from cover to cover, Perl does support many Unicode features.
People who want to learn to use Unicode in Perl, should probably read
-L<the Perl Unicode tutorial|perlunitut> before reading this reference
-document.
+the L<Perl Unicode tutorial, perlunitut|perlunitut> and
+L<perluniintro>, before reading
+this reference document.
+
+Also, the use of Unicode may present security issues that aren't obvious.
+Read L<Unicode Security Considerations|http://www.unicode.org/reports/tr36>.
=over 4
+=item Safest if you "use feature 'unicode_strings'"
+
+In order to preserve backward compatibility, Perl does not turn
+on full internal Unicode support unless the pragma
+C<use feature 'unicode_strings'> is specified. (This is automatically
+selected if you use C<use 5.012> or higher.) Failure to do this can
+trigger unexpected surprises. See L</The "Unicode Bug"> below.
+
+This pragma doesn't affect I/O. Nor does it change the internal
+representation of strings, only their interpretation. There are still
+several places where Unicode isn't fully supported, such as in
+filenames.
+
=item Input and Output Layers
Perl knows when a filehandle uses Perl's internal Unicode encodings
(UTF-8, or UTF-EBCDIC if in EBCDIC) if the filehandle is opened with
-the ":utf8" layer. Other encodings can be converted to Perl's
+the ":encoding(utf8)" layer. Other encodings can be converted to Perl's
encoding on input or from Perl's encoding on output by use of the
":encoding(...)" layer. See L<open>.
To indicate that Perl source itself is in UTF-8, use C<use utf8;>.
-=item Regular Expressions
-
-The regular expression compiler produces polymorphic opcodes. That is,
-the pattern adapts to the data and automatically switches to the Unicode
-character scheme when presented with data that is internally encoded in
-UTF-8 -- or instead uses a traditional byte scheme when presented with
-byte data.
-
=item C<use utf8> still needed to enable UTF-8/UTF-EBCDIC in scripts
As a compatibility measure, the C<use utf8> pragma must be explicitly
implicit upgrading from byte strings to Unicode strings assumes that
they were encoded in I<ISO 8859-1 (Latin-1)>, but Unicode strings are
downgraded with UTF-8 encoding. This happens because the first 256
-codepoints in Unicode happens to agree with Latin-1.
+codepoints in Unicode happens to agree with Latin-1.
See L</"Byte and Character Semantics"> for more details.
=head2 Byte and Character Semantics
-Beginning with version 5.6, Perl uses logically-wide characters to
-represent strings internally.
-
-In future, Perl-level operations will be expected to work with
-characters rather than bytes.
-
-However, as an interim compatibility measure, Perl aims to
-provide a safe migration path from byte semantics to character
-semantics for programs. For operations where Perl can unambiguously
-decide that the input data are characters, Perl switches to
-character semantics. For operations where this determination cannot
-be made without additional information from the user, Perl decides in
-favor of compatibility and chooses to use byte semantics.
+Perl uses logically-wide characters to represent strings internally.
+
+Starting in Perl 5.14, Perl-level operations work with
+characters rather than bytes within the scope of a
+C<L<use feature 'unicode_strings'|feature>> (or equivalently
+C<use 5.012> or higher). (This is not true if bytes have been
+explicitly requested by C<L<use bytes|bytes>>, nor necessarily true
+for interactions with the platform's operating system.)
+
+For earlier Perls, and when C<unicode_strings> is not in effect, Perl
+provides a fairly safe environment that can handle both types of
+semantics in programs. For operations where Perl can unambiguously
+decide that the input data are characters, Perl switches to character
+semantics. For operations where this determination cannot be made
+without additional information from the user, Perl decides in favor of
+compatibility and chooses to use byte semantics.
+
+When C<use locale> (but not C<use locale ':not_characters'>) is in
+effect, Perl uses the semantics associated with the current locale.
+(C<use locale> overrides C<use feature 'unicode_strings'> in the same scope;
+while C<use locale ':not_characters'> effectively also selects
+C<use feature 'unicode_strings'> in its scope; see L<perllocale>.)
+Otherwise, Perl uses the platform's native
+byte semantics for characters whose code points are less than 256, and
+Unicode semantics for those greater than 255. That means that non-ASCII
+characters are undefined except for their
+ordinal numbers. This means that none have case (upper and lower), nor are any
+a member of character classes, like C<[:alpha:]> or C<\w>. (But all do belong
+to the C<\W> class or the Perl regular expression extension C<[:^alpha:]>.)
This behavior preserves compatibility with earlier versions of Perl,
which allowed byte semantics in Perl operations only if
-none of the program's inputs were marked as being as source of Unicode
+none of the program's inputs were marked as being a source of Unicode
character data. Such data may come from filehandles, from calls to
external programs, from information provided by the system (such as %ENV),
or from literals and constants in the source text.
-The C<bytes> pragma will always, regardless of platform, force byte
-semantics in a particular lexical scope. See L<bytes>.
-
The C<utf8> pragma is primarily a compatibility device that enables
recognition of UTF-(8|EBCDIC) in literals encountered by the parser.
Note that this pragma is only required while Perl defaults to byte
semantics; when character semantics become the default, this pragma
may become a no-op. See L<utf8>.
-Unless explicitly stated, Perl operators use character semantics
-for Unicode data and byte semantics for non-Unicode data.
-The decision to use character semantics is made transparently. If
-input data comes from a Unicode source--for example, if a character
-encoding layer is added to a filehandle or a literal Unicode
-string constant appears in a program--character semantics apply.
-Otherwise, byte semantics are in effect. The C<bytes> pragma should
-be used to force byte semantics on Unicode data.
-
If strings operating under byte semantics and strings with Unicode
-character data are concatenated, the new string will be created by
-decoding the byte strings as I<ISO 8859-1 (Latin-1)>, even if the
-old Unicode string used EBCDIC. This translation is done without
-regard to the system's native 8-bit encoding.
+character data are concatenated, the new string will have
+character semantics. This can cause surprises: See L</BUGS>, below.
+You can choose to be warned when this happens. See L<encoding::warnings>.
Under character semantics, many operations that formerly operated on
bytes now operate on characters. A character in Perl is
occur directly within the literal strings in UTF-8 encoding, or UTF-16.
(The former requires a BOM or C<use utf8>, the latter requires a BOM.)
-Unicode characters can also be added to a string by using the C<\x{...}>
+Unicode characters can also be added to a string by using the C<\N{U+...}>
notation. The Unicode code for the desired character, in hexadecimal,
-should be placed in the braces. For instance, a smiley face is
-C<\x{263A}>. This encoding scheme only works for all characters, but
-for characters under 0x100, note that Perl may use an 8 bit encoding
-internally, for optimization and/or backward compatibility.
+should be placed in the braces, after the C<U>. For instance, a smiley face is
+C<\N{U+263A}>.
-Additionally, if you
+Alternatively, you can use the C<\x{...}> notation for characters 0x100 and
+above. For characters below 0x100 you may get byte semantics instead of
+character semantics; see L</The "Unicode Bug">. On EBCDIC machines there is
+the additional problem that the value for such characters gives the EBCDIC
+character rather than the Unicode one, thus it is more portable to use
+C<\N{U+...}> instead.
- use charnames ':full';
+Additionally, you can use the C<\N{...}> notation and put the official
+Unicode character name within the braces, such as
+C<\N{WHITE SMILING FACE}>. This automatically loads the L<charnames>
+module with the C<:full> and C<:short> options. If you prefer different
+options for this module, you can instead, before the C<\N{...}>,
+explicitly load it with your desired options; for example,
-you can use the C<\N{...}> notation and put the official Unicode
-character name within the braces, such as C<\N{WHITE SMILING FACE}>.
+ use charnames ':loose';
=item *
=item *
-Character classes in regular expressions match characters instead of
+Bracketed character classes in regular expressions match characters instead of
bytes and match against the character properties specified in the
Unicode properties database. C<\w> can be used to match a Japanese
ideograph, for instance.
=item *
-Named Unicode properties, scripts, and block ranges may be used like
-character classes via the C<\p{}> "matches property" construct and
+Named Unicode properties, scripts, and block ranges may be used (like bracketed
+character classes) by using the C<\p{}> "matches property" construct and
the C<\P{}> negation, "doesn't match property".
-
See L</"Unicode Character Properties"> for more details.
You can define your own character properties and use them
in the regular expression with the C<\p{}> or C<\P{}> construct.
-
See L</"User-Defined Character Properties"> for more details.
=item *
-The special pattern C<\X> matches any extended Unicode
-sequence--"a combining character sequence" in Standardese--where the
-first character is a base character and subsequent characters are mark
-characters that apply to the base character. C<\X> is equivalent to
-C<(?:\PM\pM*)>.
+The special pattern C<\X> matches a logical character, an "extended grapheme
+cluster" in Standardese. In Unicode what appears to the user to be a single
+character, for example an accented C<G>, may in fact be composed of a sequence
+of characters, in this case a C<G> followed by an accent character. C<\X>
+will match the entire sequence.
=item *
when character input is provided. Note that C<uc()>, or C<\U> in
interpolated strings, translates to uppercase, while C<ucfirst>,
or C<\u> in interpolated strings, translates to titlecase in languages
-that make the distinction.
+that make the distinction (which is equivalent to uppercase in languages
+without the distinction).
=item *
automatically switch to using character positions, including
C<chop()>, C<chomp()>, C<substr()>, C<pos()>, C<index()>, C<rindex()>,
C<sprintf()>, C<write()>, and C<length()>. An operator that
-specifically does not switch is C<vec()>. Operators that really don't
-care include operators that treat strings as a bucket of bits such as
+specifically does not switch is C<vec()>. Operators that really don't
+care include operators that treat strings as a bucket of bits such as
C<sort()>, and operators dealing with filenames.
=item *
-The C<pack()>/C<unpack()> letter C<C> does I<not> change, since it is often
+The C<pack()>/C<unpack()> letter C<C> does I<not> change, since it is often
used for byte-oriented formats. Again, think C<char> in the C language.
There is a new C<U> specifier that converts between Unicode characters
=item *
-lc(), uc(), lcfirst(), and ucfirst() work for the following cases:
-
-=over 8
-
-=item *
-
-the case mapping is from a single Unicode character to another
-single Unicode character, or
-
-=item *
-
-the case mapping is from a single Unicode character to more
-than one Unicode character.
-
-=back
-
-Things to do with locales (Lithuanian, Turkish, Azeri) do B<not> work
-since Perl does not understand the concept of Unicode locales.
-
-See the Unicode Technical Report #21, Case Mappings, for more details.
-
-But you can also define your own mappings to be used in the lc(),
-lcfirst(), uc(), and ucfirst() (or their string-inlined versions).
-
-See L</"User-Defined Case Mappings"> for more details.
+There is a CPAN module, L<Unicode::Casing>, which allows you to define
+your own mappings to be used in C<lc()>, C<lcfirst()>, C<uc()>,
+C<ucfirst()>, and C<fc> (or their double-quoted string inlined
+versions such as C<\U>).
