implement the Unicode standard or the accompanying technical reports
from cover to cover, Perl does support many Unicode features.
+People who want to learn to use Unicode in Perl, should probably read
+the L<Perl Unicode tutorial, perlunitut|perlunitut>, 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 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 using a particular encoding,
-see L<encoding>.
+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 Unicode data--or instead uses
-a traditional byte scheme when presented with byte data.
+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
machines. B<These are the only times when an explicit C<use utf8>
is needed.> See L<utf8>.
-You can also use the C<encoding> pragma to change the default encoding
-of the data in your script; see L<encoding>.
+=item BOM-marked scripts and UTF-16 scripts autodetected
+
+If a Perl script begins marked with the Unicode BOM (UTF-16LE, UTF16-BE,
+or UTF-8), or if the script looks like non-BOM-marked UTF-16 of either
+endianness, Perl will correctly read in the script as Unicode.
+(BOMless UTF-8 cannot be effectively recognized or differentiated from
+ISO 8859-1 or other eight-bit encodings.)
+
+=item C<use encoding> needed to upgrade non-Latin-1 byte strings
+
+By default, there is a fundamental asymmetry in Perl's Unicode model:
+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.
+
+See L</"Byte and Character Semantics"> for more details.
=back
be made without additional information from the user, Perl decides in
favor of compatibility and chooses to use byte semantics.
+Under byte semantics, when C<use locale> is in effect, Perl uses the
+semantics associated with the current locale. Absent a C<use locale>, and
+absent a C<use feature 'unicode_strings'> pragma, Perl currently uses US-ASCII
+(or Basic Latin in Unicode terminology) byte semantics, meaning that characters
+whose ordinal numbers are in the range 128 - 255 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.
-On Windows platforms, if the C<-C> command line switch is used or the
-${^WIDE_SYSTEM_CALLS} global flag is set to C<1>, all system calls
-will use the corresponding wide-character APIs. This feature is
-available only on Windows to conform to the API standard already
-established for that platform--and there are very few non-Windows
-platforms that have Unicode-aware APIs.
-
The C<bytes> pragma will always, regardless of platform, force byte
semantics in a particular lexical scope. See L<bytes>.
+The C<use feature 'unicode_strings'> pragma is intended always,
+regardless of platform, to force character (Unicode) semantics in a
+particular lexical scope.
+See L</The "Unicode Bug"> below.
+
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
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.
+be used to force byte semantics on Unicode data, and the C<use feature
+'unicode_strings'> pragma to force Unicode semantics on byte data (though in
+5.12 it isn't fully implemented).
If strings operating under byte semantics and strings with Unicode
-character data are concatenated, the new string will be upgraded to
-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, so to change this for systems with non-Latin-1 and
-non-EBCDIC native encodings use the C<encoding> pragma. See
-L<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
Strings--including hash keys--and regular expression patterns may
contain characters that have an ordinal value larger than 255.
-If you use a Unicode editor to edit your program, Unicode characters
-may occur directly within the literal strings in one of the various
-Unicode encodings (UTF-8, UTF-EBCDIC, UCS-2, etc.), but will be recognized
-as such and converted to Perl's internal representation only if the
-appropriate L<encoding> is specified.
+If you use a Unicode editor to edit your program, Unicode characters may
+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{...}> 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 characters
-with a code of 0x100 or above.
+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, after the C<U>. For instance, a smiley face is
+C<\N{U+263A}>.
+
+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.
Additionally, if you
you can use the C<\N{...}> notation and put the official Unicode
character name within the braces, such as C<\N{WHITE SMILING FACE}>.
-
+See L<charnames>.
=item *
=item *
Regular expressions match characters instead of bytes. "." matches
-a character instead of a byte. The C<\C> pattern is provided to force
-a match a single byte--a C<char> in C, hence C<\C>.
+a character instead of a byte.
=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
-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>.
+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 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 *
+
+The C<tr///> operator translates characters instead of bytes. Note
+that the C<tr///CU> functionality has been removed. For similar
+functionality see pack('U0', ...) and pack('C0', ...).
+
+=item *
+
+Case translation operators use the Unicode case translation tables
+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 (which is equivalent to uppercase in languages
+without the distinction).
+
+=item *
+
+Most operators that deal with positions or lengths in a string will
+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
+C<sort()>, and operators dealing with filenames.
+
+=item *
+
+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
+and code points. There is also a C<W> specifier that is the equivalent of
+C<chr>/C<ord> and properly handles character values even if they are above 255.
+
+=item *
+
+The C<chr()> and C<ord()> functions work on characters, similar to
+C<pack("W")> and C<unpack("W")>, I<not> C<pack("C")> and
+C<unpack("C")>. C<pack("C")> and C<unpack("C")> are methods for
+emulating byte-oriented C<chr()> and C<ord()> on Unicode strings.
+While these methods reveal the internal encoding of Unicode strings,
+that is not something one normally needs to care about at all.
+
+=item *
+
+The bit string operators, C<& | ^ ~>, can operate on character data.
+However, for backward compatibility, such as when using bit string
+operations when characters are all less than 256 in ordinal value, one
+should not use C<~> (the bit complement) with characters of both
+values less than 256 and values greater than 256. Most importantly,
+DeMorgan's laws (C<~($x|$y) eq ~$x&~$y> and C<~($x&$y) eq ~$x|~$y>)
+will not hold. The reason for this mathematical I<faux pas> is that
+the complement cannot return B<both> the 8-bit (byte-wide) bit
+complement B<and> the full character-wide bit complement.
+
+=item *
+
+You can define your own mappings to be used in C<lc()>,
+C<lcfirst()>, C<uc()>, and C<ucfirst()> (or their double-quoted string inlined
+versions such as C<\U>). See
+L<User-Defined Case-Mappings|/"User-Defined Case Mappings (for serious hackers only)">
+for more details.
+
+=back
+
+=over 4
+
+=item *
+
+And finally, C<scalar reverse()> reverses by character rather than by byte.
+
+=back
+
+=head2 Unicode Character Properties
+
+Most Unicode character properties are accessible by using regular expressions.
+They are used (like bracketed character classes) by using the C<\p{}> "matches
+property" construct and the C<\P{}> negation, "doesn't match property".
+
+Note that 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.
+
+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 a number of different
+values, such as Left, Right, Whitespace, and others. To match these, one needs
+to specify 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 which is more
+descriptive and hence it is easier to understand what it means. Thus the "L"
+and "Letter" 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 the 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, in most cases, white space and even
+hyphens can 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 employed is in the middle of numbers, and the Perl
+extension properties that begin or end with an underscore. Stricter matching
+cares about white space (except adjacent to the non-word characters) and
+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}>.
