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, experimentally, it also matches the vertical tab, C<\cK>.
+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 ...
=item otherwise ...
-C<\s> matches [\t\n\f\r\cK ] and, starting, experimentally in Perl
+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.
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). It uses the platform's
+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>.
=item [1]
-Prior to Perl v5.18, C<\s> did not match the vertical tab. The change
-in v5.18 is considered an experiment, which means it could be backed out
-in v5.20 or v5.22 if experience indicates that it breaks too much
-existing code. If this change adversely affects you, send email to
-C<perlbug@perl.org>; if it affects you positively, email
-C<perlthanks@perl.org>. In the meantime, C<[^\S\cK]> (obscurely)
-matches what C<\s> traditionally did.
+Prior to Perl v5.18, C<\s> did not match the vertical tab.
+C<[^\S\cK]> (obscurely) matches what C<\s> traditionally did.
=item [2]
-------
-* There is an exception to a bracketed character class matching a
-single character only. When the class is to match caselessly under C</i>
-matching rules, and a character that is explicitly mentioned inside the
-class matches a
+* 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
-(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,
+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 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,
+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/i # Doesn't match
- 'ss' =~ /\A[\0-\N{LATIN SMALL LETTER SHARP S}]\z/i # No match
- 'ss' =~ /\A[\xDF-\xDF]\z/i # Matches on ASCII platforms, since \XDF
- # is LATIN SMALL LETTER SHARP S, and the
- # range is just a single element
+ '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 an
+extended L<C<(?[...])>|/Extended Bracketed Character Classes>
+class; and only the first code point is used (with
+a C<regexp>-type warning raised) otherwise.
+
+=back
+
=head3 Special Characters Inside a Bracketed Character Class
Most characters that are meta characters in regular expressions (that
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.
Examples:
"+" =~ /[+?*]/ # Match, "+" in a character class is not special.
- "\cH" =~ /[\b]/ # Match, \b inside in a character class.
+ "\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 Character Ranges
# 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
else don't list it first.
In inverted bracketed character classes, Perl ignores the Unicode rules
-that normally say that certain characters should match a sequence of
-multiple characters under caseless C</i> matching. Following those
-rules could lead to highly confusing situations:
+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!
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.
+latter. (See note in L</Bracketed Character Classes> above.)
Examples:
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
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.
+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]
=item [6]
-C<\p{SpacePerl}> and C<\p{Space}> match identically starting with Perl
+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{SpacePerl}> does not match the vertical tab, C<\cK>.
+matching, C<\p{XPerlSpace}> did not match the vertical tab, C<\cK>.
Same for the two ASCII-only range forms.
=back
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
+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{}>.
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} ])/
! complement
-All the binary operators left associate, and are of equal precedence.
-The unary operator right associates, and has higher precedence. Use
-parentheses to override the default associations. Some feedback we've
-received indicates a desire for intersection to have higher precedence
-than union. This is something that feedback from the field may cause us
-to change in future releases; you may want to parenthesize copiously to
-avoid such changes affecting your code, until this feature is no longer
-considered experimental.
+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:
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; C<E<sol>x> is turned on even within bracketed
-character classes, except you can't have comments inside them. Hence,
+white space within it; a limited version of C<E<sol>x> is turned on even
+within bracketed character classes, with only the SPACE and TAB (C<\t>)
+characters allowed, and no comments. Hence,
(?[ [#] ])
=item 1
-This construct cannot be used within the scope of
-C<use locale> (or the C<E<sol>l> regex modifier).
+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
=back
-The C<E<sol>x> processing within this class is an extended form.
-Besides the characters that are considered white space in normal C</x>
-processing, there are 5 others, recommended by the Unicode standard:
-
- U+0085 NEXT LINE
- U+200E LEFT-TO-RIGHT MARK
- U+200F RIGHT-TO-LEFT MARK
- U+2028 LINE SEPARATOR
- U+2029 PARAGRAPH SEPARATOR
-
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
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