+(Prior to Perl 5.16, this functionality was partially provided
+in the Perl core, but suffered from a number of insurmountable
+drawbacks, so the CPAN module was written instead.)
=back
=head2 Unicode Character Properties
-Named Unicode properties, scripts, and block ranges may be used like
-character classes via the C<\p{}> "matches property" construct and
-the C<\P{}> negation, "doesn't match property".
-
-For instance, C<\p{Lu}> matches any character with the Unicode "Lu"
-(Letter, uppercase) property, while C<\p{M}> matches any character
-with an "M" (mark--accents and such) property. Brackets are not
-required for single letter properties, so C<\p{M}> is equivalent to
-C<\pM>. Many predefined properties are available, such as
-C<\p{Mirrored}> and C<\p{Tibetan}>.
-
-The official Unicode script and block names have spaces and dashes as
-separators, but for convenience you can use dashes, spaces, or
-underbars, and case is unimportant. It is recommended, however, that
-for consistency you use the following naming: the official Unicode
-script, property, or block name (see below for the additional rules
-that apply to block names) with whitespace and dashes removed, and the
-words "uppercase-first-lowercase-rest". C<Latin-1 Supplement> thus
-becomes C<Latin1Supplement>.
+(The only time that Perl considers a sequence of individual code
+points as a single logical character is in the C<\X> construct, already
+mentioned above. Therefore "character" in this discussion means a single
+Unicode code point.)
+
+Very nearly all Unicode character properties are accessible through
+regular expressions by using the C<\p{}> "matches property" construct
+and the C<\P{}> "doesn't match property" for its negation.
+
+For instance, C<\p{Uppercase}> matches any single character with the Unicode
+"Uppercase" property, while C<\p{L}> matches any character with a
+General_Category of "L" (letter) property. Brackets are not
+required for single letter property names, so C<\p{L}> is equivalent to C<\pL>.
+
+More formally, C<\p{Uppercase}> matches any single character whose Unicode
+Uppercase property value is True, and C<\P{Uppercase}> matches any character
+whose Uppercase property value is False, and they could have been written as
+C<\p{Uppercase=True}> and C<\p{Uppercase=False}>, respectively.
+
+This formality is needed when properties are not binary; that is, if they can
+take on more values than just True and False. For example, the Bidi_Class (see
+L</"Bidirectional Character Types"> below), can take on several different
+values, such as Left, Right, Whitespace, and others. To match these, one needs
+to specify both the property name (Bidi_Class), AND the value being
+matched against
+(Left, Right, etc.). This is done, as in the examples above, by having the
+two components separated by an equal sign (or interchangeably, a colon), like
+C<\p{Bidi_Class: Left}>.
+
+All Unicode-defined character properties may be written in these compound forms
+of C<\p{property=value}> or C<\p{property:value}>, but Perl provides some
+additional properties that are written only in the single form, as well as
+single-form short-cuts for all binary properties and certain others described
+below, in which you may omit the property name and the equals or colon
+separator.
+
+Most Unicode character properties have at least two synonyms (or aliases if you
+prefer): a short one that is easier to type and a longer one that is more
+descriptive and hence easier to understand. Thus the "L" and "Letter" properties
+above are equivalent and can be used interchangeably. Likewise,
+"Upper" is a synonym for "Uppercase", and we could have written
+C<\p{Uppercase}> equivalently as C<\p{Upper}>. Also, there are typically
+various synonyms for the values the property can be. For binary properties,
+"True" has 3 synonyms: "T", "Yes", and "Y"; and "False has correspondingly "F",
+"No", and "N". But be careful. A short form of a value for one property may
+not mean the same thing as the same short form for another. Thus, for the
+General_Category property, "L" means "Letter", but for the Bidi_Class property,
+"L" means "Left". A complete list of properties and synonyms is in
+L<perluniprops>.
+
+Upper/lower case differences in property names and values are irrelevant;
+thus C<\p{Upper}> means the same thing as C<\p{upper}> or even C<\p{UpPeR}>.
+Similarly, you can add or subtract underscores anywhere in the middle of a
+word, so that these are also equivalent to C<\p{U_p_p_e_r}>. And white space
+is irrelevant adjacent to non-word characters, such as the braces and the equals
+or colon separators, so C<\p{ Upper }> and C<\p{ Upper_case : Y }> are
+equivalent to these as well. In fact, white space and even
+hyphens can usually be added or deleted anywhere. So even C<\p{ Up-per case = Yes}> is
+equivalent. All this is called "loose-matching" by Unicode. The few places
+where stricter matching is used is in the middle of numbers, and in the Perl
+extension properties that begin or end with an underscore. Stricter matching
+cares about white space (except adjacent to non-word characters),
+hyphens, and non-interior underscores.
You can also use negation in both C<\p{}> and C<\P{}> by introducing a caret
(^) between the first brace and the property name: C<\p{^Tamil}> is
equal to C<\P{Tamil}>.
-B<NOTE: the properties, scripts, and blocks listed here are as of
-Unicode 5.0.0 in July 2006.>
-
-=over 4
-
-=item General Category
-
-Here are the basic Unicode General Category properties, followed by their
-long form. You can use either; C<\p{Lu}> and C<\p{UppercaseLetter}>,
-for instance, are identical.
+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.
+And the second set is
+C<Uppercase>,
+C<Lowercase>,
+and C<Titlecase>,
+all of which match C<Cased> under C</i> matching.
+This set also includes its subsets C<PosixUpper> and C<PosixLower> both
+of which under C</i> matching match C<PosixAlpha>.
+(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
+letters, so they aren't C<Cased_Letter>s.)
+
+The result is undefined if you try to match a non-Unicode code point
+(that is, one above 0x10FFFF) against a Unicode property. Currently, a
+warning is raised, and the match will fail. In some cases, this is
+counterintuitive, as both these fail:
+
+ chr(0x110000) =~ \p{ASCII_Hex_Digit=True} # Fails.
+ chr(0x110000) =~ \p{ASCII_Hex_Digit=False} # Fails!
+
+=head3 B<General_Category>
+
+Every Unicode character is assigned a general category, which is the "most
+usual categorization of a character" (from
+L<http://www.unicode.org/reports/tr44>).
+
+The compound way of writing these is like C<\p{General_Category=Number}>
+(short, C<\p{gc:n}>). But Perl furnishes shortcuts in which everything up
+through the equal or colon separator is omitted. So you can instead just write
+C<\pN>.
+
+Here are the short and long forms of the General Category properties:
Short Long
L Letter
- LC CasedLetter
- Lu UppercaseLetter
- Ll LowercaseLetter
- Lt TitlecaseLetter
- Lm ModifierLetter
- Lo OtherLetter
+ LC, L& Cased_Letter (that is: [\p{Ll}\p{Lu}\p{Lt}])
+ Lu Uppercase_Letter
+ Ll Lowercase_Letter
+ Lt Titlecase_Letter
+ Lm Modifier_Letter
+ Lo Other_Letter
M Mark
- Mn NonspacingMark
- Mc SpacingMark
- Me EnclosingMark
+ Mn Nonspacing_Mark
+ Mc Spacing_Mark
+ Me Enclosing_Mark
N Number
- Nd DecimalNumber
- Nl LetterNumber
- No OtherNumber
-
- P Punctuation
- Pc ConnectorPunctuation
- Pd DashPunctuation
- Ps OpenPunctuation
- Pe ClosePunctuation
- Pi InitialPunctuation
+ Nd Decimal_Number (also Digit)
+ Nl Letter_Number
+ No Other_Number
+
+ P Punctuation (also Punct)
+ Pc Connector_Punctuation
+ Pd Dash_Punctuation
+ Ps Open_Punctuation
+ Pe Close_Punctuation
+ Pi Initial_Punctuation
(may behave like Ps or Pe depending on usage)
- Pf FinalPunctuation
+ Pf Final_Punctuation
(may behave like Ps or Pe depending on usage)
- Po OtherPunctuation
+ Po Other_Punctuation
S Symbol
- Sm MathSymbol
- Sc CurrencySymbol
- Sk ModifierSymbol
- So OtherSymbol
+ Sm Math_Symbol
+ Sc Currency_Symbol
+ Sk Modifier_Symbol
+ So Other_Symbol
Z Separator
- Zs SpaceSeparator
- Zl LineSeparator
- Zp ParagraphSeparator
+ Zs Space_Separator
+ Zl Line_Separator
+ Zp Paragraph_Separator
C Other
- Cc Control
+ Cc Control (also Cntrl)
Cf Format
- Cs Surrogate (not usable)
- Co PrivateUse
+ Cs Surrogate
+ Co Private_Use
Cn Unassigned
Single-letter properties match all characters in any of the
two-letter sub-properties starting with the same letter.
-C<LC> and C<L&> are special cases, which are aliases for the set of
-C<Ll>, C<Lu>, and C<Lt>.
-
-Because Perl hides the need for the user to understand the internal
-representation of Unicode characters, there is no need to implement
-the somewhat messy concept of surrogates. C<Cs> is therefore not
-supported.
+C<LC> and C<L&> are special: both are aliases for the set consisting of everything matched by C<Ll>, C<Lu>, and C<Lt>.
-=item Bidirectional Character Types
+=head3 B<Bidirectional Character Types>
-Because scripts differ in their directionality--Hebrew is
-written right to left, for example--Unicode supplies these properties in
-the BidiClass class:
+Because scripts differ in their directionality (Hebrew and Arabic are
+written right to left, for example) Unicode supplies these properties in
+the Bidi_Class class:
Property Meaning
LRE Left-to-Right Embedding
LRO Left-to-Right Override
R Right-to-Left
- AL Right-to-Left Arabic
+ AL Arabic Letter
RLE Right-to-Left Embedding
RLO Right-to-Left Override
PDF Pop Directional Format
EN European Number
- ES European Number Separator
- ET European Number Terminator
+ ES European Separator
+ ET European Terminator
AN Arabic Number
- CS Common Number Separator
+ CS Common Separator
NSM Non-Spacing Mark
BN Boundary Neutral
B Paragraph Separator
WS Whitespace
ON Other Neutrals
-For example, C<\p{BidiClass:R}> matches characters that are normally
+This property is always written in the compound form.
+For example, C<\p{Bidi_Class:R}> matches characters that are normally
written right to left.