-Here are the basic Unicode General Category properties, followed by their
-long form. You can use either; C<\p{Lu}> and C<\p{LowercaseLetter}>,
-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 to be
+letters, so they aren't C<Cased_Letter>s.)
+L<perluniprops> includes a notation for all forms that have C</i>
+differences.
+
+=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
- 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<L&> is a special case, which is an alias for C<Ll>, C<Lu>, and C<Lt>.
+C<LC> and C<L&> are special cases, which are both aliases for the set consisting of everything matched by 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.
+=head3 B<Bidirectional Character Types>
-Because scripts differ in their directionality--Hebrew is
-written right to left, for example--Unicode supplies these properties:
+Because scripts differ in their directionality (Hebrew is
+written right to left, for example) Unicode supplies these properties in
+the Bidi_Class class:
Property Meaning
- BidiL Left-to-Right
- BidiLRE Left-to-Right Embedding
- BidiLRO Left-to-Right Override
- BidiR Right-to-Left
- BidiAL Right-to-Left Arabic
- BidiRLE Right-to-Left Embedding
- BidiRLO Right-to-Left Override
- BidiPDF Pop Directional Format
- BidiEN European Number
- BidiES European Number Separator
- BidiET European Number Terminator
- BidiAN Arabic Number
- BidiCS Common Number Separator
- BidiNSM Non-Spacing Mark
- BidiBN Boundary Neutral
- BidiB Paragraph Separator
- BidiS Segment Separator
- BidiWS Whitespace
- BidiON Other Neutrals
-
-For example, C<\p{BidiR}> matches characters that are normally
+ L Left-to-Right
+ LRE Left-to-Right Embedding
+ LRO Left-to-Right Override
+ R Right-to-Left
+ AL Arabic Letter
+ RLE Right-to-Left Embedding
+ RLO Right-to-Left Override
+ PDF Pop Directional Format
+ EN European Number
+ ES European Separator
+ ET European Terminator
+ AN Arabic Number
+ CS Common Separator
+ NSM Non-Spacing Mark
+ BN Boundary Neutral
+ B Paragraph Separator
+ S Segment Separator
+ WS Whitespace
+ ON Other Neutrals
+
+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.
-=back
+=head3 B<Scripts>
-=head2 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
- Bengali
- Bopomofo
- Buhid
- CanadianAboriginal
- Cherokee
- Cyrillic
- Deseret
- Devanagari
- Ethiopic
- Georgian
- Gothic
- Greek
- Gujarati
- Gurmukhi
- Han
- Hangul
- Hanunoo
- Hebrew
- Hiragana
- Inherited
- Kannada
- Katakana
- Khmer
- Lao
- Latin
- Malayalam
- Mongolian
- Myanmar
- Ogham
- OldItalic
- Oriya
- Runic
- Sinhala
- Syriac
- Tagalog
- Tagbanwa
- Tamil
- Telugu
- Thaana
- Thai
- Tibetan
- Yi
-
-Extended property classes can supplement the basic
-properties, defined by the F<PropList> Unicode database:
-
- ASCIIHexDigit
- BidiControl
- Dash
- Deprecated
- Diacritic
- Extender
- GraphemeLink
- HexDigit
- Hyphen
- Ideographic
- IDSBinaryOperator
- IDSTrinaryOperator
- JoinControl
- LogicalOrderException
- NoncharacterCodePoint
- OtherAlphabetic
- OtherDefaultIgnorableCodePoint
- OtherGraphemeExtend
- OtherLowercase
- OtherMath
- OtherUppercase
- QuotationMark
- Radical
- SoftDotted
- TerminalPunctuation
- UnifiedIdeograph
- WhiteSpace
-
-and there are further derived properties:
-
- Alphabetic Lu + Ll + Lt + Lm + Lo + OtherAlphabetic
- Lowercase Ll + OtherLowercase
- Uppercase Lu + OtherUppercase
- Math Sm + OtherMath
-
- ID_Start Lu + Ll + Lt + Lm + Lo + Nl
- ID_Continue ID_Start + Mn + Mc + Nd + Pc
-
- Any Any character
- Assigned Any non-Cn character (i.e. synonym for \P{Cn})
- Unassigned Synonym for \p{Cn}
- Common Any character (or unassigned code point)
- not explicitly assigned to a script
+The world's languages are written in a number of 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 property gives what script a given character is in,
+and the property can be specified with the compound form like
+C<\p{Script=Hebrew}> (short: C<\p{sc=hebr}>). Perl furnishes shortcuts for all
+script names. You can omit everything up through the equals (or colon), and
+simply write C<\p{Latin}> or C<\P{Cyrillic}>.
+
+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}>.
