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PERLUNICODE(1) Perl Programmers Reference Guide PERLUNICODE(1)
NAME
perlunicode - Unicode support in Perl
DESCRIPTION
Important Caveats
Unicode support is an extensive requirement. While Perl does not implement the Unicode
standard or the accompanying technical reports from cover to cover, Perl does support many
Unicode features.
People who want to learn to use Unicode in Perl, should probably read the Perl Unicode
tutorial before reading this reference document.
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 encoding on input or from Perl's encoding on
output by use of the ":encoding(...)" layer. See open.
To indicate that Perl source itself is in UTF-8, use "use utf8;".
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.
"use utf8" still needed to enable UTF-8/UTF-EBCDIC in scripts
As a compatibility measure, the "use utf8" pragma must be explicitly included to
enable recognition of UTF-8 in the Perl scripts themselves (in string or regular
expression literals, or in identifier names) on ASCII-based machines or to recognize
UTF-EBCDIC on EBCDIC-based machines. These are the only times when an explicit "use
utf8" is needed. See utf8.
BOM-marked scripts and UTF-16 scripts autodetected
If a Perl script begins marked with the Unicode BOM (UTF-16LE, UTF16-BE, or UTF-8), or
if the script looks like non-BOM-marked UTF-16 of either endianness, Perl will
correctly read in the script as Unicode. (BOMless UTF-8 cannot be effectively
recognized or differentiated from ISO 8859-1 or other eight-bit encodings.)
"use encoding" needed to upgrade non-Latin-1 byte strings
By default, there is a fundamental asymmetry in Perl's Unicode model: implicit
upgrading from byte strings to Unicode strings assumes that they were encoded in ISO
8859-1 (Latin-1), but Unicode strings are downgraded with UTF-8 encoding. This
happens because the first 256 codepoints in Unicode happens to agree with Latin-1.
See "Byte and Character Semantics" for more details.
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.
This behavior preserves compatibility with earlier versions of Perl, which allowed byte
semantics in Perl operations only if none of the program's inputs were marked as being as
source of Unicode character data. Such data may come from filehandles, from calls to
external programs, from information provided by the system (such as %ENV), or from
literals and constants in the source text.
The "bytes" pragma will always, regardless of platform, force byte semantics in a
particular lexical scope. See bytes.
The "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 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 "bytes"
pragma should be used to force byte semantics on Unicode data.
If strings operating under byte semantics and strings with Unicode character data are
concatenated, the new string will be created by decoding the byte strings as ISO 8859-1
(Latin-1), even if the old Unicode string used EBCDIC. This translation is done without
regard to the system's native 8-bit encoding.
Under character semantics, many operations that formerly operated on bytes now operate on
characters. A character in Perl is logically just a number ranging from 0 to 2**31 or so.
Larger characters may encode into longer sequences of bytes internally, but this internal
detail is mostly hidden for Perl code. See perluniintro for more.
Effects of Character Semantics
Character semantics have the following effects:
o Strings--including hash keys--and regular expression patterns may contain characters
that have an ordinal value larger than 255.
If you use a Unicode editor to edit your program, Unicode characters may occur
directly within the literal strings in UTF-8 encoding, or UTF-16. (The former
requires a BOM or "use utf8", the latter requires a BOM.)
Unicode characters can also be added to a string by using the "\x{...}" notation. The
Unicode code for the desired character, in hexadecimal, should be placed in the
braces. For instance, a smiley face is "\x{263A}". This encoding scheme only works
for all characters, but for characters under 0x100, note that Perl may use an 8 bit
encoding internally, for optimization and/or backward compatibility.
Additionally, if you
use charnames ':full';
you can use the "\N{...}" notation and put the official Unicode character name within
the braces, such as "\N{WHITE SMILING FACE}".
o If an appropriate encoding is specified, identifiers within the Perl script may
contain Unicode alphanumeric characters, including ideographs. Perl does not
currently attempt to canonicalize variable names.
o Regular expressions match characters instead of bytes. "." matches a character
instead of a byte.
o Character classes in regular expressions match characters instead of bytes and match
against the character properties specified in the Unicode properties database. "\w"
can be used to match a Japanese ideograph, for instance.
o Named Unicode properties, scripts, and block ranges may be used like character classes
via the "\p{}" "matches property" construct and the "\P{}" negation, "doesn't match
property".
See "Unicode Character Properties" for more details.
You can define your own character properties and use them in the regular expression
with the "\p{}" or "\P{}" construct.
See "User-Defined Character Properties" for more details.
o The special pattern "\X" matches any extended Unicode sequence--"a combining character
sequence" in Standardese--where the first character is a base character and subsequent
characters are mark characters that apply to the base character. "\X" is equivalent
to "(?:\PM\pM*)".
o The "tr///" operator translates characters instead of bytes. Note that the "tr///CU"
functionality has been removed. For similar functionality see pack('U0', ...) and
pack('C0', ...).
o Case translation operators use the Unicode case translation tables when character
input is provided. Note that "uc()", or "\U" in interpolated strings, translates to
uppercase, while "ucfirst", or "\u" in interpolated strings, translates to titlecase
in languages that make the distinction.
o Most operators that deal with positions or lengths in a string will automatically
switch to using character positions, including "chop()", "chomp()", "substr()",
"pos()", "index()", "rindex()", "sprintf()", "write()", and "length()". An operator
that specifically does not switch is "vec()". Operators that really don't care
include operators that treat strings as a bucket of bits such as "sort()", and
operators dealing with filenames.
o The "pack()"/"unpack()" letter "C" does not change, since it is often used for byte-
oriented formats. Again, think "char" in the C language.