-=item Scripts
-
-The script names which can be used by C<\p{...}> and C<\P{...}>,
-such as in C<\p{Latin}> or C<\p{Cyrillic}>, are as follows:
-
- Arabic
- Armenian
- Balinese
- Bengali
- Bopomofo
- Braille
- Buginese
- Buhid
- CanadianAboriginal
- Cherokee
- Coptic
- Cuneiform
- Cypriot
- Cyrillic
- Deseret
- Devanagari
- Ethiopic
- Georgian
- Glagolitic
- Gothic
- Greek
- Gujarati
- Gurmukhi
- Han
- Hangul
- Hanunoo
- Hebrew
- Hiragana
- Inherited
- Kannada
- Katakana
- Kharoshthi
- Khmer
- Lao
- Latin
- Limbu
- LinearB
- Malayalam
- Mongolian
- Myanmar
- NewTaiLue
- Nko
- Ogham
- OldItalic
- OldPersian
- Oriya
- Osmanya
- PhagsPa
- Phoenician
- Runic
- Shavian
- Sinhala
- SylotiNagri
- Syriac
- Tagalog
- Tagbanwa
- TaiLe
- Tamil
- Telugu
- Thaana
- Thai
- Tibetan
- Tifinagh
- Ugaritic
- Yi
-
-=item Extended property classes
-
-Extended property classes can supplement the basic
-properties, defined by the F<PropList> Unicode database:
-
- ASCIIHexDigit
- BidiControl
- Dash
- Deprecated
- Diacritic
- Extender
- HexDigit
- Hyphen
- Ideographic
- IDSBinaryOperator
- IDSTrinaryOperator
- JoinControl
- LogicalOrderException
- NoncharacterCodePoint
- OtherAlphabetic
- OtherDefaultIgnorableCodePoint
- OtherGraphemeExtend
- OtherIDStart
- OtherIDContinue
- OtherLowercase
- OtherMath
- OtherUppercase
- PatternSyntax
- PatternWhiteSpace
- QuotationMark
- Radical
- SoftDotted
- STerm
- TerminalPunctuation
- UnifiedIdeograph
- VariationSelector
- WhiteSpace
-
-and there are further derived properties:
-
- Alphabetic = Lu + Ll + Lt + Lm + Lo + Nl + OtherAlphabetic
- Lowercase = Ll + OtherLowercase
- Uppercase = Lu + OtherUppercase
- Math = Sm + OtherMath
-
- IDStart = Lu + Ll + Lt + Lm + Lo + Nl + OtherIDStart
- IDContinue = IDStart + Mn + Mc + Nd + Pc + OtherIDContinue
-
- DefaultIgnorableCodePoint
- = OtherDefaultIgnorableCodePoint
- + Cf + Cc + Cs + Noncharacters + VariationSelector
- - WhiteSpace - FFF9..FFFB (Annotation Characters)
-
- Any = Any code points (i.e. U+0000 to U+10FFFF)
- Assigned = Any non-Cn code points (i.e. synonym for \P{Cn})
- Unassigned = Synonym for \p{Cn}
- ASCII = ASCII (i.e. U+0000 to U+007F)
-
- Common = Any character (or unassigned code point)
- not explicitly assigned to a script
-
-=item Use of "Is" Prefix
+=head3 B<Scripts>
+
+The world's languages are written in many different scripts. This sentence
+(unless you're reading it in translation) is written in Latin, while Russian is
+written in Cyrillic, and Greek is written in, well, Greek; Japanese mainly in
+Hiragana or Katakana. There are many more.
+
+The Unicode Script and Script_Extensions properties give what script a
+given character is in. Either property can be specified with the
+compound form like
+C<\p{Script=Hebrew}> (short: C<\p{sc=hebr}>), or
+C<\p{Script_Extensions=Javanese}> (short: C<\p{scx=java}>).
+In addition, Perl furnishes shortcuts for all
+C<Script> property names. You can omit everything up through the equals
+(or colon), and simply write C<\p{Latin}> or C<\P{Cyrillic}>.
+(This is not true for C<Script_Extensions>, which is required to be
+written in the compound form.)
+
+The difference between these two properties involves characters that are
+used in multiple scripts. For example the digits '0' through '9' are
+used in many parts of the world. These are placed in a script named
+C<Common>. Other characters are used in just a few scripts. For
+example, the "KATAKANA-HIRAGANA DOUBLE HYPHEN" is used in both Japanese
+scripts, Katakana and Hiragana, but nowhere else. The C<Script>
+property places all characters that are used in multiple scripts in the
+C<Common> script, while the C<Script_Extensions> property places those
+that are used in only a few scripts into each of those scripts; while
+still using C<Common> for those used in many scripts. Thus both these
+match:
+
+ "0" =~ /\p{sc=Common}/ # Matches
+ "0" =~ /\p{scx=Common}/ # Matches
+
+and only the first of these match:
+
+ "\N{KATAKANA-HIRAGANA DOUBLE HYPHEN}" =~ /\p{sc=Common} # Matches
+ "\N{KATAKANA-HIRAGANA DOUBLE HYPHEN}" =~ /\p{scx=Common} # No match
+
+And only the last two of these match:
+
+ "\N{KATAKANA-HIRAGANA DOUBLE HYPHEN}" =~ /\p{sc=Hiragana} # No match
+ "\N{KATAKANA-HIRAGANA DOUBLE HYPHEN}" =~ /\p{sc=Katakana} # No match
+ "\N{KATAKANA-HIRAGANA DOUBLE HYPHEN}" =~ /\p{scx=Hiragana} # Matches
+ "\N{KATAKANA-HIRAGANA DOUBLE HYPHEN}" =~ /\p{scx=Katakana} # Matches
+
+C<Script_Extensions> is thus an improved C<Script>, in which there are
+fewer characters in the C<Common> script, and correspondingly more in
+other scripts. It is new in Unicode version 6.0, and its data are likely
+to change significantly in later releases, as things get sorted out.
+
+(Actually, besides C<Common>, the C<Inherited> script, contains
+characters that are used in multiple scripts. These are modifier
+characters which modify other characters, and inherit the script value
+of the controlling character. Some of these are used in many scripts,
+and so go into C<Inherited> in both C<Script> and C<Script_Extensions>.
+Others are used in just a few scripts, so are in C<Inherited> in
+C<Script>, but not in C<Script_Extensions>.)
+
+It is worth stressing that there are several different sets of digits in
+Unicode that are equivalent to 0-9 and are matchable by C<\d> in a
+regular expression. If they are used in a single language only, they
+are in that language's C<Script> and C<Script_Extension>. If they are
+used in more than one script, they will be in C<sc=Common>, but only
+if they are used in many scripts should they be in C<scx=Common>.
+
+A complete list of scripts and their shortcuts is in L<perluniprops>.
+
+=head3 B<Use of "Is" Prefix>
For backward compatibility (with Perl 5.6), all properties mentioned
-so far may have C<Is> prepended to their name, so C<\P{IsLu}>, for
-example, is equal to C<\P{Lu}>.
+so far may have C<Is> or C<Is_> prepended to their name, so C<\P{Is_Lu}>, for
+example, is equal to C<\P{Lu}>, and C<\p{IsScript:Arabic}> is equal to
+C<\p{Arabic}>.
-=item Blocks
+=head3 B<Blocks>
In addition to B<scripts>, Unicode also defines B<blocks> of
characters. The difference between scripts and blocks is that the
concept of scripts is closer to natural languages, while the concept
-of blocks is more of an artificial grouping based on groups of 256
-Unicode characters. For example, the C<Latin> script contains letters
-from many blocks but does not contain all the characters from those
-blocks. It does not, for example, contain digits, because digits are
-shared across many scripts. Digits and similar groups, like
-punctuation, are in a category called C<Common>.
-
-For more about scripts, see the UAX#24 "Script Names":
-
- http://www.unicode.org/reports/tr24/
-
-For more about blocks, see:
-
- http://www.unicode.org/Public/UNIDATA/Blocks.txt
-
-Block names are given with the C<In> prefix. For example, the
-Katakana block is referenced via C<\p{InKatakana}>. The C<In>
-prefix may be omitted if there is no naming conflict with a script
-or any other property, but it is recommended that C<In> always be used
-for block tests to avoid confusion.
-
-These block names are supported:
-
- InAegeanNumbers
- InAlphabeticPresentationForms
- InAncientGreekMusicalNotation
- InAncientGreekNumbers
- InArabic
- InArabicPresentationFormsA
- InArabicPresentationFormsB
- InArabicSupplement
- InArmenian
- InArrows
- InBalinese
- InBasicLatin
- InBengali
- InBlockElements
- InBopomofo
- InBopomofoExtended
- InBoxDrawing
- InBraillePatterns
- InBuginese
- InBuhid
- InByzantineMusicalSymbols
- InCJKCompatibility
- InCJKCompatibilityForms
- InCJKCompatibilityIdeographs
- InCJKCompatibilityIdeographsSupplement
- InCJKRadicalsSupplement
- InCJKStrokes
- InCJKSymbolsAndPunctuation
- InCJKUnifiedIdeographs
- InCJKUnifiedIdeographsExtensionA
- InCJKUnifiedIdeographsExtensionB
- InCherokee
- InCombiningDiacriticalMarks
- InCombiningDiacriticalMarksSupplement
- InCombiningDiacriticalMarksforSymbols
- InCombiningHalfMarks
- InControlPictures
- InCoptic
- InCountingRodNumerals
- InCuneiform
- InCuneiformNumbersAndPunctuation
- InCurrencySymbols
- InCypriotSyllabary
- InCyrillic
- InCyrillicSupplement
- InDeseret
- InDevanagari
- InDingbats
- InEnclosedAlphanumerics
- InEnclosedCJKLettersAndMonths
- InEthiopic
- InEthiopicExtended
- InEthiopicSupplement
- InGeneralPunctuation
- InGeometricShapes
- InGeorgian
- InGeorgianSupplement
- InGlagolitic
- InGothic
- InGreekExtended
- InGreekAndCoptic
- InGujarati
- InGurmukhi
- InHalfwidthAndFullwidthForms
- InHangulCompatibilityJamo
- InHangulJamo
- InHangulSyllables
- InHanunoo
- InHebrew
- InHighPrivateUseSurrogates
- InHighSurrogates
- InHiragana
- InIPAExtensions
- InIdeographicDescriptionCharacters
- InKanbun
- InKangxiRadicals
- InKannada
- InKatakana
- InKatakanaPhoneticExtensions
- InKharoshthi
- InKhmer
- InKhmerSymbols
- InLao
- InLatin1Supplement
- InLatinExtendedA
- InLatinExtendedAdditional
- InLatinExtendedB
- InLatinExtendedC
- InLatinExtendedD
- InLetterlikeSymbols
- InLimbu
- InLinearBIdeograms
- InLinearBSyllabary
- InLowSurrogates
- InMalayalam
- InMathematicalAlphanumericSymbols
- InMathematicalOperators
- InMiscellaneousMathematicalSymbolsA
- InMiscellaneousMathematicalSymbolsB
- InMiscellaneousSymbols
- InMiscellaneousSymbolsAndArrows
- InMiscellaneousTechnical
- InModifierToneLetters
- InMongolian
- InMusicalSymbols
- InMyanmar
- InNKo
- InNewTaiLue
- InNumberForms
- InOgham
- InOldItalic
- InOldPersian
- InOpticalCharacterRecognition
- InOriya
- InOsmanya
- InPhagspa
- InPhoenician
- InPhoneticExtensions
- InPhoneticExtensionsSupplement
- InPrivateUseArea
- InRunic
- InShavian
- InSinhala
- InSmallFormVariants
- InSpacingModifierLetters
- InSpecials
- InSuperscriptsAndSubscripts
- InSupplementalArrowsA
- InSupplementalArrowsB
- InSupplementalMathematicalOperators
- InSupplementalPunctuation
- InSupplementaryPrivateUseAreaA
- InSupplementaryPrivateUseAreaB
- InSylotiNagri
- InSyriac
- InTagalog
- InTagbanwa
- InTags
- InTaiLe
- InTaiXuanJingSymbols
- InTamil
- InTelugu
- InThaana
- InThai
- InTibetan
- InTifinagh
- InUgaritic
- InUnifiedCanadianAboriginalSyllabics
- InVariationSelectors
- InVariationSelectorsSupplement
- InVerticalForms
- InYiRadicals
- InYiSyllables
- InYijingHexagramSymbols
+of blocks is more of an artificial grouping based on groups of Unicode
+characters with consecutive ordinal values. For example, the "Basic Latin"
+block is all characters whose ordinals are between 0 and 127, inclusive; in
+other words, the ASCII characters. The "Latin" script contains some letters
+from this as well as several other blocks, like "Latin-1 Supplement",
+"Latin Extended-A", etc., but it does not contain all the characters from
+those blocks. It does not, for example, contain the digits 0-9, because
+those digits are shared across many scripts, and hence are in the
+C<Common> script.
