from cover to cover, Perl does support many Unicode features.
People who want to learn to use Unicode in Perl, should probably read
-L<the Perl Unicode tutorial, perlunitut|perlunitut>, before reading
+the L<Perl Unicode tutorial, perlunitut|perlunitut> and
+L<perluniintro>, before reading
this reference document.
+Also, the use of Unicode may present security issues that aren't obvious.
+Read L<Unicode Security Considerations|http://www.unicode.org/reports/tr36>.
+
=over 4
+=item Safest if you C<use feature 'unicode_strings'>
+
+In order to preserve backward compatibility, Perl does not turn
+on full internal Unicode support unless the pragma
+C<use feature 'unicode_strings'> is specified. (This is automatically
+selected if you use C<use 5.012> or higher.) Failure to do this can
+trigger unexpected surprises. See L</The "Unicode Bug"> below.
+
+This pragma doesn't affect I/O. Nor does it change the internal
+representation of strings, only their interpretation. There are still
+several places where Unicode isn't fully supported, such as in
+filenames.
+
=item Input and Output Layers
Perl knows when a filehandle uses Perl's internal Unicode encodings
(UTF-8, or UTF-EBCDIC if in EBCDIC) if the filehandle is opened with
-the ":utf8" layer. Other encodings can be converted to Perl's
+the C<: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>.
+C<:encoding(...)> layer. See L<open>.
To indicate that Perl source itself is in UTF-8, use C<use utf8;>.
-=item Regular Expressions
-
-The regular expression compiler produces polymorphic opcodes. That is,
-the pattern adapts to the data and automatically switches to the Unicode
-character scheme when presented with data that is internally encoded in
-UTF-8 -- or instead uses a traditional byte scheme when presented with
-byte data.
-
=item C<use utf8> still needed to enable UTF-8/UTF-EBCDIC in scripts
As a compatibility measure, the C<use utf8> pragma must be explicitly
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
+=item C<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
+If a Perl script begins marked with the Unicode C<BOM> (UTF-16LE, UTF16-BE,
+or UTF-8), or if the script looks like non-C<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
+(C<BOM>less UTF-8 cannot be effectively recognized or differentiated from
ISO 8859-1 or other eight-bit encodings.)
=item C<use encoding> needed to upgrade non-Latin-1 byte strings
=head2 Byte and Character Semantics
-Beginning with version 5.6, Perl uses logically-wide characters to
-represent strings internally.
-
-In future, Perl-level operations will be expected to work with
-characters rather than bytes.
-
-However, as an interim compatibility measure, Perl aims to
-provide a safe migration path from byte semantics to character
-semantics for programs. For operations where Perl can unambiguously
-decide that the input data are characters, Perl switches to
-character semantics. For operations where this determination cannot
-be made without additional information from the user, Perl decides in
-favor of compatibility and chooses to use byte semantics.
-
-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
+Perl uses logically-wide characters to represent strings internally.
+
+Starting in Perl 5.14, Perl-level operations work with
+characters rather than bytes within the scope of a
+C<L<use feature 'unicode_strings'|feature>> (or equivalently
+C<use 5.012> or higher). (This is not true if bytes have been
+explicitly requested by C<L<use bytes|bytes>>, nor necessarily true
+for interactions with the platform's operating system.)
+
+For earlier Perls, and when C<unicode_strings> is not in effect, Perl
+provides a fairly safe environment that can handle both types of
+semantics in programs. For operations where Perl can unambiguously
+decide that the input data are characters, Perl switches to character
+semantics. For operations where this determination cannot be made
+without additional information from the user, Perl decides in favor of
+compatibility and chooses to use byte semantics.
+
+When C<use locale> (but not C<use locale ':not_characters'>) is in
+effect, Perl uses the semantics associated with the current locale.
+(C<use locale> overrides C<use feature 'unicode_strings'> in the same scope;
+while C<use locale ':not_characters'> effectively also selects
+C<use feature 'unicode_strings'> in its scope; see L<perllocale>.)
+Otherwise, Perl uses the platform's native
+byte semantics for characters whose code points are less than 256, and
+Unicode semantics for those greater than 255. That means that non-ASCII
+characters are undefined except for their
ordinal numbers. This means that none have case (upper and lower), nor are any
a member of character classes, like C<[:alpha:]> or C<\w>. (But all do belong
to the C<\W> class or the Perl regular expression extension C<[:^alpha:]>.)
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),
+external programs, from information provided by the system (such as C<%ENV>),
or from literals and constants in the source text.
-The C<bytes> pragma will always, regardless of platform, force byte
-semantics in a particular lexical scope. See L<bytes>.
-
-The C<use feature 'unicode_strings'> pragma is intended to always, regardless
-of platform, force Unicode semantics in a particular lexical scope. In
-release 5.12, it is partially implemented, applying only to case changes.
-See L</The "Unicode Bug"> below.
-
The C<utf8> pragma is primarily a compatibility device that enables
recognition of UTF-(8|EBCDIC) in literals encountered by the parser.
Note that this pragma is only required while Perl defaults to byte
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
+character semantics. This can cause surprises: See L</BUGS>, below.
+You can choose to be warned when this happens. See C<L<encoding::warnings>>.
Under character semantics, many operations that formerly operated on
bytes now operate on characters. A character in Perl is
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.)
+(The former requires a C<BOM> or C<use utf8>, the latter requires a C<BOM>.)
-Unicode characters can also be added to a string by using the C<\x{...}>
+Unicode characters can also be added to a string by using the C<\N{U+...}>
notation. The Unicode code for the desired character, in hexadecimal,
-should be placed in the braces. For instance, a smiley face is
-C<\x{263A}>. This encoding scheme works for all characters, but
-for characters under 0x100, note that Perl may use an 8 bit encoding
-internally, for optimization and/or backward compatibility.
+should be placed in the braces, after the C<U>. For instance, a smiley face is
+C<\N{U+263A}>.
-Additionally, if you
+Alternatively, you can use the C<\x{...}> notation for characters C<0x100> and
+above. For characters below C<0x100> you may get byte semantics instead of
+character semantics; see L</The "Unicode Bug">. On EBCDIC machines there is
+the additional problem that the value for such characters gives the EBCDIC
+character rather than the Unicode one, thus it is more portable to use
+C<\N{U+...}> instead.
- use charnames ':full';
+Additionally, you can use the C<\N{...}> notation and put the official
+Unicode character name within the braces, such as
+C<\N{WHITE SMILING FACE}>. This automatically loads the L<charnames>
+module with the C<:full> and C<:short> options. If you prefer different
+options for this module, you can instead, before the C<\N{...}>,
+explicitly load it with your desired options; for example,
-you can use the C<\N{...}> notation and put the official Unicode
-character name within the braces, such as C<\N{WHITE SMILING FACE}>.
+ use charnames ':loose';
=item *
=item *
-Regular expressions match characters instead of bytes. "." matches
+Regular expressions match characters instead of bytes. C<"."> matches
a character instead of a byte.
=item *
-Character classes in regular expressions match characters instead of
+Bracketed character classes in regular expressions match characters instead of
bytes and match against the character properties specified in the
Unicode properties database. C<\w> can be used to match a Japanese
ideograph, for instance.
=item *
-Named Unicode properties, scripts, and block ranges may be used like
-character classes via the C<\p{}> "matches property" construct and
+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.
=item *
-You can define your own mappings to be used in lc(),
-lcfirst(), uc(), and ucfirst() (or their string-inlined versions).
-See L</"User-Defined Case Mappings"> for more details.
+There is a CPAN module, C<L<Unicode::Casing>>, which allows you to define
+your own mappings to be used in C<lc()>, C<lcfirst()>, C<uc()>,
+C<ucfirst()>, and C<fc> (or their double-quoted string inlined
+versions such as C<\U>).
+(Prior to Perl 5.16, this functionality was partially provided
+in the Perl core, but suffered from a number of insurmountable
+drawbacks, so the CPAN module was written instead.)
=back
=head2 Unicode Character Properties
-Most Unicode character properties are accessible by using regular expressions.
-They are used like character classes via the C<\p{}> "matches property"
-construct and the C<\P{}> negation, "doesn't match property".
-
-For instance, C<\p{Uppercase}> matches any 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 properties, so C<\p{L}> is equivalent to C<\pL>.
-
-More formally, C<\p{Uppercase}> matches any 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, I<etc.>). This is done, as in the examples above, by having the
+(The only time that Perl considers a sequence of individual code
+points as a single logical character is in the C<\X> construct, already
+mentioned above. Therefore "character" in this discussion means a single
+Unicode code point.)
+
+Very nearly all Unicode character properties are accessible through
+regular expressions by using the C<\p{}> "matches property" construct
+and the C<\P{}> "doesn't match property" for its negation.
