=head2 Important Caveats
-Unicode support is an extensive requirement. While perl does not
+Unicode support is an extensive requirement. While Perl does not
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 Disciplines
+=item Input and Output Layers
-A filehandle can be marked as containing perl's internal Unicode
-encoding (UTF-8 or UTF-EBCDIC) by opening it with the ":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>.
+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 ":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 mark the Perl source itself as being in 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 switch to the Unicode
-character scheme when presented with Unicode data, or a traditional
-byte scheme when presented with byte data.
+the pattern adapts to the data and automatically switches to the Unicode
+character scheme when presented with data that is internally encoded in
+UTF-8, or instead uses a traditional byte scheme when presented with
+byte data.
=item C<use utf8> still needed to enable UTF-8/UTF-EBCDIC in scripts
-As a compatibility measure, this pragma must be explicitly used to
-enable recognition of UTF-8 in the Perl scripts themselves on ASCII
-based machines, or to recognize UTF-EBCDIC on EBCDIC based machines.
-B<NOTE: this should be the only place where an explicit C<use utf8>
-is needed>.
+As a compatibility measure, the C<use utf8> pragma must be explicitly
+included to enable recognition of UTF-8 in the Perl scripts themselves
+(in string or regular expression literals, or in identifier names) on
+ASCII-based machines or to recognize UTF-EBCDIC on EBCDIC-based
+machines. B<These are the only times when an explicit C<use utf8>
+is needed.> See L<utf8>.
+
+=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.)
-You can also use the C<encoding> pragma to change the default encoding
-of the data in your script; see L<encoding>.
+=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
-=head2 Byte and Character semantics
+=head2 Byte and Character Semantics
-Beginning with version 5.6, Perl uses logically wide characters to
+Beginning with version 5.6, Perl uses logically-wide characters to
represent strings internally.
-In future, Perl-level operations can be expected to work with
-characters rather than bytes, in general.
+In future, Perl-level operations will be expected to work with
+characters rather than bytes.
-However, as strictly an interim compatibility measure, Perl aims to
+However, as an interim compatibility measure, Perl aims to
provide a safe migration path from byte semantics to character
semantics for programs. For operations where Perl can unambiguously
-decide that the input data is characters, Perl now switches to
+decide that the input data are characters, Perl switches to
character semantics. For operations where this determination cannot
be made without additional information from the user, Perl decides in
-favor of compatibility, and chooses to use byte semantics.
+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, but only as long as
-none of the program's inputs are marked as being as source of Unicode
+which allowed byte semantics in Perl operations only if
+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. Note that this is
-currently only implemented on Windows since other platforms lack an
-API standard on this area.
+The C<bytes> pragma will always, regardless of platform, force byte
+semantics in a particular lexical scope. See L<bytes>.
-Regardless of the above, the C<bytes> pragma can always be used to
-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 until a future version of Perl
-in which character semantics will become the default. This pragma may
-then become a no-op. See L<utf8>.
-
-Unless mentioned otherwise, Perl operators will use character semantics
-when they are dealing with Unicode data, and byte semantics otherwise.
-Thus, character semantics for these operations apply transparently; if
-the input data came from a Unicode source (for example, by adding a
-character encoding discipline to the filehandle whence it came, or a
-literal Unicode string constant in the program), character semantics
-apply; otherwise, byte semantics are in effect. To force byte semantics
-on Unicode data, the C<bytes> pragma should be used.
-
-Notice that if you concatenate strings with byte semantics and strings
-with Unicode character data, the bytes will by default be upgraded
-I<as if they were ISO 8859-1 (Latin-1)> (or if in EBCDIC, after a
-translation to ISO 8859-1). This is done without regard to the
-system's native 8-bit encoding, so to change this for systems with
-non-Latin-1 (or non-EBCDIC) native encodings, use the C<encoding>
-pragma, see L<encoding>.
+Note that this pragma is only required while Perl defaults to byte
+semantics; when character semantics become the default, this pragma
+may become a no-op. See L<utf8>.
+
+Unless explicitly stated, Perl operators use character semantics
+for Unicode data and byte semantics for non-Unicode data.
+The decision to use character semantics is made transparently. If
+input data comes from a Unicode source--for example, if a character
+encoding layer is added to a filehandle or a literal Unicode
+string constant appears in a program--character semantics apply.
+Otherwise, byte semantics are in effect. The C<bytes> pragma should
+be used to force byte semantics on Unicode data, 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 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 change to operating on characters. A character in Perl is
+bytes now operate on characters. A character in Perl is
logically just a number ranging from 0 to 2**31 or so. Larger
-characters may encode to longer sequences of bytes internally, but
-this is just an internal detail which is hidden at the Perl level.
-See L<perluniintro> for more on this.
+characters may encode into longer sequences of bytes internally, but
+this internal detail is mostly hidden for Perl code.
+See L<perluniintro> for more.