+
+For more about scripts versus blocks, see UAX#24 "Unicode Script Property":
+L<http://www.unicode.org/reports/tr24>
+
+The C<Script> or C<Script_Extensions> properties are likely to be the
+ones you want to use when processing
+natural language; the Block property may occasionally be useful in working
+with the nuts and bolts of Unicode.
+
+Block names are matched in the compound form, like C<\p{Block: Arrows}> or
+C<\p{Blk=Hebrew}>. Unlike most other properties, only a few block names have a
+Unicode-defined short name. But Perl does provide a (slight) shortcut: You
+can say, for example C<\p{In_Arrows}> or C<\p{In_Hebrew}>. For backwards
+compatibility, the C<In> prefix may be omitted if there is no naming conflict
+with a script or any other property, and you can even use an C<Is> prefix
+instead in those cases. But it is not a good idea to do this, for a couple
+reasons:
+
+=over 4
+
+=item 1
+
+It is confusing. There are many naming conflicts, and you may forget some.
+For example, C<\p{Hebrew}> means the I<script> Hebrew, and NOT the I<block>
+Hebrew. But would you remember that 6 months from now?
+
+=item 2
+
+It is unstable. A new version of Unicode may preempt the current meaning by
+creating a property with the same name. There was a time in very early Unicode
+releases when C<\p{Hebrew}> would have matched the I<block> Hebrew; now it
+doesn't.
+
+=back
+
+Some people prefer to always use C<\p{Block: foo}> and C<\p{Script: bar}>
+instead of the shortcuts, whether for clarity, because they can't remember the
+difference between 'In' and 'Is' anyway, or they aren't confident that those who
+eventually will read their code will know that difference.
+
+A complete list of blocks and their shortcuts is in L<perluniprops>.
+
+=head3 B<Other Properties>
+
+There are many more properties than the very basic ones described here.
+A complete list is in L<perluniprops>.
+
+Unicode defines all its properties in the compound form, so all single-form
+properties are Perl extensions. Most of these are just synonyms for the
+Unicode ones, but some are genuine extensions, including several that are in
+the compound form. And quite a few of these are actually recommended by Unicode
+(in L<http://www.unicode.org/reports/tr18>).
+
+This section gives some details on all extensions that aren't just
+synonyms for compound-form Unicode properties
+(for those properties, you'll have to refer to the
+L<Unicode Standard|http://www.unicode.org/reports/tr44>.
+
+=over
+
+=item B<C<\p{All}>>
+
+This matches any of the 1_114_112 Unicode code points. It is a synonym for
+C<\p{Any}>.
+
+=item B<C<\p{Alnum}>>
+
+This matches any C<\p{Alphabetic}> or C<\p{Decimal_Number}> character.
+
+=item B<C<\p{Any}>>
+
+This matches any of the 1_114_112 Unicode code points. It is a synonym for
+C<\p{All}>.
+
+=item B<C<\p{ASCII}>>
+
+This matches any of the 128 characters in the US-ASCII character set,
+which is a subset of Unicode.
+
+=item B<C<\p{Assigned}>>
+
+This matches any assigned code point; that is, any code point whose general
+category is not Unassigned (or equivalently, not Cn).
+
+=item B<C<\p{Blank}>>
+
+This is the same as C<\h> and C<\p{HorizSpace}>: A character that changes the
+spacing horizontally.
+
+=item B<C<\p{Decomposition_Type: Non_Canonical}>> (Short: C<\p{Dt=NonCanon}>)
+
+Matches a character that has a non-canonical decomposition.
+
+To understand the use of this rarely used property=value combination, it is
+necessary to know some basics about decomposition.
+Consider a character, say H. It could appear with various marks around it,
+such as an acute accent, or a circumflex, or various hooks, circles, arrows,
+I<etc.>, above, below, to one side or the other, etc. There are many
+possibilities among the world's languages. The number of combinations is
+astronomical, and if there were a character for each combination, it would
+soon exhaust Unicode's more than a million possible characters. So Unicode
+took a different approach: there is a character for the base H, and a
+character for each of the possible marks, and these can be variously combined
+to get a final logical character. So a logical character--what appears to be a
+single character--can be a sequence of more than one individual characters.
+This is called an "extended grapheme cluster"; Perl furnishes the C<\X>
+regular expression construct to match such sequences.
+
+But Unicode's intent is to unify the existing character set standards and
+practices, and several pre-existing standards have single characters that
+mean the same thing as some of these combinations. An example is ISO-8859-1,
+which has quite a few of these in the Latin-1 range, an example being "LATIN
+CAPITAL LETTER E WITH ACUTE". Because this character was in this pre-existing
+standard, Unicode added it to its repertoire. But this character is considered
+by Unicode to be equivalent to the sequence consisting of the character
+"LATIN CAPITAL LETTER E" followed by the character "COMBINING ACUTE ACCENT".
+
+"LATIN CAPITAL LETTER E WITH ACUTE" is called a "pre-composed" character, and
+its equivalence with the sequence is called canonical equivalence. All
+pre-composed characters are said to have a decomposition (into the equivalent
+sequence), and the decomposition type is also called canonical.
+
+However, many more characters have a different type of decomposition, a
+"compatible" or "non-canonical" decomposition. The sequences that form these
+decompositions are not considered canonically equivalent to the pre-composed
+character. An example, again in the Latin-1 range, is the "SUPERSCRIPT ONE".
+It is somewhat like a regular digit 1, but not exactly; its decomposition
+into the digit 1 is called a "compatible" decomposition, specifically a
+"super" decomposition. There are several such compatibility
+decompositions (see L<http://www.unicode.org/reports/tr44>), including one
+called "compat", which means some miscellaneous type of decomposition
+that doesn't fit into the decomposition categories that Unicode has chosen.
+
+Note that most Unicode characters don't have a decomposition, so their
+decomposition type is "None".
+
+For your convenience, Perl has added the C<Non_Canonical> decomposition
+type to mean any of the several compatibility decompositions.
+
+=item B<C<\p{Graph}>>
+
+Matches any character that is graphic. Theoretically, this means a character
+that on a printer would cause ink to be used.
+
+=item B<C<\p{HorizSpace}>>
+
+This is the same as C<\h> and C<\p{Blank}>: a character that changes the
+spacing horizontally.
+
+=item B<C<\p{In=*}>>
+
+This is a synonym for C<\p{Present_In=*}>
+
+=item B<C<\p{PerlSpace}>>
+
+This is the same as C<\s>, restricted to ASCII, namely C<S<[ \f\n\r\t]>>
+and starting in Perl v5.18, experimentally, a vertical tab.
+
+Mnemonic: Perl's (original) space
+
+=item B<C<\p{PerlWord}>>
+
+This is the same as C<\w>, restricted to ASCII, namely C<[A-Za-z0-9_]>
+
+Mnemonic: Perl's (original) word.
+
+=item B<C<\p{Posix...}>>
+
+There are several of these, which are equivalents using the C<\p>
+notation for Posix classes and are described in
+L<perlrecharclass/POSIX Character Classes>.
+
+=item B<C<\p{Present_In: *}>> (Short: C<\p{In=*}>)
+
+This property is used when you need to know in what Unicode version(s) a
+character is.
+
+The "*" above stands for some two digit Unicode version number, such as
+C<1.1> or C<4.0>; or the "*" can also be C<Unassigned>. This property will
+match the code points whose final disposition has been settled as of the
+Unicode release given by the version number; C<\p{Present_In: Unassigned}>
+will match those code points whose meaning has yet to be assigned.
+
+For example, C<U+0041> "LATIN CAPITAL LETTER A" was present in the very first
+Unicode release available, which is C<1.1>, so this property is true for all
+valid "*" versions. On the other hand, C<U+1EFF> was not assigned until version
+5.1 when it became "LATIN SMALL LETTER Y WITH LOOP", so the only "*" that
+would match it are 5.1, 5.2, and later.
+
+Unicode furnishes the C<Age> property from which this is derived. The problem
+with Age is that a strict interpretation of it (which Perl takes) has it
+matching the precise release a code point's meaning is introduced in. Thus
+C<U+0041> would match only 1.1; and C<U+1EFF> only 5.1. This is not usually what
+you want.
+
+Some non-Perl implementations of the Age property may change its meaning to be
+the same as the Perl Present_In property; just be aware of that.
+
+Another confusion with both these properties is that the definition is not
+that the code point has been I<assigned>, but that the meaning of the code point
+has been I<determined>. This is because 66 code points will always be
+unassigned, and so the Age for them is the Unicode version in which the decision
+to make them so was made. For example, C<U+FDD0> is to be permanently
+unassigned to a character, and the decision to do that was made in version 3.1,
+so C<\p{Age=3.1}> matches this character, as also does C<\p{Present_In: 3.1}> and up.
+
+=item B<C<\p{Print}>>
+
+This matches any character that is graphical or blank, except controls.
+
+=item B<C<\p{SpacePerl}>>
+
+This is the same as C<\s>, including beyond ASCII.
+
+Mnemonic: Space, as modified by Perl. (It doesn't include the vertical tab
+which both the Posix standard and Unicode consider white space.)
+
+=item B<C<\p{Title}>> and B<C<\p{Titlecase}>>
+
+Under case-sensitive matching, these both match the same code points as
+C<\p{General Category=Titlecase_Letter}> (C<\p{gc=lt}>). The difference
+is that under C</i> caseless matching, these match the same as
+C<\p{Cased}>, whereas C<\p{gc=lt}> matches C<\p{Cased_Letter>).
+
+=item B<C<\p{VertSpace}>>
+
+This is the same as C<\v>: A character that changes the spacing vertically.
+
+=item B<C<\p{Word}>>
+
+This is the same as C<\w>, including over 100_000 characters beyond ASCII.
+
+=item B<C<\p{XPosix...}>>
+
+There are several of these, which are the standard Posix classes
+extended to the full Unicode range. They are described in
+L<perlrecharclass/POSIX Character Classes>.
=back
=head2 User-Defined Character Properties
-You can define your own character properties by defining subroutines
-whose names begin with "In" or "Is". The subroutines can be defined in
-any package. The user-defined properties can be used in the regular
-expression C<\p> and C<\P> constructs; if you are using a user-defined
-property from a package other than the one you are in, you must specify
-its package in the C<\p> or C<\P> construct.