-=head2 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 UTR #24:
-
- http://www.unicode.org/unicode/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:
-
- InAlphabeticPresentationForms
- InArabic
- InArabicPresentationFormsA
- InArabicPresentationFormsB
- InArmenian
- InArrows
- InBasicLatin
- InBengali
- InBlockElements
- InBopomofo
- InBopomofoExtended
- InBoxDrawing
- InBraillePatterns
- InBuhid
- InByzantineMusicalSymbols
- InCJKCompatibility
- InCJKCompatibilityForms
- InCJKCompatibilityIdeographs
- InCJKCompatibilityIdeographsSupplement
- InCJKRadicalsSupplement
- InCJKSymbolsAndPunctuation
- InCJKUnifiedIdeographs
- InCJKUnifiedIdeographsExtensionA
- InCJKUnifiedIdeographsExtensionB
- InCherokee
- InCombiningDiacriticalMarks
- InCombiningDiacriticalMarksforSymbols
- InCombiningHalfMarks
- InControlPictures
- InCurrencySymbols
- InCyrillic
- InCyrillicSupplementary
- InDeseret
- InDevanagari
- InDingbats
- InEnclosedAlphanumerics
- InEnclosedCJKLettersAndMonths
- InEthiopic
- InGeneralPunctuation
- InGeometricShapes
- InGeorgian
- InGothic
- InGreekExtended
- InGreekAndCoptic
- InGujarati
- InGurmukhi
- InHalfwidthAndFullwidthForms
- InHangulCompatibilityJamo
- InHangulJamo
- InHangulSyllables
- InHanunoo
- InHebrew
- InHighPrivateUseSurrogates
- InHighSurrogates
- InHiragana
- InIPAExtensions
- InIdeographicDescriptionCharacters
- InKanbun
- InKangxiRadicals
- InKannada
- InKatakana
- InKatakanaPhoneticExtensions
- InKhmer
- InLao
- InLatin1Supplement
- InLatinExtendedA
- InLatinExtendedAdditional
- InLatinExtendedB
- InLetterlikeSymbols
- InLowSurrogates
- InMalayalam
- InMathematicalAlphanumericSymbols
- InMathematicalOperators
- InMiscellaneousMathematicalSymbolsA
- InMiscellaneousMathematicalSymbolsB
- InMiscellaneousSymbols
- InMiscellaneousTechnical
- InMongolian
- InMusicalSymbols
- InMyanmar
- InNumberForms
- InOgham
- InOldItalic
- InOpticalCharacterRecognition
- InOriya
- InPrivateUseArea
- InRunic
- InSinhala
- InSmallFormVariants
- InSpacingModifierLetters
- InSpecials
- InSuperscriptsAndSubscripts
- InSupplementalArrowsA
- InSupplementalArrowsB
- InSupplementalMathematicalOperators
- InSupplementaryPrivateUseAreaA
- InSupplementaryPrivateUseAreaB
- InSyriac
- InTagalog
- InTagbanwa
- InTags
- InTamil
- InTelugu
- InThaana
- InThai
- InTibetan
- InUnifiedCanadianAboriginalSyllabics
- InVariationSelectors
- InYiRadicals
- InYiSyllables
+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 block as well as several more, 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. The digits 0-9 and similar groups,
+like punctuation, are in the script called C<Common>. There is also a
+script called C<Inherited> for characters that modify other characters,
+and inherit the script value of the controlling character. (Note that
+there are a number of 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
+script. Only the sets that are used across languages 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 Script property is likely to be the one you want to use when processing
+natural language; the Block property may 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 *
+=item 1
-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*)>.
+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 *
+=item 2
-The C<tr///> operator translates characters instead of bytes. Note
-that the C<tr///CU> functionality has been removed. For similar
-functionality see pack('U0', ...) and pack('C0', ...).
+It is unstable. A new version of Unicode may pre-empt 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.
-=item *
+=back
-Case translation operators use the Unicode case translation tables
-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.
+Some people just prefer to always use C<\p{Block: foo}> and C<\p{Script: bar}>
+instead of the shortcuts, for clarity, and because they can't remember the
+difference between 'In' and 'Is' anyway (or aren't confident that those who
+eventually will read their code will know).
-=item *
+A complete list of blocks and their shortcuts is in L<perluniprops>.
-Most operators that deal with positions or lengths in a string will
-automatically switch to using character positions, including
-C<chop()>, C<substr()>, C<pos()>, C<index()>, C<rindex()>,
-C<sprintf()>, C<write()>, and C<length()>. Operators that
-specifically do not switch include C<vec()>, C<pack()>, and
-C<unpack()>. Operators that really don't care include C<chomp()>,
-operators that treats strings as a bucket of bits such as C<sort()>,
-and operators dealing with filenames.
+=head3 B<Other Properties>
-=item *
+There are many more properties than the very basic ones described here.
+A complete list is in L<perluniprops>.
-The C<pack()>/C<unpack()> letters C<c> and C<C> do I<not> change,
-since they are often used for byte-oriented formats. Again, think
-C<char> in the C language.
+Unicode defines all its properties in the compound form, so all single-form
+properties are Perl extensions. A number of these are just synonyms for the
+Unicode ones, but some are genunine extensions, including a couple 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>).
-There is a new C<U> specifier that converts between Unicode characters
-and code points.
+This section gives some details on all the extensions that aren't synonyms for
+compound-form Unicode properties (for those, you'll have to refer to the
+L<Unicode Standard|http://www.unicode.org/reports/tr44>.
-=item *
+=over
-The C<chr()> and C<ord()> functions work on characters, similar to
-C<pack("U")> and C<unpack("U")>, I<not> C<pack("C")> and
-C<unpack("C")>. C<pack("C")> and C<unpack("C")> are methods for
-emulating byte-oriented C<chr()> and C<ord()> on Unicode strings.
-While these methods reveal the internal encoding of Unicode strings,
-that is not something one normally needs to care about at all.
+=item B<C<\p{All}>>
-=item *
+This matches any of the 1_114_112 Unicode code points. It is a synonym for
+C<\p{Any}>.
-The bit string operators, C<& | ^ ~>, can operate on character data.
-However, for backward compatibility, such as when using bit string
-operations when characters are all less than 256 in ordinal value, one
-should not use C<~> (the bit complement) with characters of both
-values less than 256 and values greater than 256. Most importantly,
-DeMorgan's laws (C<~($x|$y) eq ~$x&~$y> and C<~($x&$y) eq ~$x|~$y>)
-will not hold. The reason for this mathematical I<faux pas> is that
-the complement cannot return B<both> the 8-bit (byte-wide) bit
-complement B<and> the full character-wide bit complement.
+=item B<C<\p{Alnum}>>
-=item *
+This matches any C<\p{Alphabetic}> or C<\p{Decimal_Number}> character.
-lc(), uc(), lcfirst(), and ucfirst() work for the following cases:
+=item B<C<\p{Any}>>
-=over 8
+This matches any of the 1_114_112 Unicode code points. It is a synonym for
+C<\p{All}>.
-=item *
+=item B<C<\p{Assigned}>>
-the case mapping is from a single Unicode character to another
-single Unicode character, or
+This matches any assigned code point; that is, any code point whose general
+category is not Unassigned (or equivalently, not Cn).
-=item *
+=item B<C<\p{Blank}>>
-the case mapping is from a single Unicode character to more
-than one Unicode character.
+This is the same as C<\h> and C<\p{HorizSpace}>: A character that changes the
+spacing horizontally.
-=back
+=item B<C<\p{Decomposition_Type: Non_Canonical}>> (Short: C<\p{Dt=NonCanon}>)
-Things to do with locales (Lithuanian, Turkish, Azeri) do B<not> work
-since Perl does not understand the concept of Unicode locales.
+Matches a character that has a non-canonical decomposition.
-See the Unicode Technical Report #21, Case Mappings, for more details.
+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 and/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 they can be combined variously
+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>
+construct to match such sequences.)
-=back
+But Unicode's intent is to unify the existing character set standards and
+practices, and a number of 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 first the character
+"LATIN CAPITAL LETTER E", then the character "COMBINING ACUTE ACCENT".