There is a new "U" specifier that converts between Unicode characters and code points.
There is also a "W" specifier that is the equivalent of "chr"/"ord" and properly
handles character values even if they are above 255.
o The "chr()" and "ord()" functions work on characters, similar to "pack("W")" and
"unpack("W")", not "pack("C")" and "unpack("C")". "pack("C")" and "unpack("C")" are
methods for emulating byte-oriented "chr()" and "ord()" on Unicode strings. While
these methods reveal the internal encoding of Unicode strings, that is not something
one normally needs to care about at all.
o The bit string operators, "& | ^ ~", can operate on character data. However, for
backward compatibility, such as when using bit string operations when characters are
all less than 256 in ordinal value, one should not use "~" (the bit complement) with
characters of both values less than 256 and values greater than 256. Most
importantly, DeMorgan's laws ("~($x|$y) eq ~$x&~$y" and "~($x&$y) eq ~$x|~$y") will
not hold. The reason for this mathematical faux pas is that the complement cannot
return both the 8-bit (byte-wide) bit complement and the full character-wide bit
complement.
o lc(), uc(), lcfirst(), and ucfirst() work for the following cases:
o the case mapping is from a single Unicode character to another single Unicode
character, or
o the case mapping is from a single Unicode character to more than one Unicode
character.
Things to do with locales (Lithuanian, Turkish, Azeri) do not work since Perl does not
understand the concept of Unicode locales.
See the Unicode Technical Report #21, Case Mappings, for more details.
But you can also define your own mappings to be used in the lc(), lcfirst(), uc(), and
ucfirst() (or their string-inlined versions).
See "User-Defined Case Mappings" for more details.
o And finally, "scalar reverse()" reverses by character rather than by byte.
Unicode Character Properties
Named Unicode properties, scripts, and block ranges may be used like character classes via
the "\p{}" "matches property" construct and the "\P{}" negation, "doesn't match property".
For instance, "\p{Lu}" matches any character with the Unicode "Lu" (Letter, uppercase)
property, while "\p{M}" matches any character with an "M" (mark--accents and such)
property. Brackets are not required for single letter properties, so "\p{M}" is
equivalent to "\pM". Many predefined properties are available, such as "\p{Mirrored}" and
"\p{Tibetan}".
The official Unicode script and block names have spaces and dashes as separators, but for
convenience you can use dashes, spaces, or underbars, and case is unimportant. It is
recommended, however, that for consistency you use the following naming: the official
Unicode script, property, or block name (see below for the additional rules that apply to
block names) with whitespace and dashes removed, and the words "uppercase-first-lowercase-
rest". "Latin-1 Supplement" thus becomes "Latin1Supplement".
You can also use negation in both "\p{}" and "\P{}" by introducing a caret (^) between the
first brace and the property name: "\p{^Tamil}" is equal to "\P{Tamil}".
NOTE: the properties, scripts, and blocks listed here are as of Unicode 5.0.0 in July
2006.
General Category
Here are the basic Unicode General Category properties, followed by their long form.
You can use either; "\p{Lu}" and "\p{UppercaseLetter}", for instance, are identical.
Short Long
L Letter
LC CasedLetter
Lu UppercaseLetter
Ll LowercaseLetter
Lt TitlecaseLetter
Lm ModifierLetter
Lo OtherLetter
M Mark
Mn NonspacingMark
Mc SpacingMark
Me EnclosingMark
N Number
Nd DecimalNumber
Nl LetterNumber
No OtherNumber
P Punctuation
Pc ConnectorPunctuation
Pd DashPunctuation
Ps OpenPunctuation
Pe ClosePunctuation
Pi InitialPunctuation
(may behave like Ps or Pe depending on usage)
Pf FinalPunctuation
(may behave like Ps or Pe depending on usage)
Po OtherPunctuation
S Symbol
Sm MathSymbol
Sc CurrencySymbol
Sk ModifierSymbol
So OtherSymbol
Z Separator
Zs SpaceSeparator
Zl LineSeparator
Zp ParagraphSeparator
C Other
Cc Control
Cf Format
Cs Surrogate (not usable)
Co PrivateUse
Cn Unassigned
Single-letter properties match all characters in any of the two-letter sub-properties
starting with the same letter. "LC" and "L&" are special cases, which are aliases for
the set of "Ll", "Lu", and "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. "Cs" is therefore not supported.
Bidirectional Character Types
Because scripts differ in their directionality--Hebrew is written right to left, for
example--Unicode supplies these properties in the BidiClass class:
Property Meaning
L Left-to-Right
LRE Left-to-Right Embedding
LRO Left-to-Right Override
R Right-to-Left
AL Right-to-Left Arabic
RLE Right-to-Left Embedding
RLO Right-to-Left Override
PDF Pop Directional Format
EN European Number
ES European Number Separator
ET European Number Terminator
AN Arabic Number
CS Common Number Separator
NSM Non-Spacing Mark
BN Boundary Neutral
B Paragraph Separator
S Segment Separator
WS Whitespace
ON Other Neutrals
For example, "\p{BidiClass:R}" matches characters that are normally written right to
left.