+You can define your own binary character properties by defining subroutines
+whose names begin with "In" or "Is". (The experimental feature
+L<perlre/(?[ ])> provides an alternative which allows more complex
+definitions.) The subroutines can be defined in any
+package. The user-defined properties can be used in the regular expression
+C<\p> and C<\P> constructs; if you are using a user-defined property from a
+package other than the one you are in, you must specify its package in the
+C<\p> or C<\P> construct.
- # assuming property IsForeign defined in Lang::
+ # assuming property Is_Foreign defined in Lang::
package main; # property package name required
if ($txt =~ /\p{Lang::IsForeign}+/) { ... }
Note that the effect is compile-time and immutable once defined.
+However, the subroutines are passed a single parameter, which is 0 if
+case-sensitive matching is in effect and non-zero if caseless matching
+is in effect. The subroutine may return different values depending on
+the value of the flag, and one set of values will immutably be in effect
+for all case-sensitive matches, and the other set for all case-insensitive
+matches.
+
+Note that if the regular expression is tainted, then Perl will die rather
+than calling the subroutine, where the name of the subroutine is
+determined by the tainted data.
The subroutines must return a specially-formatted string, with one
or more newline-separated lines. Each line must be one of the following:
=item *
+A single hexadecimal number denoting a Unicode code point to include.
+
+=item *
+
Two hexadecimal numbers separated by horizontal whitespace (space or
tabular characters) denoting a range of Unicode code points to include.
=item *
Something to include, prefixed by "+": a built-in character
-property (prefixed by "utf8::") or a user-defined character property,
+property (prefixed by "utf8::") or a fully qualified (including package
+name) user-defined character property,
to represent all the characters in that property; two hexadecimal code
points for a range; or a single hexadecimal code point.
=item *
Something to exclude, prefixed by "-": an existing character
-property (prefixed by "utf8::") or a user-defined character property,
+property (prefixed by "utf8::") or a fully qualified (including package
+name) user-defined character property,
to represent all the characters in that property; two hexadecimal code
points for a range; or a single hexadecimal code point.
=item *
Something to negate, prefixed "!": an existing character
-property (prefixed by "utf8::") or a user-defined character property,
+property (prefixed by "utf8::") or a fully qualified (including package
+name) user-defined character property,
to represent all the characters in that property; two hexadecimal code
points for a range; or a single hexadecimal code point.
=item *
Something to intersect with, prefixed by "&": an existing character
-property (prefixed by "utf8::") or a user-defined character property,
+property (prefixed by "utf8::") or a fully qualified (including package
+name) user-defined character property,
for all the characters except the characters in the property; two
hexadecimal code points for a range; or a single hexadecimal code point.
syllabaries (hiragana and katakana), you can define
sub InKana {
- return <<END;
+ return <<END;
3040\t309F
30A0\t30FF
END
You could also have used the existing block property names:
sub InKana {
- return <<'END';
+ return <<'END';
+utf8::InHiragana
+utf8::InKatakana
END
the non-characters:
sub InKana {
- return <<'END';
+ return <<'END';
+utf8::InHiragana
+utf8::InKatakana
-utf8::IsCn
The negation is useful for defining (surprise!) negated classes.
sub InNotKana {
- return <<'END';
+ return <<'END';
!utf8::InHiragana
-utf8::InKatakana
+utf8::IsCn
END
}
-Intersection is useful for getting the common characters matched by
-two (or more) classes.
+This will match all non-Unicode code points, since every one of them is
+not in Kana. You can use intersection to exclude these, if desired, as
+this modified example shows:
- sub InFooAndBar {
+ sub InNotKana {
return <<'END';
- +main::Foo
- &main::Bar
+ !utf8::InHiragana
+ -utf8::InKatakana
+ +utf8::IsCn
+ &utf8::Any
END
}
-It's important to remember not to use "&" for the first set -- that
-would be intersecting with nothing (resulting in an empty set).
-
-A final note on the user-defined property tests: they will be used
-only if the scalar has been marked as having Unicode characters.
-Old byte-style strings will not be affected.
+C<&utf8::Any> must be the last line in the definition.
-=head2 User-Defined Case Mappings
+Intersection is used generally for getting the common characters matched
+by two (or more) classes. It's important to remember not to use "&" for
+the first set; that would be intersecting with nothing, resulting in an
+empty set.
-You can also define your own mappings to be used in the lc(),
-lcfirst(), uc(), and ucfirst() (or their string-inlined versions).
-The principle is similar to that of user-defined character
-properties: to define subroutines in the C<main> package
-with names like C<ToLower> (for lc() and lcfirst()), C<ToTitle> (for
-the first character in ucfirst()), and C<ToUpper> (for uc(), and the
-rest of the characters in ucfirst()).
+(Note that official Unicode properties differ from these in that they
+automatically exclude non-Unicode code points and a warning is raised if
+a match is attempted on one of those.)
-The string returned by the subroutines needs now to be three
-hexadecimal numbers separated by tabulators: start of the source
-range, end of the source range, and start of the destination range.
-For example:
+=head2 User-Defined Case Mappings (for serious hackers only)
- sub ToUpper {
- return <<END;
- 0061\t0063\t0041
- END
- }
-
-defines an uc() mapping that causes only the characters "a", "b", and
-"c" to be mapped to "A", "B", "C", all other characters will remain
-unchanged.
-
-If there is no source range to speak of, that is, the mapping is from
-a single character to another single character, leave the end of the
-source range empty, but the two tabulator characters are still needed.
-For example:
-
- sub ToLower {
- return <<END;
- 0041\t\t0061
- END
- }
-
-defines a lc() mapping that causes only "A" to be mapped to "a", all
-other characters will remain unchanged.
-
-(For serious hackers only) If you want to introspect the default
-mappings, you can find the data in the directory
-C<$Config{privlib}>/F<unicore/To/>. The mapping data is returned as
-the here-document, and the C<utf8::ToSpecFoo> are special exception
-mappings derived from <$Config{privlib}>/F<unicore/SpecialCasing.txt>.
-The C<Digit> and C<Fold> mappings that one can see in the directory
-are not directly user-accessible, one can use either the
-C<Unicode::UCD> module, or just match case-insensitively (that's when
-the C<Fold> mapping is used).
-
-A final note on the user-defined case mappings: they will be used
-only if the scalar has been marked as having Unicode characters.
-Old byte-style strings will not be affected.
+B<This feature has been removed as of Perl 5.16.>
+The CPAN module L<Unicode::Casing> provides better functionality without
+the drawbacks that this feature had. If you are using a Perl earlier
+than 5.16, this feature was most fully documented in the 5.14 version of
+this pod:
+L<http://perldoc.perl.org/5.14.0/perlunicode.html#User-Defined-Case-Mappings-%28for-serious-hackers-only%29>
=head2 Character Encodings for Input and Output
=head2 Unicode Regular Expression Support Level
-The following list of Unicode support for regular expressions describes
-all the features currently supported. The references to "Level N"
+The following list of Unicode supported features for regular expressions describes
+all features currently directly supported by core Perl. The references to "Level N"
and the section numbers refer to the Unicode Technical Standard #18,
-"Unicode Regular Expressions", version 11, in May 2005.
+"Unicode Regular Expressions", version 13, from August 2008.
=over 4
Level 1 - Basic Unicode Support
- RL1.1 Hex Notation - done [1]
- RL1.2 Properties - done [2][3]
- RL1.2a Compatibility Properties - done [4]
- RL1.3 Subtraction and Intersection - MISSING [5]
- RL1.4 Simple Word Boundaries - done [6]
- RL1.5 Simple Loose Matches - done [7]
- RL1.6 Line Boundaries - MISSING [8]
- RL1.7 Supplementary Code Points - done [9]
-
- [1] \x{...}
- [2] \p{...} \P{...}
- [3] supports not only minimal list (general category, scripts,
- Alphabetic, Lowercase, Uppercase, WhiteSpace,
- NoncharacterCodePoint, DefaultIgnorableCodePoint, Any,
- ASCII, Assigned), but also bidirectional types, blocks, etc.
- (see L</"Unicode Character Properties">)
- [4] \d \D \s \S \w \W \X [:prop:] [:^prop:]
- [5] can use regular expression look-ahead [a] or
- user-defined character properties [b] to emulate set operations
- [6] \b \B
- [7] note that Perl does Full case-folding in matching, not Simple:
- for example U+1F88 is equivalent with U+1F00 U+03B9,
- not with 1F80. This difference matters for certain Greek
- capital letters with certain modifiers: the Full case-folding
- decomposes the letter, while the Simple case-folding would map
- it to a single character.
- [8] should do ^ and $ also on U+000B (\v in C), FF (\f), CR (\r),
- CRLF (\r\n), NEL (U+0085), LS (U+2028), and PS (U+2029);
- should also affect <>, $., and script line numbers;
- should not split lines within CRLF [c] (i.e. there is no empty
- line between \r and \n)
- [9] UTF-8/UTF-EBDDIC used in perl allows not only U+10000 to U+10FFFF
- but also beyond U+10FFFF [d]
-
-[a] You can mimic class subtraction using lookahead.
+ RL1.1 Hex Notation - done [1]
+ RL1.2 Properties - done [2][3]
+ RL1.2a Compatibility Properties - done [4]
+ RL1.3 Subtraction and Intersection - experimental [5]
+ RL1.4 Simple Word Boundaries - done [6]
+ RL1.5 Simple Loose Matches - done [7]
+ RL1.6 Line Boundaries - MISSING [8][9]
+ RL1.7 Supplementary Code Points - done [10]
+
+=over 4
+
+=item [1]
+
+\x{...}
+
+=item [2]
+
+\p{...} \P{...}
+
+=item [3]
+
+supports not only minimal list, but all Unicode character properties (see Unicode Character Properties above)
+
+=item [4]
+
+\d \D \s \S \w \W \X [:prop:] [:^prop:]
+
+=item [5]
+
+The experimental feature in v5.18 "(?[...])" accomplishes this. See
+L<perlre/(?[ ])>. If you don't want to use an experimental feature,
+you can use one of the following:
+
+=over 4
+
+=item * Regular expression look-ahead
+
+You can mimic class subtraction using lookahead.
For example, what UTS#18 might write as
- [{Greek}-[{UNASSIGNED}]]
+ [{Block=Greek}-[{UNASSIGNED}]]
in Perl can be written as:
- (?!\p{Unassigned})\p{InGreekAndCoptic}
- (?=\p{Assigned})\p{InGreekAndCoptic}
+ (?!\p{Unassigned})\p{Block=Greek}
+ (?=\p{Assigned})\p{Block=Greek}
But in this particular example, you probably really want
- \p{GreekAndCoptic}
+ \p{Greek}
which will match assigned characters known to be part of the Greek script.
-Also see the Unicode::Regex::Set module, it does implement the full
-UTS#18 grouping, intersection, union, and removal (subtraction) syntax.