-=over 4
+"LATIN CAPITAL LETTER E WITH ACUTE" is called a "pre-composed" character, and
+the 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.
-=item *
+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 kind of 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.
-And finally, C<scalar reverse()> reverses by character rather than by byte.
+Note that most Unicode characters don't have a decomposition, so their
+decomposition type is "None".
+
+Perl has added the C<Non_Canonical> type, for your convenience, to mean any of
+the 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]>>.
+
+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{PosixAlnum}>>
+
+This matches any alphanumeric character in the ASCII range, namely
+C<[A-Za-z0-9]>.
+
+=item B<C<\p{PosixAlpha}>>
+
+This matches any alphabetic character in the ASCII range, namely C<[A-Za-z]>.
+
+=item B<C<\p{PosixBlank}>>
+
+This matches any blank character in the ASCII range, namely C<S<[ \t]>>.
+
+=item B<C<\p{PosixCntrl}>>
+
+This matches any control character in the ASCII range, namely C<[\x00-\x1F\x7F]>
+
+=item B<C<\p{PosixDigit}>>
+
+This matches any digit character in the ASCII range, namely C<[0-9]>.
+
+=item B<C<\p{PosixGraph}>>
+
+This matches any graphical character in the ASCII range, namely C<[\x21-\x7E]>.
+
+=item B<C<\p{PosixLower}>>
+
+This matches any lowercase character in the ASCII range, namely C<[a-z]>.
+
+=item B<C<\p{PosixPrint}>>
+
+This matches any printable character in the ASCII range, namely C<[\x20-\x7E]>.
+These are the graphical characters plus SPACE.
+
+=item B<C<\p{PosixPunct}>>
+
+This matches any punctuation character in the ASCII range, namely
+C<[\x21-\x2F\x3A-\x40\x5B-\x60\x7B-\x7E]>. These are the
+graphical characters that aren't word characters. Note that the Posix standard
+includes in its definition of punctuation, those characters that Unicode calls
+"symbols."
+
+=item B<C<\p{PosixSpace}>>
+
+This matches any space character in the ASCII range, namely
+C<S<[ \f\n\r\t\x0B]>> (the last being a vertical tab).
+
+=item B<C<\p{PosixUpper}>>
+
+This matches any uppercase character in the ASCII range, namely C<[A-Z]>.
+
+=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 assigned, but that the meaning of the code point
+has been determined. This is because 66 code points will always be
+unassigned, and, so the Age for them is the Unicode version the decision to
+make them so was made in. 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 and C<\p{Present_In: 3.1}> and up
+matches as well.
+
+=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 to be space.)
+
+=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 beyond ASCII.
=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 must be defined
-in the C<main> package. The user-defined properties can be used in the
-regular expression C<\p> and C<\P> constructs. Note that the effect
-is compile-time and immutable once defined.
+You can define your own binary 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.
+
+ # assuming property Is_Foreign defined in Lang::
+ package main; # property package name required
+ if ($txt =~ /\p{Lang::IsForeign}+/) { ... }
+
+ package Lang; # property package name not required
+ if ($txt =~ /\p{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; 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::"), to represent all the characters in that
-property; two hexadecimal code points for a range; or a single
-hexadecimal code point.
+property (prefixed by "utf8::") or a 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::"), for all the characters in that
-property; two hexadecimal code points for a range; or a single
-hexadecimal code point.
+property (prefixed by "utf8::") or a 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::") for all the characters except the
-characters in the property; two hexadecimal code points for a range;
-or a single hexadecimal code point.
+property (prefixed by "utf8::") or a 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,
+for all the characters except the characters in the property; two
+hexadecimal code points for a range; or a single hexadecimal code point.
=back
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
}
-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 the same: 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()).
+Intersection is useful for getting the common characters matched by
+two (or more) classes.
-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:
+ sub InFooAndBar {
+ return <<'END';
+ +main::Foo
+ &main::Bar
+ END
+ }
+
+It's important to remember not to use "&" for the first set; that
+would be intersecting with nothing (resulting in an empty set).
+
+=head2 User-Defined Case Mappings (for serious hackers only)
+
+B<This featured is deprecated and is scheduled to be removed in Perl
+5.16.>
+The CPAN module L<Unicode::Casing> provides better functionality
+without the drawbacks described below.
+
+You can define your own mappings to be used in C<lc()>,
+C<lcfirst()>, C<uc()>, and C<ucfirst()> (or their string-inlined versions,
+C<\L>, C<\l>, C<\U>, and C<\u>). The mappings are currently only valid
+on strings encoded in UTF-8, but see below for a partial workaround for
+this restriction.
+
+The principle is similar to that of user-defined character
+properties: define subroutines that do the mappings.
+C<ToLower> is used for C<lc()>, C<\L>, C<lcfirst()>, and C<\l>; C<ToTitle> for
+C<ucfirst()> and C<\u>; and C<ToUpper> for C<uc()> and C<\U>.
+
+C<ToUpper()> should look something like this:
sub ToUpper {
- return <<END;
- 0061\t0063\t0041
+ return <<END;
+ 0061\t007A\t0041
+ 0101\t\t0100
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.
+This sample C<ToUpper()> has the effect of mapping "a-z" to "A-Z", 0x101
+to 0x100, and all other characters map to themselves. The first
+returned line means to map the code point at 0x61 ("a") to 0x41 ("A"),
+the code point at 0x62 ("b") to 0x42 ("B"), ..., 0x7A ("z") to 0x5A
+("Z"). The second line maps just the code point 0x101 to 0x100. Since
+there are no other mappings defined, all other code points map to
+themselves.
+
+This mechanism is not well behaved as far as affecting other packages
+and scopes. All non-threaded programs have exactly one uppercasing
+behavior, one lowercasing behavior, and one titlecasing behavior in
+effect for utf8-encoded strings for the duration of the program. Each
+of these behaviors is irrevocably determined the first time the
+corresponding function is called to change a utf8-encoded string's case.
+If a corresponding C<To-> function has been defined in the package that
+makes that first call, the mapping defined by that function will be the
+mapping used for the duration of the program's execution across all
+packages and scopes. If no corresponding C<To-> function has been
+defined in that package, the standard official mapping will be used for
+all packages and scopes, and any corresponding C<To-> function anywhere
+will be ignored. Threaded programs have similar behavior. If the
+program's casing behavior has been decided at the time of a thread's
+creation, the thread will inherit that behavior. But, if the behavior
+hasn't been decided, the thread gets to decide for itself, and its
+decision does not affect other threads nor its creator.