Scripts
The script names which can be used by "\p{...}" and "\P{...}", such as in "\p{Latin}"
or "\p{Cyrillic}", are as follows:
Arabic
Armenian
Balinese
Bengali
Bopomofo
Braille
Buginese
Buhid
CanadianAboriginal
Cherokee
Coptic
Cuneiform
Cypriot
Cyrillic
Deseret
Devanagari
Ethiopic
Georgian
Glagolitic
Gothic
Greek
Gujarati
Gurmukhi
Han
Hangul
Hanunoo
Hebrew
Hiragana
Inherited
Kannada
Katakana
Kharoshthi
Khmer
Lao
Latin
Limbu
LinearB
Malayalam
Mongolian
Myanmar
NewTaiLue
Nko
Ogham
OldItalic
OldPersian
Oriya
Osmanya
PhagsPa
Phoenician
Runic
Shavian
Sinhala
SylotiNagri
Syriac
Tagalog
Tagbanwa
TaiLe
Tamil
Telugu
Thaana
Thai
Tibetan
Tifinagh
Ugaritic
Yi
Extended property classes
Extended property classes can supplement the basic properties, defined by the PropList
Unicode database:
ASCIIHexDigit
BidiControl
Dash
Deprecated
Diacritic
Extender
HexDigit
Hyphen
Ideographic
IDSBinaryOperator
IDSTrinaryOperator
JoinControl
LogicalOrderException
NoncharacterCodePoint
OtherAlphabetic
OtherDefaultIgnorableCodePoint
OtherGraphemeExtend
OtherIDStart
OtherIDContinue
OtherLowercase
OtherMath
OtherUppercase
PatternSyntax
PatternWhiteSpace
QuotationMark
Radical
SoftDotted
STerm
TerminalPunctuation
UnifiedIdeograph
VariationSelector
WhiteSpace
and there are further derived properties:
Alphabetic = Lu + Ll + Lt + Lm + Lo + Nl + OtherAlphabetic
Lowercase = Ll + OtherLowercase
Uppercase = Lu + OtherUppercase
Math = Sm + OtherMath
IDStart = Lu + Ll + Lt + Lm + Lo + Nl + OtherIDStart
IDContinue = IDStart + Mn + Mc + Nd + Pc + OtherIDContinue
DefaultIgnorableCodePoint
= OtherDefaultIgnorableCodePoint
+ Cf + Cc + Cs + Noncharacters + VariationSelector
- WhiteSpace - FFF9..FFFB (Annotation Characters)
Any = Any code points (i.e. U+0000 to U+10FFFF)
Assigned = Any non-Cn code points (i.e. synonym for \P{Cn})
Unassigned = Synonym for \p{Cn}
ASCII = ASCII (i.e. U+0000 to U+007F)
Common = Any character (or unassigned code point)
not explicitly assigned to a script
Use of "Is" Prefix
For backward compatibility (with Perl 5.6), all properties mentioned so far may have
"Is" prepended to their name, so "\P{IsLu}", for example, is equal to "\P{Lu}".
Blocks
In addition to scripts, Unicode also defines blocks of characters. The difference
between scripts and blocks is that the concept of scripts is closer to natural
languages, while the concept of blocks is more of an artificial grouping based on
groups of 256 Unicode characters. For example, the "Latin" script contains letters
from many blocks but does not contain all the characters from those blocks. It does
not, for example, contain digits, because digits are shared across many scripts.
Digits and similar groups, like punctuation, are in a category called "Common".
For more about scripts, see the UAX#24 "Script Names":
http://www.unicode.org/reports/tr24/
For more about blocks, see:
http://www.unicode.org/Public/UNIDATA/Blocks.txt
Block names are given with the "In" prefix. For example, the Katakana block is
referenced via "\p{InKatakana}". The "In" prefix may be omitted if there is no naming
conflict with a script or any other property, but it is recommended that "In" always
be used for block tests to avoid confusion.
These block names are supported:
InAegeanNumbers
InAlphabeticPresentationForms
InAncientGreekMusicalNotation
InAncientGreekNumbers
InArabic
InArabicPresentationFormsA
InArabicPresentationFormsB
InArabicSupplement
InArmenian
InArrows
InBalinese
InBasicLatin
InBengali
InBlockElements
InBopomofo
InBopomofoExtended
InBoxDrawing
InBraillePatterns
InBuginese
InBuhid
InByzantineMusicalSymbols
InCJKCompatibility
InCJKCompatibilityForms
InCJKCompatibilityIdeographs
InCJKCompatibilityIdeographsSupplement
InCJKRadicalsSupplement
InCJKStrokes
InCJKSymbolsAndPunctuation
InCJKUnifiedIdeographs
InCJKUnifiedIdeographsExtensionA
InCJKUnifiedIdeographsExtensionB
InCherokee
InCombiningDiacriticalMarks
InCombiningDiacriticalMarksSupplement
InCombiningDiacriticalMarksforSymbols
InCombiningHalfMarks
InControlPictures
InCoptic
InCountingRodNumerals
InCuneiform
InCuneiformNumbersAndPunctuation
InCurrencySymbols
InCypriotSyllabary
InCyrillic
InCyrillicSupplement
InDeseret
InDevanagari
InDingbats
InEnclosedAlphanumerics
InEnclosedCJKLettersAndMonths
InEthiopic
InEthiopicExtended
InEthiopicSupplement
InGeneralPunctuation
InGeometricShapes
InGeorgian
InGeorgianSupplement
InGlagolitic
InGothic
InGreekExtended
InGreekAndCoptic
InGujarati
InGurmukhi
InHalfwidthAndFullwidthForms
InHangulCompatibilityJamo
InHangulJamo
InHangulSyllables
InHanunoo
InHebrew
InHighPrivateUseSurrogates
InHighSurrogates
InHiragana
InIPAExtensions
InIdeographicDescriptionCharacters
InKanbun
InKangxiRadicals
InKannada
InKatakana
InKatakanaPhoneticExtensions
InKharoshthi
InKhmer
InKhmerSymbols
InLao
InLatin1Supplement
InLatinExtendedA
InLatinExtendedAdditional
InLatinExtendedB
InLatinExtendedC
InLatinExtendedD
InLetterlikeSymbols
InLimbu
InLinearBIdeograms
InLinearBSyllabary
InLowSurrogates
InMalayalam
InMathematicalAlphanumericSymbols