-=head2 Effects of character semantics
+=head2 Effects of Character Semantics
Character semantics have the following effects:
=item *
-Strings (including hash keys) and regular expression patterns may
+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 are 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<\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}>.
-You can also get Unicode characters into a string by using the C<\x{...}>
-notation, putting the Unicode code for the desired character, in
-hexadecimal, into the curlies. For instance, a smiley face is C<\x{263A}>.
-This works only for characters with a code 0x100 and above.
+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
use charnames ':full';
-you can use the C<\N{...}> notation, putting the official Unicode character
-name within the curlies. For example, C<\N{WHITE SMILING FACE}>.
-This works for all characters that have names.
+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 *
If an appropriate L<encoding> is specified, identifiers within the
Perl script may contain Unicode alphanumeric characters, including
-ideographs. (You are currently on your own when it comes to using the
-canonical forms of characters--Perl doesn't (yet) attempt to
-canonicalize variable names for you.)
+ideographs. Perl does not currently attempt to canonicalize variable
+names.
=item *
-Regular expressions match characters instead of bytes. For instance,
-"." matches a character instead of a byte. (However, the C<\C> pattern
-is provided to force a match a single byte ("C<char>" in C, hence C<\C>).)
+Regular expressions match characters instead of bytes. "." matches
+a character instead of a byte.
=item *
-Character classes in regular expressions match characters instead of
-bytes, and match against the character properties specified in the
-Unicode properties database. So C<\w> can be used to match an
+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 new C<\p{}> (matches property) and C<\P{}>
-(doesn't match property) constructs. For instance, C<\p{Lu}> matches any
-character with the Unicode "Lu" (Letter, uppercase) property, while
-C<\p{M}> matches any character with a "M" (mark -- accents and such)
-property. Single letter properties may omit the brackets, so that can be
-written C<\pM> also. 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 have dashes, spaces, and underbars
-at every word division, and you need not care about correct casing. It is
-recommended, however, that for consistency you use the following naming:
-the official Unicode script, block, or property name (see below for the
-additional rules that apply to block names), with whitespace and dashes
-removed, and the words "uppercase-first-lowercase-rest". That is, "Latin-1
-Supplement" becomes "Latin1Supplement".
-
-You can also negate both C<\p{}> and C<\P{}> by introducing a caret
-(^) between the first curly and the property name: C<\p{^Tamil}> is
+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, e.g. C<\p{Lu}> and C<\p{LowercaseLetter}>
-are identical).
+=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
+ Co Private_Use
Cn Unassigned
-The single-letter properties match all characters in any of the
+Single-letter properties match all characters in any of the
two-letter sub-properties starting with the same letter.
-There's also C<L&> 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, it has no need to support the
-somewhat messy concept of surrogates. Therefore, the C<Cs> property is not
+representation of Unicode characters, there is no need to implement
+the somewhat messy concept of surrogates. C<Cs> is therefore not
supported.
-Because scripts differ in their directionality (for example Hebrew is
-written right to left), Unicode supplies these properties:
+=head3 B<Bidirectional Character Types>
+
+Because scripts differ in their directionality (Hebrew is
+written right to left, for example) Unicode supplies these properties in
+the 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 all 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.
+=head3 B<Scripts>
+
+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> 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}>.
+
+=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 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 digits, because digits are
+shared across many scripts. Digits 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.
+
+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 1
+
+It is confusing. There are many naming conflicts, and you may forget some.
+For example, C<\p{Hebrew}> means the I<script> Hebrew, and NOT the I<block>
+Hebrew. But would you remember that 6 months from now?
+
+=item 2
+
+It is unstable. A new version of Unicode may 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.
+
=back
-=head2 Scripts
-
-The scripts available via C<\p{...}> and C<\P{...}>, for example
-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
-
-There are also extended property classes that 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 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
-
-For backward compatibility, all properties mentioned so far may have C<Is>
-prepended to their name (e.g. C<\P{IsLu}> is equal to C<\P{Lu}>).
-
-=head2 Blocks
-
-In addition to B<scripts>, Unicode also defines B<blocks> of characters.
-The difference between scripts and blocks is that the scripts concept is
-closer to natural languages, while the blocks concept is more an artificial
-grouping based on groups of mostly 256 Unicode characters. For example, the
-C<Latin> script contains letters from many blocks. On the other hand, the
-C<Latin> script 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 other 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
-
-Blocks 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
-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
+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).
-=over 4
+A complete list of blocks and their shortcuts is in L<perluniprops>.
-=item *
+=head3 B<Other Properties>
-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. It is equivalent to
-C<(?:\PM\pM*)>.
+There are many more properties than the very basic ones described here.
+A complete list is in L<perluniprops>.
-=item *
+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>).
-The C<tr///> operator translates characters instead of bytes. Note
-that the C<tr///CU> functionality has been removed, as the interface
-was a mistake. For similar functionality see pack('U0', ...) and
-pack('C0', ...).