+
+As shown by the example above, you have to furnish a complete mapping;
+you can't just override a couple of characters and leave the rest
+unchanged. You can find all the official mappings in the directory
+C<$Config{privlib}>F</unicore/To/>. The mapping data is returned as the
+here-document. The C<utf8::ToSpecI<Foo>> hashes in those files are special
+exception mappings derived from
+C<$Config{privlib}>F</unicore/SpecialCasing.txt>. (The "Digit" and
+"Fold" mappings that one can see in the directory are not directly
+user-accessible, one can use either the L<Unicode::UCD> module, or just match
+case-insensitively, which is what uses the "Fold" mapping. Neither are user
+overridable.)
+
+If you have many mappings to change, you can take the official mapping data,
+change by hand the affected code points, and place the whole thing into your
+subroutine. But this will only be valid on Perls that use the same Unicode
+version. Another option would be to have your subroutine read the official
+mapping file(s) and overwrite the affected code points.
+
+If you have only a few mappings to change, starting in 5.14 you can use the
+following trick, here illustrated for Turkish.
+
+ use Config;
+ use charnames ":full";
+
+ sub ToUpper {
+ my $official = do "$Config{privlib}/unicore/To/Upper.pl";
+ $utf8::ToSpecUpper{'i'} =
+ "\N{LATIN CAPITAL LETTER I WITH DOT ABOVE}";
+ return $official;
+ }
-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:
+This takes the official mappings and overrides just one, for "LATIN SMALL
+LETTER I". The keys to the hash must be the bytes that form the UTF-8
+(on EBCDIC platforms, UTF-EBCDIC) of the character, as illustrated by
+the inverse function.
sub ToLower {
- return <<END;
- 0041\t\t0061
- END
+ my $official = do $lower;
+ $utf8::ToSpecLower{"\xc4\xb0"} = "i";
+ return $official;
}
-defines a lc() mapping that causes only "A" to be mapped to "a", all
-other characters will remain unchanged.
+This example is for an ASCII platform, and C<\xc4\xb0> is the string of
+bytes that together form the UTF-8 that represents C<\N{LATIN CAPITAL
+LETTER I WITH DOT ABOVE}>, C<U+0130>. You can avoid having to figure out
+these bytes, and at the same time make it work on all platforms by
+instead writing:
-(For serious hackers only) If you want to introspect the default
-mappings, you can find the data in the directory
-C<$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).
+ sub ToLower {
+ my $official = do $lower;
+ my $sequence = "\N{LATIN CAPITAL LETTER I WITH DOT ABOVE}";
+ utf8::encode($sequence);
+ $utf8::ToSpecLower{$sequence} = "i";
+ return $official;
+ }
-A final note on the user-defined property tests and mappings: they
-will be used only if the scalar has been marked as having Unicode
-characters. Old byte-style strings will not be affected.
+This works because C<utf8::encode()> takes the single character and
+converts it to the sequence of bytes that constitute it. Note that we took
+advantage of the fact that C<"i"> is the same in UTF-8 or UTF_EBCIDIC as not;
+otherwise we would have had to write
+
+ $utf8::ToSpecLower{$sequence} = "\N{LATIN SMALL LETTER I}";
+
+in the ToLower example, and in the ToUpper example, use
+
+ my $sequence = "\N{LATIN SMALL LETTER I}";
+ utf8::encode($sequence);
+
+A big caveat to the above trick, and to this whole mechanism in general,
+is that they work only on strings encoded in UTF-8. You can partially
+get around this by using C<use subs>. (But better to just convert to
+use L<Unicode::Casing>.) For example:
+(The trick illustrated here does work in earlier releases, but only if all the
+characters you want to override have ordinal values of 256 or higher, or
+if you use the other tricks given just below.)
+
+The mappings are in effect only for the package they are defined in, and only
+on scalars that have been marked as having Unicode characters, for example by
+using C<utf8::upgrade()>. Although probably not advisable, you can
+cause the mappings to be used globally by importing into C<CORE::GLOBAL>
+(see L<CORE>).
+
+You can partially get around the restriction that the source strings
+must be in utf8 by using C<use subs> (or by importing with C<CORE::GLOBAL>
+importation) by:
+
+ use subs qw(uc ucfirst lc lcfirst);
+
+ sub uc($) {
+ my $string = shift;
+ utf8::upgrade($string);
+ return CORE::uc($string);
+ }
+
+ sub lc($) {
+ my $string = shift;
+ utf8::upgrade($string);
+
+ # Unless an I is before a dot_above, it turns into a dotless i.
+ # (The character class with the combining classes matches non-above
+ # marks following the I. Any number of these may be between the 'I' and
+ # the dot_above, and the dot_above will still apply to the 'I'.
+ use charnames ":full";
+ $string =~
+ s/I
+ (?! [^\p{ccc=0}\p{ccc=Above}]* \N{COMBINING DOT ABOVE} )
+ /\N{LATIN SMALL LETTER DOTLESS I}/gx;
+
+ # But when the I is followed by a dot_above, remove the
+ # dot_above so the end result will be i.
+ $string =~ s/I
+ ([^\p{ccc=0}\p{ccc=Above}]* )
+ \N{COMBINING DOT ABOVE}
+ /i$1/gx;
+ return CORE::lc($string);
+ }
+
+These examples (also for Turkish) make sure the input is in UTF-8, and then
+call the corresponding official function, which will use the C<ToUpper()> and
+C<ToLower()> functions you have defined.
+(For Turkish, there are other required functions: C<ucfirst>, C<lcfirst>,
+and C<ToTitle>. These are very similar to the ones given above.)
+
+The reason this is a partial fix is that it doesn't affect the C<\l>,
+C<\L>, C<\u>, and C<\U> case change operations in regular expressions,
+which still require the source to be encoded in utf8 (see L</The "Unicode
+Bug">). (Again, use L<Unicode::Casing> instead.)
+
+The C<lc()> example shows how you can add context-dependent casing. Note
+that context-dependent casing suffers from the problem that the string
+passed to the casing function may not have sufficient context to make
+the proper choice. And, it will not be called for C<\l>, C<\L>, C<\u>,
+and C<\U>.
=head2 Character Encodings for Input and Output
The following list of Unicode support for regular expressions describes
all the features currently supported. The references to "Level N"
-and the section numbers refer to the Unicode Technical Report 18,
-"Unicode Regular Expression Guidelines".