InMathematicalOperators
InMiscellaneousMathematicalSymbolsA
InMiscellaneousMathematicalSymbolsB
InMiscellaneousSymbols
InMiscellaneousSymbolsAndArrows
InMiscellaneousTechnical
InModifierToneLetters
InMongolian
InMusicalSymbols
InMyanmar
InNKo
InNewTaiLue
InNumberForms
InOgham
InOldItalic
InOldPersian
InOpticalCharacterRecognition
InOriya
InOsmanya
InPhagspa
InPhoenician
InPhoneticExtensions
InPhoneticExtensionsSupplement
InPrivateUseArea
InRunic
InShavian
InSinhala
InSmallFormVariants
InSpacingModifierLetters
InSpecials
InSuperscriptsAndSubscripts
InSupplementalArrowsA
InSupplementalArrowsB
InSupplementalMathematicalOperators
InSupplementalPunctuation
InSupplementaryPrivateUseAreaA
InSupplementaryPrivateUseAreaB
InSylotiNagri
InSyriac
InTagalog
InTagbanwa
InTags
InTaiLe
InTaiXuanJingSymbols
InTamil
InTelugu
InThaana
InThai
InTibetan
InTifinagh
InUgaritic
InUnifiedCanadianAboriginalSyllabics
InVariationSelectors
InVariationSelectorsSupplement
InVerticalForms
InYiRadicals
InYiSyllables
InYijingHexagramSymbols
User-Defined Character Properties
You can define your own character properties by defining subroutines whose names begin
with "In" or "Is". The subroutines can be defined in any package. The user-defined
properties can be used in the regular expression "\p" and "\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 "\p" or "\P" construct.
# assuming property IsForeign defined in Lang::
package main; # property package name required
if ($txt =~ /\p{Lang::IsForeign}+/) { ... }
package Lang; # property package name not required
if ($txt =~ /\p{IsForeign}+/) { ... }
Note that the effect is compile-time and immutable once defined.
The subroutines must return a specially-formatted string, with one or more newline-
separated lines. Each line must be one of the following:
o A single hexadecimal number denoting a Unicode code point to include.
o Two hexadecimal numbers separated by horizontal whitespace (space or tabular
characters) denoting a range of Unicode code points to include.
o Something to include, prefixed by "+": a built-in character property (prefixed by
"utf8::") or a user-defined character property, to represent all the characters in
that property; two hexadecimal code points for a range; or a single hexadecimal code
point.
o Something to exclude, prefixed by "-": an existing character property (prefixed by
"utf8::") or a user-defined character property, to represent all the characters in
that property; two hexadecimal code points for a range; or a single hexadecimal code
point.
o Something to negate, prefixed "!": an existing character property (prefixed by
"utf8::") or a user-defined character property, to represent all the characters in
that property; two hexadecimal code points for a range; or a single hexadecimal code
point.
o Something to intersect with, prefixed by "&": an existing character property (prefixed
by "utf8::") or a user-defined character property, for all the characters except the
characters in the property; two hexadecimal code points for a range; or a single
hexadecimal code point.
For example, to define a property that covers both the Japanese syllabaries (hiragana and
katakana), you can define
sub InKana {
return <<END;
3040\t309F
30A0\t30FF
END
}
Imagine that the here-doc end marker is at the beginning of the line. Now you can use
"\p{InKana}" and "\P{InKana}".
You could also have used the existing block property names:
sub InKana {
return <<'END';
+utf8::InHiragana
+utf8::InKatakana
END
}
Suppose you wanted to match only the allocated characters, not the raw block ranges: in
other words, you want to remove the non-characters:
sub InKana {
return <<'END';
+utf8::InHiragana
+utf8::InKatakana
-utf8::IsCn
END
}
The negation is useful for defining (surprise!) negated classes.
sub InNotKana {
return <<'END';
!utf8::InHiragana
-utf8::InKatakana
+utf8::IsCn
END
}
Intersection is useful for getting the common characters matched by two (or more) classes.
sub InFooAndBar {
return <<'END';
+main::Foo
&main::Bar
END
}
It's important to remember not to use "&" for the first set -- that would be intersecting
with nothing (resulting in an empty set).
User-Defined Case Mappings
You can also define your own mappings to be used in the lc(), lcfirst(), uc(), and
ucfirst() (or their string-inlined versions). The principle is similar to that of user-
defined character properties: to define subroutines in the "main" package with names like
"ToLower" (for lc() and lcfirst()), "ToTitle" (for the first character in ucfirst()), and
"ToUpper" (for uc(), and the rest of the characters in ucfirst()).
The string returned by the subroutines needs now to be three hexadecimal numbers separated
by tabulators: start of the source range, end of the source range, and start of the
destination range. For example:
sub ToUpper {
return <<END;
0061\t0063\t0041
END
}
defines an uc() mapping that causes only the characters "a", "b", and "c" to be mapped to
"A", "B", "C", all other characters will remain unchanged.