+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
-Case translation operators use the Unicode case translation tables
-when provided character input. Note that C<uc()> (also known as C<\U>
-in doublequoted strings) translates to uppercase, while C<ucfirst>
-(also known as C<\u> in doublequoted strings) translates to titlecase
-(for languages that make the distinction). Naturally the
-corresponding backslash sequences have the same semantics.
+=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}>.
-Most operators that deal with positions or lengths in the 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 don't switch include C<vec()>, C<pack()>, and
-C<unpack()>. Operators that really don't care include C<chomp()>, as
-well as any other operator that treats a string as a bucket of bits,
-such as C<sort()>, and the operators dealing with filenames.
+=item B<C<\p{Alnum}>>
-=item *
+This matches any C<\p{Alphabetic}> or C<\p{Decimal_Number}> character.
-The C<pack()>/C<unpack()> letters "C<c>" and "C<C>" do I<not> change,
-since they're often used for byte-oriented formats. (Again, think
-"C<char>" in the C language.) However, there is a new "C<U>" specifier
-that will convert between Unicode characters and integers.
+=item B<C<\p{Any}>>
-=item *
+This matches any of the 1_114_112 Unicode code points. It is a synonym for
+C<\p{All}>.
-The C<chr()> and C<ord()> functions work on characters. This is like
-C<pack("U")> and C<unpack("U")>, not like C<pack("C")> and
-C<unpack("C")>. In fact, the latter are how you now emulate
-byte-oriented C<chr()> and C<ord()> for Unicode strings.
-(Note that this reveals the internal encoding of Unicode strings,
-which is not something one normally needs to care about at all.)
+=item B<C<\p{Assigned}>>
-=item *
+This matches any assigned code point; that is, any code point whose general
+category is not Unassigned (or equivalently, not Cn).
-The bit string operators C<& | ^ ~> can operate on character data.
-However, for backward compatibility reasons (bit string operations
-when the characters all are less than 256 in ordinal value) one should
-not mix C<~> (the bit complement) and characters both less than 256 and
-equal or greater than 256. Most importantly, the DeMorgan's laws
-(C<~($x|$y) eq ~$x&~$y>, C<~($x&$y) eq ~$x|~$y>) won't hold.
-Another way to look at this 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{Blank}>>
-=item *
+This is the same as C<\h> and C<\p{HorizSpace}>: A character that changes the
+spacing horizontally.
-lc(), uc(), lcfirst(), and ucfirst() work for the following cases:
+=item B<C<\p{Decomposition_Type: Non_Canonical}>> (Short: C<\p{Dt=NonCanon}>)
-=over 8
+Matches a character that has a non-canonical decomposition.
-=item *
+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.)
-the case mapping is from a single Unicode character to another
-single Unicode character
+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".
-=item *
+"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.
-the case mapping is from a single Unicode character to more
-than one Unicode character
+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.
-=back
+Note that most Unicode characters don't have a decomposition, so their
+decomposition type is "None".
-What doesn't yet work are the following cases:
+Perl has added the C<Non_Canonical> type, for your convenience, to mean any of
+the compatibility decompositions.
-=over 8
+=item B<C<\p{Graph}>>
-=item *
+Matches any character that is graphic. Theoretically, this means a character
+that on a printer would cause ink to be used.
-the "final sigma" (Greek)
+=item B<C<\p{HorizSpace}>>
-=item *
+This is the same as C<\h> and C<\p{Blank}>: A character that changes the
+spacing horizontally.
-anything to with locales (Lithuanian, Turkish, Azeri)
+=item B<C<\p{In=*}>>
-=back
+This is a synonym for C<\p{Present_In=*}>
-See the Unicode Technical Report #21, Case Mappings, for more details.
+=item B<C<\p{PerlSpace}>>
-=item *
+This is the same as C<\s>, restricted to ASCII, namely C<S<[ \f\n\r\t]>>.
-And finally, C<scalar reverse()> reverses by character rather than by byte.
+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
+=head2 User-Defined Character Properties
-You can define your own character properties by defining subroutines
-that have names beginning with "In" or "Is". The subroutines must be
-visible in the package that uses the properties. The user-defined
-properties can be used in the regular expression C<\p> and C<\P>
-constructs.
+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.
-The subroutines must return a specially formatted string: one or more
-newline-separated lines. Each line must be one of the following:
+ # 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.
+
+The subroutines must return a specially-formatted string, with one
+or more newline-separated lines. Each line must be one of the following:
=over 4
=item *
+A single hexadecimal number denoting a Unicode code point to include.
+
+=item *
+
Two hexadecimal numbers separated by horizontal whitespace (space or
-tabulator characters) denoting a range of Unicode codepoints to include.
+tabular characters) denoting a range of Unicode code points to include.
=item *
-Something to include, prefixed by "+": either an built-in character
-property (prefixed by "utf8::"), for all the characters in that
-property; or two hexadecimal codepoints for a range; or a single
-hexadecimal codepoint.