+and the section numbers refer to the Unicode Technical Standard #18,
+"Unicode Regular Expressions", version 11, in May 2005.
=over 4
Level 1 - Basic Unicode Support
- 2.1 Hex Notation - done [1]
- Named Notation - done [2]
- 2.2 Categories - done [3][4]
- 2.3 Subtraction - MISSING [5][6]
- 2.4 Simple Word Boundaries - done [7]
- 2.5 Simple Loose Matches - done [8]
- 2.6 End of Line - MISSING [9][10]
-
- [ 1] \x{...}
- [ 2] \N{...}
- [ 3] . \p{...} \P{...}
- [ 4] now scripts (see UTR#24 Script Names) in addition to blocks
- [ 5] have negation
- [ 6] can use regular expression look-ahead [a]
- or user-defined character properties [b] to emulate subtraction
- [ 7] include Letters in word characters
- [ 8] 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.
- [ 9] see UTR#13 Unicode Newline Guidelines
- [10] should do ^ and $ also on \x{85}, \x{2028} and \x{2029}
- (should also affect <>, $., and script line numbers)
- (the \x{85}, \x{2028} and \x{2029} do match \s)
+ 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, but all Unicode character
+ properties (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 (but with
+ bugs), not Simple: for example U+1F88 is equivalent to
+ U+1F00 U+03B9, not with 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.
+ [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.
-For example, what TR18 might write as
+For example, what UTS#18 might write as
[{Greek}-[{UNASSIGNED}]]
which will match assigned characters known to be part of the Greek script.
-[b] See L</"User-Defined Character Properties">.
+Also see the Unicode::Regex::Set module, it does implement the full
+UTS#18 grouping, intersection, union, and removal (subtraction) syntax.
+
+[b] '+' for union, '-' for removal (set-difference), '&' for intersection
+(see L</"User-Defined Character Properties">)
+
+[c] Try the C<:crlf> layer (see L<PerlIO>).
+
+[d] U+FFFF will currently generate a warning message if 'utf8' warnings are
+ enabled
=item *
Level 2 - Extended Unicode Support
- 3.1 Surrogates - MISSING [11]
- 3.2 Canonical Equivalents - MISSING [12][13]
- 3.3 Locale-Independent Graphemes - MISSING [14]
- 3.4 Locale-Independent Words - MISSING [15]
- 3.5 Locale-Independent Loose Matches - MISSING [16]
+ 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 - MISSING [16]
+ RL2.6 Wildcard Properties - MISSING
- [11] Surrogates are solely a UTF-16 concept and Perl's internal
- representation is UTF-8. The Encode module does UTF-16, though.
- [12] see UTR#15 Unicode Normalization
- [13] have Unicode::Normalize but not integrated to regexes
- [14] have \X but at this level . should equal that
- [15] need three classes, not just \w and \W
- [16] see UTR#21 Case Mappings
+ [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] see UAX#21 "Case Mappings"
+ [16] missing loose match [e]
-=item *
+[e] C<\N{...}> allows namespaces (see L<charnames>).
-Level 3 - Locale-Sensitive Support
-
- 4.1 Locale-Dependent Categories - MISSING
- 4.2 Locale-Dependent Graphemes - MISSING [16][17]
- 4.3 Locale-Dependent Words - MISSING
- 4.4 Locale-Dependent Loose Matches - MISSING
- 4.5 Locale-Dependent Ranges - MISSING
+=item *
- [16] see UTR#10 Unicode Collation Algorithms
- [17] have Unicode::Collate but not integrated to regexes
+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
+ ( RL3.8 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")
=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
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 before several of the byte entries above marked by '*'. 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:
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
=item *
-UTF-16, UTF-16BE, UTF16-LE, Surrogates, and BOMs (Byte Order Marks)
+UTF-16, UTF-16BE, UTF-16LE, Surrogates, and BOMs (Byte Order Marks)
The followings items are mostly for reference and general Unicode
knowledge, Perl doesn't use these constructs internally.
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 the all code points, not just Unicode ones, 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 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, UTF32-LE
+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
=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".
+
=head2 Security Implications of Unicode
+Read L<Unicode Security Considerations|http://www.unicode.org/reports/tr36>.
+Also, note the following:
+
=over 4
=item *
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.
=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.
-
-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.
+Regular expression pattern matching may surprise you if you're not
+accustomed to Unicode. Starting in Perl 5.14, there are a number of
+modifiers available that control this. For convenience, they will be
+referred to in this section using the notation, e.g., C<"/a"> even
+though in 5.14, they are not usable in a postfix form after the
+(typical) trailing slash of a regular expression. (In 5.14, they are
+usable only infix, for example by C</(?a:foo)/>, or by setting them to
+apply across a scope by, e.g., C<use re '/a';>. It is planned to lift
+this restriction in 5.16.)
+
+The C<"/l"> modifier says that the regular expression should match based
+on whatever locale is in effect at execution time. For example, C<\w>
+will match the "word" characters of that locale, and C<"/i">
+case-insensitive matching will match according to the locale's case
+folding rules. See L<perllocale>). C<\d> will likely match just 10
+digit characters. This modifier is automatically selected within the
+scope of either C<use locale> or C<use re '/l'>.
+
+The C<"/u"> modifier says that the regular expression should match based
+on Unicode semantics. C<\w> will match any of the more than 100_000
+word characters in Unicode. 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. Similarly, all the characters that
+are decimal digits somewhere in the world will match C<\d>; this is
+hundreds, not 10, possible matches. (And some of those digits look like
+some of the 10 ASCII digits, but mean a different number, so a human
+could easily think a number is a different quantity than it really is.)
+Also, case-insensitive matching works on the full set of Unicode
+characters. The "KELVIN SIGN", for example matches the letters "k" and
+"K"; and "LATIN SMALL LETTER LONG S" (which looks very much like an "f",
+and was common in the 18th century but is now obsolete), matches "s" and
+"S". This modifier is automatically selected within the scope of either
+C<use re '/u'> or C<use feature 'unicode_strings'> (which in turn is
+selected by C<use 5.012>.