If there is no source range to speak of, that is, the mapping is from a single character
to another single character, leave the end of the source range empty, but the two
tabulator characters are still needed. For example:
sub ToLower {
return <<END;
0041\t\t0061
END
}
defines a lc() mapping that causes only "A" to be mapped to "a", all other characters will
remain unchanged.
(For serious hackers only) If you want to introspect the default mappings, you can find
the data in the directory $Config{privlib}/unicore/To/. The mapping data is returned as
the here-document, and the "utf8::ToSpecFoo" are special exception mappings derived from
<$Config{privlib}>/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
"Unicode::UCD" module, or just match case-insensitively (that's when the "Fold" mapping is
used).
A final note on the user-defined case mappings: they will be used only if the scalar has
been marked as having Unicode characters. Old byte-style strings will not be affected.
Character Encodings for Input and Output
See Encode.
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" and the section numbers refer to the
Unicode Technical Standard #18, "Unicode Regular Expressions", version 11, in May 2005.
o Level 1 - Basic Unicode Support
RL1.1 Hex Notation - done [1]
RL1.2 Properties - done [2][3]
RL1.2a Compatibility Properties - done [4]
RL1.3 Subtraction and Intersection - MISSING [5]
RL1.4 Simple Word Boundaries - done [6]
RL1.5 Simple Loose Matches - done [7]
RL1.6 Line Boundaries - MISSING [8]
RL1.7 Supplementary Code Points - done [9]
[1] \x{...}
[2] \p{...} \P{...}
[3] supports not only minimal list (general category, scripts,
Alphabetic, Lowercase, Uppercase, WhiteSpace,
NoncharacterCodePoint, DefaultIgnorableCodePoint, Any,
ASCII, Assigned), but also bidirectional types, blocks, etc.
(see L</"Unicode Character Properties">)
[4] \d \D \s \S \w \W \X [:prop:] [:^prop:]
[5] can use regular expression look-ahead [a] or
user-defined character properties [b] to emulate set operations
[6] \b \B
[7] note that Perl does Full case-folding in matching, not Simple:
for example U+1F88 is equivalent with U+1F00 U+03B9,
not with 1F80. This difference matters for certain Greek
capital letters with certain modifiers: the Full case-folding
decomposes the letter, while the Simple case-folding would map
it to a single character.
[8] should do ^ and $ also on U+000B (\v in C), FF (\f), CR (\r),
CRLF (\r\n), NEL (U+0085), LS (U+2028), and PS (U+2029);
should also affect <>, $., and script line numbers;
should not split lines within CRLF [c] (i.e. there is no empty
line between \r and \n)
[9] UTF-8/UTF-EBDDIC used in perl allows not only U+10000 to U+10FFFF
but also beyond U+10FFFF [d]
[a] You can mimic class subtraction using lookahead. For example, what UTS#18 might
write as
[{Greek}-[{UNASSIGNED}]]
in Perl can be written as:
(?!\p{Unassigned})\p{InGreekAndCoptic}
(?=\p{Assigned})\p{InGreekAndCoptic}
But in this particular example, you probably really want
\p{GreekAndCoptic}
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.
[b] '+' for union, '-' for removal (set-difference), '&' for intersection (see "User-
Defined Character Properties")
[c] Try the ":crlf" layer (see PerlIO).
[d] Avoid "use warning 'utf8';" (or say "no warning 'utf8';") to allow U+FFFF
("\x{FFFF}").
o Level 2 - Extended Unicode Support
RL2.1 Canonical Equivalents - MISSING [10][11]
RL2.2 Default Grapheme Clusters - MISSING [12][13]
RL2.3 Default Word Boundaries - MISSING [14]
RL2.4 Default Loose Matches - MISSING [15]
RL2.5 Name Properties - MISSING [16]
RL2.6 Wildcard Properties - MISSING
[10] see UAX#15 "Unicode Normalization Forms"
[11] have Unicode::Normalize but not integrated to regexes
[12] have \X but at this level . should equal that
[13] UAX#29 "Text Boundaries" considers CRLF and Hangul syllable
clusters as a single grapheme cluster.
[14] see UAX#29, Word Boundaries
[15] see UAX#21 "Case Mappings"
[16] have \N{...} but neither compute names of CJK Ideographs
and Hangul Syllables nor use a loose match [e]
[e] "\N{...}" allows namespaces (see charnames).
o Level 3 - Tailored Support
RL3.1 Tailored Punctuation - MISSING
RL3.2 Tailored Grapheme Clusters - MISSING [17][18]
RL3.3 Tailored Word Boundaries - MISSING
RL3.4 Tailored Loose Matches - MISSING
RL3.5 Tailored Ranges - MISSING
RL3.6 Context Matching - MISSING [19]
RL3.7 Incremental Matches - MISSING
( RL3.8 Unicode Set Sharing )
RL3.9 Possible Match Sets - MISSING
RL3.10 Folded Matching - MISSING [20]
RL3.11 Submatchers - MISSING
[17] see UAX#10 "Unicode Collation Algorithms"
[18] have Unicode::Collate but not integrated to regexes
[19] have (?<=x) and (?=x), but look-aheads or look-behinds should see
outside of the target substring
[20] need insensitive matching for linguistic features other than case;
for example, hiragana to katakana, wide and narrow, simplified Han
to traditional Han (see UTR#30 "Character Foldings")
Unicode Encodings
Unicode characters are assigned to code points, which are abstract numbers. To use these
numbers, various encodings are needed.
o 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.
The following table is from Unicode 3.2.
Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte
U+0000..U+007F 00..7F
U+0080..U+07FF C2..DF 80..BF
U+0800..U+0FFF E0 A0..BF 80..BF
U+1000..U+CFFF E1..EC 80..BF 80..BF
U+D000..U+D7FF ED 80..9F 80..BF
U+D800..U+DFFF ******* ill-formed *******
U+E000..U+FFFF EE..EF 80..BF 80..BF
U+10000..U+3FFFF F0 90..BF 80..BF 80..BF
U+40000..U+FFFFF F1..F3 80..BF 80..BF 80..BF
U+100000..U+10FFFF F4 80..8F 80..BF 80..BF
Note the "A0..BF" in "U+0800..U+0FFF", the "80..9F" in "U+D000...U+D7FF", the "90..B"F
in "U+10000..U+3FFFF", and the "80...8F" in "U+100000..U+10FFFF". The "gaps" are
caused by legal UTF-8 avoiding non-shortest encodings: it is technically possible to
UTF-8-encode a single code point in different ways, but that is explicitly forbidden,
and the shortest possible encoding should always be used. So that's what Perl does.
Another way to look at it is via bits:
Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte
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 leading bits of the
start byte tell how many bytes the are in the encoded character.
o UTF-EBCDIC
Like UTF-8 but EBCDIC-safe, in the way that UTF-8 is ASCII-safe.
o UTF-16, UTF-16BE, UTF-16LE, Surrogates, and BOMs (Byte Order Marks)
The followings items are mostly for reference and general Unicode knowledge, Perl
doesn't use these constructs internally.
UTF-16 is a 2 or 4 byte encoding. The Unicode code points "U+0000..U+FFFF" are stored
in a single 16-bit unit, and the code points "U+10000..U+10FFFF" in two 16-bit units.
The latter case is using surrogates, the first 16-bit unit being the high surrogate,
and the second being the low surrogate.
Surrogates are code points set aside to encode the "U+10000..U+10FFFF" range of
Unicode code points in pairs of 16-bit units. The high surrogates are the range
"U+D800..U+DBFF", and the low surrogates are the range "U+DC00..U+DFFF". The
surrogate encoding is
$hi = ($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.
Because of the 16-bitness, UTF-16 is byte-order dependent. UTF-16 itself can be used
for in-memory computations, but if storage or transfer is required either UTF-16BE
(big-endian) or UTF-16LE (little-endian) encodings must be chosen.
This introduces another problem: what if you just know that your data is UTF-16, but
you don't know which endianness? Byte Order Marks, or BOMs, are a solution to this.
A special character has been reserved in Unicode to function as a byte order marker:
the character with the code point "U+FEFF" is the BOM.
The trick is that if you read a BOM, you will know the byte order, since if it was
written on a big-endian platform, you will read the bytes "0xFE 0xFF", but if it was
written on a little-endian platform, you will read the bytes "0xFF 0xFE". (And if the
originating platform was writing in UTF-8, you will read the bytes "0xEF 0xBB 0xBF".)
The way this trick works is that the character with the code point "U+FFFE" is
guaranteed not to be a valid Unicode character, so the sequence of bytes "0xFF 0xFE"
is unambiguously "BOM, represented in little-endian format" and cannot be "U+FFFE",
represented in big-endian format".
o UTF-32, UTF-32BE, UTF-32LE
The UTF-32 family is pretty much like the UTF-16 family, expect that the units are
32-bit, and therefore the surrogate scheme is not needed. The BOM signatures will be
"0x00 0x00 0xFE 0xFF" for BE and "0xFF 0xFE 0x00 0x00" for LE.
o UCS-2, UCS-4
Encodings defined by the ISO 10646 standard. UCS-2 is a 16-bit encoding. Unlike
UTF-16, UCS-2 is not extensible beyond "U+FFFF", because it does not use surrogates.
UCS-4 is a 32-bit encoding, functionally identical to UTF-32.
o UTF-7
A seven-bit safe (non-eight-bit) encoding, which is useful if the transport or storage
is not eight-bit safe. Defined by RFC 2152.
Security Implications of Unicode
o Malformed UTF-8
Unfortunately, the specification of UTF-8 leaves some room for interpretation of how
many bytes of encoded output one should generate from one input Unicode character.
Strictly speaking, the shortest possible sequence of UTF-8 bytes should be generated,
because otherwise there is potential for an input buffer overflow at the receiving end
of a UTF-8 connection. Perl always generates the shortest length UTF-8, and with
warnings on Perl will warn about non-shortest length UTF-8 along with other
malformations, such as the surrogates, which are not real Unicode code points.
o Regular expressions behave slightly differently between byte data and character
(Unicode) data. For example, the "word character" character class "\w" will work
differently depending on if data is eight-bit bytes or Unicode.
In the first case, the set of "\w" characters is either small--the default set of
alphabetic characters, digits, and the "_"--or, if you are using a locale (see
perllocale), the "\w" might contain a few more letters according to your language and
country.
In the second case, the "\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 somewhere as
"\w". For example, your locale might not think that LATIN SMALL LETTER ETH is a
letter (unless you happen to speak Icelandic), but Unicode does.
As discussed elsewhere, Perl has one foot (two hooves?) planted in each of two worlds:
the old world of bytes and the new world of characters, upgrading from bytes to
characters when necessary. If your legacy code does not explicitly use Unicode, no
automatic switch-over to characters should happen. Characters shouldn't get
downgraded to bytes, either. It is possible to accidentally mix bytes and characters,
however (see perluniintro), in which case "\w" in regular expressions might start
behaving differently. Review your code. Use warnings and the "strict" pragma.