+Something to include, prefixed by "+": a built-in character
+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 "-": either an existing character
-property (prefixed by "utf8::"), for all the characters in that
-property; or two hexadecimal codepoints for a range; or a single
-hexadecimal codepoint.
+Something to exclude, prefixed by "-": an existing character
+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 "!": either an existing character
-property (prefixed by "utf8::") for all the characters except the
-characters in the property; or two hexadecimal codepoints for a range;
-or a single hexadecimal codepoint.
+Something to negate, prefixed "!": an existing character
+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
}
-=head2 Character encodings for input and output
+Intersection is useful for getting the common characters matched by
+two (or more) classes.
+
+ 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)
+
+You can also 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\t007A\t0041
+ 0101\t\t0100
+ END
+ }
+
+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 you can use the
+following trick (but see below for a big caveat), 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;
+ }
+
+This takes the official mappings and overrides just one, for "LATIN SMALL
+LETTER I". Each hash key must be the string of bytes that form the UTF-8
+(on EBCDIC platforms, UTF-EBCDIC) of the character, as illustrated by
+the inverse function.
+
+ sub ToLower {
+ my $official = do $lower;
+ $utf8::ToSpecLower{"\xc4\xb0"} = "i";
+ return $official;
+ }
+
+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:
+
+ 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;
+ }
+
+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>. For example:
+
+ 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 work-around is that it doesn't affect the C<\l>,
+C<\L>, C<\u>, and C<\U> case change operations, which still require the source
+to be encoded in utf8 (see L</The "Unicode Bug">).
+
+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
See L<Encode>.
=head2 Unicode Regular Expression Support Level
-The following list of Unicode regular expression support describes
-feature by feature the Unicode support implemented in Perl as of Perl
-5.8.0. The "Level N" and the section numbers refer to the Unicode
-Technical Report 18, "Unicode Regular Expression Guidelines".
+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 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 casefolding in matching, not Simple:
- for example U+1F88 is equivalent with U+1F000 U+03B9,
- not with 1F80. This difference matters for certain Greek
- capital letters with certain modifiers: the Full casefolding
- decomposes the letter, while the Simple casefolding 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}]]
But in this particular example, you probably really want
- \p{Greek}
+ \p{GreekAndCoptic}
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
- 3.2 Canonical Equivalents - MISSING [11][12]
- 3.3 Locale-Independent Graphemes - MISSING [13]
- 3.4 Locale-Independent Words - MISSING [14]
- 3.5 Locale-Independent Loose Matches - MISSING [15]
-
- [11] see UTR#15 Unicode Normalization
- [12] have Unicode::Normalize but not integrated to regexes
- [13] have \X but at this level . should equal that
- [14] need three classes, not just \w and \W
- [15] see UTR#21 Case Mappings
+ 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
-=item *
+ [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]
-Level 3 - Locale-Sensitive Support
+[e] C<\N{...}> allows namespaces (see L<charnames>).
- 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
=head2 Unicode Encodings
-Unicode characters are assigned to I<code points> which are abstract
-numbers. To use these numbers various encodings are needed.
+Unicode characters are assigned to I<code points>, which are abstract
+numbers. To use these numbers, various encodings are needed.
=over 4
UTF-8
UTF-8 is a variable-length (1 to 6 bytes, current character allocations
-require 4 bytes), byteorder independent encoding. For ASCII, UTF-8 is
-transparent (and we really do mean 7-bit ASCII, not another 8-bit encoding).
+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.
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..BFÂ Â
- U+1000..U+CFFF E1..EC 80..BF 80..BFÂ Â
- U+D000..U+D7FF ED 80..9F 80..BFÂ Â
- U+D800..U+DFFF ******* ill-formed *******
- U+E000..U+FFFF EE..EF 80..BF 80..BFÂ Â
- U+10000..U+3FFFF F0 90..BF 80..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 +++++++ 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+40000..U+FFFFF F1..F3 80..BF 80..BF 80..BF
U+100000..U+10FFFF F4 80..8F 80..BF 80..BF
-Note the A0..BF in U+0800..U+0FFF, the 80..9F in U+D000...U+D7FF,
-the 90..BF in U+10000..U+3FFFF, and the 80...8F in 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 (and that is 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).
-Or, another way to look at it, as bits:
+Another way to look at it is via bits:
Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte
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.
=item *
UTF-EBCDIC
-Like UTF-8, but EBCDIC-safe, as UTF-8 is ASCII-safe.
+Like UTF-8 but EBCDIC-safe, in the way that UTF-8 is ASCII-safe.
=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, Perl doesn't
-use them internally.)
+The followings items are mostly for reference and general Unicode
+knowledge, Perl doesn't use these constructs internally.