+
+For instance, C<\p{Uppercase}> matches any single character with the Unicode
+C<"Uppercase"> property, while C<\p{L}> matches any character with a
+C<General_Category> of C<"L"> (letter) property (see
+L</General_Category> below). 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
+C<Uppercase> property value is C<True>, and C<\P{Uppercase}> matches any character
+whose C<Uppercase> property value is C<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 C<True> and C<False>. For example, the
+C<Bidi_Class> property (see L</"Bidirectional Character Types"> below),
+can take on several different
+values, such as C<Left>, C<Right>, C<Whitespace>, and others. To match these, one needs
+to specify both the property name (C<Bidi_Class>), AND the value being
+matched against
+(C<Left>, C<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
+of C<\p{I<property>=I<value>}> or C<\p{I<property>:I<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,
+prefer): a short one that is easier to type and a longer one that is more
+descriptive and hence easier to understand. Thus the C<"L"> and
+C<"Letter"> properties above are equivalent and can be used
+interchangeably. Likewise, C<"Upper"> is a synonym for C<"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, C<"True"> has 3 synonyms: C<"T">,
+C<"Yes">, and C<"Y">; and C<"False"> has correspondingly C<"F">,
+C<"No">, and C<"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 C<L</General_Category>> property, C<"L"> means
+C<"Letter">, but for the L<C<Bidi_Class>|/Bidirectional Character Types>
+property, C<"L"> means C<"Left">. A complete list of properties and
+synonyms is in L<perluniprops>.
+
+Upper/lower case differences in property names and values are irrelevant;
thus C<\p{Upper}> means the same thing as C<\p{upper}> or even C<\p{UpPeR}>.
Similarly, you can add or subtract underscores anywhere in the middle of a
word, so that these are also equivalent to C<\p{U_p_p_e_r}>. And white space
is irrelevant adjacent to non-word characters, such as the braces and the equals
-or colon separators so C<\p{ Upper }> and C<\p{ Upper_case : Y }> are
-equivalent to these as well. In fact, in most cases, white space and even
-hyphens can be added or deleted anywhere. So even C<\p{ Up-per case = Yes}> is
+or colon separators, so C<\p{ Upper }> and C<\p{ Upper_case : Y }> are
+equivalent to these as well. In fact, white space and even
+hyphens can usually be added or deleted anywhere. So even C<\p{ Up-per case = Yes}> is
equivalent. All this is called "loose-matching" by Unicode. The few places
-where stricter matching is employed is in the middle of numbers, and the Perl
+where stricter matching is used is in the middle of numbers, and in the Perl
extension properties that begin or end with an underscore. Stricter matching
-cares about white space (except adjacent to the non-word characters) and
+cares about white space (except adjacent to non-word characters),
hyphens, and non-interior underscores.
You can also use negation in both C<\p{}> and C<\P{}> by introducing a caret
-(^) between the first brace and the property name: C<\p{^Tamil}> is
+(C<^>) between the first brace and the property name: C<\p{^Tamil}> is
equal to C<\P{Tamil}>.
+Almost all properties are immune to case-insensitive matching. That is,
+adding a C</i> regular expression modifier does not change what they
+match. There are two sets that are affected.
+The first set is
+C<Uppercase_Letter>,
+C<Lowercase_Letter>,
+and C<Titlecase_Letter>,
+all of which match C<Cased_Letter> under C</i> matching.
+And the second set is
+C<Uppercase>,
+C<Lowercase>,
+and C<Titlecase>,
+all of which match C<Cased> under C</i> matching.
+This set also includes its subsets C<PosixUpper> and C<PosixLower> both
+of which under C</i> match C<PosixAlpha>.
+(The difference between these sets is that some things, such as Roman
+numerals, come in both upper and lower case so they are C<Cased>, but aren't considered
+letters, so they aren't C<Cased_Letter>s.)
+
+See L</Beyond Unicode code points> for special considerations when
+matching Unicode properties against non-Unicode code points.
+
=head3 B<General_Category>
Every Unicode character is assigned a general category, which is the "most
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:
+Here are the short and long forms of the values the C<General Category> property
+can have:
Short Long
Zp Paragraph_Separator
C Other
- Cc Control (also Cntrl)
+ Cc Control (also Cntrl)
Cf Format
- Cs Surrogate (not usable)
+ Cs Surrogate
Co Private_Use
Cn Unassigned
Single-letter properties match all characters in any of the
two-letter sub-properties starting with the same letter.
-C<LC> and C<L&> are special cases, which are aliases for the set of
-C<Ll>, C<Lu>, and C<Lt>.
-
-Because Perl hides the need for the user to understand the internal
-representation of Unicode characters, there is no need to implement
-the somewhat messy concept of surrogates. C<Cs> is therefore not
-supported.
+C<LC> and C<L&> are special: both are aliases for the set consisting of everything matched by C<Ll>, C<Lu>, and C<Lt>.
=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:
+Because scripts differ in their directionality (Hebrew and Arabic are
+written right to left, for example) Unicode supplies a C<Bidi_Class> property.
+Some of the values this property can have are:
- Property Meaning
+ Value Meaning
L Left-to-Right
LRE Left-to-Right Embedding
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.
+written right to left. Unlike the
+C<L</General_Category>> property, this
+property can have more values added in a future Unicode release. Those
+listed above comprised the complete set for many Unicode releases, but
+others were added in Unicode 6.3; you can always find what the
+current ones are in in L<perluniprops>. And
+L<http://www.unicode.org/reports/tr9/> describes how to use them.
=head3 B<Scripts>
-The world's languages are written in a number of scripts. This sentence
+The world's languages are written in many different scripts. This sentence
(unless you're reading it in translation) is written in Latin, while Russian is
-written in Cyrllic, and Greek is written in, well, Greek; Japanese mainly in
+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 can be matched 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}>.
+The Unicode Script and Script_Extensions properties give what script a
+given character is in. Either property can be specified with the
+compound form like
+C<\p{Script=Hebrew}> (short: C<\p{sc=hebr}>), or
+C<\p{Script_Extensions=Javanese}> (short: C<\p{scx=java}>).
+In addition, Perl furnishes shortcuts for all
+C<Script> property names. You can omit everything up through the equals
+(or colon), and simply write C<\p{Latin}> or C<\P{Cyrillic}>.
+(This is not true for C<Script_Extensions>, which is required to be
+written in the compound form.)
+
+The difference between these two properties involves characters that are
+used in multiple scripts. For example the digits '0' through '9' are
+used in many parts of the world. These are placed in a script named
+C<Common>. Other characters are used in just a few scripts. For
+example, the C<"KATAKANA-HIRAGANA DOUBLE HYPHEN"> is used in both Japanese
+scripts, Katakana and Hiragana, but nowhere else. The C<Script>
+property places all characters that are used in multiple scripts in the
+C<Common> script, while the C<Script_Extensions> property places those
+that are used in only a few scripts into each of those scripts; while
+still using C<Common> for those used in many scripts. Thus both these
+match:
+
+ "0" =~ /\p{sc=Common}/ # Matches
+ "0" =~ /\p{scx=Common}/ # Matches
+
+and only the first of these match:
+
+ "\N{KATAKANA-HIRAGANA DOUBLE HYPHEN}" =~ /\p{sc=Common} # Matches
+ "\N{KATAKANA-HIRAGANA DOUBLE HYPHEN}" =~ /\p{scx=Common} # No match
+
+And only the last two of these match:
+
+ "\N{KATAKANA-HIRAGANA DOUBLE HYPHEN}" =~ /\p{sc=Hiragana} # No match
+ "\N{KATAKANA-HIRAGANA DOUBLE HYPHEN}" =~ /\p{sc=Katakana} # No match
+ "\N{KATAKANA-HIRAGANA DOUBLE HYPHEN}" =~ /\p{scx=Hiragana} # Matches
+ "\N{KATAKANA-HIRAGANA DOUBLE HYPHEN}" =~ /\p{scx=Katakana} # Matches
+
+C<Script_Extensions> is thus an improved C<Script>, in which there are
+fewer characters in the C<Common> script, and correspondingly more in
+other scripts. It is new in Unicode version 6.0, and its data are likely
+to change significantly in later releases, as things get sorted out.
+
+(Actually, besides C<Common>, the C<Inherited> script, contains
+characters that are used in multiple scripts. These are modifier
+characters which modify other characters, and inherit the script value
+of the controlling character. Some of these are used in many scripts,
+and so go into C<Inherited> in both C<Script> and C<Script_Extensions>.
+Others are used in just a few scripts, so are in C<Inherited> in
+C<Script>, but not in C<Script_Extensions>.)
+
+It is worth stressing that there are several different sets of digits in
+Unicode that are equivalent to 0-9 and are matchable by C<\d> in a
+regular expression. If they are used in a single language only, they
+are in that language's C<Script> and C<Script_Extension>. If they are
+used in more than one script, they will be in C<sc=Common>, but only
+if they are used in many scripts should they be in C<scx=Common>.
A complete list of scripts and their shortcuts is in L<perluniprops>.
-=head3 B<Use of "Is" Prefix>
+=head3 B<Use of the C<"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
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", I<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.
+characters with consecutive ordinal values. For example, the C<"Basic Latin">
+block is all characters whose ordinals are between 0 and 127, inclusive; in
+other words, the ASCII characters. The C<"Latin"> script contains some letters
+from this as well as several other blocks, like C<"Latin-1 Supplement">,
+C<"Latin Extended-A">, etc., but it does not contain all the characters from
+those blocks. It does not, for example, contain the digits 0-9, because
+those digits are shared across many scripts, and hence are in the
+C<Common> script.