Unicode in Perl on EBCDIC
The way Unicode is handled on EBCDIC platforms is still experimental. On such platforms,
references to UTF-8 encoding in this document and elsewhere should be read as meaning the
UTF-EBCDIC specified in Unicode Technical Report 16, unless ASCII vs. EBCDIC issues are
specifically discussed. There is no "utfebcdic" pragma or ":utfebcdic" layer; rather,
"utf8" and ":utf8" are reused to mean the platform's "natural" 8-bit encoding of Unicode.
See perlebcdic for more discussion of the issues.
Locales
Usually locale settings and Unicode do not affect each other, but there are a couple of
exceptions:
o You can enable automatic UTF-8-ification of your standard file handles, default
"open()" layer, and @ARGV by using either the "-C" command line switch or the
"PERL_UNICODE" environment variable, see perlrun for the documentation of the "-C"
switch.
o 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.
When Unicode Does Not Happen
While Perl does have extensive ways to input and output in Unicode, and few other 'entry
points' like the @ARGV which can be interpreted as Unicode (UTF-8), there still are many
places where Unicode (in some encoding or another) could be given as arguments or received
as results, or both, but it is not.
The following are such interfaces. 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
"encoding" pragma has been used.
One reason why Perl does not attempt to resolve the role of Unicode in this cases is that
the answers are highly dependent on the operating 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?
o chdir, chmod, chown, chroot, exec, link, lstat, mkdir, rename, rmdir, stat, symlink,
truncate, unlink, utime, -X
o %ENV
o glob (aka the <*>)
o open, opendir, sysopen
o qx (aka the backtick operator), system
o readdir, readlink
Forcing Unicode in Perl (Or Unforcing Unicode in Perl)
Sometimes (see "When Unicode Does Not Happen") there are situations where you simply need
to force Perl to believe that a byte string is UTF-8, or vice versa. The low-level calls
utf8::upgrade($bytestring) and utf8::downgrade($utf8string) are the answers.
Do not use them without careful thought, though: Perl may easily get very confused, angry,
or even crash, if you suddenly change the 'nature' of scalar like that. Especially
careful you have to be if you use the utf8::upgrade(): any random byte string is not valid
UTF-8.
Using Unicode in XS
If you want to handle Perl Unicode in XS extensions, you may find the following C APIs
useful. See also "Unicode Support" in perlguts for an explanation about Unicode at the XS
level, and perlapi for the API details.
o "DO_UTF8(sv)" returns true if the "UTF8" flag is on and the bytes pragma is not in
effect. "SvUTF8(sv)" returns true is the "UTF8" flag is on; the bytes pragma is
ignored. The "UTF8" flag being on does 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 "UTF8" flag means is that the sequence of octets in the
representation of the scalar is the sequence of UTF-8 encoded code points of the
characters of a string. The "UTF8" flag being off means that each octet in this
representation encodes a single character with code point 0..255 within the string.
Perl's Unicode model is not to use UTF-8 until it is absolutely necessary.
o "uvuni_to_utf8(buf, chr)" writes a Unicode character code point into a buffer encoding
the code point as UTF-8, and returns a pointer pointing after the UTF-8 bytes.
o "utf8_to_uvuni(buf, lenp)" reads UTF-8 encoded bytes from a buffer and returns the
Unicode character code point and, optionally, the length of the UTF-8 byte sequence.
o "utf8_length(start, end)" returns the length of the UTF-8 encoded buffer in
characters. "sv_len_utf8(sv)" returns the length of the UTF-8 encoded scalar.
o "sv_utf8_upgrade(sv)" converts the string of the scalar to its UTF-8 encoded form.
"sv_utf8_downgrade(sv)" does the opposite, if possible. "sv_utf8_encode(sv)" is like
sv_utf8_upgrade except that it does not set the "UTF8" flag. "sv_utf8_decode()" does
the opposite of "sv_utf8_encode()". Note that none of these are to be used as
general-purpose encoding or decoding interfaces: "use Encode" for that.
"sv_utf8_upgrade()" is affected by the encoding pragma but "sv_utf8_downgrade()" is
not (since the encoding pragma is designed to be a one-way street).
o is_utf8_char(s) returns true if the pointer points to a valid UTF-8 character.
o "is_utf8_string(buf, len)" returns true if "len" bytes of the buffer are valid UTF-8.
o "UTF8SKIP(buf)" will return the number of bytes in the UTF-8 encoded character in the
buffer. "UNISKIP(chr)" will return the number of bytes required to UTF-8-encode the
Unicode character code point. "UTF8SKIP()" is useful for example for iterating over
the characters of a UTF-8 encoded buffer; "UNISKIP()" is useful, for example, in
computing the size required for a UTF-8 encoded buffer.
o "utf8_distance(a, b)" will tell the distance in characters between the two pointers
pointing to the same UTF-8 encoded buffer.
o "utf8_hop(s, off)" will return a pointer to an UTF-8 encoded buffer that is "off"
(positive or negative) Unicode characters displaced from the UTF-8 buffer "s". Be
careful not to overstep the buffer: "utf8_hop()" will merrily run off the end or the
beginning of the buffer if told to do so.
o "pv_uni_display(dsv, spv, len, pvlim, flags)" and "sv_uni_display(dsv, ssv, pvlim,
flags)" are useful for debugging the output of Unicode strings and scalars. By
default they are useful only for debugging--they display all characters as hexadecimal
code points--but with the flags "UNI_DISPLAY_ISPRINT", "UNI_DISPLAY_BACKSLASH", and
"UNI_DISPLAY_QQ" you can make the output more readable.
o "ibcmp_utf8(s1, pe1, u1, l1, u1, s2, pe2, l2, u2)" can be used to compare two strings
case-insensitively in Unicode. For case-sensitive comparisons you can just use
"memEQ()" and "memNE()" as usual.