UTF-16 is a 2 or 4 byte encoding. The Unicode code points
-0x0000..0xFFFF are stored in two 16-bit units, and the code points
-0x010000..0x10FFFF in two 16-bit units. The latter case is
+C<U+0000..U+FFFF> are stored in a single 16-bit unit, and the code
+points C<U+10000..U+10FFFF> in two 16-bit units. The latter case is
using I<surrogates>, the first 16-bit unit being the I<high
surrogate>, and the second being the I<low surrogate>.
-Surrogates are code points set aside to encode the 0x01000..0x10FFFF
+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 0xD800..0xDBFF, and the I<low surrogates>
-are the range 0xDC00..0xDFFFF. The surrogate encoding is
+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);
+ $uni = 0x10000 + ($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 (C<-w> or C<use
-warnings;>) because those code points are not valid for a Unicode
-character.
+will get a warning, if warnings are turned on, because those code
+points are not valid for a Unicode character.
-Because of the 16-bitness, UTF-16 is byteorder dependent. UTF-16
+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
-transfer is required, either UTF-16BE (Big Endian) or UTF-16LE
-(Little Endian) must be chosen.
+transfer is required either UTF-16BE (big-endian) or UTF-16LE
+(little-endian) encodings must be chosen.
This introduces another problem: what if you just know that your data
-is UTF-16, but you don't know which endianness? Byte Order Marks
-(BOMs) are a solution to this. A special character has been reserved
+is UTF-16, but you don't know which endianness? Byte Order Marks, or
+BOMs, are a solution to this. A special character has been reserved
in Unicode to function as a byte order marker: the character with the
-code point 0xFEFF is the BOM.
+code point C<U+FEFF> is the BOM.
The trick is that if you read a BOM, you will know the byte order,
-since if it was written on a big endian platform, you will read the
-bytes 0xFE 0xFF, but if it was written on a little endian platform,
-you will read the bytes 0xFF 0xFE. (And if the originating platform
-was writing in UTF-8, you will read the bytes 0xEF 0xBB 0xBF.)
+since if it was written on a big-endian platform, you will read the
+bytes C<0xFE 0xFF>, but if it was written on a little-endian platform,
+you will read the bytes C<0xFF 0xFE>. (And if the originating platform
+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
-0xFFFE is guaranteed not to be a valid Unicode character, so the
-sequence of bytes 0xFF 0xFE is unambiguously "BOM, represented in
-little-endian format" and cannot be "0xFFFE, represented in big-endian
-format".
+C<U+FFFE> is guaranteed not to be a valid Unicode character, 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". (Actually, C<U+FFFE> is legal for use by your program, even for
+input/output, but better not use it if you need a BOM. But it is "illegal for
+interchange", so that an unsuspecting program won't get confused.)
=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
-needed. The BOM signatures will be 0x00 0x00 0xFE 0xFF for BE and
-0xFF 0xFE 0x00 0x00 for LE.
+needed. The BOM signatures will be C<0x00 0x00 0xFE 0xFF> for BE and
+C<0xFF 0xFE 0x00 0x00> for LE.
=item *
UCS-2, UCS-4
Encodings defined by the ISO 10646 standard. UCS-2 is a 16-bit
-encoding, UCS-4 is a 32-bit encoding. Unlike UTF-16, UCS-2
-is not extensible beyond 0xFFFF, because it does not use surrogates.
+encoding. Unlike UTF-16, UCS-2 is not extensible beyond C<U+FFFF>,
+because it does not use surrogates. UCS-4 is a 32-bit encoding,
+functionally identical to UTF-32.
=item *
UTF-7
-A seven-bit safe (non-eight-bit) encoding, useful if the
-transport/storage is not eight-bit safe. Defined by RFC 2152.
+A seven-bit safe (non-eight-bit) encoding, which is useful if the
+transport or storage is not eight-bit safe. Defined by RFC 2152.
=back
=head2 Security Implications of Unicode
+Read L<Unicode Security Considerations|http://www.unicode.org/reports/tr36>.
+Also, note the following:
+
=over 4
=item *
Unfortunately, the specification of UTF-8 leaves some room for
interpretation of how many bytes of encoded output one should generate
-from one input Unicode character. Strictly speaking, one is supposed
-to always generate the shortest possible sequence of UTF-8 bytes,
-because otherwise there is potential for input buffer overflow at
+from one input Unicode character. Strictly speaking, the shortest
+possible sequence of UTF-8 bytes should be generated,
+because otherwise there is potential for an input buffer overflow at
the receiving end of a UTF-8 connection. Perl always generates the
-shortest length UTF-8, and with warnings on (C<-w> or C<use
-warnings;>) Perl will warn about non-shortest length UTF-8 (and other
-malformations, too, such as the surrogates, which are not real
-Unicode code points.)
+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 when the data is all eight-bit bytes
-or when the data is Unicode.
+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
+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,
-and most importantly, even in the set of the first 256 characters, it
-will most probably be different: as opposed to most locales (which are
-specific to a language and country pair) Unicode classifies all the
-characters that are letters 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.