For more about scripts versus blocks, see UAX#24 "Unicode Script Property":
L<http://www.unicode.org/reports/tr24>
-The 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.
+The C<Script> or C<Script_Extensions> properties are likely to be the
+ones you want to use when processing
+natural language; the C<Block> property may occasionally be useful in working
+with the nuts and bolts of Unicode.
Block names are matched in the compound form, like C<\p{Block: Arrows}> or
-C<\p{Blk=Hebrew}>. Unlike most other properties only a few block names have a
+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
=item 2
-It is unstable. A new version of Unicode may pre-empt the current meaning by
+It is unstable. A new version of Unicode may preempt the current meaning by
creating a property with the same name. There was a time in very early Unicode
releases when C<\p{Hebrew}> would have matched the I<block> Hebrew; now it
doesn't.
=back
-Some people 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).
+Some people prefer to always use C<\p{Block: foo}> and C<\p{Script: bar}>
+instead of the shortcuts, whether for clarity, because they can't remember the
+difference between 'In' and 'Is' anyway, or they aren't confident that those who
+eventually will read their code will know that difference.
A complete list of blocks and their shortcuts is in L<perluniprops>.
A complete list is in L<perluniprops>.
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
+properties are Perl extensions. Most of these are just synonyms for the
+Unicode ones, but some are genuine extensions, including several that are in
the compound form. And quite a few of these are actually recommended by Unicode
(in L<http://www.unicode.org/reports/tr18>).
-This section gives some details on all the extensions that aren't synonyms for
-compound-form Unicode properties (for those, you'll have to refer to the
+This section gives some details on all extensions that aren't just
+synonyms for compound-form Unicode properties
+(for those properties, you'll have to refer to the
L<Unicode Standard|http://www.unicode.org/reports/tr44>.
=over
=item B<C<\p{All}>>
-This matches any of the 1_114_112 Unicode code points. It is a synonym for
-C<\p{Any}>.
+This matches every possible code point. It is equivalent to C<qr/./s>.
+Unlike all the other non-user-defined C<\p{}> property matches, no
+warning is ever generated if this is property is matched against a
+non-Unicode code point (see L</Beyond Unicode code points> below).
=item B<C<\p{Alnum}>>
=item B<C<\p{Any}>>
-This matches any of the 1_114_112 Unicode code points. It is a synonym for
-C<\p{All}>.
+This matches any of the 1_114_112 Unicode code points. It is a synonym
+for C<\p{Unicode}>.
+
+=item B<C<\p{ASCII}>>
+
+This matches any of the 128 characters in the US-ASCII character set,
+which is a subset of Unicode.
=item B<C<\p{Assigned}>>
-This matches any assigned code point; that is, any code point whose general
-category is not Unassigned (or equivalently, not Cn).
+This matches any assigned code point; that is, any code point whose L<general
+category|/General_Category> is not C<Unassigned> (or equivalently, not C<Cn>).
=item B<C<\p{Blank}>>
Matches a character that has a non-canonical decomposition.
-To understand the use of this rarely used property=value combination, it is
+To understand the use of this rarely used I<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, I<etc.> There are many
+I<etc.>, above, below, to one side or the other, etc. There are many
possibilities among the world's languages. The number of combinations is
astronomical, and if there were a character for each combination, it would
soon exhaust Unicode's more than a million possible characters. So Unicode
took a different approach: there is a character for the base H, and a
-character for each of the possible marks, and they can be combined variously
+character for each of the possible marks, and these can be variously combined
to get a final logical character. So a logical character--what appears to be a
single character--can be a sequence of more than one individual characters.
-This is called an "extended grapheme cluster". (Perl furnishes the C<\X>
-construct to match such sequences.)
+This is called an "extended grapheme cluster"; Perl furnishes the C<\X>
+regular expression construct to match such sequences.
But Unicode's intent is to unify the existing character set standards and
-practices, and a number of pre-existing standards have single characters that
+practices, and several pre-existing standards have single characters that
mean the same thing as some of these combinations. An example is ISO-8859-1,
-which has quite a few of these in the Latin-1 range, an example being "LATIN
-CAPITAL LETTER E WITH ACUTE". Because this character was in this pre-existing
+which has quite a few of these in the Latin-1 range, an example being C<"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".
+by Unicode to be equivalent to the sequence consisting of the character
+C<"LATIN CAPITAL LETTER E"> followed by the character C<"COMBINING ACUTE ACCENT">.
-"LATIN CAPITAL LETTER E WITH ACUTE" is called a "pre-composed" character, and
-the equivalence with the sequence is called canonical equivalence. All
+C<"LATIN CAPITAL LETTER E WITH ACUTE"> is called a "pre-composed" character, and
+its equivalence with the sequence is called canonical equivalence. All
pre-composed characters are said to have a decomposition (into the equivalent
-sequence) and the decomposition type is also called canonical.
+sequence), and the decomposition type is also called canonical.
However, many more characters have a different type of decomposition, a
"compatible" or "non-canonical" decomposition. The sequences that form these
decompositions are not considered canonically equivalent to the pre-composed
-character. An example, again in the Latin-1 range, is the "SUPERSCRIPT ONE".
-It is kind of like a regular digit 1, but not exactly; its decomposition
+character. An example, again in the Latin-1 range, is the C<"SUPERSCRIPT ONE">.
+It is somewhat like a regular digit 1, but not exactly; its decomposition
into the digit 1 is called a "compatible" decomposition, specifically a
"super" decomposition. There are several such compatibility
decompositions (see L<http://www.unicode.org/reports/tr44>), including one
-called "compat" which means some miscellaneous type of decomposition
-that doesn't fit into the decomposition categories that Unicode has chosen.
+called "compat", which means some miscellaneous type of decomposition
+that doesn't fit into the decomposition categories that Unicode has chosen.
Note that most Unicode characters don't have a decomposition, so their
-decomposition type is "None".
+decomposition type is C<"None">.
-Perl has added the C<Non_Canonical> type, for your convenience, to mean any of
-the compatibility decompositions.
+For your convenience, Perl has added the C<Non_Canonical> decomposition
+type to mean any of the several compatibility decompositions.
=item B<C<\p{Graph}>>
=item B<C<\p{HorizSpace}>>
-This is the same as C<\h> and C<\p{Blank}>: A character that changes the
+This is the same as C<\h> and C<\p{Blank}>: a character that changes the
spacing horizontally.
-=item B<C<\p{In=*}>>
+=item B<C<\p{In=*}>>
This is a synonym for C<\p{Present_In=*}>
=item B<C<\p{PerlSpace}>>
-This is the same as C<\s>, restricted to ASCII, namely C<S<[ \f\n\r\t]>>.
+This is the same as C<\s>, restricted to ASCII, namely C<S<[ \f\n\r\t]>>
+and starting in Perl v5.18, experimentally, a vertical tab.
Mnemonic: Perl's (original) space
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{Posix...}>>
-=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]>.
+There are several of these, which are equivalents using the C<\p{}>
+notation for Posix classes and are described in
+L<perlrecharclass/POSIX Character Classes>.
=item B<C<\p{Present_In: *}>> (Short: C<\p{In=*}>)
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
+For example, C<U+0041> C<"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
+5.1 when it became C<"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
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.
+the same as the Perl C<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
+that the code point has been I<assigned>, but that the meaning of the code point
+has been I<determined>. This is because 66 code points will always be
+unassigned, and so the C<Age> for them is the Unicode version in which the decision
+to make them so was made. For example, C<U+FDD0> is to be permanently
unassigned to a character, and the decision to do that was made in version 3.1,
-so C<\p{Age=3.1}> matches this character and C<\p{Present_In: 3.1}> and up
-matches as well.
+so C<\p{Age=3.1}> matches this character, as also does C<\p{Present_In: 3.1}> and up.
=item B<C<\p{Print}>>
-This matches any character that is graphical or is space, but not a control.
+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.)
+which both the Posix standard and Unicode consider white space.)
+
+=item B<C<\p{Title}>> and B<C<\p{Titlecase}>>
+
+Under case-sensitive matching, these both match the same code points as
+C<\p{General Category=Titlecase_Letter}> (C<\p{gc=lt}>). The difference
+is that under C</i> caseless matching, these match the same as
+C<\p{Cased}>, whereas C<\p{gc=lt}> matches C<\p{Cased_Letter>).
+
+=item B<C<\p{Unicode}>>
+
+This matches any of the 1_114_112 Unicode code points.
+C<\p{Any}>.
=item B<C<\p{VertSpace}>>
=item B<C<\p{Word}>>
-This is the same as C<\w>, including beyond ASCII.
+This is the same as C<\w>, including over 100_000 characters beyond ASCII.
+
+=item B<C<\p{XPosix...}>>
+
+There are several of these, which are the standard Posix classes
+extended to the full Unicode range. They are described in
+L<perlrecharclass/POSIX Character Classes>.