For more information, see perlapi, and utf8.c and utf8.h in the Perl source code
distribution.
BUGS
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.
Interaction with Extensions
When Perl exchanges data with an extension, the extension should be able to understand the
UTF8 flag and act accordingly. If the extension doesn't know about the flag, it's likely
that the extension will return incorrectly-flagged data.
So if you're working with Unicode data, consult the documentation of every module you're
using if there are any issues with Unicode data exchange. If the documentation does not
talk about Unicode at all, suspect the worst and probably look at the source to learn how
the module is implemented. Modules written completely in Perl shouldn't cause problems.
Modules that directly or indirectly access code written in other programming languages are
at risk.
For affected functions, the simple strategy to avoid data corruption is to always make the
encoding of the exchanged data explicit. Choose an encoding that you know the extension
can handle. Convert arguments passed to the extensions to that encoding and convert
results back from that encoding. Write wrapper functions that do the conversions for you,
so you can later change the functions when the extension catches up.
To provide an example, let's say the popular Foo::Bar::escape_html 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)));
}
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 "Foo::Bar" extension, written in C, provides a "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
If it does not yet provide support for any encoding, one could write a derived class with
such a "param" method:
sub param {
my($self,$name,$value) = @_;
utf8::upgrade($name); # make sure it is UTF-8 encoded
if (defined $value) {
utf8::upgrade($value); # make sure it is UTF-8 encoded
return $self->SUPER::param($name,$value);
} else {
my $ret = $self->SUPER::param($name);
Encode::_utf8_on($ret); # we know, it is UTF-8 encoded
return $ret;
}
}
Some extensions provide filters on data entry/exit points, such as
DB_File::filter_store_key and family. Look out for such filters in the documentation of
your extensions, they can make the transition to Unicode data much easier.
Speed
Some functions are slower when working on UTF-8 encoded strings than on byte encoded
strings. All functions that need to hop over characters such as length(), substr() or
index(), or matching regular expressions can work much faster when the underlying data are
byte-encoded.
In Perl 5.8.0 the slowness was often quite spectacular; in Perl 5.8.1 a caching scheme was
introduced which will hopefully make the slowness somewhat less spectacular, at least for
some operations. In general, operations with UTF-8 encoded strings are still slower. As
an example, the Unicode properties (character classes) like "\p{Nd}" are known to be quite
a bit slower (5-20 times) than their simpler counterparts like "\d" (then again, there 268
Unicode characters matching "Nd" compared with the 10 ASCII characters matching "d").
Porting code from perl-5.6.X
Perl 5.8 has a different Unicode model from 5.6. In 5.6 the programmer was required to use
the "utf8" pragma to declare that a given scope expected to deal with Unicode data and had
to make sure that only Unicode data were reaching that scope. If you have code that is
working with 5.6, you will need some of the following adjustments to your code. The
examples are written such that the code will continue to work under 5.6, so you should be
safe to try them out.
o A filehandle that should read or write UTF-8
if ($] > 5.007) {
binmode $fh, ":encoding(utf8)";
}
o A scalar that is going to be passed to some extension
Be it Compress::Zlib, Apache::Request or any extension that has no mention of Unicode
in the manpage, you need to make sure that the UTF8 flag is stripped off. Note that at
the time of this writing (October 2002) the mentioned modules are not UTF-8-aware.
Please check the documentation to verify if this is still true.
if ($] > 5.007) {
require Encode;
$val = Encode::encode_utf8($val); # make octets
}
o A scalar we got back from an extension
If you believe the scalar comes back as UTF-8, you will most likely want the UTF8 flag
restored:
if ($] > 5.007) {
require Encode;
$val = Encode::decode_utf8($val);
}
o Same thing, if you are really sure it is UTF-8
if ($] > 5.007) {
require Encode;
Encode::_utf8_on($val);
}
o A wrapper for fetchrow_array and fetchrow_hashref
When the database contains only UTF-8, a wrapper function or method is a convenient
way to replace all your fetchrow_array and fetchrow_hashref calls. A wrapper function
will also make it easier to adapt to future enhancements in your database driver. Note
that at the time of this writing (October 2002), the DBI has no standardized way to
deal with UTF-8 data. Please check the documentation to verify if that is still true.
sub fetchrow {
my($self, $sth, $what) = @_; # $what is one of fetchrow_{array,hashref}
if ($] < 5.007) {
return $sth->$what;
} else {
require Encode;
if (wantarray) {
my @arr = $sth->$what;
for (@arr) {
defined && /[^\000-\177]/ && Encode::_utf8_on($_);
}
return @arr;
} else {
my $ret = $sth->$what;
if (ref $ret) {
for my $k (keys %$ret) {
defined && /[^\000-\177]/ && Encode::_utf8_on($_) for $ret->{$k};
}
return $ret;
} else {
defined && /[^\000-\177]/ && Encode::_utf8_on($_) for $ret;
return $ret;
}
}
}
}
o A large scalar that you know can only contain ASCII
Scalars that contain only ASCII and are marked as UTF-8 are sometimes a drag to your
program. If you recognize such a situation, just remove the UTF8 flag:
utf8::downgrade($val) if $] > 5.007;
SEE ALSO
perlunitut, perluniintro, Encode, open, utf8, bytes, perlretut, "${^UNICODE}" in perlvar
perl v5.10.0 2011-06-30 PERLUNICODE(1)
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