-
-As discussed elsewhere, Perl tries to stand one leg (two legs, as
-camels are quadrupeds?) in two worlds: the old world of bytes and the new
-world of characters, upgrading from bytes to characters when necessary.
-If your legacy code is not explicitly using Unicode, no automatic
-switchover to characters should happen, and characters shouldn't get
-downgraded back to bytes, either. It is possible to accidentally mix
-bytes and characters, however (see L<perluniintro>), in which case the
-C<\w> might start behaving differently. Review your code.
+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.
+
+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
+characters, upgrading from bytes to characters when necessary.
+If your legacy code does not explicitly use Unicode, no automatic
+switch-over to characters should happen. Characters shouldn't get
+downgraded to bytes, either. It is possible to accidentally mix bytes
+and characters, however (see L<perluniintro>), in which case C<\w> in
+regular expressions might start behaving differently. Review your
+code. Use warnings and the C<strict> pragma.
=back
=head2 Unicode in Perl on EBCDIC
-The way Unicode is handled on EBCDIC platforms is still rather
-experimental. On such a platform, references to UTF-8 encoding in this
-document and elsewhere should be read as meaning UTF-EBCDIC as
-specified in Unicode Technical Report 16 unless ASCII vs EBCDIC issues
+The way Unicode is handled on EBCDIC platforms is still
+experimental. On such platforms, references to UTF-8 encoding in this
+document and elsewhere should be read as meaning the UTF-EBCDIC
+specified in Unicode Technical Report 16, unless ASCII vs. EBCDIC issues
are specifically discussed. There is no C<utfebcdic> pragma or
-":utfebcdic" layer, rather, "utf8" and ":utf8" are re-used to mean
+":utfebcdic" layer; rather, "utf8" and ":utf8" are reused to mean
the platform's "natural" 8-bit encoding of Unicode. See L<perlebcdic>
for more discussion of the issues.
=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 *
+
+You can enable automatic UTF-8-ification of your standard file
+handles, default C<open()> layer, and C<@ARGV> by using either
+the C<-C> command line switch or the C<PERL_UNICODE> environment
+variable, see L<perlrun> for the documentation of the C<-C> switch.
+
+=item *
+
+Perl tries really hard to work both with Unicode and the old
+byte-oriented world. Most often this is nice, but sometimes Perl's
+straddling of the proverbial fence causes problems. Here's an example
+of how things can go wrong. A locale can define a code point to be
+anything it wants. It could make 'A' into a control character, for example.
+But strings encoded in utf8 always have Unicode semantics, so an 'A' in
+such a string is always an uppercase letter, never a control, no matter
+what the locale says it should be.
+
+=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 *
-If your locale environment variables (LANGUAGE, LC_ALL, LC_CTYPE, LANG)
-contain the strings 'UTF-8' or 'UTF8' (case-insensitive matching),
-the default encoding of your STDIN, STDOUT, and STDERR, and of
-B<any subsequent file open>, is UTF-8.
+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 *
-Perl tries really hard to work both with Unicode and the old byte
-oriented world: most often this is nice, but sometimes this causes
-problems.
+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 *
+
+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 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 following C APIs useful (see perlapi for details):
+If you want to handle Perl Unicode in XS extensions, you may find the
+following C APIs useful. See also L<perlguts/"Unicode Support"> for an
+explanation about Unicode at the XS level, and L<perlapi> for the API
+details.
=over 4
=item *
-DO_UTF8(sv) returns true if the UTF8 flag is on and the bytes pragma
-is not in effect. SvUTF8(sv) returns true is the UTF8 flag is on, the
-bytes pragma is ignored. The 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 even are any characters in the scalar.
-What the UTF8 flag means is that the sequence of octets in the
-representation of the scalar is the sequence of UTF-8 encoded
-code points of the characters of a string. The UTF8 flag being
-off means that each octet in this representation encodes a single
-character with codepoint 0..255 within the string. Perl's Unicode
-model is not to use UTF-8 until it's really necessary.
+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 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
+in the scalar. What the C<UTF8> flag means is that the sequence of
+octets in the representation of the scalar is the sequence of UTF-8
+encoded code points of the characters of a string. The C<UTF8> flag
+being off means that each octet in this representation encodes a
+single character with code point 0..255 within the string. Perl's
+Unicode model is not to use UTF-8 until it is absolutely necessary.
=item *
-uvuni_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.
+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. It works appropriately on EBCDIC machines.
=item *
-utf8_to_uvuni(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).
+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. It works appropriately on EBCDIC machines.
=item *
-utf8_length(start, end) returns the length of the UTF-8 encoded buffer
-in characters. sv_len_utf8(sv) returns the length of the UTF-8 encoded
+C<utf8_length(start, end)> returns the length of the UTF-8 encoded buffer
+in characters. C<sv_len_utf8(sv)> returns the length of the UTF-8 encoded
scalar.
=item *
-sv_utf8_upgrade(sv) converts the string of the scalar to its UTF-8
-encoded form. sv_utf8_downgrade(sv) does the opposite (if possible).