=back
+
=head2 User-Defined Character Properties
You can define your own binary character properties by defining subroutines
-whose names begin with "In" or "Is". The subroutines can be defined in any
+whose names begin with C<"In"> or C<"Is">. (The experimental feature
+L<perlre/(?[ ])> provides an alternative which allows more complex
+definitions.) The subroutines can be defined in any
package. The user-defined properties can be used in the regular expression
-C<\p> and C<\P> constructs; if you are using a user-defined property from a
+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.
+C<\p{}> or C<\P{}> construct.
# assuming property Is_Foreign defined in Lang::
package main; # property package name required
Note that the effect is compile-time and immutable once defined.
+However, the subroutines are passed a single parameter, which is 0 if
+case-sensitive matching is in effect and non-zero if caseless matching
+is in effect. The subroutine may return different values depending on
+the value of the flag, and one set of values will immutably be in effect
+for all case-sensitive matches, and the other set for all case-insensitive
+matches.
+
+Note that if the regular expression is tainted, then Perl will die rather
+than calling the subroutine when the name of the subroutine is
+determined by the tainted data.
The subroutines must return a specially-formatted string, with one
or more newline-separated lines. Each line must be one of the following:
=item *
-A single hexadecimal number denoting a Unicode code point to include.
+A single hexadecimal number denoting a code point to include.
=item *
Two hexadecimal numbers separated by horizontal whitespace (space or
-tabular characters) denoting a range of Unicode code points to include.
+tabular characters) denoting a range of code points to include.
=item *
-Something to include, prefixed by "+": a built-in character
-property (prefixed by "utf8::") or a user-defined character property,
+Something to include, prefixed by C<"+">: a built-in character
+property (prefixed by C<"utf8::">) or a fully qualified (including package
+name) user-defined character property,
to represent all the characters in that property; two hexadecimal code
points for a range; or a single hexadecimal code point.
=item *
-Something to exclude, prefixed by "-": an existing character
-property (prefixed by "utf8::") or a user-defined character property,
+Something to exclude, prefixed by C<"-">: an existing character
+property (prefixed by C<"utf8::">) or a fully qualified (including package
+name) user-defined character property,
to represent all the characters in that property; two hexadecimal code
points for a range; or a single hexadecimal code point.
=item *
-Something to negate, prefixed "!": an existing character
-property (prefixed by "utf8::") or a user-defined character property,
+Something to negate, prefixed C<"!">: an existing character
+property (prefixed by C<"utf8::">) or a fully qualified (including package
+name) user-defined character property,
to represent all the characters in that property; two hexadecimal code
points for a range; or a single hexadecimal code point.
=item *
-Something to intersect with, prefixed by "&": an existing character
-property (prefixed by "utf8::") or a user-defined character property,
+Something to intersect with, prefixed by C<"&">: an existing character
+property (prefixed by C<"utf8::">) or a fully qualified (including package
+name) user-defined character property,
for all the characters except the characters in the property; two
hexadecimal code points for a range; or a single hexadecimal code point.
syllabaries (hiragana and katakana), you can define
sub InKana {
- return <<END;
+ return <<END;
3040\t309F
30A0\t30FF
END
You could also have used the existing block property names:
sub InKana {
- return <<'END';
+ return <<'END';
+utf8::InHiragana
+utf8::InKatakana
END
the non-characters:
sub InKana {
- return <<'END';
+ return <<'END';
+utf8::InHiragana
+utf8::InKatakana
-utf8::IsCn
The negation is useful for defining (surprise!) negated classes.
sub InNotKana {
- return <<'END';
+ return <<'END';
!utf8::InHiragana
-utf8::InKatakana
+utf8::IsCn
END
}
-Intersection is useful for getting the common characters matched by
-two (or more) classes.
+This will match all non-Unicode code points, since every one of them is
+not in Kana. You can use intersection to exclude these, if desired, as
+this modified example shows:
- sub InFooAndBar {
+ sub InNotKana {
return <<'END';
- +main::Foo
- &main::Bar
+ !utf8::InHiragana
+ -utf8::InKatakana
+ +utf8::IsCn
+ &utf8::Any
END
}
-It's important to remember not to use "&" for the first set -- that
-would be intersecting with nothing (resulting in an empty set).
+C<&utf8::Any> must be the last line in the definition.
-=head2 User-Defined Case Mappings
+Intersection is used generally for getting the common characters matched
+by two (or more) classes. It's important to remember not to use C<"&"> for
+the first set; that would be intersecting with nothing, resulting in an
+empty set.
-You can also define your own mappings to be used in the lc(),
-lcfirst(), uc(), and ucfirst() (or their string-inlined versions).
-The principle is similar to that of user-defined character
-properties: to define subroutines
-with names like C<ToLower> (for lc() and lcfirst()), C<ToTitle> (for
-the first character in ucfirst()), and C<ToUpper> (for uc(), and the
-rest of the characters in ucfirst()).
+Unlike non-user-defined C<\p{}> property matches, no warning is ever
+generated if these properties are matched against a non-Unicode code
+point (see L</Beyond Unicode code points> below).
-The string returned by the subroutines needs to be two hexadecimal numbers
-separated by two tabulators: the two numbers being, respectively, the source
-code point and the destination code point. For example:
+=head2 User-Defined Case Mappings (for serious hackers only)
- sub ToUpper {
- return <<END;
- 0061\t\t0041
- END
- }
-
-defines an uc() mapping that causes only the character "a"
-to be mapped to "A"; all other characters will remain unchanged.
-
-(For serious hackers only) The above means 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 mappings in the directory
-C<$Config{privlib}>/F<unicore/To/>. The mapping data is returned as the
-here-document, and the C<utf8::ToSpecFoo> are special exception mappings
-derived from <$Config{privlib}>/F<unicore/SpecialCasing.txt>. The "Digit" and
-"Fold" mappings that one can see in the directory are not directly
-user-accessible, one can use either the C<Unicode::UCD> module, or just match
-case-insensitively (that's when the "Fold" mapping is used).
-
-The mappings will only take effect on scalars that have been marked as having
-Unicode characters, for example by using C<utf8::upgrade()>.
-Old byte-style strings are not affected.
-
-The mappings are in effect for the package they are defined in.
+B<This feature has been removed as of Perl 5.16.>
+The CPAN module C<L<Unicode::Casing>> provides better functionality without
+the drawbacks that this feature had. If you are using a Perl earlier
+than 5.16, this feature was most fully documented in the 5.14 version of
+this pod:
+L<http://perldoc.perl.org/5.14.0/perlunicode.html#User-Defined-Case-Mappings-%28for-serious-hackers-only%29>
=head2 Character Encodings for Input and Output
=head2 Unicode Regular Expression Support Level
-The following list of Unicode support for regular expressions describes
-all the features currently supported. The references to "Level N"
+The following list of Unicode supported features for regular expressions describes
+all features currently directly supported by core Perl. The references to "Level N"
and the section numbers refer to the Unicode Technical Standard #18,
-"Unicode Regular Expressions", version 11, in May 2005.
+"Unicode Regular Expressions", version 13, from August 2008.
=over 4
Level 1 - Basic Unicode Support
- RL1.1 Hex Notation - done [1]
- RL1.2 Properties - done [2][3]
- RL1.2a Compatibility Properties - done [4]
- RL1.3 Subtraction and Intersection - MISSING [5]
- RL1.4 Simple Word Boundaries - done [6]
- RL1.5 Simple Loose Matches - done [7]
- RL1.6 Line Boundaries - MISSING [8]
- RL1.7 Supplementary Code Points - done [9]
-
- [1] \x{...}
- [2] \p{...} \P{...}
- [3] supports not only minimal list, 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.
+ RL1.1 Hex Notation - done [1]
+ RL1.2 Properties - done [2][3]
+ RL1.2a Compatibility Properties - done [4]
+ RL1.3 Subtraction and Intersection - experimental [5]
+ RL1.4 Simple Word Boundaries - done [6]
+ RL1.5 Simple Loose Matches - done [7]
+ RL1.6 Line Boundaries - MISSING [8][9]
+ RL1.7 Supplementary Code Points - done [10]
+
+=over 4
+
+=item [1]
+
+C<\x{...}>
+
+=item [2]
+
+C<\p{...}> C<\P{...}>
+
+=item [3]
+
+supports not only minimal list, but all Unicode character properties (see Unicode Character Properties above)
+
+=item [4]
+
+C<\d> C<\D> C<\s> C<\S> C<\w> C<\W> C<\X> C<[:I<prop>:]> C<[:^I<prop>:]>
+
+=item [5]
+
+The experimental feature in v5.18 C<"(?[...])"> accomplishes this. See
+L<perlre/(?[ ])>. If you don't want to use an experimental feature,
+you can use one of the following:
+
+=over 4
+
+=item * Regular expression look-ahead
+
+You can mimic class subtraction using lookahead.
For example, what UTS#18 might write as
- [{Greek}-[{UNASSIGNED}]]
+ [{Block=Greek}-[{UNASSIGNED}]]
in Perl can be written as:
- (?!\p{Unassigned})\p{InGreekAndCoptic}
- (?=\p{Assigned})\p{InGreekAndCoptic}
+ (?!\p{Unassigned})\p{Block=Greek}
+ (?=\p{Assigned})\p{Block=Greek}
But in this particular example, you probably really want
- \p{GreekAndCoptic}
+ \p{Greek}
which will match assigned characters known to be part of the Greek script.
