_or_lao ])/;
+
+compiles to
+
+ qr/(?[ \p{Digit} & \p{Thai} + \p{Lao} ])/;
+
+But this does not have the effect that someone reading the code would
+likely expect, as the intersection applies just to C<\p{Thai}>,
+excluding the Laotian. Pitfalls like this can be avoided by
+parenthesizing the component pieces:
+
+ my $thai_or_lao = '( \p{Thai} + \p{Lao} )';
+
+But any modifiers will still apply to all the components:
+
+ my $lower = '\p{Lower} + \p{Digit}';
+ qr/(?[ \p{Greek} & $lower ])/i;
+
+matches upper case things. You can avoid surprises by making the
+components into instances of this construct by compiling them:
+
+ my $thai_or_lao = qr/(?[ \p{Thai} + \p{Lao} ])/;
+ my $lower = qr/(?[ \p{Lower} + \p{Digit} ])/;
+
+When these are embedded in another pattern, what they match does not
+change, regardless of parenthesization or what modifiers are in effect
+in that outer pattern.
- $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.
+Due to the way that Perl parses things, your parentheses and brackets
+may need to be balanced, even including comments. If you run into any
+examples, please send them to C<perlbug@perl.org>, so that we can have a
+concrete example for this man page.
-=cut
+We may change it so that things that remain legal uses in normal bracketed
+character classes might become illegal within this experimental
+construct. One proposal, for example, is to forbid adjacent uses of the
+same character, as in C<(?[ [aa] ])>. The motivation for such a change
+is that this usage is likely a typo, as the second "a" adds nothing.
https://perl5.git.perl.org / perl5.git / blobdiff