+=item * CPAN module L<Unicode::Regex::Set>
+
+It does implement the full UTS#18 grouping, intersection, union, and
+removal (subtraction) syntax.
+
+=item * L</"User-Defined Character Properties">
+
+'+' for union, '-' for removal (set-difference), '&' for intersection
+
+=back
+
+=item [6]
+
+\b \B
+
+=item [7]
-[b] '+' for union, '-' for removal (set-difference), '&' for intersection
-(see L</"User-Defined Character Properties">)
+Note that Perl does Full case-folding in matching (but with bugs), not Simple: for example U+1F88 is equivalent to U+1F00 U+03B9, instead of just U+1F80. This difference matters mainly for certain Greek capital letters with certain modifiers: the Full case-folding decomposes the letter, while the Simple case-folding would map it to a single character.
-[c] Try the C<:crlf> layer (see L<PerlIO>).
+=item [8]
-[d] Avoid C<use warning 'utf8';> (or say C<no warning 'utf8';>) to allow
-U+FFFF (C<\x{FFFF}>).
+Should do ^ and $ also on U+000B (\v in C), FF (\f), CR (\r), CRLF
+(\r\n), NEL (U+0085), LS (U+2028), and PS (U+2029); should also affect
+<>, $., and script line numbers; should not split lines within CRLF
+(i.e. there is no empty line between \r and \n). For CRLF, try the
+C<:crlf> layer (see L<PerlIO>).
+
+=item [9]
+
+Linebreaking conformant with UAX#14 "Unicode Line Breaking Algorithm" is available through the Unicode::LineBreaking module.
+
+=item [10]
+
+UTF-8/UTF-EBDDIC used in Perl allows not only U+10000 to
+U+10FFFF but also beyond U+10FFFF
+
+=back
=item *
Level 2 - Extended Unicode Support
- RL2.1 Canonical Equivalents - MISSING [10][11]
- RL2.2 Default Grapheme Clusters - MISSING [12][13]
- RL2.3 Default Word Boundaries - MISSING [14]
- RL2.4 Default Loose Matches - MISSING [15]
- RL2.5 Name Properties - MISSING [16]
- RL2.6 Wildcard Properties - MISSING
-
- [10] see UAX#15 "Unicode Normalization Forms"
- [11] have Unicode::Normalize but not integrated to regexes
- [12] have \X but at this level . should equal that
- [13] UAX#29 "Text Boundaries" considers CRLF and Hangul syllable
- clusters as a single grapheme cluster.
- [14] see UAX#29, Word Boundaries
- [15] see UAX#21 "Case Mappings"
- [16] have \N{...} but neither compute names of CJK Ideographs
- and Hangul Syllables nor use a loose match [e]
-
-[e] C<\N{...}> allows namespaces (see L<charnames>).
+ RL2.1 Canonical Equivalents - MISSING [10][11]
+ RL2.2 Default Grapheme Clusters - MISSING [12]
+ RL2.3 Default Word Boundaries - MISSING [14]
+ RL2.4 Default Loose Matches - MISSING [15]
+ RL2.5 Name Properties - DONE
+ RL2.6 Wildcard Properties - MISSING
+
+ [10] see UAX#15 "Unicode Normalization Forms"
+ [11] have Unicode::Normalize but not integrated to regexes
+ [12] have \X but we don't have a "Grapheme Cluster Mode"
+ [14] see UAX#29, Word Boundaries
+ [15] This is covered in Chapter 3.13 (in Unicode 6.0)
=item *
Level 3 - Tailored Support
- RL3.1 Tailored Punctuation - MISSING
- RL3.2 Tailored Grapheme Clusters - MISSING [17][18]
- RL3.3 Tailored Word Boundaries - MISSING
- RL3.4 Tailored Loose Matches - MISSING
- RL3.5 Tailored Ranges - MISSING
- RL3.6 Context Matching - MISSING [19]
- RL3.7 Incremental Matches - MISSING
+ RL3.1 Tailored Punctuation - MISSING
+ RL3.2 Tailored Grapheme Clusters - MISSING [17][18]
+ RL3.3 Tailored Word Boundaries - MISSING
+ RL3.4 Tailored Loose Matches - MISSING
+ RL3.5 Tailored Ranges - MISSING
+ RL3.6 Context Matching - MISSING [19]
+ RL3.7 Incremental Matches - MISSING
( RL3.8 Unicode Set Sharing )
- RL3.9 Possible Match Sets - MISSING
- RL3.10 Folded Matching - MISSING [20]
- RL3.11 Submatchers - MISSING
-
- [17] see UAX#10 "Unicode Collation Algorithms"
- [18] have Unicode::Collate but not integrated to regexes
- [19] have (?<=x) and (?=x), but look-aheads or look-behinds should see
- outside of the target substring
- [20] need insensitive matching for linguistic features other than case;
- for example, hiragana to katakana, wide and narrow, simplified Han
- to traditional Han (see UTR#30 "Character Foldings")
+ RL3.9 Possible Match Sets - MISSING
+ RL3.10 Folded Matching - MISSING [20]
+ RL3.11 Submatchers - MISSING
+
+ [17] see UAX#10 "Unicode Collation Algorithms"
+ [18] have Unicode::Collate but not integrated to regexes
+ [19] have (?<=x) and (?=x), but look-aheads or look-behinds
+ should see outside of the target substring
+ [20] need insensitive matching for linguistic features other
+ than case; for example, hiragana to katakana, wide and
+ narrow, simplified Han to traditional Han (see UTR#30
+ "Character Foldings")
=back
UTF-8
-UTF-8 is a variable-length (1 to 6 bytes, current character allocations
-require 4 bytes), byte-order independent encoding. For ASCII (and we
-really do mean 7-bit ASCII, not another 8-bit encoding), UTF-8 is
-transparent.
+UTF-8 is a variable-length (1 to 4 bytes), byte-order independent
+encoding. For ASCII (and we really do mean 7-bit ASCII, not another
+8-bit encoding), UTF-8 is transparent.
The following table is from Unicode 3.2.
- Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte
+ Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte
U+0000..U+007F 00..7F
- U+0080..U+07FF C2..DF 80..BF
- U+0800..U+0FFF E0 A0..BF 80..BF
+ U+0080..U+07FF * C2..DF 80..BF
+ U+0800..U+0FFF E0 * A0..BF 80..BF
U+1000..U+CFFF E1..EC 80..BF 80..BF
U+D000..U+D7FF ED 80..9F 80..BF
- U+D800..U+DFFF ******* ill-formed *******
+ U+D800..U+DFFF +++++ utf16 surrogates, not legal utf8 +++++
U+E000..U+FFFF EE..EF 80..BF 80..BF
- U+10000..U+3FFFF F0 90..BF 80..BF 80..BF
+ U+10000..U+3FFFF F0 * 90..BF 80..BF 80..BF
U+40000..U+FFFFF F1..F3 80..BF 80..BF 80..BF
U+100000..U+10FFFF F4 80..8F 80..BF 80..BF
-Note the C<A0..BF> in C<U+0800..U+0FFF>, the C<80..9F> in
-C<U+D000...U+D7FF>, the C<90..B>F in C<U+10000..U+3FFFF>, and the
-C<80...8F> in C<U+100000..U+10FFFF>. The "gaps" are caused by legal
-UTF-8 avoiding non-shortest encodings: it is technically possible to
-UTF-8-encode a single code point in different ways, but that is
-explicitly forbidden, and the shortest possible encoding should always
-be used. So that's what Perl does.
+Note the gaps marked by "*" before several of the byte entries above. These are
+caused by legal UTF-8 avoiding non-shortest encodings: it is technically
+possible to UTF-8-encode a single code point in different ways, but that is
+explicitly forbidden, and the shortest possible encoding should always be used
+(and that is what Perl does).
Another way to look at it is via bits:
- Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte
+ Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte
- 0aaaaaaa 0aaaaaaa
- 00000bbbbbaaaaaa 110bbbbb 10aaaaaa
- ccccbbbbbbaaaaaa 1110cccc 10bbbbbb 10aaaaaa
- 00000dddccccccbbbbbbaaaaaa 11110ddd 10cccccc 10bbbbbb 10aaaaaa
+ 0aaaaaaa 0aaaaaaa
+ 00000bbbbbaaaaaa 110bbbbb 10aaaaaa
+ ccccbbbbbbaaaaaa 1110cccc 10bbbbbb 10aaaaaa
+ 00000dddccccccbbbbbbaaaaaa 11110ddd 10cccccc 10bbbbbb 10aaaaaa
-As you can see, the continuation bytes all begin with C<10>, and the
-leading bits of the start byte tell how many bytes the are in the
+As you can see, the continuation bytes all begin with "10", and the
+leading bits of the start byte tell how many bytes there are in the
encoded character.
+The original UTF-8 specification allowed up to 6 bytes, to allow
+encoding of numbers up to 0x7FFF_FFFF. Perl continues to allow those,
+and has extended that up to 13 bytes to encode code points up to what
+can fit in a 64-bit word. However, Perl will warn if you output any of
+these as being non-portable; and under strict UTF-8 input protocols,
+they are forbidden.
+
+The Unicode non-character code points are also disallowed in UTF-8 in
+"open interchange". See L</Non-character code points>.
+
=item *
UTF-EBCDIC
The followings items are mostly for reference and general Unicode
knowledge, Perl doesn't use these constructs internally.
-UTF-16 is a 2 or 4 byte encoding. The Unicode code points
-C<U+0000..U+FFFF> are stored in a single 16-bit unit, and the code
+Like UTF-8, UTF-16 is a variable-width encoding, but where
+UTF-8 uses 8-bit code units, UTF-16 uses 16-bit code units.
+All code points occupy either 2 or 4 bytes in UTF-16: code points
+C<U+0000..U+FFFF> are stored in a single 16-bit unit, and code
points C<U+10000..U+10FFFF> in two 16-bit units. The latter case is
using I<surrogates>, the first 16-bit unit being the I<high
surrogate>, and the second being the I<low surrogate>.
Surrogates are code points set aside to encode the C<U+10000..U+10FFFF>
range of Unicode code points in pairs of 16-bit units. The I<high
-surrogates> are the range C<U+D800..U+DBFF>, and the I<low surrogates>
+surrogates> are the range C<U+D800..U+DBFF> and the I<low surrogates>
are the range C<U+DC00..U+DFFF>. The surrogate encoding is
- $hi = ($uni - 0x10000) / 0x400 + 0xD800;
- $lo = ($uni - 0x10000) % 0x400 + 0xDC00;
+ $hi = ($uni - 0x10000) / 0x400 + 0xD800;
+ $lo = ($uni - 0x10000) % 0x400 + 0xDC00;
and the decoding is
- $uni = 0x10000 + ($hi - 0xD800) * 0x400 + ($lo - 0xDC00);
-
-If you try to generate surrogates (for example by using chr()), you
-will get a warning if warnings are turned on, because those code
-points are not valid for a Unicode character.
+ $uni = 0x10000 + ($hi - 0xD800) * 0x400 + ($lo - 0xDC00);
Because of the 16-bitness, UTF-16 is byte-order dependent. UTF-16
itself can be used for in-memory computations, but if storage or
was writing in UTF-8, you will read the bytes C<0xEF 0xBB 0xBF>.)