-Also see the Unicode::Regex::Set module, it does implement the full
-UTS#18 grouping, intersection, union, and removal (subtraction) syntax.
+=item * CPAN module C<L<Unicode::Regex::Set>>
+
+It does implement the full UTS#18 grouping, intersection, union, and
+removal (subtraction) syntax.
+
+=item * L</"User-Defined Character Properties">
-[b] '+' for union, '-' for removal (set-difference), '&' for intersection
-(see L</"User-Defined Character Properties">)
+C<"+"> for union, C<"-"> for removal (set-difference), C<"&"> for intersection
-[c] Try the C<:crlf> layer (see L<PerlIO>).
+=back
+
+=item [6]
+
+C<\b> C<\B>
+
+=item [7]
+
+Note that Perl does Full case-folding in matching (but with bugs), not
+Simple: for example C<U+1F88> is equivalent to C<U+1F00 U+03B9>, instead of
+just C<U+1F80>. This difference matters mainly for certain Greek capital
+letters with certain modifiers: the Full case-folding decomposes the
+letter, while the Simple case-folding would map it to a single
+character.
+
+=item [8]
+
+Should do C<^> and C<$> also on C<U+000B> (C<\v> in C), C<FF> (C<\f>),
+C<CR> (C<\r>), C<CRLF> (C<\r\n>), C<NEL> (C<U+0085>), C<LS> (C<U+2028>),
+and C<PS> (C<U+2029>); should also affect C<E<lt>E<gt>>, C<$.>, and
+script line numbers; should not split lines within C<CRLF> (i.e. there
+is no empty line between C<\r> and C<\n>). For C<CRLF>, try the
+C<:crlf> layer (see L<PerlIO>).
-[d] U+FFFF will currently generate a warning message if 'utf8' warnings are
- enabled
+=item [9]
+
+Linebreaking conformant with L<UAX#14 "Unicode Line Breaking
+Algorithm"|http://www.unicode.org/reports/tr14>
+is available through the C<L<Unicode::LineBreak>> module.
+
+=item [10]
+
+UTF-8/UTF-EBDDIC used in Perl allows not only C<U+10000> to
+C<U+10FFFF> but also beyond C<U+10FFFF>
+
+=back
=item *
Level 2 - Extended Unicode Support
- 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
-
- [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] have \N{...} but neither compute names of CJK Ideographs
- and Hangul Syllables nor use a loose match [e]
+ RL2.1 Canonical Equivalents - MISSING [10][11]
+ RL2.2 Default Grapheme Clusters - MISSING [12]
+ RL2.3 Default Word Boundaries - MISSING [14]
+ RL2.4 Default Loose Matches - MISSING [15]
+ RL2.5 Name Properties - DONE
+ RL2.6 Wildcard Properties - MISSING
-[e] C<\N{...}> allows namespaces (see L<charnames>).
+ [10] see UAX#15 "Unicode Normalization Forms"
+ [11] have Unicode::Normalize but not integrated to regexes
+ [12] have \X but we don't have a "Grapheme Cluster Mode"
+ [14] see UAX#29, Word Boundaries
+ [15] This is covered in Chapter 3.13 (in Unicode 6.0)
=item *
Level 3 - Tailored Support
- RL3.1 Tailored Punctuation - MISSING
- RL3.2 Tailored Grapheme Clusters - MISSING [17][18]
- RL3.3 Tailored Word Boundaries - MISSING
- RL3.4 Tailored Loose Matches - MISSING
- RL3.5 Tailored Ranges - MISSING
- RL3.6 Context Matching - MISSING [19]
- RL3.7 Incremental Matches - MISSING
+ RL3.1 Tailored Punctuation - MISSING
+ RL3.2 Tailored Grapheme Clusters - MISSING [17][18]
+ RL3.3 Tailored Word Boundaries - MISSING
+ RL3.4 Tailored Loose Matches - MISSING
+ RL3.5 Tailored Ranges - MISSING
+ RL3.6 Context Matching - MISSING [19]
+ RL3.7 Incremental Matches - MISSING
( RL3.8 Unicode Set Sharing )
- RL3.9 Possible Match Sets - MISSING
- RL3.10 Folded Matching - MISSING [20]
- RL3.11 Submatchers - MISSING
-
- [17] see UAX#10 "Unicode Collation Algorithms"
- [18] have Unicode::Collate but not integrated to regexes
- [19] have (?<=x) and (?=x), but look-aheads or look-behinds should see
- outside of the target substring
- [20] need insensitive matching for linguistic features other than case;
- for example, hiragana to katakana, wide and narrow, simplified Han
- to traditional Han (see UTR#30 "Character Foldings")
+ RL3.9 Possible Match Sets - MISSING
+ RL3.10 Folded Matching - MISSING [20]
+ RL3.11 Submatchers - MISSING
+
+ [17] see UAX#10 "Unicode Collation Algorithms"
+ [18] have Unicode::Collate but not integrated to regexes
+ [19] have (?<=x) and (?=x), but look-aheads or look-behinds
+ should see outside of the target substring
+ [20] need insensitive matching for linguistic features other
+ than case; for example, hiragana to katakana, wide and
+ narrow, simplified Han to traditional Han (see UTR#30
+ "Character Foldings")
=back
UTF-8
-UTF-8 is a variable-length (1 to 6 bytes, current character allocations
-require 4 bytes), byte-order independent encoding. For ASCII (and we
-really do mean 7-bit ASCII, not another 8-bit encoding), UTF-8 is
-transparent.
+UTF-8 is a variable-length (1 to 4 bytes), byte-order independent
+encoding. For ASCII (and we really do mean 7-bit ASCII, not another
+8-bit encoding), UTF-8 is transparent.
The following table is from Unicode 3.2.
- Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte
+ Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte
- U+0000..U+007F 00..7F
+ U+0000..U+007F 00..7F
U+0080..U+07FF * C2..DF 80..BF
- U+0800..U+0FFF E0 * A0..BF 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+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
+ 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 gaps before several of the byte entries above marked by '*'. These are
+Note the gaps marked by "*" before several of the byte entries above. These are
caused by legal UTF-8 avoiding non-shortest encodings: it is technically
possible to UTF-8-encode a single code point in different ways, but that is
explicitly forbidden, and the shortest possible encoding should always be used
Another way to look at it is via bits:
- Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte
+ Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte
- 0aaaaaaa 0aaaaaaa
- 00000bbbbbaaaaaa 110bbbbb 10aaaaaa
- ccccbbbbbbaaaaaa 1110cccc 10bbbbbb 10aaaaaa
- 00000dddccccccbbbbbbaaaaaa 11110ddd 10cccccc 10bbbbbb 10aaaaaa
+ 0aaaaaaa 0aaaaaaa
+ 00000bbbbbaaaaaa 110bbbbb 10aaaaaa
+ ccccbbbbbbaaaaaa 1110cccc 10bbbbbb 10aaaaaa
+ 00000dddccccccbbbbbbaaaaaa 11110ddd 10cccccc 10bbbbbb 10aaaaaa
-As you can see, the continuation bytes all begin with "10", and the
+As you can see, the continuation bytes all begin with C<"10">, and the
leading bits of the start byte tell how many bytes there are in the
encoded character.
+The original UTF-8 specification allowed up to 6 bytes, to allow
+encoding of numbers up to C<0x7FFF_FFFF>. Perl continues to allow those,
+and has extended that up to 13 bytes to encode code points up to what
+can fit in a 64-bit word. However, Perl will warn if you output any of
+these as being non-portable; and under strict UTF-8 input protocols,
+they are forbidden.
+
+The Unicode non-character code points are also disallowed in UTF-8 in
+"open interchange". See L</Non-character code points>.
+
=item *
UTF-EBCDIC
=item *
-UTF-16, UTF-16BE, UTF-16LE, Surrogates, and BOMs (Byte Order Marks)
+UTF-16, UTF-16BE, UTF-16LE, Surrogates, and C<BOM>s (Byte Order Marks)
The followings items are mostly for reference and general Unicode
knowledge, Perl doesn't use these constructs internally.
-UTF-16 is a 2 or 4 byte encoding. The Unicode code points
-C<U+0000..U+FFFF> are stored in a single 16-bit unit, and the code
+Like UTF-8, UTF-16 is a variable-width encoding, but where
+UTF-8 uses 8-bit code units, UTF-16 uses 16-bit code units.