+
+The C<"/a"> modifier is like the C<"/u"> modifier, except that it
+restricts certain constructs to match only in the ASCII range. C<\w>
+will match only the 63 characters "[A-Za-z0-9_]"; C<\d>, only the 10
+digits 0-9; C<\s>, only the five characters "[ \f\n\r\t]"; and the
+C<"[[:posix:]]"> classes only the appropriate ASCII characters. (See
+L<perlrecharclass>.) This modifier is like the C<"/u"> modifier in that
+things like "KELVIN SIGN" match the letters "k" and "K"; and non-ASCII
+characters continue to have Unicode semantics. This modifier is
+recommended for people who only incidentally use Unicode. One can write
+C<\d> with confidence that it will only match ASCII characters, and
+should the need arise to match beyond ASCII, you can use C<\p{Digit}> or
+C<\p{Word}>. (See L<perlrecharclass> for how to extend C<\s>, and the
+Posix classes beyond ASCII under this modifier.) This modifier is
+automatically selected within the scope of C<use re '/a'>.
+
+The C<"/d"> modifier gives the regular expression behavior that Perl has
+had between 5.6 and 5.12. For backwards compatibility it is selected
+by default, but it leads to a number of issues, as outlined in
+L</The "Unicode Bug">. When this modifier is in effect, regular
+expression matching uses the semantics of what is called the "C" or
+"Posix" locale, unless the pattern or target string of the match is
+encoded in UTF-8, in which case it uses Unicode semantics. That is, it
+uses what this document calls "byte" semantics unless there is some
+UTF-8-ness involved, in which case it uses "character" semantics. Note
+that byte semantics are not the same as C<"/a"> matching, as the former
+doesn't know about the characters that are in the Latin-1 range which
+aren't ASCII (such as "LATIN SMALL LETTER ETH), but C<"/a"> does.
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
regular expressions might start behaving differently. Review your
code. Use warnings and the C<strict> pragma.
+There are some additional rules as to which of these modifiers is in
+effect if there are contradictory rules present. First, an explicit
+modifier in a regular expression always overrides any pragmas. And a
+modifier in an inner cluster or capture group overrides one in an outer
+group (for that inner group only). If both C<use locale> and C<use
+feature 'unicode_strings> are in effect, the C<"/l"> modifier is
+selected. And finally, a C<use re> that specifies a modifier has
+precedence over both those pragmas.
+
=back
=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:
+there are exceptions:
=over 4
=item *
-If your locale environment variables (LANGUAGE, LC_ALL, LC_CTYPE, LANG)
-contain the strings 'UTF-8' or 'UTF8' (case-insensitive matching),
-the default encodings of your STDIN, STDOUT, and STDERR, and of
-B<any subsequent file open>, are considered to be UTF-8.
+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 *
=back
+=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
+results, or both, but it is not.
+
+The following are such interfaces. Also, see L</The "Unicode Bug">.
+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.
+
+One reason why Perl does not attempt to resolve the role of Unicode in
+these cases 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?
+
+=over 4
+
+=item *
+
+chdir, chmod, chown, chroot, exec, link, lstat, mkdir,
+rename, rmdir, stat, symlink, truncate, unlink, utime, -X
+
+=item *
+
+%ENV
+
+=item *
+
+glob (aka the <*>)
+
+=item *
+
+open, opendir, sysopen
+
+=item *
+
+qx (aka the backtick operator), system
+
+=item *
+
+readdir, readlink
+
+=back
+
+=head2 The "Unicode Bug"
+
+The term, the "Unicode bug" has been applied to an inconsistency with the
+Unicode characters whose ordinals are 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.
+
+In character semantics they are interpreted as Unicode code points, which means
+they have the same semantics as Latin-1 (ISO-8859-1).
+
+In byte semantics, 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>. (On EBCDIC platforms, the behavior may
+be different from this, depending on the underlying C language library
+functions.)
+
+The behavior is known to have effects on 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 regular expression
+substitutions.
+
+=item *
+
+Using caseless (C</i>) regular expression matching
+
+=item *
+
+Matching a number of 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:]]>.
+
+=item *
+
+In C<quotemeta> or its inline equivalent C<\Q>, all characters whose
+code points are above 127 are not quoted in UTF-8 encoded strings, but
+all are quoted in UTF-8 strings.
+
+=item *
+
+User-defined case change mappings. You can create a C<ToUpper()> function, for
+example, which overrides Perl's built-in case mappings. The scalar must be
+encoded in utf8 for your function to actually be invoked.
+
+=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'
+ $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.
+
+Starting in Perl 5.14, C<use feature 'unicode_strings'> can be used to
+cause Perl to use Unicode semantics on all string operations within the
+scope of the feature subpragma. Regular expressions compiled in its
+scope retain that behavior even when executed or compiled into larger
+regular expressions outside the scope. (The pragma does not, however,
+affect the C<quotemeta> behavior. Not does it affect the deprecated
+user-defined case changing operations. These still require a UTF-8
+encoded string to operate.)
+
+In Perl 5.12, the subpragma affected casing changes, but not regular
+expressions. See L<perlfunc/lc> for details on how this pragma works in
+combination with various others for casing.
+
+For earlier Perls, or when a string is passed to a function outside the
+subpragma's scope, a workaround is to always call C<utf8::upgrade($string)>,
+or to use the standard module L<Encode>. Also, a scalar that has any characters
+whose ordinal is above 0x100, or which were specified using either of the
+C<\N{...}> notations will automatically have character semantics.
+
+=head2 Forcing Unicode in Perl (Or Unforcing Unicode in Perl)
+
+Sometimes (see L</"When Unicode Does Not Happen"> or L</The "Unicode Bug">)
+there are situations where you simply need to force a byte
+string into UTF-8, or vice versa. The low-level calls
+utf8::upgrade($bytestring) and utf8::downgrade($utf8string[, FAIL_OK]) are
+the answers.
+
+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
If you want to handle Perl Unicode in XS extensions, you may find the
=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, 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<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 version of Unicode that you want 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 F<INSTALL>).
+
+It is even possible to copy the built files to a different directory, and then
+change F<utf8_heavy.pl> in the directory C<\$Config{privlib}> to point to the
+new directory, or maybe make a copy of that directory before making the change,
+and using C<@INC> or the C<-I> run-time flag to switch between versions at will
+(but because of caching, not in the middle of a process), but all this is
+beyond the scope of these instructions.
+
=head1 BUGS
=head2 Interaction with Locales
Unicode support will also tend to run slower. Use of locales with
Unicode is discouraged.
+=head2 Problems with characters in the Latin-1 Supplement range
+
+See L</The "Unicode Bug">
+
+=head2 Problems with case-insensitive regular expression matching
+
+There are problems with case-insensitive matches, including those involving
+character classes (enclosed in [square brackets]), characters whose fold
+is to multiple characters (such as the single character LATIN SMALL LIGATURE
+FFL matches case-insensitively with the 3-character string C<ffl>), and
+characters in the Latin-1 Supplement.