The way this trick works is that the character with the code point
-C<U+FFFE> is guaranteed not to be a valid Unicode character, so the
+C<U+FFFE> is not supposed to be in input streams, so the
sequence of bytes C<0xFF 0xFE> is unambiguously "BOM, represented in
little-endian format" and cannot be C<U+FFFE>, represented in big-endian
format".
+Surrogates have no meaning in Unicode outside their use in pairs to
+represent other code points. However, Perl allows them to be
+represented individually internally, for example by saying
+C<chr(0xD801)>, so that all code points, not just those valid for open
+interchange, are
+representable. Unicode does define semantics for them, such as their
+General Category is "Cs". But because their use is somewhat dangerous,
+Perl will warn (using the warning category "surrogate", which is a
+sub-category of "utf8") if an attempt is made
+to do things like take the lower case of one, or match
+case-insensitively, or to output them. (But don't try this on Perls
+before 5.14.)
+
=item *
UTF-32, UTF-32BE, UTF-32LE
The UTF-32 family is pretty much like the UTF-16 family, expect that
the units are 32-bit, and therefore the surrogate scheme is not
-needed. The BOM signatures will be C<0x00 0x00 0xFE 0xFF> for BE and
-C<0xFF 0xFE 0x00 0x00> for LE.
+needed. UTF-32 is a fixed-width encoding. The BOM signatures are
+C<0x00 0x00 0xFE 0xFF> for BE and C<0xFF 0xFE 0x00 0x00> for LE.
=item *
UCS-2, UCS-4
-Encodings defined by the ISO 10646 standard. UCS-2 is a 16-bit
+Legacy, fixed-width encodings defined by the ISO 10646 standard. UCS-2 is a 16-bit
encoding. Unlike UTF-16, UCS-2 is not extensible beyond C<U+FFFF>,
because it does not use surrogates. UCS-4 is a 32-bit encoding,
-functionally identical to UTF-32.
+functionally identical to UTF-32 (the difference being that
+UCS-4 forbids neither surrogates nor code points larger than 0x10_FFFF).
=item *
=back
+=head2 Non-character code points
+
+66 code points are set aside in Unicode as "non-character code points".
+These all have the Unassigned (Cn) General Category, and they never will
+be assigned. These are never supposed to be in legal Unicode input
+streams, so that code can use them as sentinels that can be mixed in
+with character data, and they always will be distinguishable from that data.
+To keep them out of Perl input streams, strict UTF-8 should be
+specified, such as by using the layer C<:encoding('UTF-8')>. The
+non-character code points are the 32 between U+FDD0 and U+FDEF, and the
+34 code points U+FFFE, U+FFFF, U+1FFFE, U+1FFFF, ... U+10FFFE, U+10FFFF.
+Some people are under the mistaken impression that these are "illegal",
+but that is not true. An application or cooperating set of applications
+can legally use them at will internally; but these code points are
+"illegal for open interchange". Therefore, Perl will not accept these
+from input streams unless lax rules are being used, and will warn
+(using the warning category "nonchar", which is a sub-category of "utf8") if
+an attempt is made to output them.
+
+=head2 Beyond Unicode code points
+
+The maximum Unicode code point is U+10FFFF. But Perl accepts code
+points up to the maximum permissible unsigned number available on the
+platform. However, Perl will not accept these from input streams unless
+lax rules are being used, and will warn (using the warning category
+"non_unicode", which is a sub-category of "utf8") if an attempt is made to
+operate on or output them. For example, C<uc(0x11_0000)> will generate
+this warning, returning the input parameter as its result, as the upper
+case of every non-Unicode code point is the code point itself.
+
=head2 Security Implications of Unicode
+Read L<Unicode Security Considerations|http://www.unicode.org/reports/tr36>.
+Also, note the following:
+
=over 4
=item *
Malformed UTF-8
-Unfortunately, the specification of UTF-8 leaves some room for
+Unfortunately, the original specification of UTF-8 leaves some room for
interpretation of how many bytes of encoded output one should generate
from one input Unicode character. Strictly speaking, the shortest
possible sequence of UTF-8 bytes should be generated,
because otherwise there is potential for an input buffer overflow at
the receiving end of a UTF-8 connection. Perl always generates the
-shortest length UTF-8, and with warnings on Perl will warn about
+shortest length UTF-8, and with warnings on, Perl will warn about
non-shortest length UTF-8 along with other malformations, such as the
-surrogates, which are not real Unicode code points.
+surrogates, which are not Unicode code points valid for interchange.
=item *
-Regular expressions behave slightly differently between byte data and
-character (Unicode) data. For example, the "word character" character
-class C<\w> will work differently depending on if data is eight-bit bytes
-or Unicode.
+Regular expression pattern matching may surprise you if you're not
+accustomed to Unicode. Starting in Perl 5.14, several pattern
+modifiers are available to control this, called the character set
+modifiers. Details are given in L<perlre/Character set modifiers>.
-In the first case, the set of C<\w> characters is either small--the
-default set of alphabetic characters, digits, and the "_"--or, if you
-are using a locale (see L<perllocale>), the C<\w> might contain a few
-more letters according to your language and country.
-
-In the second case, the C<\w> set of characters is much, much larger.
-Most importantly, even in the set of the first 256 characters, it will
-probably match different characters: unlike most locales, which are
-specific to a language and country pair, Unicode classifies all the
-characters that are letters I<somewhere> as C<\w>. For example, your
-locale might not think that LATIN SMALL LETTER ETH is a letter (unless
-you happen to speak Icelandic), but Unicode does.
+=back
As discussed elsewhere, Perl has one foot (two hooves?) planted in
each of two worlds: the old world of bytes and the new world of
switch-over to characters should happen. Characters shouldn't get
downgraded to bytes, either. It is possible to accidentally mix bytes
and characters, however (see L<perluniintro>), in which case C<\w> in
-regular expressions might start behaving differently. Review your
-code. Use warnings and the C<strict> pragma.
-
-=back
+regular expressions might start behaving differently (unless the C</a>
+modifier is in effect). Review your code. Use warnings and the C<strict> pragma.
=head2 Unicode in Perl on EBCDIC
=head2 Locales
-Usually locale settings and Unicode do not affect each other, but
-there are a couple of exceptions:
-
-=over 4
-
-=item *
-
-You can enable automatic UTF-8-ification of your standard file
-handles, default C<open()> layer, and C<@ARGV> by using either
-the C<-C> command line switch or the C<PERL_UNICODE> environment
-variable, see L<perlrun> for the documentation of the C<-C> switch.
-
-=item *
-
-Perl tries really hard to work both with Unicode and the old
-byte-oriented world. Most often this is nice, but sometimes Perl's
-straddling of the proverbial fence causes problems.
-
-=back
+See L<perllocale/Unicode and UTF-8>
=head2 When Unicode Does Not Happen
While Perl does have extensive ways to input and output in Unicode,
-and few other 'entry points' like the @ARGV which can be interpreted
-as Unicode (UTF-8), there still are many places where Unicode (in some
-encoding or another) could be given as arguments or received as
+and a few other "entry points" like the @ARGV array (which can sometimes be
+interpreted as UTF-8), there are still many places where Unicode
+(in some encoding or another) could be given as arguments or received as
results, or both, but it is not.
-The following are such interfaces. For all of these interfaces Perl
-currently (as of 5.8.3) simply assumes byte strings both as arguments
-and results, or UTF-8 strings if the C<encoding> pragma has been used.
+The following are such interfaces. Also, see L</The "Unicode Bug">.
+For all of these interfaces Perl
+currently (as of v5.16.0) simply assumes byte strings both as arguments
+and results, or UTF-8 strings if the (problematic) C<encoding> pragma has been used.
-One reason why Perl does not attempt to resolve the role of Unicode in
-this cases is that the answers are highly dependent on the operating
+One reason that Perl does not attempt to resolve the role of Unicode in
+these situations is that the answers are highly dependent on the operating
system and the file system(s). For example, whether filenames can be
-in Unicode, and in exactly what kind of encoding, is not exactly a
-portable concept. Similarly for the qx and system: how well will the
-'command line interface' (and which of them?) handle Unicode?
+in Unicode and in exactly what kind of encoding, is not exactly a
+portable concept. Similarly for C<qx> and C<system>: how well will the
+"command-line interface" (and which of them?) handle Unicode?
=over 4
=item *
-chdir, chmod, chown, chroot, exec, link, lstat, mkdir,
+chdir, chmod, chown, chroot, exec, link, lstat, mkdir,
rename, rmdir, stat, symlink, truncate, unlink, utime, -X
=item *
=back
+=head2 The "Unicode Bug"
+
+The term, "Unicode bug" has been applied to an inconsistency
+on ASCII platforms with the
+Unicode code points in the Latin-1 Supplement block, that
+is, between 128 and 255. Without a locale specified, unlike all other
+characters or code points, these characters have very different semantics in
+byte semantics versus character semantics, unless
+C<use feature 'unicode_strings'> is specified, directly or indirectly.
+(It is indirectly specified by a C<use v5.12> or higher.)
+
+In character semantics these upper-Latin1 characters are interpreted as
+Unicode code points, which means
+they have the same semantics as Latin-1 (ISO-8859-1).
+
+In byte semantics (without C<unicode_strings>), they are considered to
+be unassigned characters, meaning that the only semantics they have is
+their ordinal numbers, and that they are
+not members of various character classes. None are considered to match C<\w>
+for example, but all match C<\W>.
+
+Perl 5.12.0 added C<unicode_strings> to force character semantics on
+these code points in some circumstances, which fixed portions of the
+bug; Perl 5.14.0 fixed almost all of it; and Perl 5.16.0 fixed the
+remainder (so far as we know, anyway). The lesson here is to enable
+C<unicode_strings> to avoid the headaches described below.
+
+The old, problematic behavior affects these areas:
+
+=over 4
+
+=item *
+
+Changing the case of a scalar, that is, using C<uc()>, C<ucfirst()>, C<lc()>,
+and C<lcfirst()>, or C<\L>, C<\U>, C<\u> and C<\l> in double-quotish
+contexts, such as regular expression substitutions.
+Under C<unicode_strings> starting in Perl 5.12.0, character semantics are
+generally used. See L<perlfunc/lc> for details on how this works
+in combination with various other pragmas.
+
+=item *
+
+Using caseless (C</i>) regular expression matching.
+Starting in Perl 5.14.0, regular expressions compiled within
+the scope of C<unicode_strings> use character semantics
+even when executed or compiled into larger
+regular expressions outside the scope.
+
+=item *
+
+Matching any of several properties in regular expressions, namely C<\b>,
+C<\B>, C<\s>, C<\S>, C<\w>, C<\W>, and all the Posix character classes
+I<except> C<[[:ascii:]]>.
+Starting in Perl 5.14.0, regular expressions compiled within
+the scope of C<unicode_strings> use character semantics
+even when executed or compiled into larger
+regular expressions outside the scope.