-sv_utf8_encode(sv) is like sv_utf8_upgrade but the UTF8 flag does not
-get turned on. sv_utf8_decode() does the opposite of sv_utf8_encode().
-Note that none of these are to be used as general purpose encoding/decoding
-interfaces: use Encode for that. sv_utf8_upgrade() is affected by the
-encoding pragma, but sv_utf8_downgrade() is not (since the encoding
-pragma is designed to be a one-way street).
+C<sv_utf8_upgrade(sv)> converts the string of the scalar to its UTF-8
+encoded form. C<sv_utf8_downgrade(sv)> does the opposite, if
+possible. C<sv_utf8_encode(sv)> is like sv_utf8_upgrade except that
+it does not set the C<UTF8> flag. C<sv_utf8_decode()> does the
+opposite of C<sv_utf8_encode()>. Note that none of these are to be
+used as general-purpose encoding or decoding interfaces: C<use Encode>
+for that. C<sv_utf8_upgrade()> is affected by the encoding pragma
+but C<sv_utf8_downgrade()> is not (since the encoding pragma is
+designed to be a one-way street).
=item *
-is_utf8_char(s) returns true if the pointer points to a valid UTF-8
+C<is_utf8_char(s)> returns true if the pointer points to a valid UTF-8
character.
=item *
-is_utf8_string(buf, len) returns true if the len bytes of the buffer
+C<is_utf8_string(buf, len)> returns true if C<len> bytes of the buffer
are valid UTF-8.
=item *
-UTF8SKIP(buf) will return the number of bytes in the UTF-8 encoded
-character in the buffer. UNISKIP(chr) will return the number of bytes
-required to UTF-8-encode the Unicode character code point. UTF8SKIP()
+C<UTF8SKIP(buf)> will return the number of bytes in the UTF-8 encoded
+character in the buffer. C<UNISKIP(chr)> will return the number of bytes
+required to UTF-8-encode the Unicode character code point. C<UTF8SKIP()>
is useful for example for iterating over the characters of a UTF-8
-encoded buffer; UNISKIP() is useful for example in computing
+encoded buffer; C<UNISKIP()> is useful, for example, in computing
the size required for a UTF-8 encoded buffer.
=item *
-utf8_distance(a, b) will tell the distance in characters between the
+C<utf8_distance(a, b)> will tell the distance in characters between the
two pointers pointing to the same UTF-8 encoded buffer.
=item *
-utf8_hop(s, off) will return a pointer to an 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: utf8_hop()
-will merrily run off the end or the beginning if told to do so.
+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
+buffer if told to do so.
=item *
-pv_uni_display(dsv, spv, len, pvlim, flags) and sv_uni_display(dsv,
-ssv, pvlim, flags) are useful for debug output of Unicode strings and
-scalars. By default they are useful only for debug: they display
-B<all> characters as hexadecimal code points, but with the flags
-UNI_DISPLAY_ISPRINT and UNI_DISPLAY_BACKSLASH you can make the output
-more readable.
+C<pv_uni_display(dsv, spv, len, pvlim, flags)> and
+C<sv_uni_display(dsv, ssv, pvlim, flags)> are useful for debugging the
+output of Unicode strings and scalars. By default they are useful
+only for debugging--they display B<all> characters as hexadecimal code
+points--but with the flags C<UNI_DISPLAY_ISPRINT>,
+C<UNI_DISPLAY_BACKSLASH>, and C<UNI_DISPLAY_QQ> you can make the
+output more readable.
=item *
-ibcmp_utf8(s1, pe1, u1, 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 memEQ() and memNE()
-as usual.)
+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, 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
+C<\$Config{privlib}>/F<unicore>. (C<\%Config> is available from the Config
+module.) Follow the instructions in F<README.perl> in that directory to change
+some of their names, and then run F<make>.
+
+It is even possible to download them 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
+=head2 Interaction with Locales
+
+Use of locales with Unicode data may lead to odd results. Currently,
+Perl attempts to attach 8-bit locale info to characters in the range
+0..255, but this technique is demonstrably incorrect for locales that
+use characters above that range when mapped into Unicode. Perl's
+Unicode support will also tend to run slower. Use of locales with
+Unicode is discouraged.
+
+=head2 Problems with characters in the Latin-1 Supplement range
-Use of locales with Unicode data may lead to odd results. Currently
-there is some attempt to apply 8-bit locale info to characters in the
-range 0..255, but this is demonstrably incorrect for locales that use
-characters above that range when mapped into Unicode. It will also
-tend to run slower. Use of locales with Unicode is discouraged.
+See L</The "Unicode Bug">
-=head2 Interaction with extensions
+=head2 Problems with case-insensitive regular expression matching
-When perl exchanges data with an extension, the extension should be
-able to understand the UTF-8 flag and act accordingly. If the
-extension doesn't know about the flag, the risk is high that it will
-return data that are incorrectly flagged.