+
=head2 Interaction with Extensions
When Perl exchanges data with an extension, the extension should be
-able to understand the UTF-8 flag and act accordingly. If the
+able to understand the UTF8 flag and act accordingly. If the
extension doesn't know about the flag, it's likely that the extension
will return incorrectly-flagged data.
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
sub param {
my($self,$name,$value) = @_;
utf8::upgrade($name); # make sure it is UTF-8 encoded
- if (defined $value)
+ if (defined $value) {
utf8::upgrade($value); # make sure it is UTF-8 encoded
return $self->SUPER::param($name,$value);
} else {
Some functions are slower when working on UTF-8 encoded strings than
on byte encoded strings. All functions that need to hop over
-characters such as length(), substr() or index() can work B<much>
-faster when the underlying data are byte-encoded. Witness the
-following benchmark:
-
- % perl -e '
- use Benchmark;
- use strict;
- our $l = 10000;
- our $u = our $b = "x" x $l;
- substr($u,0,1) = "\x{100}";
- timethese(-2,{
- LENGTH_B => q{ length($b) },
- LENGTH_U => q{ length($u) },
- SUBSTR_B => q{ substr($b, $l/4, $l/2) },
- SUBSTR_U => q{ substr($u, $l/4, $l/2) },
- });
- '
- Benchmark: running LENGTH_B, LENGTH_U, SUBSTR_B, SUBSTR_U for at least 2 CPU seconds...
- LENGTH_B: 2 wallclock secs ( 2.36 usr + 0.00 sys = 2.36 CPU) @ 5649983.05/s (n=13333960)
- LENGTH_U: 2 wallclock secs ( 2.11 usr + 0.00 sys = 2.11 CPU) @ 12155.45/s (n=25648)
- SUBSTR_B: 3 wallclock secs ( 2.16 usr + 0.00 sys = 2.16 CPU) @ 374480.09/s (n=808877)
- SUBSTR_U: 2 wallclock secs ( 2.11 usr + 0.00 sys = 2.11 CPU) @ 6791.00/s (n=14329)
-
-The numbers show an incredible slowness on long UTF-8 strings. You
-should carefully avoid using these functions in tight loops. If you
-want to iterate over characters, the superior coding technique would
-split the characters into an array instead of using substr, as the following
-benchmark shows:
-
- % perl -e '
- use Benchmark;
- use strict;
- our $l = 10000;
- our $u = our $b = "x" x $l;
- substr($u,0,1) = "\x{100}";
- timethese(-5,{
- SPLIT_B => q{ for my $c (split //, $b){} },
- SPLIT_U => q{ for my $c (split //, $u){} },
- SUBSTR_B => q{ for my $i (0..length($b)-1){my $c = substr($b,$i,1);} },
- SUBSTR_U => q{ for my $i (0..length($u)-1){my $c = substr($u,$i,1);} },
- });
- '
- Benchmark: running SPLIT_B, SPLIT_U, SUBSTR_B, SUBSTR_U for at least 5 CPU seconds...
- SPLIT_B: 6 wallclock secs ( 5.29 usr + 0.00 sys = 5.29 CPU) @ 56.14/s (n=297)
- SPLIT_U: 5 wallclock secs ( 5.17 usr + 0.01 sys = 5.18 CPU) @ 55.21/s (n=286)
- SUBSTR_B: 5 wallclock secs ( 5.34 usr + 0.00 sys = 5.34 CPU) @ 123.22/s (n=658)
- SUBSTR_U: 7 wallclock secs ( 6.20 usr + 0.00 sys = 6.20 CPU) @ 0.81/s (n=5)
-
-Even though the algorithm based on C<substr()> is faster than
-C<split()> for byte-encoded data, it pales in comparison to the speed
-of C<split()> when used with UTF-8 data.
+characters such as length(), substr() or index(), or matching regular
+expressions can work B<much> faster when the underlying data are
+byte-encoded.
+
+In Perl 5.8.0 the slowness was often quite spectacular; in Perl 5.8.1
+a caching scheme was introduced which will hopefully make the slowness
+somewhat less spectacular, at least for some operations. In general,
+operations with UTF-8 encoded strings are still slower. As an example,
+the Unicode properties (character classes) like C<\p{Nd}> are known to
+be quite a bit slower (5-20 times) than their simpler counterparts
+like C<\d> (then again, there 268 Unicode characters matching C<Nd>
+compared with the 10 ASCII characters matching C<d>).
+
+=head2 Problems on EBCDIC platforms
+
+There are a number of known problems with Perl on EBCDIC platforms. If you
+want to use Perl there, send email to perlbug@perl.org.
+
+In earlier versions, when byte and character data were concatenated,
+the new string was sometimes created by
+decoding the byte strings as I<ISO 8859-1 (Latin-1)>, even if the
+old Unicode string used EBCDIC.
+
+If you find any of these, please report them as bugs.
=head2 Porting code from perl-5.6.X
A filehandle that should read or write UTF-8
if ($] > 5.007) {
- binmode $fh, ":utf8";
+ binmode $fh, ":encoding(utf8)";
}
=item *
Be it Compress::Zlib, Apache::Request or any extension that has no
mention of Unicode in the manpage, you need to make sure that the
-UTF-8 flag is stripped off. Note that at the time of this writing
+UTF8 flag is stripped off. Note that at the time of this writing
(October 2002) the mentioned modules are not UTF-8-aware. Please
check the documentation to verify if this is still true.
A scalar we got back from an extension
If you believe the scalar comes back as UTF-8, you will most likely
-want the UTF-8 flag restored:
+want the UTF8 flag restored:
if ($] > 5.007) {
require Encode;
that is still true.
sub fetchrow {
- my($self, $sth, $what) = @_; # $what is one of fetchrow_{array,hashref}
+ # $what is one of fetchrow_{array,hashref}
+ my($self, $sth, $what) = @_;
if ($] < 5.007) {
return $sth->$what;
} else {
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 $ret;
} else {
Scalars that contain only ASCII and are marked as UTF-8 are sometimes
a drag to your program. If you recognize such a situation, just remove
-the UTF-8 flag:
+the UTF8 flag:
utf8::downgrade($val) if $] > 5.007;
=head1 SEE ALSO
-L<perluniintro>, L<encoding>, L<Encode>, L<open>, L<utf8>, L<bytes>,
-L<perlretut>, L<perlvar/"${^WIDE_SYSTEM_CALLS}">
+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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