+All code points occupy either 2 or 4 bytes in UTF-16: code points
+C<U+0000..U+FFFF> are stored in a single 16-bit unit, and code
points C<U+10000..U+10FFFF> in two 16-bit units. The latter case is
using I<surrogates>, the first 16-bit unit being the I<high
surrogate>, and the second being the I<low surrogate>.
surrogates> are the range C<U+D800..U+DBFF> and the I<low surrogates>
are the range C<U+DC00..U+DFFF>. The surrogate encoding is
- $hi = ($uni - 0x10000) / 0x400 + 0xD800;
- $lo = ($uni - 0x10000) % 0x400 + 0xDC00;
+ $hi = ($uni - 0x10000) / 0x400 + 0xD800;
+ $lo = ($uni - 0x10000) % 0x400 + 0xDC00;
and the decoding is
- $uni = 0x10000 + ($hi - 0xD800) * 0x400 + ($lo - 0xDC00);
-
-If you try to generate surrogates (for example by using chr()), you
-will get a warning, if warnings are turned on, because those code
-points are not valid for a Unicode character.
+ $uni = 0x10000 + ($hi - 0xD800) * 0x400 + ($lo - 0xDC00);
Because of the 16-bitness, UTF-16 is byte-order dependent. UTF-16
itself can be used for in-memory computations, but if storage or
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, or
-BOMs, are a solution to this. A special character has been reserved
+C<BOM>s, 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 C<U+FEFF> is the BOM.
+code point C<U+FEFF> is the C<BOM>.
-The trick is that if you read a BOM, you will know the byte order,
+The trick is that if you read a C<BOM>, you will know the byte order,
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
-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
+C<U+FFFE> is not supposed to be in input streams, so the
+sequence of bytes C<0xFF 0xFE> is unambiguously "C<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.)
+format".
+
+Surrogates have no meaning in Unicode outside their use in pairs to
+represent other code points. However, Perl allows them to be
+represented individually internally, for example by saying
+C<chr(0xD801)>, so that all code points, not just those valid for open
+interchange, are
+representable. Unicode does define semantics for them, such as their
+C<L</General_Category>> is C<"Cs">. But because their use is somewhat dangerous,
+Perl will warn (using the warning category C<"surrogate">, which is a
+sub-category of C<"utf8">) if an attempt is made
+to do things like take the lower case of one, or match
+case-insensitively, or to output them. (But don't try this on Perls
+before 5.14.)
=item *
The UTF-32 family is pretty much like the UTF-16 family, expect that
the units are 32-bit, and therefore the surrogate scheme is not
-needed. The BOM signatures will be C<0x00 0x00 0xFE 0xFF> for BE and
-C<0xFF 0xFE 0x00 0x00> for LE.
+needed. UTF-32 is a fixed-width encoding. The C<BOM> signatures are
+C<0x00 0x00 0xFE 0xFF> for BE and C<0xFF 0xFE 0x00 0x00> for LE.
=item *
UCS-2, UCS-4
-Encodings defined by the ISO 10646 standard. UCS-2 is a 16-bit
+Legacy, fixed-width encodings defined by the ISO 10646 standard. UCS-2 is a 16-bit
encoding. Unlike UTF-16, UCS-2 is not extensible beyond C<U+FFFF>,
because it does not use surrogates. UCS-4 is a 32-bit encoding,
-functionally identical to UTF-32.
+functionally identical to UTF-32 (the difference being that
+UCS-4 forbids neither surrogates nor code points larger than C<0x10_FFFF>).
=item *
=back
+=head2 Non-character code points
+
+66 code points are set aside in Unicode as "non-character code points".
+These all have the C<Unassigned> (C<Cn>) C<L</General_Category>>, and
+they never will
+be assigned. These are never supposed to be in legal Unicode input
+streams, so that code can use them as sentinels that can be mixed in
+with character data, and they always will be distinguishable from that data.
+To keep them out of Perl input streams, strict UTF-8 should be
+specified, such as by using the layer C<:encoding('UTF-8')>. The
+non-character code points are the 32 between C<U+FDD0> and C<U+FDEF>, and the
+34 code points C<U+FFFE>, C<U+FFFF>, C<U+1FFFE>, C<U+1FFFF>, ... C<U+10FFFE>, C<U+10FFFF>.
+Some people are under the mistaken impression that these are "illegal",
+but that is not true. An application or cooperating set of applications
+can legally use them at will internally; but these code points are
+"illegal for open interchange". Therefore, Perl will not accept these
+from input streams unless lax rules are being used, and will warn
+(using the warning category C<"nonchar">, which is a sub-category of C<"utf8">) if
+an attempt is made to output them.
+
+=head2 Beyond Unicode code points
+
+The maximum Unicode code point is C<U+10FFFF>, and Unicode only defines
+operations on code points up through that. But Perl works on code
+points up to the maximum permissible unsigned number available on the
+platform. However, Perl will not accept these from input streams unless
+lax rules are being used, and will warn (using the warning category
+C<"non_unicode">, which is a sub-category of C<"utf8">) if any are output.
+
+Since Unicode rules are not defined on these code points, if a
+Unicode-defined operation is done on them, Perl uses what we believe are
+sensible rules, while generally warning, using the C<"non_unicode">
+category. For example, C<uc("\x{11_0000}")> will generate such a
+warning, returning the input parameter as its result, since Perl defines
+the uppercase of every non-Unicode code point to be the code point
+itself. In fact, all the case changing operations, not just
+uppercasing, work this way.
+
+The situation with matching Unicode properties in regular expressions,
+the C<\p{}> and C<\P{}> constructs, against these code points is not as
+clear cut, and how these are handled has changed as we've gained
+experience.
+
+One possibility is to treat any match against these code points as
+undefined. But since Perl doesn't have the concept of a match being
+undefined, it converts this to failing or C<FALSE>. This is almost, but
+not quite, what Perl did from v5.14 (when use of these code points
+became generally reliable) through v5.18. The difference is that Perl
+treated all C<\p{}> matches as failing, but all C<\P{}> matches as
+succeeding.
+
+One problem with this is that it leads to unexpected, and confusting
+results in some cases:
+
+ chr(0x110000) =~ \p{ASCII_Hex_Digit=True} # Failed on <= v5.18
+ chr(0x110000) =~ \p{ASCII_Hex_Digit=False} # Failed! on <= v5.18
+
+That is, it treated both matches as undefined, and converted that to
+false (raising a warning on each). The first case is the expected
+result, but the second is likely counterintuitive: "How could both be
+false when they are complements?" Another problem was that the
+implementation optimized many Unicode property matches down to already
+existing simpler, faster operations, which don't raise the warning. We
+chose to not forgo those optimizations, which help the vast majority of
+matches, just to generate a warning for the unlikely event that an
+above-Unicode code point is being matched against.
+
+As a result of these problems, starting in v5.20, what Perl does is
+to treat non-Unicode code points as just typical unassigned Unicode
+characters, and matches accordingly. (Note: Unicode has atypical
+unassigned code points. For example, it has non-character code points,
+and ones that, when they do get assigned, are destined to be written
+Right-to-left, as Arabic and Hebrew are. Perl assumes that no
+non-Unicode code point has any atypical properties.)
+
+Perl, in most cases, will raise a warning when matching an above-Unicode
+code point against a Unicode property when the result is C<TRUE> for
+C<\p{}>, and C<FALSE> for C<\P{}>. For example:
+
+ chr(0x110000) =~ \p{ASCII_Hex_Digit=True} # Fails, no warning
+ chr(0x110000) =~ \p{ASCII_Hex_Digit=False} # Succeeds, with warning
+
+In both these examples, the character being matched is non-Unicode, so
+Unicode doesn't define how it should match. It clearly isn't an ASCII
+hex digit, so the first example clearly should fail, and so it does,
+with no warning. But it is arguable that the second example should have
+an undefined, hence C<FALSE>, result. So a warning is raised for it.
+
+Thus the warning is raised for many fewer cases than in earlier Perls,
+and only when what the result is could be arguable. It turns out that
+none of the optimizations made by Perl (or are ever likely to be made)
+cause the warning to be skipped, so it solves both problems of Perl's
+earlier approach. The most commonly used property that is affected by
+this change is C<\p{Unassigned}> which is a short form for
+C<\p{General_Category=Unassigned}>. Starting in v5.20, all non-Unicode
+code points are considered C<Unassigned>. In earlier releases the
+matches failed because the result was considered undefined.
+
+The only place where the warning is not raised when it might ought to
+have been is if optimizations cause the whole pattern match to not even
+be attempted. For example, Perl may figure out that for a string to
+match a certain regular expression pattern, the string has to contain
+the substring C<"foobar">. Before attempting the match, Perl may look
+for that substring, and if not found, immediately fail the match without
+actually trying it; so no warning gets generated even if the string
+contains an above-Unicode code point.
+
+This behavior is more "Do what I mean" than in earlier Perls for most
+applications. But it catches fewer issues for code that needs to be
+strictly Unicode compliant. Therefore there is an additional mode of
+operation available to accommodate such code. This mode is enabled if a
+regular expression pattern is compiled within the lexical scope where
+the C<"non_unicode"> warning class has been made fatal, say by:
+
+ use warnings FATAL => "non_unicode"
+
+(see L<perllexwarn>). In this mode of operation, Perl will raise the
+warning for all matches against a non-Unicode code point (not just the
+arguable ones), and it skips the optimizations that might cause the
+warning to not be output. (It currently still won't warn if the match
+isn't even attempted, like in the C<"foobar"> example above.)