+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 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.
So if you're working with Unicode data, consult the documentation of
every module you're using if there are any issues with Unicode data
exchange. If the documentation does not talk about Unicode at all,
suspect the worst and probably look at the source to learn how the
-module is implemented. Modules written completely in perl shouldn't
+module is implemented. Modules written completely in Perl shouldn't
cause problems. Modules that directly or indirectly access code written
in other programming languages are at risk.
-For affected functions the simple strategy to avoid data corruption is
+For affected functions, the simple strategy to avoid data corruption is
to always make the encoding of the exchanged data explicit. Choose an
-encoding you know the extension can handle. Convert arguments passed
+encoding that you know the extension can handle. Convert arguments passed
to the extensions to that encoding and convert results back from that
encoding. Write wrapper functions that do the conversions for you, so
you can later change the functions when the extension catches up.
-To provide an example let's say the popular Foo::Bar::escape_html
+To provide an example, let's say the popular Foo::Bar::escape_html
function doesn't deal with Unicode data yet. The wrapper function
would convert the argument to raw UTF-8 and convert the result back to
-perl's internal representation like so:
+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 {
the documentation of your extensions, they can make the transition to
Unicode data much easier.
-=head2 speed
+=head2 Speed
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 and you
-should carefully avoid to use these functions within tight loops. For
-example if you want to iterate over characters, it is infinitely
-better to split into an array than to use 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)
-
-You see, the algorithm based on substr() was faster with byte encoded
-data but it is pathologically slow 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
+
+Perl 5.8 has a different Unicode model from 5.6. In 5.6 the programmer
+was required to use the C<utf8> pragma to declare that a given scope
+expected to deal with Unicode data and had to make sure that only
+Unicode data were reaching that scope. If you have code that is
+working with 5.6, you will need some of the following adjustments to
+your code. The examples are written such that the code will continue
+to work under 5.6, so you should be safe to try them out.
+
+=over 4
+
+=item *
+
+A filehandle that should read or write UTF-8
+
+ if ($] > 5.007) {
+ binmode $fh, ":encoding(utf8)";
+ }
+
+=item *
+
+A scalar that is going to be passed to some extension
+
+Be it Compress::Zlib, Apache::Request or any extension that has no
+mention of Unicode in the manpage, you need to make sure that the
+UTF8 flag is stripped off. Note that at the time of this writing
+(October 2002) the mentioned modules are not UTF-8-aware. Please
+check the documentation to verify if this is still true.
+
+ if ($] > 5.007) {
+ require Encode;
+ $val = Encode::encode_utf8($val); # make octets
+ }
+
+=item *
+
+A scalar we got back from an extension
+
+If you believe the scalar comes back as UTF-8, you will most likely
+want the UTF8 flag restored:
+
+ if ($] > 5.007) {
+ require Encode;
+ $val = Encode::decode_utf8($val);
+ }
+
+=item *
+
+Same thing, if you are really sure it is UTF-8
+
+ if ($] > 5.007) {
+ require Encode;
+ Encode::_utf8_on($val);
+ }
+
+=item *
+
+A wrapper for fetchrow_array and fetchrow_hashref
+
+When the database contains only UTF-8, a wrapper function or method is
+a convenient way to replace all your fetchrow_array and
+fetchrow_hashref calls. A wrapper function will also make it easier to
+adapt to future enhancements in your database driver. Note that at the
+time of this writing (October 2002), the DBI has no standardized way
+to deal with UTF-8 data. Please check the documentation to verify if
+that is still true.
+
+ sub fetchrow {
+ # $what is one of fetchrow_{array,hashref}
+ my($self, $sth, $what) = @_;
+ if ($] < 5.007) {
+ return $sth->$what;
+ } else {
+ require Encode;
+ if (wantarray) {
+ my @arr = $sth->$what;
+ for (@arr) {
+ defined && /[^\000-\177]/ && Encode::_utf8_on($_);
+ }
+ return @arr;
+ } else {
+ my $ret = $sth->$what;
+ if (ref $ret) {
+ for my $k (keys %$ret) {
+ defined
+ && /[^\000-\177]/
+ && Encode::_utf8_on($_) for $ret->{$k};
+ }
+ return $ret;
+ } else {
+ defined && /[^\000-\177]/ && Encode::_utf8_on($_) for $ret;
+ return $ret;
+ }
+ }
+ }
+ }
+
+
+=item *
+
+A large scalar that you know can only contain ASCII
+
+Scalars that contain only ASCII and are marked as UTF-8 are sometimes
+a drag to your program. If you recognize such a situation, just remove
+the UTF8 flag:
+
+ utf8::downgrade($val) if $] > 5.007;
+
+=back
=head1 SEE ALSO
-L<perluniintro>, L<encoding>, L<Encode>, L<open>, L<utf8>, L<bytes>,
-L<perlretut>, L<perlvar/"${^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
https://perl5.git.perl.org / perl5.git / blobdiff