+
+=item *
+
+In C<quotemeta> or its inline equivalent C<\Q>, no code points above 127
+are quoted in UTF-8 encoded strings, but in byte encoded strings, code
+points between 128-255 are always quoted.
+Starting in Perl 5.16.0, consistent quoting rules are used within the
+scope of C<unicode_strings>, as described in L<perlfunc/quotemeta>.
+
+=back
+
+This behavior can lead to unexpected results in which a string's semantics
+suddenly change if a code point above 255 is appended to or removed from it,
+which changes the string's semantics from byte to character or vice versa. As
+an example, consider the following program and its output:
+
+ $ perl -le'
+ no feature 'unicode_strings';
+ $s1 = "\xC2";
+ $s2 = "\x{2660}";
+ for ($s1, $s2, $s1.$s2) {
+ print /\w/ || 0;
+ }
+ '
+ 0
+ 0
+ 1
+
+If there's no C<\w> in C<s1> or in C<s2>, why does their concatenation have one?
+
+This anomaly stems from Perl's attempt to not disturb older programs that
+didn't use Unicode, and hence had no semantics for characters outside of the
+ASCII range (except in a locale), along with Perl's desire to add Unicode
+support seamlessly. The result wasn't seamless: these characters were
+orphaned.
+
+For Perls earlier than those described above, or when a string is passed
+to a function outside the subpragma's scope, a workaround is to always
+call C<utf8::upgrade($string)>,
+or to use the standard module L<Encode>. Also, a scalar that has any characters
+whose ordinal is above 0x100, or which were specified using either of the
+C<\N{...}> notations, will automatically have character semantics.
+
=head2 Forcing Unicode in Perl (Or Unforcing Unicode in Perl)
-Sometimes (see L</"When Unicode Does Not Happen">) there are
-situations where you simply need to force Perl to believe that a byte
-string is UTF-8, or vice versa. The low-level calls
-utf8::upgrade($bytestring) and utf8::downgrade($utf8string) are
+Sometimes (see L</"When Unicode Does Not Happen"> or L</The "Unicode Bug">)
+there are situations where you simply need to force a byte
+string into UTF-8, or vice versa. The low-level calls
+utf8::upgrade($bytestring) and utf8::downgrade($utf8string[, FAIL_OK]) are
the answers.
-Do not use them without careful thought, though: Perl may easily get
-very confused, angry, or even crash, if you suddenly change the 'nature'
-of scalar like that. Especially careful you have to be if you use the
-utf8::upgrade(): any random byte string is not valid UTF-8.
+Note that utf8::downgrade() can fail if the string contains characters
+that don't fit into a byte.
+
+Calling either function on a string that already is in the desired state is a
+no-op.
=head2 Using Unicode in XS
=item *
C<DO_UTF8(sv)> returns true if the C<UTF8> flag is on and the bytes
-pragma is not in effect. C<SvUTF8(sv)> returns true is the C<UTF8>
+pragma is not in effect. C<SvUTF8(sv)> returns true if the C<UTF8>
flag is on; the bytes pragma is ignored. The C<UTF8> flag being on
does B<not> mean that there are any characters of code points greater
than 255 (or 127) in the scalar or that there are even any characters
=item *
-C<uvuni_to_utf8(buf, chr)> writes a Unicode character code point into
+C<uvchr_to_utf8(buf, chr)> writes a Unicode character code point into
a buffer encoding the code point as UTF-8, and returns a pointer
-pointing after the UTF-8 bytes.
+pointing after the UTF-8 bytes. It works appropriately on EBCDIC machines.
=item *
-C<utf8_to_uvuni(buf, lenp)> reads UTF-8 encoded bytes from a buffer and
+C<utf8_to_uvchr_buf(buf, bufend, lenp)> reads UTF-8 encoded bytes from a
+buffer and
returns the Unicode character code point and, optionally, the length of
-the UTF-8 byte sequence.
+the UTF-8 byte sequence. It works appropriately on EBCDIC machines.
=item *
=item *
-C<is_utf8_char(s)> returns true if the pointer points to a valid UTF-8
-character.
+C<is_utf8_string(buf, len)> returns true if C<len> bytes of the buffer
+are valid UTF-8.
=item *
-C<is_utf8_string(buf, len)> returns true if C<len> bytes of the buffer
-are valid UTF-8.
+C<is_utf8_char_buf(buf, buf_end)> returns true if the pointer points to
+a valid UTF-8 character.
=item *
=item *
-C<utf8_hop(s, off)> will return a pointer to an UTF-8 encoded buffer
+C<utf8_hop(s, off)> will return a pointer to a UTF-8 encoded buffer
that is C<off> (positive or negative) Unicode characters displaced
from the UTF-8 buffer C<s>. Be careful not to overstep the buffer:
C<utf8_hop()> will merrily run off the end or the beginning of the
=item *
-C<ibcmp_utf8(s1, pe1, u1, l1, u1, s2, pe2, l2, u2)> can be used to
+C<foldEQ_utf8(s1, pe1, l1, u1, s2, pe2, l2, u2)> can be used to
compare two strings case-insensitively in Unicode. For case-sensitive
-comparisons you can just use C<memEQ()> and C<memNE()> as usual.
+comparisons you can just use C<memEQ()> and C<memNE()> as usual, except
+if one string is in utf8 and the other isn't.
=back
For more information, see L<perlapi>, and F<utf8.c> and F<utf8.h>
in the Perl source code distribution.
+=head2 Hacking Perl to work on earlier Unicode versions (for very serious hackers only)
+
+Perl by default comes with the latest supported Unicode version built in, but
+you can change to use any earlier one.
+
+Download the files in the desired version of Unicode from the Unicode web
+site L<http://www.unicode.org>). These should replace the existing files in
+F<lib/unicore> in the Perl source tree. Follow the instructions in
+F<README.perl> in that directory to change some of their names, and then build
+perl (see L<INSTALL>).
+
=head1 BUGS
=head2 Interaction with Locales
-Use of locales with Unicode data may lead to odd results. Currently,
-Perl attempts to attach 8-bit locale info to characters in the range
-0..255, but this technique is demonstrably incorrect for locales that
-use characters above that range when mapped into Unicode. Perl's
-Unicode support will also tend to run slower. Use of locales with
-Unicode is discouraged.
+See L<perllocale/Unicode and UTF-8>
+
+=head2 Problems with characters in the Latin-1 Supplement range
+
+See L</The "Unicode Bug">
=head2 Interaction with Extensions
When Perl exchanges data with an extension, the extension should be
able to understand the UTF8 flag and act accordingly. If the
-extension doesn't know about the flag, it's likely that the extension
+extension doesn't recognize that flag, it's likely that the extension
will return incorrectly-flagged data.
So if you're working with Unicode data, consult the documentation of
Perl's internal representation like so:
sub my_escape_html ($) {
- my($what) = shift;
- return unless defined $what;
- Encode::decode_utf8(Foo::Bar::escape_html(Encode::encode_utf8($what)));
+ my($what) = shift;
+ return unless defined $what;
+ Encode::decode_utf8(Foo::Bar::escape_html(
+ Encode::encode_utf8($what)));
}
Sometimes, when the extension does not convert data but just stores
-and retrieves them, you will be in a position to use the otherwise
+and retrieves them, you will be able to use the otherwise
dangerous Encode::_utf8_on() function. Let's say the popular
C<Foo::Bar> extension, written in C, provides a C<param> method that
lets you store and retrieve data according to these prototypes:
operations with UTF-8 encoded strings are still slower. As an example,
the Unicode properties (character classes) like C<\p{Nd}> are known to
be quite a bit slower (5-20 times) than their simpler counterparts
-like C<\d> (then again, there 268 Unicode characters matching C<Nd>
+like C<\d> (then again, there are hundreds of Unicode characters matching C<Nd>
compared with the 10 ASCII characters matching C<d>).
+=head2 Problems on EBCDIC platforms
+
+There are several known problems with Perl on EBCDIC platforms. If you
+want to use Perl there, send email to perlbug@perl.org.
+
+In earlier versions, when byte and character data were concatenated,
+the new string was sometimes created by
+decoding the byte strings as I<ISO 8859-1 (Latin-1)>, even if the
+old Unicode string used EBCDIC.
+
+If you find any of these, please report them as bugs.
+
=head2 Porting code from perl-5.6.X
Perl 5.8 has a different Unicode model from 5.6. In 5.6 the programmer
your code. The examples are written such that the code will continue
to work under 5.6, so you should be safe to try them out.
-=over 4
+=over 3
=item *
A filehandle that should read or write UTF-8
- if ($] > 5.007) {
- binmode $fh, ":utf8";
+ if ($] > 5.008) {
+ binmode $fh, ":encoding(utf8)";
}
=item *
Be it Compress::Zlib, Apache::Request or any extension that has no
mention of Unicode in the manpage, you need to make sure that the
UTF8 flag is stripped off. Note that at the time of this writing
-(October 2002) the mentioned modules are not UTF-8-aware. Please
+(January 2012) the mentioned modules are not UTF-8-aware. Please
check the documentation to verify if this is still true.
- if ($] > 5.007) {
+ if ($] > 5.008) {
require Encode;
$val = Encode::encode_utf8($val); # make octets
}
If you believe the scalar comes back as UTF-8, you will most likely
want the UTF8 flag restored:
- if ($] > 5.007) {
+ if ($] > 5.008) {
require Encode;
$val = Encode::decode_utf8($val);
}
Same thing, if you are really sure it is UTF-8
- if ($] > 5.007) {
+ if ($] > 5.008) {
require Encode;
Encode::_utf8_on($val);
}
a convenient way to replace all your fetchrow_array and
fetchrow_hashref calls. A wrapper function will also make it easier to
adapt to future enhancements in your database driver. Note that at the
-time of this writing (October 2002), the DBI has no standardized way
+time of this writing (January 2012), the DBI has no standardized way
to deal with UTF-8 data. Please check the documentation to verify if
that is still true.
sub fetchrow {
- my($self, $sth, $what) = @_; # $what is one of fetchrow_{array,hashref}
- if ($] < 5.007) {
+ # $what is one of fetchrow_{array,hashref}
+ my($self, $sth, $what) = @_;
+ if ($] < 5.008) {
return $sth->$what;
} else {
require Encode;
my $ret = $sth->$what;
if (ref $ret) {
for my $k (keys %$ret) {
- defined && /[^\000-\177]/ && Encode::_utf8_on($_) for $ret->{$k};
+ defined
+ && /[^\000-\177]/
+ && Encode::_utf8_on($_) for $ret->{$k};
}
return $ret;
} else {
a drag to your program. If you recognize such a situation, just remove
the UTF8 flag:
- utf8::downgrade($val) if $] > 5.007;
+ utf8::downgrade($val) if $] > 5.008;
=back
=head1 SEE ALSO
-L<perlunitut>, L<perluniintro>, L<Encode>, L<open>, L<utf8>, L<bytes>,
+L<perlunitut>, L<perluniintro>, L<perluniprops>, L<Encode>, L<open>, L<utf8>, L<bytes>,
L<perlretut>, L<perlvar/"${^UNICODE}">
+L<http://www.unicode.org/reports/tr44>).
=cut
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