+
+In summary, Perl now normally treats non-Unicode code points as typical
+Unicode unassigned code points for regular expression matches, raising a
+warning only when it is arguable what the result should be. However, if
+this warning has been made fatal, it isn't skipped.
+
+There is one exception to all this. C<\p{All}> looks like a Unicode
+property, but it is a Perl extension that is defined to be true for all
+possible code points, Unicode or not, so no warning is ever generated
+when matching this against a non-Unicode code point. (Prior to v5.20,
+it was an exact synonym for C<\p{Any}>, matching code points C<0>
+through C<0x10FFFF>.)
+
=head2 Security Implications of Unicode
Read L<Unicode Security Considerations|http://www.unicode.org/reports/tr36>.
Malformed UTF-8
-Unfortunately, the specification of UTF-8 leaves some room for
+Unfortunately, the original specification of UTF-8 leaves some room for
interpretation of how many bytes of encoded output one should generate
from one input Unicode character. Strictly speaking, the shortest
possible sequence of UTF-8 bytes should be generated,
the receiving end of a UTF-8 connection. Perl always generates the
shortest length UTF-8, and with warnings on, Perl will warn about
non-shortest length UTF-8 along with other malformations, such as the
-surrogates, which are not real Unicode code points.
+surrogates, which are not Unicode code points valid for interchange.
=item *
-Regular expressions behave slightly differently between byte data and
-character (Unicode) data. For example, the "word character" character
-class C<\w> will work differently depending on if data is eight-bit bytes
-or Unicode.
-
-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.
+Regular expression pattern matching may surprise you if you're not
+accustomed to Unicode. Starting in Perl 5.14, several pattern
+modifiers are available to control this, called the character set
+modifiers. Details are given in L<perlre/Character set modifiers>.
-In the second case, the C<\w> set of characters is much, much larger.
-Most importantly, even in the set of the first 256 characters, it will
-probably match different characters: unlike most locales, which are
-specific to a language and country pair, Unicode classifies all the
-characters that are letters I<somewhere> as C<\w>. For example, your
-locale might not think that LATIN SMALL LETTER ETH is a letter (unless
-you happen to speak Icelandic), but Unicode does.
+=back
As discussed elsewhere, Perl has one foot (two hooves?) planted in
each of two worlds: the old world of bytes and the new world of
switch-over to characters should happen. Characters shouldn't get
downgraded to bytes, either. It is possible to accidentally mix bytes
and characters, however (see L<perluniintro>), in which case C<\w> in
-regular expressions might start behaving differently. Review your
-code. Use warnings and the C<strict> pragma.
-
-=back
+regular expressions might start behaving differently (unless the C</a>
+modifier is in effect). Review your code. Use warnings and the C<strict> pragma.
=head2 Unicode in Perl on EBCDIC
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 reused to mean
+C<":utfebcdic"> layer; rather, C<"utf8"> and C<":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:
-
-=over 4
-
-=item *
-
-You can enable automatic UTF-8-ification of your standard file
-handles, default C<open()> layer, and C<@ARGV> by using either
-the C<-C> command line switch or the C<PERL_UNICODE> environment
-variable, see L<perlrun> for the documentation of the C<-C> switch.
-
-=item *
-
-Perl tries really hard to work both with Unicode and the old
-byte-oriented world. Most often this is nice, but sometimes Perl's
-straddling of the proverbial fence causes problems.
-
-=back
+See L<perllocale/Unicode and UTF-8>
=head2 When Unicode Does Not Happen
While Perl does have extensive ways to input and output in Unicode,
-and few other 'entry points' like the @ARGV which can be interpreted
-as Unicode (UTF-8), there still are many places where Unicode (in some
-encoding or another) could be given as arguments or received as
+and a few other "entry points" like the C<@ARGV> array (which can sometimes be
+interpreted as UTF-8), there are still many places where Unicode
+(in some encoding or another) could be given as arguments or received as
results, or both, but it is not.
The following are such interfaces. 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.
+currently (as of v5.16.0) simply assumes byte strings both as arguments
+and results, or UTF-8 strings if the (problematic) C<encoding> pragma has been used.
-One reason why Perl does not attempt to resolve the role of Unicode in
-these cases is that the answers are highly dependent on the operating
+One reason that Perl does not attempt to resolve the role of Unicode in
+these situations is that the answers are highly dependent on the operating
system and the file system(s). For example, whether filenames can be
-in Unicode, and in exactly what kind of encoding, is not exactly a
-portable concept. Similarly for the qx and system: how well will the
-'command line interface' (and which of them?) handle Unicode?
+in Unicode and in exactly what kind of encoding, is not exactly a
+portable concept. Similarly for C<qx> and C<system>: how well will the
+"command-line interface" (and which of them?) handle Unicode?
=over 4
=item *
-chdir, chmod, chown, chroot, exec, link, lstat, mkdir,
-rename, rmdir, stat, symlink, truncate, unlink, utime, -X
+C<chdir>, C<chmod>, C<chown>, C<chroot>, C<exec>, C<link>, C<lstat>, C<mkdir>,
+C<rename>, C<rmdir>, C<stat>, C<symlink>, C<truncate>, C<unlink>, C<utime>, C<-X>
=item *
-%ENV
+C<%ENV>
=item *
-glob (aka the <*>)
+C<glob> (aka the C<E<lt>*E<gt>>)
=item *
-open, opendir, sysopen
+C<open>, C<opendir>, C<sysopen>
=item *
-qx (aka the backtick operator), system
+C<qx> (aka the backtick operator), C<system>
=item *
-readdir, readlink
+C<readdir>, C<readlink>
=back
=head2 The "Unicode Bug"
-The term, the "Unicode bug" has been applied to an inconsistency with the
-Unicode characters whose code points are in the Latin-1 Supplement block, that
+The term, "Unicode bug" has been applied to an inconsistency
+on ASCII platforms with the
+Unicode code points in the C<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.
+byte semantics versus character semantics, unless
+C<use feature 'unicode_strings'> is specified, directly or indirectly.
+(It is indirectly specified by a C<use v5.12> or higher.)
-In character semantics they are interpreted as Unicode code points, which means
+In character semantics these upper-Latin1 characters are interpreted as
+Unicode code points, which means
they have the same semantics as Latin-1 (ISO-8859-1).
-In byte semantics, they are considered to be unassigned characters, meaning
-that the only semantics they have is their ordinal numbers, and that they are
+In byte semantics (without C<unicode_strings>), they are considered to
+be unassigned characters, meaning that the only semantics they have is
+their ordinal numbers, and that they are
not members of various character classes. None are considered to match C<\w>
-for example, but all match C<\W>. (On EBCDIC platforms, the behavior may
-be different from this, depending on the underlying C language library
-functions.)
+for example, but all match C<\W>.
-The behavior is known to have effects on these areas:
+Perl 5.12.0 added C<unicode_strings> to force character semantics on
+these code points in some circumstances, which fixed portions of the
+bug; Perl 5.14.0 fixed almost all of it; and Perl 5.16.0 fixed the
+remainder (so far as we know, anyway). The lesson here is to enable
+C<unicode_strings> to avoid the headaches described below.
+
+The old, problematic behavior affects these areas:
=over 4
=item *
Changing the case of a scalar, that is, using C<uc()>, C<ucfirst()>, C<lc()>,
-and C<lcfirst()>, or C<\L>, C<\U>, C<\u> and C<\l> in regular expression
-substitutions.
+and C<lcfirst()>, or C<\L>, C<\U>, C<\u> and C<\l> in double-quotish
+contexts, such as regular expression substitutions.
+Under C<unicode_strings> starting in Perl 5.12.0, character semantics are
+generally used. See L<perlfunc/lc> for details on how this works
+in combination with various other pragmas.
=item *
-Using caseless (C</i>) regular expression matching
+Using caseless (C</i>) regular expression matching.
+Starting in Perl 5.14.0, regular expressions compiled within
+the scope of C<unicode_strings> use character semantics
+even when executed or compiled into larger
+regular expressions outside the scope.
=item *
-Matching a number of properties in regular expressions, such as C<\w>
+Matching any of several properties in regular expressions, namely C<\b>,
+C<\B>, C<\s>, C<\S>, C<\w>, C<\W>, and all the Posix character classes
+I<except> C<[[:ascii:]]>.
+Starting in Perl 5.14.0, regular expressions compiled within
+the scope of C<unicode_strings> use character semantics
+even when executed or compiled into larger
+regular expressions outside the scope.
=item *
-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.
+In C<quotemeta> or its inline equivalent C<\Q>, no code points above 127
+are quoted in UTF-8 encoded strings, but in byte encoded strings, code
+points between 128-255 are always quoted.
+Starting in Perl 5.16.0, consistent quoting rules are used within the
+scope of C<unicode_strings>, as described in L<perlfunc/quotemeta>.
=back
an example, consider the following program and its output:
$ perl -le'
+ no feature 'unicode_strings';
$s1 = "\xC2";
$s2 = "\x{2660}";
for ($s1, $s2, $s1.$s2) {
support seamlessly. The result wasn't seamless: these characters were
orphaned.
-Work is being done to correct this, but only some of it was complete in time
-for the 5.12 release. What has been finished is the important part of the case
-changing component. Due to concerns, and some evidence, that older code might
-have come to rely on the existing behavior, the new behavior must be explicitly
-enabled by the feature C<unicode_strings> in the L<feature> pragma, even though
-no new syntax is involved.
-
-See L<perlfunc/lc> for details on how this pragma works in combination with
-various others for casing. Even though the pragma only affects casing
-operations in the 5.12 release, it is planned to have it affect all the
-problematic behaviors in later releases: you can't have one without them all.
-
-In the meantime, a workaround is to always call utf8::upgrade($string), or to
-use the standard modules L<Encode> or L<charnames>.
+For Perls earlier than those described above, or when a string is passed
+to a function outside the subpragma's scope, a workaround is to always
+call L<C<utf8::upgrade($string)>|utf8/Utility functions>,
+or to use the standard module L<Encode>. Also, a scalar that has any characters
+whose ordinal is C<0x100> or above, 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
+L<C<utf8::upgrade($bytestring)>|utf8/Utility functions> and
+L<C<utf8::downgrade($utf8string[, FAIL_OK])>|utf8/Utility functions> are
the answers.
-Note that utf8::downgrade() can fail if the string contains characters
+Note that C<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
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
+flag is on; the C<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
=item *
-C<utf8_to_uvchr(buf, lenp)> reads UTF-8 encoded bytes from a buffer and
+C<utf8_to_uvchr_buf(buf, bufend, lenp)> reads UTF-8 encoded bytes from a
+buffer and
returns the Unicode character code point and, optionally, the length of
the UTF-8 byte sequence. It works appropriately on EBCDIC machines.
=item *
-C<is_utf8_char(s)> returns true if the pointer points to a valid UTF-8
-character.
+C<is_utf8_string(buf, len)> returns true if C<len> bytes of the buffer
+are valid UTF-8.
=item *
-C<is_utf8_string(buf, len)> returns true if C<len> bytes of the buffer
-are valid UTF-8.
+C<is_utf8_char_buf(buf, buf_end)> returns true if the pointer points to
+a valid UTF-8 character.
=item *
=item *
-C<ibcmp_utf8(s1, pe1, l1, u1, s2, pe2, l2, u2)> can be used to
+C<foldEQ_utf8(s1, pe1, l1, u1, s2, pe2, l2, u2)> can be used to
compare two strings case-insensitively in Unicode. For case-sensitive
-comparisons you can just use C<memEQ()> and C<memNE()> as usual.
+comparisons you can just use C<memEQ()> and C<memNE()> as usual, except
+if one string is in utf8 and the other isn't.
=back
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
+Download the files in the desired version of Unicode from the Unicode web
site L<http://www.unicode.org>). These should replace the existing files in
-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.
+F<lib/unicore> in the Perl source tree. Follow the instructions in
+F<README.perl> in that directory to change some of their names, and then build
+perl (see L<INSTALL>).
=head1 BUGS
=head2 Interaction with Locales
-Use of locales with Unicode data may lead to odd results. Currently,
-Perl attempts to attach 8-bit locale info to characters in the range
-0..255, but this technique is demonstrably incorrect for locales that
-use characters above that range when mapped into Unicode. Perl's
-Unicode support will also tend to run slower. Use of locales with
-Unicode is discouraged.
+See L<perllocale/Unicode and UTF-8>
=head2 Problems with characters in the Latin-1 Supplement range
See L</The "Unicode Bug">
-=head2 Problems with case-insensitive regular expression matching
-
-There are problems with case-insensitive matches, including those involving
-character classes (enclosed in [square brackets]), characters whose fold
-is to multiple characters (such as the single character LATIN SMALL LIGATURE
-FFL matches case-insensitively with the 3-character string C<ffl>), and
-characters in the Latin-1 Supplement.
-
=head2 Interaction with Extensions
When Perl exchanges data with an extension, the extension should be
able to understand the UTF8 flag and act accordingly. If the
-extension doesn't know about the flag, it's likely that the extension
+extension doesn't recognize that flag, it's likely that the extension
will return incorrectly-flagged data.
So if you're working with Unicode data, consult the documentation of
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 C<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:
sub my_escape_html ($) {
- my($what) = shift;
- return unless defined $what;
- Encode::decode_utf8(Foo::Bar::escape_html(Encode::encode_utf8($what)));
+ my($what) = shift;
+ return unless defined $what;
+ Encode::decode_utf8(Foo::Bar::escape_html(
+ Encode::encode_utf8($what)));
}
Sometimes, when the extension does not convert data but just stores
-and retrieves them, you will be in a position to use the otherwise
-dangerous Encode::_utf8_on() function. Let's say the popular
-C<Foo::Bar> extension, written in C, provides a C<param> method that
-lets you store and retrieve data according to these prototypes:
+and retrieves them, you will be able to use the otherwise
+dangerous L<C<Encode::_utf8_on()>|Encode/_utf8_on> function. Let's say
+the popular C<Foo::Bar> extension, written in C, provides a C<param>
+method that lets you store and retrieve data according to these prototypes:
$self->param($name, $value); # set a scalar
$value = $self->param($name); # retrieve a scalar
}
Some extensions provide filters on data entry/exit points, such as
-DB_File::filter_store_key and family. Look out for such filters in
+C<DB_File::filter_store_key> and family. Look out for such filters in
the documentation of your extensions, they can make the transition to
Unicode data much easier.
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(), or matching regular
-expressions can work B<much> faster when the underlying data are
+characters such as C<length()>, C<substr()> or C<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
operations with UTF-8 encoded strings are still slower. As an example,
the Unicode properties (character classes) like C<\p{Nd}> are known to
be quite a bit slower (5-20 times) than their simpler counterparts
-like C<\d> (then again, there 268 Unicode characters matching C<Nd>
+like C<\d> (then again, there are hundreds of Unicode characters matching C<Nd>
compared with the 10 ASCII characters matching C<d>).
=head2 Problems on EBCDIC platforms
-There are a number of known problems with Perl on EBCDIC platforms. If you
+There are several known problems with Perl on EBCDIC platforms. If you
want to use Perl there, send email to perlbug@perl.org.
In earlier versions, when byte and character data were concatenated,
your code. The examples are written such that the code will continue
to work under 5.6, so you should be safe to try them out.
-=over 4
+=over 3
=item *
A filehandle that should read or write UTF-8
- if ($] > 5.007) {
+ if ($] > 5.008) {
binmode $fh, ":encoding(utf8)";
}
A scalar that is going to be passed to some extension
-Be it Compress::Zlib, Apache::Request or any extension that has no
+Be it C<Compress::Zlib>, C<Apache::Request> or any extension that has no
mention of Unicode in the manpage, you need to make sure that the
UTF8 flag is stripped off. Note that at the time of this writing
-(October 2002) the mentioned modules are not UTF-8-aware. Please
+(January 2012) the mentioned modules are not UTF-8-aware. Please
check the documentation to verify if this is still true.
- if ($] > 5.007) {
+ if ($] > 5.008) {
require Encode;
$val = Encode::encode_utf8($val); # make octets
}
If you believe the scalar comes back as UTF-8, you will most likely
want the UTF8 flag restored:
- if ($] > 5.007) {
+ if ($] > 5.008) {
require Encode;
$val = Encode::decode_utf8($val);
}
Same thing, if you are really sure it is UTF-8
- if ($] > 5.007) {
+ if ($] > 5.008) {
require Encode;
Encode::_utf8_on($val);
}
=item *
-A wrapper for fetchrow_array and fetchrow_hashref
+A wrapper for L<DBI> C<fetchrow_array> and C<fetchrow_hashref>
When the database contains only UTF-8, a wrapper function or method is
-a convenient way to replace all your fetchrow_array and
-fetchrow_hashref calls. A wrapper function will also make it easier to
+a convenient way to replace all your C<fetchrow_array> and
+C<fetchrow_hashref> calls. A wrapper function will also make it easier to
adapt to future enhancements in your database driver. Note that at the
-time of this writing (October 2002), the DBI has no standardized way
-to deal with UTF-8 data. Please check the documentation to verify if
+time of this writing (January 2012), the DBI has no standardized way
+to deal with UTF-8 data. Please check the L<DBI documentation|DBI> to verify if
that is still true.
sub fetchrow {
- my($self, $sth, $what) = @_; # $what is one of fetchrow_{array,hashref}
- if ($] < 5.007) {
+ # $what is one of fetchrow_{array,hashref}
+ my($self, $sth, $what) = @_;
+ if ($] < 5.008) {
return $sth->$what;
} else {
require Encode;
my $ret = $sth->$what;
if (ref $ret) {
for my $k (keys %$ret) {
- defined && /[^\000-\177]/ && Encode::_utf8_on($_) for $ret->{$k};
+ defined
+ && /[^\000-\177]/
+ && Encode::_utf8_on($_) for $ret->{$k};
}
return $ret;
} else {
a drag to your program. If you recognize such a situation, just remove
the UTF8 flag:
- utf8::downgrade($val) if $] > 5.007;
+ utf8::downgrade($val) if $] > 5.008;
=back
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